Triple-Stimuli-Responsive Smart Nanocontainers Enhanced Self

Subscriber access provided by Iowa State University | Library

Applications of Polymer, Composite, and Coating Materials

Triple Stimuli-Responsive Smart Nanocontainers Enhanced SelfHealing Anticorrosion Coatings for Protection of Aluminum Alloy Ting Wang, Juan Du, Sheng Ye, LingHua Tan, and JiaJun Fu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b19950 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 5, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Triple stimuli-responsive smart nanocontainers enhanced self-healing anticorrosion coatings for protection of aluminum alloy Ting Wang,† Juan Du,† Sheng Ye,†,‡ Linghua Tan*,‡ and JiaJun Fu*,†

†

School of Chemical Engineering, Nanjing University of Science and Technology,

Nanjing 210094, P. R. China. E-mail: [email protected]

‡

National Special Superfine Powder Engineering Research Centre, Nanjing University

of Science and Technology, Nanjing 210094, P. R. China. E-mail: [email protected]

KEYWORDS: nanocontainers, stimuli-feedback, self-healing anticorrosion coatings

1

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 64

ABSTRACT: Novel Acid/Alkali/corrosion potential triple stimuli-responsive smart nanocontainers (TSR-SNs) were successfully assembled to regulate the release of encapsulated corrosion inhibitor, benzotriazole (BTA) by installing specially-structured bistable pseudorotaxanes as supramolecular nanovalves onto orifices of mesoporous silica nanoparticles. In normal condition, BTA molecules were sealed in the mesopores. Upon any stimulus of acid, alkali or corrosion potential, BTA molecules were quickly released due to the open states of supramolecular nanovalves. TSR-SNs as smart nanocontainers were added into SiO2-ZrO2 sol-gel coating to fabricate stimuli-feedback, corrosion-compensating self-healing anticorrosion coating (SF-SHAC). Compared with the conventional pH responsive smart nanocontainers synthesized for SHAC, TSR-SNs not only respond the pH changes occurring on corrosive micro-regions, more importantly, but also feel the corrosion potential of aluminium alloys and give the quick feedback. This design avoids wasting smart nanocontainers due to the local-dependent, gradient pH stimuli intensities and obviously enhances the response sensitivity of SFSHAC. Electrochemical impedance spectroscopy and salt spray tests prove the 2


Page 3 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


excellent physical barrier of SF-SHAC. Through scanning vibrating electrode technique measurements, SF-SHAC doped with TSR-SNs demonstrates the faster inhibiting rates for corrosive micro-cathodic/anodic current densities than other control SHACs. The new incorporated corrosion potential responsive function ensures the efficient working efficiency of TSR-SNs and makes the full use of the preloaded corrosion inhibitors as repair factors.

Introduction

Aluminum alloys are the second-largest metallic engineering material after steel, which have been widely used in aerospace, automobile and shipbuilding industries due to their high strength-to-weight ratio, good electrical/thermal conductivities, castability and recyclability, etc.1 Various alloying elements are added to aluminum to improve the mechanical properties and thermal stability, which inevitably leads to the formation of the heterogeneous structure. The galvanic interaction, which was caused by potential difference between Al-rich matrix phase and secondary phase particles, is detrimental

3



Page 4 of 64

to aluminum alloys by initiating localized corrosion.2 Chromate conversion coatings (CCCs) are acknowledged internationally as one of the most effective tactics for controlling the corrosion issue of aluminum alloys via deposition of an intelligent stable protective coating layer between the matrix and corrosive media.3 However, unfortunately, considering the toxicity and carcinogenicity of Cr(Ⅵ), the need for developing qualified chromate-free pretreatment coatings to replace CCCs is extremely urgent.

Inspired by the self-healing mechanism of CCCs, which involves the directional migration of Cr(Ⅵ) and local passivation on the exposed metal surface, a series selfhealing anticorrosion coatings (SHACs) were designed based on same philosophy.4 SHACs are capable of providing the autonomic response to the internal defects within coatings and self-repairing by various chemical or physical approaches, which can maintain the integrity of SHACs, recover the anticorrosion function and prevent the rapid failure of coatings. Based on the features of CCCs, Möhwald and Shchukin have proposed the novel type of stimuli-feedback, corrosion inhibitor-compensating SHACs 4


Page 5 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(SF-SHACs), which are mainly composed of “host” component (physical barrier coating, such as sol-gel coating, polymeric coating) and “guest” component (smart nanocontainers distributed in the barrier coatings).5-7 To date, stimuli such as pH,8 redox,9 ion strength,10 mechanical impact,11 and electrochemical potential12 have been introduced to SF-SHACs. Once corrosive species penetrate through barrier defense and initiate local corrosion, smart nanocontainers will automatically respond to environmental changes at corrosive micro-regions and give feedback to release entrapped corrosion inhibitors, adsorbing on metallic surface, forming molecular protective films and thus stopping the spread of corrosion. Smart nanocontainers play important roles in accomplishing presenting functions of SF-SHACs.3,13-17 In the first place, smart nanocontainers accommodate corrosion inhibitors, acting as coating repair factor, which not only avoid the directional contact between corrosion inhibitors and barrier

coatings

but

also

prevent

premature

leakage

by

installing

suitable

gatekeepers.18-21 Secondly, the sensitivity of smart nanocontainers determines the feedback rate of SF-SHACs. The rapid feedback after local corrosion onset is 5



Page 6 of 64

necessary; otherwise, the accumulation of corrosion products will undoubtedly influence the adsorption of corrosion inhibitors. It is well acknowledged that the acidic centers are generated by the dissolution of aluminum and subsequent hydrolysis of Al3+ in the corrosive micro-anodic regions; while in the micro-cathodic regions, the alkaline centers concurrently appear owning to the oxygen reduction reaction.22-24 Taking advantage of pH as corrosion stimuli, polyelectrolytes layer-by-layer assembly technique,25 endcapping method,26 and molecular assembly technique9 have been adopted to construct stimuli-responsive shells for regulating in/out states of corrosion inhibitors. However, scanning ion-selective electrode technique data done by Lamaka, Montemor and Gnedenkov have proved that pH stimuli intensities are gradient and locationdependent.27-30 The majority of the current smart nanocontainers cannot sensitively feel the relatively weak pH stimuli around corrosion interface acidic/alkaline centres, and the corrosion inhibitors are still encapsulated when local corrosion occurs, which will dramatically undermine self-healing effects. Shortening the distance between smart nanocontainers and metallic surface is an effective solution to increase self-healing rate. 6


Page 7 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Li and colleagues fabricated the smart nanocontainers containing magnetic multi-wall carbon nanotubes.31 The external magnetic field altered the distribution of smart nanocontainers, made them gather in the surface of aluminium alloy, shorten the migration route of corrosion inhibitors, and thus accelerate the initial self-healing efficiency. Our research team prepared Fe3O4@mSiO2 as magnetic scaffolds and obtained the similar experimental results.32 Endowing smart nanocontainers with desired stimuli-responsive capacities is another alternative to enhance the feedback rate of SF-SHACs, which attracts increasing attentions but is still full of challenges.

Herein, in order to improve the corrosion resistance of aluminum alloy with SF-SHACs, we synthesized the acid/alkali/corrosion potential triple stimuli-responsive smart nanocontainers (TSR-SNs) according to the characteristics of environmental stimuli around corrosive micro-regions of aluminum alloys. TSR-SNs were incorporated into SiO2-ZrO2 sol-gel coating to construct SF-SHACs. As the core components, TSR-SNs are made of mesoporous silica nanoparticles for accommodating corrosion inhibitors, benzotriazole (BTA), and specially-designed bistable pesudorotaxanes installed on the 7



Page 8 of 64

orifices of mesopores, comprising cucurbit[7]uril (CB[7]) macrocycles and molecular stalks,

N-{2[(2-aminoethyl)disulfanyl]ethyl}-4-(1’-carboxyferrocenyl)

butan-1-amine

(FcCA-Cys) containing two recognizable motifs, ferrocenecarboxylic acid (FcCA) and cystamine (Cys). Under normal conditions, CB[7] macrocycles reside on the Cys motifs, blocking the release channels for BTA molecules. Once receiving acidic or alkaline attack, supramolecular nanovalves are activated through movement of CB[7] macrocycles along molecular stalks or dissociation of supramolecular assemblies (CB[7]·FcCA-Cys), and thus BTA molecules are rapidly released. More importantly, TSR-SNs can also respond to the corrosion potential of aluminium alloys, capture the electrons transferring from micro-anodic to micro-cathodic regions, and self-degrade supramolecular nanovalves. Supramolecular assembly technique provides a facile method to assemble triple stimuli-responsive controlled release systems, which enhance the working efficiency of doped TSR-SNs and make the best use of corrosion inhibitors

as

efficiently

as

possible.

SF-SHACs

incorporated

with

TSR-SNs

8


Page 9 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


demonstrating the excellent anticorrosion performance and featuring with rapid feedback rate after local corrosion for protection of aluminum alloys, AA2024.

Results and discussion

Construction and investigation of supramolecular nanovalves

As the core parts of TSR-SNs, the supramolecular nanovalves are in the forms of bistable pseudorotaxanes, CB[7]·FcCA-Cys. The synthetic route of molecular stalks, FcCA-Cys, is depicted in Figure 1A. The ferrocenecarboxylic acid as the starting material was firstly esterified

9



Page 10 of 64

Figure 1. Schematic representation of the preparation of (A) FcCA-Cys and (B) TSRSNs; (C) Construction route of TSR-SNs-based SF-SHAC.

into compound 2. Then, the other Cp ring was reacted with 4-chlorobutyryl chloride and Zn-Hg to obtain compound 4 through Friedel-Crafts and Clemmensen reduction reactions. Compound 4 was hydrolyzed into compound 5 in the presence of lithium 10


Page 11 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydroxide. Next, compound 5 was re-esterified with tert-butanol into compound 6 for subsequent reaction. After that, Cys was covalently bonded to compound 6 through nucleophilic substitution reaction to afford compound 7. Finally, compound 7 was hydrolyzed with trifluoroacetic acid to afford FcCA-Cys. The structure of FcCA-Cys was confirmed by 1H and 13C NMR spectra (Figure 2A).

The pH-induced conformational changes of supramolecular assemblies were characterized by 1H NMR spectroscopy. The 1H NMR spectrum of FcCA-Cys in D2O (pD=7.0) is shown in Figure 2B (a). According to the referenced pKa values of cystamine (pKa=8.97±0.1) and cyclopentadienecarboxylic acid (pKa=3.73±0.2),33 the amino group in Cys motifs is in the protonated state (–NH2+/–NH3+), on the contrary, the carboxyl group in FcCA motifs is in the deprotonated state (–COO-) under neutral condition. When 1.0 equiv. of CB[7] was added (Figure 2B (b)), the signals of Hf and Hg displayed remarkable upfield shifts (Δδf=-1.2 ppm, Δδg=-1.1 ppm), while the signals of He and Hh shifted downfield (Δδe=0.11, Δδh=0.22 ppm). The upfield shifts of Hf and Hg are mainly caused by the shielding effect, indicating the central parts of Cys motifs are 11



Page 12 of 64

included in cavities of CB[7] macrocycles. The He and Hh protons experience downfield shifts ascribing to the deshielding effect, suggesting that they are located at the carbonyl-laced portals.34 At this moment, the CB[7] macrocycles owning electron-rich interior could not settle on the FcCA motifs with negative charge (-COO-) due to the electrostatic

repulsion,

evidenced

by

the

previous

literature.35

Consequently,

CB[7]·FcCA-Cys-Ⅰ supramolecular complex was formed in neutral solution. The ITC measurement (Figure S1A, Supporting Information) verifies the high association constant between CB[7] and FcCA-Cys

12


Page 13 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (A) (a) 1H NMR and (b)

13C

NMR spectra of FcCA-Cys (DMSO-d6).; (B) 1H

NMR spectra: (a) 10 μM FcCA-Cys (D2O), pD=7; (b) 10 μM FcCA-Cys and 10 μM CB[7] (D2O), pD=7, CB[7]·FcCA-Cys-Ⅰ; (c) 10 μM CB[7] (D2O); (d) 10 μM FcCA-Cys and 10 μM CB[7] (D2O:DMSO-d6=8:2), pD=3, CB[7]·FcCA-Cys-Ⅱ; (e) 10 μM FcCA-Cys (D2O:DMSO-d6=8:2), pD=3; (f) 10 μM FcCA-Cys and 10 μM CB[7] (D2O), pD=10; (g) 10 μM FcCA-Cys (D2O), pD=10. The complexation behavior at pH 3 were studied in D2O containing 20% DMSO-d6 to increase solubility.

13



Page 14 of 64

under neutral solution (Ka=1.45×106 M-1) and a stable 1:1 stoichiometric complex. After adding DCl into CB[7]·FcCA-Cys-Ⅰ inclusion complex, all FcCA protons and adjacent Ha proton underwent an upfield shift (Figure 2B(d)), while the protons of Cys motifs remained unchanged. It is reported that neutral or cationic ferrocene derivatives can form inclusion complexes with CB[7] in aqueous solution, with association constants in the range of 109 to 1013 M-1,36 which are much higher than that of CB[7]·Cys under acid solution (Ka=1.05×106 M-1, Figure S1B, Supporting Information). Acid stimulus protonates the –COO- groups to –COOH groups in FcCA motifs, which causes a reversal of association constant between CB[7] and two recognizable motifs. Depending on the ion-dipole and hydrophobic interactions,36 CB[7] macrocycles moved from Cys motifs to FcCA motifs, and the new complex of CB[7]·FcCA-Cys-Ⅱ was assembled. When pH value was adjusted to alkali range, the deprotonation of NH2+/NH3+ groups in the Cys motifs lowered the original electrostatic attraction interactions between NH2+/NH3+ and -COO- groups, leading to the appreciable decrease of association constant between CB[7] and the Cys motifs, from 1.14×106 M-1 (neutral, Figure S1C, 14


Page 15 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Supporting Information) to 8.52×103 M-1 (alkali, Figure S1D, Supporting Information), and making CB[7] macrocycles leave from the Cys motifs. Meanwhile, FcCA motifs with negative charge also cannot provide standing sites for CB[7] macrocycles. As shown in Figure 2B (f), in the alkaline solution, the addition of CB[7] had no influence the locations of protons of FcCA-Cys, indicating the dissociation of CB[7] from FcCA-Cys.

Furthermore, the influence of reduction potential on the structure of CB[7]·FcCA-Cys-Ⅰ was investigated. The mass spectrum was employed to detect the components after receiving reduction potential. As shown in Figure S2 (Supporting Information), the peaks at 77.05 and 352.79, corresponding to the reduction products, are assigned to M3+ and [M2+K-HCOOH]+, respectively, which preliminarily demonstrate that electrons enter into cavities of CB[7], cleave the disulfide bonds protected by CB[7], and destroy the structure of CB[7]·FcCA-Cys-Ⅰ when a voltage is applied.

Preparation and characterization of TSR-SNs

15



Page 16 of 64

Mesoporous silica nanoparticles (MSNs) were prepared according to a previous literature.37 MSNs have an ordered 2D hexagonal mesostructure and a diameter of about 100 nm as determined by SA-XRD (Figure 3A (a)) and TEM (Figure 3A (b)). The specific surface area, pore size and pore volume of MSNs were 1153 m2 g-1, 2.51 nm, 0.97 cm3 g-1, respectively (Figure 3A (c)). The synthetic route of TSR-SNs is present in Figure 1B. MSNs were first modified with chloromethyltriethoxysilane (CMTES) to prepare MSNs-Cl. The FTIR of MSNs- Cl is shown in Figure 3C (b). The new bond at 2933 and 2860 cm-1 in MSNs-Cl can be assigned to C-H stretching vibrations. Furthermore, the

13C

SS-NMR (Figure 3D (b)) exhibits a resonance signal at 23.9 ppm

(Ca), which can be attributed to the methylene group of CMTES. These results demonstrate the successful functionalization of the CMTES groups. Next, MSNs-Cl was treated with FcCA-Cys via nucleophilic substitution reaction to synthesize MSNs-FcCACys. Compared with MSNs-Cl, the peak at 1666 cm-1 in the FTIR spectrum of MSNsFcCA-Cys (Figure 3C (c)) is ascribed to the carboxyl group stretching vibration, and the bending vibration of N-H appears at 1479 cm-1. Meanwhile, in Figure 3D (c), the signal 16


Page 17 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of CH2 shifts to lower magnetic fields (Ca’ 49.5 ppm). In addition, several new signals appear in the spectrum of MSNs-FcCA-Cys: (i) Cys motifs: Cb (49.5 ppm), Cc,d (30.2 ppm), Ce,f (46.1 ppm), Cg,h (22.1 ppm), Ci (21.1 ppm); (ii) FcCA motifs: Cj-o (79.0-69.8 ppm), Cp (173.7 ppm), displaying the completion of the whole functionalization process. After loading BTA and capping with CB[7], the characteristic peak of the C=O stretching vibration from CB[7] appears at 1739 cm-1 (Figure 3C(d)), revealing the encirclement of CB[7] macrocycles on the molecular stalks.

The element analyses of the powder samples were carried out using XPS (Figure 3E). The Si2s, Si2p, and O1s peaks are observed at 153, 102, and 531 eV in the spectrum of MSNs, respectively (Figure 3E (a)). For MSNs-Cl, the spectrum exhibits three new peaks, C1s, Cl2s, and Cl2p, located

17



Page 18 of 64

Figure 3. (A) (a) SA-XRD pattern, (b)TEM and (c) N2 adsorption-desorption isotherm and pore size distribution of MSNs; (B) STEM image of TSR-SNs; (C) FTIR spectra of (a) MSNs, (b) MSNs-Cl, (c) MSNs-FcCA-Cys, and (d) TSR-SNs without loading BTA; (D)

13C

SS-NMR spectra of (a) MSNs, (b) MSNs-Cl, and (c) MSNs-FcCA-Cys; (E) XPS

18


Page 19 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


spectra of (a) MSNs; (b) MSNs-Cl; and (c) MSNs-FcCA-Cys; (F) TGA curves of (a) MSNs, (b) MSNs-Cl, (c) MSNs-FcCA-Cys, (d) TSR-SNs without BTA, and (e) TSR-SNs.

at respectively 284, 269, and 199 eV (Figure 3E(b)), which confirm the presence of C and Cl elements in MSNs-Cl. Compared with MSNs-Cl, the emergence of Fe2p (712 eV), N1s (399 eV), S2s (227 eV), and S2p (162 eV) signals and the disappearance of Cl2s and Cl2p signals in MSNs-FcCA-Cys prove the incorporation of FcCA-Cys groups. STEMEDS analysis (Figure 3B) was used to observe the morphology after functionalization and further identify the element distribution of TSR-SNs. The diameter of TSR-SNs is about 100 nm, with little change in MSNs, demonstrating that the functionalization process did not inflict obvious harm to the structure of MSNs. The mapping images illustrate the uniform distribution of C, N, O, Si, S, and Fe elements in the marked area, demonstrating the mono-layered supramolecular nanovalves on surface of MSNs.

SA-XRD (Figure S3A, Supporting Information) and N2 adsorption-desorption isotherm (Figure S3B, Supporting Information), and pore size distribution (Figure S3C,

19



Page 20 of 64

Supporting Information) were also utilized to monitor the reaction process. The SA-XRD pattern of the MSNs, MSNs-Cl, and MSNs-FcCA showed three well-resolved peaks at 2.3°, 3.9 °, and 4.5°, corresponding to (100), (110), and (200) planes, and the peak intensity

decreased

as

the

functionalization

continued.

For

TSR-SNs,

the

disappearance of the characteristic diffraction planes of (110) and (200) were detected, and the intensity of (100) peak also obviously reduced. The changes of hexagonal mesostructure were also found by N2 adsorption-desorption isotherm and pore size distribution. From MSNs to TSR-SNs, the specific surface area, pore size, and pore volume presented gradually declining trend (Table S1), which can be attributed to the grafting of the molecular stalks and the filling of BTA molecules in mesopores. According to the weight losses of powder samples stemming from the decomposition of organic moiety provided by TGA (Figure 3F), the grafting densities of CMTES, FcCACys, and CB[7] were calculated to be 1.26, 0.38, and 0.19 mmol g-1 MSNs, respectively. By contrasting Figure 3F (d) and (e), the loading capacity of BTA was approximately 46.9 mg g-1 MSNs. 20


Page 21 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Triple stimuli-responsive controlled release of BTA from TSR-SNs

Alkali/acid/reduction potential stimuli-responsive release experiments were investigated by UV-Vis spectroscopy (standard calibration curve of UV/Vis absorption intensity of BTA can be seen in Figure 4 (A). Prior to pH or voltage trigger, only a negligible amount of BTA molecules leaked from TSR-SNs under neutral solution (less than 1.1% after 6.0 h), manifesting that the outside supramolecular nanovalves were on the close states. Combined with the results of 1H NMR spectra, it can be inferred that CB[7] macrocycles resided on the Cys motifs, near the pore orifices, locking the outlets for BTA molecules. Upon increasing pH values, the release of BTA molecules was observed immediately, and the release rate of BTA varied as a function of the alkalinity, the cumulative release amounts of BTA were calculated as 28.1%, 53.2%, and 81.2% at pH 9, 10, and 11, respectively after 5.5 h (Figure 4B). Similarly, the UV/Vis intensity of BTA drastically increased after the treatment with HCl solution. The BTA release rate was associated with the acidity. In the case of pH 5.0, 32.65% of BTA was released within 5.5 h, while at pH 3.0, about 83.45% of BTA was released in the same period time (Figure 4C). The 21



Page 22 of 64

abrupt release of BTA molecules is attributed to the changes of states for supramolecular nanovalves. In acidic condition, CB[7] macrocycles moved up to the FcCA motifs, leaving the gaps for BTA molecules to diffuse out; while in alkaline condition, CB[7] macrocycles separated from the molecular stalks, BTA molecules could freely escaped from TSR-SNs due to the lack of the gatekeepers. As regards reduction potential stimulus-responsive experiments, we used conductive adhesive to connect the TSR-SNs with platinum working electrode (Figure 4D). As

22


Page 23 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (A) Standard calibration curve of UV/Vis absorption intensity of BTA; (B) Alkali-triggered release profiles of BTA from TSR-SNs under different alkalinity. (C) Acid-triggered release profiles of BTA from TSR-SNs under different acidity. (D)

23



Page 24 of 64

Experimental setup of the reduction potential-triggered release. (E) Reduction potentialtriggered release profiles of BTA from TSR-SNs.

can be seen in Figure 4E, upon applying reduction potential (-1.0 V vs. SHE), the release of BTA was also accelerated (9.3% BTA per ten minutes). When the reduction potential was removed, the release curves became flat, indicating the release process was gradually stopped. The existence of the disulfide bonds is the key factor to realize reduction potential stimulus-responsive controlled release. Although the disulfide bonds are protected by CB[7] macrocycles in neutral solution, the electrons generated from reduction potential can also enter into cavities of CB[7] macrocycles, get a chance to cleave the disulfide bonds and finally lead to the fracture of supramolecular nanovalves. In order to verify our supposition, we collected the TSR-SNs after release experiments for FTIR and

13C

SS-NMR measurements. The characteristic peaks in FTIR and

13C

NMR spectra all proved that the residue organic components on surface of MSNs fully matched our expectant chemical structures (Figure S4, Supporting Information). Furthermore, the pH values of ultrapure water (with flowing oxygen) with and without 24


Page 25 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


applied voltage (-1 V vs SHE) were tested. Both of the results were similar, pH 7.0. It demonstrates that the applied voltage of -1 V vs SHE will not lead to a raise in pH value. The only reason that the BTA inhibitors released is the exertion of potential stimulus. The oxidation potential facilitate the broken parts anchoring on the working electrodes to reconnect in a certain extent,38 the reformed supramolecular nanovalves could regulate the outflow of BTA molecules again, which is responsible for the phenomenon of inhibition of release BTA.

Preparation of TSR-SNs-based SF-SHAC

In order to show the design advantages of TSR-SNs in the application of SHACs, TSRSNs were used as the guest components and doped into the organic-inorganic hybrid SiO2-ZrO2 sol-gel coating to construct TSR-SNs-based SF-SHAC. Hybrid sol-gel coatings are regarded as promising barrier defenses for corrosion protection of aluminum alloys.39 Considering the benefits of bottom-aggregation distribution for smart

25



Page 26 of 64

nanocontainers,31,32 the TSR-SNs-based SF-SHAC was deposited on the surface of AA2024 by successive dipping of

Figure 5. (A) Optical photograph of TSR-SNs-based SF-SHAC deposited on AA2024; (B) Top-view SEM images of TSR-SNs-based SF-SHAC; (C) AFM topographic images of TSR-SNs-based SF-SHAC; (D) Cross-section SEM images of TSR-SNs-based SFSHAC (left) and high-resolution SEM image of the marked zone (right); (E) EDS analysis of selected TSR-SNs.

26


Page 27 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TSR-SNs@SiO2-ZrO2 sol and pure SiO2-ZrO2 sol (Figure 1C), which aims to gather the doped TSR-SNs near surface of AA2024. The optical photograph of coated AA2024 sample is shown in Figure 5A. The boundary line between metallic substrate and TSRSNs-based SF-SHAC is distinct. Figure 5B presents top-view SEM image of TSR-SNsbased SF-SHAC, and the coating was smooth and defect-free. The root-mean-square (RMS) roughness is about 1.30 nm determined by the tapping-mode AFM topographic image (Figure 5C). The cross-section of TSR-SNs-based SF-SHAC was observed with SEM, and the thickness was 2.6 μm. At the upper position of the coating was homogeneous and flat. In contrast, some spherical particles with 100 nm diameters appeared in the bottom position of the coating (Figure 5D). EDS analysis (Figure 5E) proves that the particles contain the elements C, N, O, Fe, Si, and S, confirming the existence of doped TSR-SNs. Dynamic light scattering (DLS) measurements of TSRSNs in SiO2-ZrO2 sol was taken in Figure S5 (Supporting Information). The results show their good colloidal stability and most particles disperse uniformly and no agglomeration.

The anticorrosion performance of TSR-SNs-Based SF-SHAC 27



Page 28 of 64

In order to protrude the advantages of the TSR-SNs-based SF-SHAC (denote as Coating Ⅰ), three coatings were intentionally prepared and labeled as reference. In Coating Ⅱ, the acid/alkali dual stimuli-responsive smart nanocontainers (DSR-SNs, the synthetic route can be seen in Supporting Information) were used to replace TSR-SNs. The significant difference between DSR-SNs and TSR-SNs is that DSR-SNs cannot respond to corrosion potential stimulus. Coating Ⅲ is the pure SiO2-ZrO2 sol-gel coating and no smart nanocontainers were incorporated during preparation. Coating Ⅳ is the same as Coating Ⅰ but without BTA (Figure 6A). The adhesion test of the Coating Ⅰ and Coating Ⅱ are shown in Figure S6 (Supporting Information), there is no evident effect on adhesion whether nanocontainers are added or not in the sol-gel coating. EIS measurements, as the non-destructive and powerful technique, were conducted to evaluate the anticorrosion performances and analyze the failure process of the coatings. Figure 6B shows the Bode plots for Coating Ⅰ immersed in 0.5 M NaCl solution for different immersion time. At the beginning of immersion (1 h), the Bode spectra obtained for the four coatings have the almost same profiles, which indicates that the 28


Page 29 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


incorporation of the appropriate smart nanocontainers have the little influence on the coating thickness. The phase angle is between -80º and -90º and the slope of impedance against logf is about -1 over wide frequency range, meaning that the coatings behave nearly as capacitors and show insulting properties. Only one time constant can be found in Bode phase plots as a result of the barrier characteristic of the sol-gel

29



Page 30 of 64

Figure 6. (A) Schematic structures of Coating Ⅰ, Coating Ⅱ, Coating Ⅲ, and Coating Ⅳ; (B) Bode plots obtained on AA2024 coated with Coating Ⅰ, Coating Ⅱ, Coating Ⅲ, and Coating Ⅳ after immersion for 1 (olive), 36 (blue), 120 (red), and 480 (purple) hours in 0.5 M NaCl, respectively; (C) Optical photographs of Coating Ⅰ, Coating Ⅱ, Coating Ⅲ, and Coating Ⅳ after immersion for 120 and 480 hours in 0.5 M NaCl, respectively; (D) 30


Page 31 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The equivalent circuits used for Bode plot fitting; (E) The evolution of Rcoating (a) and Roxide (b) of Coating Ⅰ, Coating Ⅱ, Coating Ⅲ, and Coating Ⅳ.

coatings. The EIS plots greatly changed as the immersion time elapsed to 36 h. The resistive plateaus decreased continuously, indicating the gradual degradation of the barrier coatings, and the new time constants responsible for the aluminum oxide layer, with the phase angle maximum -68º, is located in the low frequency range. At this moment, the differences in the EIS plots for the four coatings were not apparent. After immersion for 120 h, Coating Ⅰ and Coating Ⅱ possess the higher corrosion protection property than Coating Ⅲ and Coating Ⅳ, mainly reflected in the following three aspects: (ⅰ) the impedance values (│Z│) at low frequency usually represents the protective properties. The │Z│0.01Hz values of Coating Ⅰ and Coating Ⅱ are basically stable, whereas the │Z│0.01Hz value of Coating Ⅲ and Coating Ⅳ decreased from 1.38×106 to 3.16×105 Ohm·cm2, and 4.75×106 to 2.78×105 Ohm·cm2, respectively, indicating the occurrence of electrochemical process on surface of AA2024. (ⅱ) In Bode phase angle plots, the third time constant assigned to the pitting onset was pronounced in the case 31



Page 32 of 64

of Coating Ⅲ and Coating Ⅳ, whereas this time constant was not detected in the phase angle plots of Coating Ⅰ and Coating Ⅱ. The optical photographs of AA2024 coated with the four coatings also confirm the protective differences. Several corrosion pitting and deposits appeared on the surface of Coating Ⅲ and Coating Ⅳ, indicating the corrosive species (Cl-, H2O, O2) had reached the metallic surface and caused local corrosion. (ⅲ) the resistive plateau corresponding to the coating resistance ranks the following order: Coating Ⅰ > Coating Ⅱ > Coating Ⅲ ≈ Coating Ⅳ, suggesting the most serious deterioration of barrier capacity for Coating Ⅲ and Coating Ⅳ. The results fully demonstrate the importance of BTA, which can be released and form protective molecular films on bare metallic substrates upon stimuli around corrosive regions. For comparison, Coating Ⅰ and Coating Ⅱ maintained the intact protection and no obvious corrosion signs were observed. At the end of the immersion of 480 h, Coating Ⅲ and Coating Ⅳ basically lost its protective ability, evidenced by severe blisters on the surface and the disappearance of resistive plateau. Although Coating Ⅰ and Coating Ⅱ also remarkably degraded, they still displayed two time constants, kept surface from 32


Page 33 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


corrosion attack, and the │Z│0.01Hz value was in the range of 1.45×106 to 1.47×106 Ohm·cm2, which is one and a half order magnitude higher than that of Coating Ⅲ and Coating Ⅳ. These phenomena confirm the better corrosion inhibition of Coating Ⅰ and Coating Ⅱ. It is not difficult to infer that either TSR-SNs or DSR-SNs play the two important roles during the whole immersion process: (ⅰ) smart nanocontainers act as nanofillers to decrease the porosity of SiO2-ZrO2 sol-gel coating, postpone the penetration rate of aggressive species and prolong the service life of sol-gel coatings; (ⅱ) smart nanocontainers can release corrosion inhibitors when corrosion occurs, which is the main reason for the stable of │Z│0.01Hz values.

The electrochemical equivalent circuits (EECs) in Figure 6D were used to fit and quantitatively interpret the impedance data, where Rs is the solution resistance, Rcoating and CPEcoating are the resistance and capacitance of the SiO2-ZrO2 sol-gel coating, Roxide and CPEoxide are the resistance and capacitance of aluminum oxide layer, and Rct and CPEdl are the charge transfer resistance and a double layer capacitance. The constant phase element (CPE) was used instead of a capacitive element (C) to account 33



Page 34 of 64

for the non-homogeneity of electrodes in the Bode plots. The selection criteria for EECs are based on the numbers of time constants. Figure 6E demonstrates the variations of the impedance parameters with immersion time. It is generally known that the Rcoating has been used for measuring porosity, and Qcoating is a parameter to reflect water absorption of coatings. During the immersion, the Rcoating values of all the four coatings exhibited notable decrease because of penetration of the electrolyte, however, the fast dropping of Rcoating (from 7.2×106 to 4960 Ohm·cm2) for Coating Ⅲ clearly corroborate that the introduction of smart nanocontainers lower amount of conductive pathways for electrolytes. The parameter of Roxide is another important index for estimate the total corrosion protection effectiveness of SF-SHACs. As shown in Figure 6E (b), the Roxide values of Coating Ⅰ and Coating Ⅱ kept relatively stable for a long time, while for Coating Ⅲ and Coating Ⅳ, Roxide value drops markedly after immersion for 480 h. It is believed that the corrosion inhibitors released from smart nanocontainers recovered the function of aluminum oxide layer and stabilized the Roxide values to a certain degree. From EIS data, there is the little difference in overall anticorrosion performances between Coating 34


Page 35 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ⅰ and Coating Ⅱ. As for Coating Ⅲ and Coating Ⅳ, the major drawback was that they provided only passive protection, and they lost their protective function when corrosive species penetrated through the passive coatings.

The protective effects of the four coatings for AA2024 were also assessed by salt spray tests (SST), which is a classic well-known method to test corrosion resistant for coatings. The tests were performed on the coated samples with “X”-type scratches. The obtained salt spray test results after exposure to salt fog after 480 h are represented in Figure S7 (Supporting Information). Coating Ⅲ showed more than 130 corrosion points, and the number of corrosion points was significantly reduced by the incorporation either TSRSNs or DSR-SNs. These data are in good agreement with the EIS data. In SST, it is remarkable that the corrosion resistance of Coating Ⅰ in “X”-type scratched area was superior to that of Coating Ⅱ. The status of “X”-type scratched area was carefully observed by the optical microscope. The scratched area of Coating Ⅰ remained metallic luster and no creepage along “X”-type scratches. However, agglomerate and white lumps were present in the “X”-type scratches of Coating Ⅱ and Coating Ⅲ. EDS results 35



Page 36 of 64

show that the lumps are composed of Al, O, Na and Cl elements, which derive from the corrosion products of aluminum hydroxide and oxychlorides.40 Furthermore, after exposure for 1920 h, the surface of Coating I showed no blisters and fragments, indicating satisfactory long-term protective performance (Figure S8, Supporting Information). The protective differences in “X”-type scratches between Coating Ⅰ and Coating Ⅱ are probably due to the different stimuli-responsive controlled release characteristic of the doped smart nanocontainers, TSR-SNs and DSR-SNs (Figure S9, Supporting Information). Furthermore, in order to highlight the effect of inhibitor molecules (BTA), the sample of Coating Ⅳ was also evaluated by SST. The corrosion degree of Coating Ⅳ is between that of Coating Ⅱ and Coating Ⅲ, which is far worse than Coating Ⅰ. Obviously, the empty nanocontainers doped in coating play an active role in some degree, but BTA molecules play more critical role.

The self-healing ability of the Coating Ⅰ, Coating Ⅱ, and Coating Ⅲ was evaluated using scanning vibrating electrode technique (SVET). Figure 7 present the optical micrograph and SVET current density maps over the scratched surface of the samples immersed in 36


Page 37 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.05 M NaCl solution. Figure 7(e) represents the maximum anodic and cathodic current densities over the defect area during the monitoring time of 150 hours in 0.05 M NaCl solution. The local current peaks in the scratched area were detected in all the three coatings after 4 h of immersion, indicating the occurrence of local corrosion. As time goes by, the changing trends of local current densities were completely different. The corrosion activity of Coating Ⅲ increased continuously from 4.3/-2.0 μA cm-2 (anodic/cathodic) after 4 h to about 13.0/-6.0 μA cm-2 after 60 h of testing (Figure 7C (e)). In contrast, a self-healing effect was observed on the Coating Ⅰ and Coating Ⅱ due to the release of BTA from TSR-SNs and DSR-SNs, respectively. However, different from EIS results, there was an obvious difference in self-healing efficiency between Coating Ⅰ and Coating Ⅱ. Through monitoring the evolutions of current densities near the scratches during the whole immersion process, it was found that Coating Ⅰ exhibited fast

37



Page 38 of 64

Figure 7. Optical micrograph (a) and SVET current density maps of (A) Coating Ⅰ, (B) Coating Ⅱ, and (C) Coating Ⅲ for immersion of 4 (b), 30 (c), 60 (d) hours, and (e) maximum anodic and cathodic current densities over the defect area during the monitoring time of 150 hours in 0.05 M NaCl solution.

inhibition rate of corrosive activities than that of Coating Ⅱ. We deliberately selected some representative time points for comparison. After 30 h of immersion, Coating Ⅰ is only a small sign of corrosion activity (Figure 7A (c)), the anodic and cathodic current density values decreased to 1.54 and -0.8 μA cm-2, respectively, which is completely disappeared at 40 h, as shown in Figure 7A (e). As for Coating Ⅱ, the anodic and 38


Page 39 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cathodic current density values were both down slightly after 30 h (2.8 μA cm-2 for anodic and -2.0 μA cm-2 for cathodic), and slowly dropped to 2.11 and -1.69 μA cm-2, respectively, then eventually suppressed for 90 h. Coating Ⅱ took 2.25 times the selfhealing time of Coating Ⅰ. Apparently, compared with Coating Ⅱ, containing pH-stimulus responsive smart nanocontainers, the incorporation of TSR-SNs effectively enhances the responsive sensitivity of the coating.

The SVET results of Coating Ⅱ showed that the anodic and cathodic corrosive activities had been inhibited, which could be ascribed to the facts that pH stimuli stemming from corrosive micro-cathodic/anodic regions opened the supramolecular nanovalves and release the corrosion inhibitors to form molecular protective films. In this work, DSRSNs were used as reference, and we found that Coating Ⅰ with TSR-SNs had the faster inhibiting rates for corrosive cathodic/anodic current densities than Coating Ⅱ, manifesting the excellent feedback rate of Coating Ⅰ. Combined with the results obtained in salt spray tests, it is certain that TSR-SNs exhibit distinct advantages during selfhealing process than DSR-SNs. As shown in Scheme 1, pH stimuli intensities around 39



Page 40 of 64

corrosive micro-regions are location-dependent. The acidic/alkaline central regions own the high stimuli intensities, while the outer regions possess the relatively low stimuli intensities. DSR-SNs cannot sensitively feel the weak pH stimuli (such as, acidic: pH 7.0-5.5, alkaline: pH 7.0-8.5) , which will make partial of DSR-SNs located in the outer regions, close the supramolecular nanovalves and prevent the flow out of corrosion inhibitors. In view of this, in order to further enhance the work efficiency of smart nanocontainers, we focused our attentions on the other reliable and case-selective trigger, corrosion potential.41 As we all known, After local corrosion onset, the surface potential of the damaged region will decrease to the corrosion potential of AA2024, about -1.05 V vs. SHE, which is sufficient to break the disulfide bonds.42 In the previous section, we have proven that TSR-SNs can respond to the reduction potential (-1.0 V vs. SHE) and release corrosion inhibitors immediately. Therefore, besides acid/alkaline stimuli-responsive features, the well-designed TSR-SNs can also respond to the corrosion potential of AA2024 stimulus, capture the electrons transferring from corrosive micro-cathodic to micro-anodic regions, self-degrade the supramolecular nanovalves 40


Page 41 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and release corrosion inhibitors. This design strategy guarantees wherever TSR-SNs are located in damaged

Scheme 1. Schematic representation of the self-healing mechanism of (A) Coating Ⅰ and (B) Coating Ⅱ.

regions, they can respond to the various environmental stimuli at the first time, quickly give a feedback to release corrosion inhibitors and increase the feedback rate of SF-

41



Page 42 of 64

SHAC. The feedback rate of SF-SHAC performs the vital role in self-healing process. If the local damaged area cannot get a remedy without delay, a large number of corrosion products will be produced. In some cases, corrosion products have been proven to slow down the penetrating rate to a certain extent,43-45 however, the loose structure cannot provide long-term corrosion inhibition capacity indefinitely. For SF-SHACs, it is expected that all the doped smart nanocontainers can accomplish the presetting functions for controlled release of corrosion inhibitors. TSR-SNs synthesized in this work prevent the undesirable leakage in normal conditions and avoid the waste of embedded BTA molecules. More importantly, TSR-SNs are endowed with the acid/alkali/corrosion potential triple stimuli responsive controlled release function via elaborate design of supramolecular nanovalves, which guarantees the reliable response to the corrosion process, helps them to work efficiently in corrosive micro-regions and resolves the problems of insensitive smart nanocontainers due to the weak environmental stimuli. The high concentration of corrosion inhibitors gathered in the local damaged area can

42


Page 43 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


easily form compact protective film on bared AA2024 surface, offering the long-lasting effective self-healing results.

Conclusions

In conclusion, the novel multiple-stimuli feedback, corrosion inhibitor-compensating SHSFAC was constructed by introducing well-designed acid/alkali/corrosion potential triple stimuli-responsive smart nanocontainers into SiO2-ZrO2 sol-gel coating for protection of AA2024. Benefiting from the triple stimuli-responsive controlled release characteristics, the smart nanocontainers can simultaneously respond to acid stimulus at micro-anodic regions, alkali stimulus at micro-cathodic regions and corrosion potential of AA2024 around corrosive regions and quickly give a feedback to release corrosion inhibitors, forming protective molecular films on bare metallic substrates. Endowing conventional pH stimuli-responsive smart nanocontainers with corrosion potential stimulusresponsive property increases the working efficiency of the doped smart nanocontainers and provides another alternative to enhance the feedback rate of SF-SHACs, which will

43



Page 44 of 64

contribute to reliable and long-lasting self-healing actions. Considering the problems of industrial application, we will devote to optimize the synthetic route of TSR-SNs and enhance the reaction efficiency in our future work.

Experimental section

Materials and methods All the chemicals were purchased from Sigma-Aldrich and Aladdin Industrial Inc. (Shanghai, China) (the detailed materials can be seen in the Supporting Information). The reagents were of analytical grade and used as received. 1H and

13C

NMR spectra

were recorded on a Bruker Avance 300 spectrometer. Mass spectra were recorded on Thermo Trace DSQ LC-MS spectrometer. Isothermal titration calorimetry (ITC) was carried out using a TA Instrument Nano ITC and ITC AFFINITY apparatus to measure the association constant between host and guest. The 13C SS-NMR were recorded on a Bruker Avance Ⅲ WB 400 NMR spectrometer using a 4 mm ZrO2 rotors spinning at 12 KHz, and Larmor frequency was set to 79.5 MHz. The morphologies of the

44


Page 45 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


nanoparticles and coatings were studied using a JEOL JSM-6390LV SEM-EDS. TEM images were taken using a JEM-2100 microscope. STEM-EDS were recorded from FEITecnai G2 F30 S-TWIN TEM operated at 200 kV. FTIR analyses were recorded on a Bruker Tensor 27 FTIR spectrometer. SA-XRD patterns were carried out on a Bruker D8 Advanced diffractometer applying monochromatized Cu Kα radiation. BET surface area and BJH pore volume were estimated by Quanta chrome Nova 1000 Micrometric apparatus at -196 ℃. TGA measurements were performed with a Mettler TGA-SDTA 851e instrument with a heating rate of 20 ℃ min-1 under nitrogen protection. XPS analyses were collected on a PHI Quantera II spectrometer with the Al Kα as X-ray source. The hydrodynamic diameters were measured by DLS using a Malvern Zetasizer 90 at 25 °C. UV-Vis absorption spectra were obtained on a Shimadzu UV-1800 spectrometer to determine the concentrations of BTA. AFM measurements were performed with a Bruker Multimode 8 Atomic Force Microscope in the tapping mode. The adhesion tests were measured with an electronically controlled hydraulic pump (PosiTest AT-A, DeFelsko). 45



Page 46 of 64

Synthesis of FcCA-Cys The synthetic route of N-{2[(2-aminoethyl)disulfanyl]ethyl}-4-(1’-carboxyferrocenyl) butan-1-amine (FcCA-Cys) is depicted in Figure 1A. The chemical structures were characterized by 1H, 13C NMR spectra and mass spectra.

Methoxycarbonylferrocene (2). To a stirred solution of ferrocenecarboxylic acid (4.0 g, 17.4 mmol) in CH3OH (120 mL) was added BF3·Et2O (12.3 mL). The reaction mixture was refluxed for 24 h. After the reaction was cooled to room temperature, a 10% NaHCO3 solution was added to adjust to pH 8, the mixture was extracted with CH2Cl2 (3×60 mL). The organic phase was washed with brine (3×60 mL), dried over anhydrous MgSO4, and the solvent was removed under vacuum. The crude product was recrystallized from petroleum ether to give 2 as an orange solid (3 g, 71% yield): 1H NMR (300 MHz, CDCl3) δ 4.81 (s, 2H), 4.40 (s, 2H), 4.21 (s, 5H), 3.81 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 172.07, 71.18, 70.96, 70.01, 69.63, 51.45.

1-(Methoxycarbonyl)-1’-(4-chlorobutanoyl)ferrocene (3). A solution of 4-chlorobutyryl chloride (0.34 mL, 3 mmol) in CH2Cl2 (5 mL) was added dropwise to a solution of 2 (0.5 46


Page 47 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


g

， 2.1 mmol) and AlCl3 (0.73 g, 5.5 mmol) in CH2Cl2 (5 mL) in an ice bath under

nitrogen atmosphere, and the reaction allowed to stir for 2 h at room temperature. The mixture was poured into ice water (300 mL) contain HCl (6 mL) and extracted with CH2Cl2 (3×60 mL). The combined organic phase was washed with brine (3×60 mL), dried over anhydrous MgSO4, and the solvent was removed under vacuum. The crude product was purified by column chromatography on silica gel (PE: Diethyl ether=2:1) to afford 3 as a dark red oil (0.6 g, 82% yield): 1H NMR (300 MHz, CDCl3) δ 4.81 (s, 4H), 4.52 (s, 2H), 4.42 (s, 2H), 3.82 (s, 3H), 3.69 (t, J = 6.3 Hz, 2H), 2.91 (t, J = 6.8 Hz, 2H), 2.23 – 2.12 (m, 2H);

13C

NMR (75 MHz, CDCl3) δ 202.22, 170.65, 79.94, 73.41, 72.59,

71.51, 70.55, 51.73, 44.68, 36.16, 26.49. 1-(methoxycarbonyl)-1’-(4-chlorobutyl)ferrocene (4). Intermediate 1 (Zn-Hg): A mixture of Zn (3g, 45.9 mmol) and HgCl2 (0.25 g, 0.92 mmol) was added into a solution of HCl (24 mol/L, 10 mL). The reaction mixture was stirred at room temperature for 30 min. The precipitate was filtered and washed with CH3OH. Zn-Hg (10 g) was added slowly to a solution of 3 (2 g, 5.74 mmol) in CH3COOH (26 mL) and HCl solution(36 wt%, 40 mL). The reaction mixture was stirred at room temperature for 1 h. The mixture was poured into water (100 mL) and extracted with CH2Cl2 (3×60 mL). The combined organic phase was washed with brine (3×60 mL), dried over anhydrous MgSO4, and the solvent was removed under vacuum. The crude product was 47



Page 48 of 64

purified by column chromatography on silica gel (CH2Cl2:CH3OH=15:1) to afford 4 as an orange oil (1.88 g, 98% yield): 1H NMR (300 MHz, CDCl3) δ 4.72 (s, 2H), 4.34 (s, 2H), 4.08 (s, 4H), 3.81 (s, 3H), 3.53 (t, J = 6.6 Hz, 2H), 2.36 – 2.23 (m, 2H), 1.77 (dd, J = 13.9, 7.1 Hz, 2H), 1.62 (dd, J = 15.1, 7.7 Hz, 2H);

13C

NMR (75 MHz, CDCl3) δ 171.87, 89.95, 71.67, 71.47, 70.54,

69.59, 68.90, 51.38, 44.75, 32.18, 28.11, 27.68. 1-(carboxyl)-1’-(4-chlorobutyl)ferrocene (5). A mixture of 4 (2 g, 6.0 mmol) and LiOH·H2O (3.6 g, 85.8 mmol) was added into a mixture of THF (240 mL) and deionized water (20 mL). The reaction mixture was refluxed for 5 d under nitrogen atmosphere. After the THF was removed under vacuum, a CH3COOH solution was added to adjust to pH 6-7, the mixture was extracted with ethyl acetate (3×60 mL). The combined organic phase was washed with brine (3×60 mL), dried over anhydrous MgSO4, and the solvent was removed under vacuum. The crude product was purified by column chromatography on silica gel (CH2Cl2:CH3OH=15:1) to afford 5 as a red solid (1 g, 52% yield): 1H NMR (300 MHz, CDCl3) δ 4.79 (s, 2H), 4.44 (s, 2H), 4.14 (d, J = 6.3 Hz, 4H), 3.53 (t, J = 6.4 Hz, 2H), 2.34 (t, J = 7.5 Hz, 2H), 1.90 – 1.68 (m, 2H), 1.64 (dd, J = 15.0, 7.6 Hz, 2H);

13C

NMR (75 MHz, CDCl3) δ 178.33, 90.18, 72.51, 71.10, 69.93, 69.34,

44.75, 32.18, 28.06, 27.46; MS (ESI): m/z calcd. for C15H17ClFeO2: 320.03 ; found: 320.95 [M+H]+. 1-(tert-Butoxycarbonyl)-1’-(4-chlorobutyl)ferrocene (6). To a solution of 5 (500 mg, 1.5 mmol) in CCl4 (4 mL) was added oxalyl chloride (0.34 mL, 4.0 mmol), and then the mixture was stirred at room temperature for 2.5 h. The solvent was removed by reduced pressure distillation, and tert-butanol (4 mL, 43.7 mmol) was added to the flask. After the reaction mixture was refluxed for 1.5 h under nitrogen atmosphere, the resultant solution was poured into NaOH solution (0.5 M, 40 mL) and extracted with diethyl ether (3×60 mL). The combined organic 48


Page 49 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


phase was dried over anhydrous MgSO4, and the solvent was removed under vacuum. The crude product was purified by column chromatography on silica gel (CH2Cl2) to afford Compound 6 as a yellow oil (0.15 g, 26% yield): 1H NMR (300 MHz, CDCl3) δ 4.67 – 4.61 (s, 2H), 4.31 – 4.27 (s, 2H), 4.10 (d, J = 1.7 Hz, 2H), 4.06 (d, J = 1.5 Hz, 2H), 3.53 (t, J = 6.6 Hz, 2H), 2.40 – 2.32 (m, 2H), 1.78 (dd, J = 14.7, 6.9 Hz, 2H), 1.64 (dd, J = 9.2, 6.2 Hz, 2H), 1.56 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 170.68, 89.72, 79.89, 73.43, 71.34, 70.59, 69.60, 68.83, 44.71, 32.17, 29.59, 28.33, 28.16, 28.06.

N-{2[(2-aminoethyl)disulfanyl]ethyl}-4-[1’-(tert-Butoxycarbonyl)ferrocenyl]

butan-1-

amine (7). Intermediate 2 (Cystamine): To a solution of cystamine dihydrochloride (4.5 g, 20 mmol) in CH2Cl2 (40 mL) was added NaOH solution (1 M, 40 mL), and then the mixture was stirred at room temperature for 5 h. The resultant solution was extracted with CH2Cl2 (3×60 mL). The combined organic phase was dried over anhydrous MgSO4, and the solvent was removed under vacuum to afford a yellow liquid (2 g, 66% yield). A solution of 6 (400 mg, 1 mmol) in CH3CN (5 mL) was added dropwise to a solution of cystamine (2.3 g ， 15 mmol) in CH3CN (5 mL), triethylamine (215 mg, 2 mmol) and K2CO3 (276 mg, 2 mmol) was added to the flask. The reaction was refluxed for 8 h under nitrogen atmosphere. The solvent was removed under vacuum. The crude

49



Page 50 of 64

product was purified by column chromatography on silica gel (CH2Cl2:CH3OH: NH3·H2O=75:5:1) to afford 7 (200 mg, 41% yield): 1H NMR (300 MHz, CDCl3) δ 4.63 (t,

J = 1.9 Hz, 2H), 4.30 – 4.25 (m, 2H), 4.08 (d, J = 1.7 Hz, 2H), 4.05 (d, J = 1.6 Hz, 2H), 3.01 (t, J = 6.2 Hz, 2H), 2.93 (t, J = 6.3 Hz, 2H), 2.82 (t, J = 6.3 Hz, 2H), 2.75 (t, J = 6.2 Hz, 2H), 2.62 (dd, J = 8.7, 4.1 Hz, 2H), 2.34 (d, J = 6.9 Hz, 2H), 1.55 (s, 9H), 1.51 (dd, J = 6.7, 3.6 Hz, 4H);

13C

NMR (75 MHz, CDCl3) δ 170.66, 90.13, 79.76, 73.27, 71.28,

70.49, 69.56, 68.67, 49.15, 47.85, 42.19, 40.37, 38.48, 29.66, 28.63, 28.29.

N-{2[(2-aminoethyl)disulfanyl]ethyl}-4-(1’-carboxyferrocenyl)butan-1-amine

(FcCA-

Cys). Trifluoroacetic acid (6 mL, 80.8 mmol) was added dropwise to a solution of 7 (200mg, 0.4 mmol) in CH2Cl2 (6 mL), and the mixture was stirred at room temperature for 8 h. The solvent was removed under vacuum. The crude product was purified by column chromatography on silica gel (CH2Cl2:CH3OH:acetic acid=4:1:0.2) to afford FcCA-Cys (140 mg, 80% yield): 1H NMR (300 MHz, DMSO-d6) δ 4.58 (s, 2H), 4.35 (s, 2H), 4.06 (s, 4H), 3.18 (s, 2H), 3.10 – 3.03 (m, 2H), 2.92 (m, 6H), 2.24 (t, J = 7.3 Hz, 2H), 1.53 (d, J = 6.7 Hz, 2H), 1.47 – 1.40 (m, 2H);

13C

NMR (75 MHz, DMSO-d6) δ 50


Page 51 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


171.65, 88.95, 71.09, 70.09, 70.09, 69.05, 68.67, 46.38, 45.31, 37.37, 33.43, 31.79, 26.82, 24.91; MS (ESI): m/z calcd. for C19H28FeN2O2S2: 436.09 ; found: 437.2 [M+H]+ Preparation of TSR-SNs and DSR-SNs The preparation route of TSR-SNs is depicted in Figure 1B. The chemical structures were characterized by 13C SS-NMR, SEM-EDS, TEM, STEM-EDS, FTIR, SA-XRD, BET, TGA, and XPS.

MSNs-Cl. MSNs (200 mg) were suspended in dry toluene (12 mL). CMTES (100 μL, 0.48 mmol) was added dropwise to the mixture and the reaction was refluxed overnight under N2 atmosphere. The product was collected by centrifugation, washed with toluene and methanol several times, and dried overnight.

MSNs-FcCA-Cys. MSNs-Cl (200 mg) were suspended in dry DMSO (10 mL). FcCACys (209 mg, 0.48 mmol) in dry DMSO (2 mL) was added dropwise to the mixture and the reaction was stirred at 60℃ under N2 atmosphere overnight. The product was obtained by centrifugation, washed with DMSO and CH3OH, and dried overnight.

51



Page 52 of 64

TSR-SNs. MSNs-FcCA-Cys (50 mg) were suspended in DMF (10 mL) containing BTA (0.8 g). The device was stirred at room temperature for 24 h. When the equilibrium was reached, a mixture of CB[7] (100 mg), NaCl (10 mg) and BTA (0.4 g) in PBS solution (pH 7.4, 5 mL) was added to the reaction and left for an extra 24 h. The product was collected by centrifugation, washed with distilled water, dried under vacuum overnight.

DSR-SNs. The detailed synthesis process, TGA and

13C

SS-NMR spectrum of DSR-

SNs can be seen in Supplementary Data (Figure S9 and S10). The loading capacity of BTA in DSR-SNs was approximately 50.2 mg g-1 MSNs. Release experiments UV-Vis absorption spectra were obtained on a Shimadzu UV-1800 spectrometer to determine the concentrations of BTA. For alkali/acid stimuli release experiments, TSRSNs were sealed in the dialysis membrane, and placed on the top of quart cuvette. PBS was added into the cuvette to ensure that TSR-SNs were immersed into the solution. For reduction potential stimulus release experiments, TSR-SNs were directly glued on 52


Page 53 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


working electrode by conductive adhesive. The voltage was reduced at -1.0 V and oxidized at +1.0 V vs SHE. An aliquot of the supernatant was withdrawn at predetermined time intervals to calculate the concentrations of BTA. Fabrication of SF-SHAC The preparation route of SF-SHAC is depicted in Figure 1C. The surface morphology and chemical components were characterized by SEM-EDS and atomic force microscope (AFM). AFM measurements were performed with a Bruker Multimode 8 Atomic Force Microscope in the tapping mode.

TSR-SNs@SiO2-ZrO2 sol. SiO2-ZrO2 sol was prepared according to a previous literature.[9] Briefly, the silane-based sol formed by reactions of (3-glycidyloxypropyl) trimethoxysilane, 2-propane, and HNO3 solution (pH=0.5) with the volume ratio of 8:8:1. The zirconia-based sol was made of ethyl acetoacetate and zirconium tetrapropoxide (70% in n-propanol) with the volume ratio of 1:1. The SiO2-ZrO2 sol was formed by mixing silane-based sol and zirconia-based sol (volume ratio of 2:1). TSR-SNs were

53



Page 54 of 64

added and evenly dispersed to SiO2-ZrO2 sol. The amount of TSR-SNs was 1 wt% (relative to SiO2-ZrO2 sol weight).

Coating Ⅰ. AA2024 was cleaned ultrasonically with alcohol and water, and then dried in the atmosphere. Coating Ⅰ was deposited on the surface of AA2024 by successive deposition of TSR-SNs@SiO2-ZrO2 coating and SiO2-ZrO2 coating using a dip-coating method. The withdraw speed was 18 cm min-1 and the immersion time was 20 s. The specimen was cured at 80 ℃ for 90 min.

Coating Ⅱ. The preparation procedure of Coating Ⅱ was as the same as that of Coating Ⅰ, except the TSR-SNs was replaced by DSR-SNs.

Coating Ⅲ. The preparation procedure of Coating Ⅲ was as the same as that of Coating Ⅰ, except for the no addition of TSR-SNs in SiO2-ZrO2 sol.

Coating Ⅳ. The preparation procedure of Coating Ⅳ was as the same as that of Coating Ⅰ, except for the no addition of BTA in TSR-SNs. Electrochemical measurements

54


Page 55 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Reduction potential stimuli release experiments and electrochemical impedance spectroscopy

(EIS)

were

performed

on

a

Princeton

PARSTAT

2273

potentiostat/galvanostat with a three-electrode corrosion cell in a Faraday cage. The working electrode is platinum electrode. The Ag/AgCl electrode (saturated, KCl) with a Luggin capillary and platinum electrode was used as reference electrode and counter electrode, respectively. The impedance measurements were carried out with the frequency range of 100 kHz to 10 mHz with 10 mV sinusoidal perturbations at OCP. The Scanning Vibrating Electrode Technique (SVET) measurements were conducted using a M370 Scanning Electrochemical Workstation (Ametek, USA). The artificial defect was made on the surface of the coating down to the metal, using a metallic needle. The diameter of the defect was around 200 μm in diameter. The coating specimens were immersed into 0.05 M NaCl solution. The Pt-blackened electrode tip, with a diameter of 20 μm, was positioned 100 μm above the surface of the coated specimens. The electrode was set to vibrate with a frequency of 75 Hz and the peak-topeak amplitude was 30 μm. The exposed area (2 mm×2 mm) containing artificial 55



Page 56 of 64

scratches were scanned with a step width of 50 μm that resulted in a 20×20 matrix. Experimental results were presented in the form of 2D maps of current density. Salt spray test The salt spray test (SST) was performed in 5% NaCl solution according to ASTM B117 standard. Crossed artificial scratches penetrated to the AA2024 substrate were carefully made using a scalpel. The specimens were placed in the SST chamber at an angle of 45°. The representative regions were recorded at different times with a digital camera.

ASSOCIATED CONTENT

Supporting Information. ITC measurement, MS spectrum of FcCA-Cys after electrolytic reduction, characterization of nanoparticles, FTIR and 13C SS-NMR spectra of TSR-SNs treated with -1.0 V potential, hydrodynamic diameters of TSR-SNs, SST tests, and the detailed synthesis process,

13C

SS-NMR and TGA spectra of DSR-SNs can be seen in

Supporting Information.

56


Page 57 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


AUTHOR INFORMATION

Corresponding Author [email protected]; [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We thank the National Nature Science Foundation of China (Grant No. 51672133 and No. U1737105); the National Science Foundation of Jiangsu Province (Grant No. BK20161496); Fundamental Research Funds for the Central University, Grants No. 30915012207 and No. 30918012201; a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

REFERENCES (1) Moreto, J. A.; Marino, C. E. B.; Bose, W. W.; Rocha, L. A.; Fernandes, J. SVET, SKP and EIS study of the corrosion behaviour of high strength Al and Al-Li alloys used in aircraft fabrication. Corros. Sci. 2014, 84, 30-41. 57



Page 58 of 64

(2) Coelho, L. B.; Mouanga, M.; Druart, M. E.; Recloux, I.; Cossement, D.; Olivier, M. G. A SVET study of the inhibitive effects of benzotriazole and cerium chloride solely and combined on an aluminium/copper galvanic coupling model. Corros. Sci. 2016, 110, 143156. (3) Wei, H. G.; Wang, Y. R.; Guo, J.; Shen, N. Z.; Jiang, D. W.; Zhang, X.; Yan, X. R.; Zhu, J. H.; Wang, Q.; Shao, L.; Lin, H. F.; Wei, S. Y.; Guo, Z. H. Advanced micro/nanocapsules for self-healing smart anticorrosion coatings. J. Mater. Chem. A 2015, 3, 469-480. (4) Pommiers, S.; Frayret, J.; Castetbon, A.; Potin-Gautier, M. Alternative conversion coatings to chromate for the protection of magnesium alloys. Corros. Sci. 2014, 84, 135-146. (5) Shchukin, D.; Moehwald, H. A Coat of Many Functions. Science 2013, 341, 1458-1459. (6) Andreeva, D. V.; Shchukin, D. G. Smart self-repairing protective coatings. Mater. Today 2008, 11, 24-30. (7) Shchukin, D. G. Container-based multifunctional self-healing polymer coatings. Polym. Chem. 2013, 4, 4871-4877. (8) Ding, C.; Liu, Y.; Wang, M.; Wang, T.; Fu, J. Self-healing, superhydrophobic coating based on mechanized silica nanoparticles for reliable protection of magnesium alloys. J. Mater. Chem. A 2016, 4, 8041-8052. (9) Wang, T.; Tan, L. H.; Ding, C. D.; Wang, M. D.; Xu, J. H.; Fu, J. J. Redox-triggered controlled release systems-based bi-layered nanocomposite coating with synergistic selfhealing property. J. Mater. Chem. A 2017, 5, 1756-1768. (10) Ghazi, A.; Ghasemi, E.; Mandavian, M.; Ramezanzadeh, B.; Rostami, M. The application of benzimidazole and zinc cations intercalated sodium montmorillonite as smart ion exchange inhibiting pigments in the epoxy ester coating. Corrosi. Sci. 2015, 94, 207-217. 58


Page 59 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(11)Fery, A.; Weinkamer, R. Mechanical properties of micro-and nanocapsules: Single-capsule measurements, Polymer 2007, 48, 7221-7235. (12)Köhler,K.; Shchukin, D. G.; Möhwald, H.; Sukhorukov, G. B. Thermal behavior of polyelectrolyte multilayer microcapsules. 1. The effect of odd and even layer number, J. Phys. Chem. B 2005, 109, 18250-18259. (13) Grigoriev, D.; Shchukina, E.; Shchukin, D. G. Nanocontainers for Self-Healing Coatings. Adv. Mater. Interfaces 2017, 4. (14) Borisova, D.; Akcakayiran, D.; Schenderlein, M.; Moehwald, H.; Shchukin, D. G. Nanocontainer-Based Anticorrosive Coatings: Effect of the Container Size on the SelfHealing Performance. Adv. Funct. Mater. 2013, 23, 3799-3812. (15) Zahidah, K. A.; Kakooei, S.; Ismail, M. C.; Raja, P. B. Halloysite nanotubes as nanocontainer for smart coating application: A review. Prog. Org. Coat. 2017, 111, 175185. (16) Saremi, M.; Yeganeh, M., Application of mesoporous silica nanocontainers as smart host of corrosion inhibitor in polypyrrole Coatings. Corros. Sci. 2014, 86, 159-170. (17) Tedim, J.; Zheludkevich, M. L.; Salak, A. N.; Lisenkov, A.; Ferreira, M. G. S. Nanostructured LDH-container layer with active protection functionality. J. Mater. Chem. 2011, 21, 15464-15470. (18) Liu, X. H.; Gu, C. J.; Wen, Z. H.; Hou, B. R. Improvement of active corrosion protection of carbon steel by water-based epoxy coating with smart CeO2 nanocontainers. Prog. Org. Coat. 2018, 115, 195-204.

59



Page 60 of 64

(19) Leal, D. A.; Riegel-Vidotti, I. C.; Ferreira, M. G. S.; Marino, C. E. B. Smart coating based on double stimuli-responsive microcapsules containing linseed oil and benzotriazole for active corrosion protection. Corros. Sci. 2018, 130, 56-63. (20) Kermannezhad, K.; Chermahini, A. N.; Momeni, M. M.; Rezaei, B. Application of aminefunctionalized MCM-41 as pH-sensitive nano container for controlled release of 2mercaptobenzoxazole corrosion inhibitor. Chem. Eng. J. 2016, 306, 849-857. (21) Zheng, Z.; Schenderlein, M.; Huang, X.; Brownball, N. J.; Blanc, F.; Shchukin, D. Influence of Functionalization of Nanocontainers on Self-Healing Anticorrosive Coatings. ACS Appl. Mater. Interfaces 2015, 7, 22756-22766. (22) Shi, H. W.; Wu, L. P.; Wang, J.; Liu, F. C.; Han, E. H. Sub-micrometer mesoporous silica containers for active protective coatings on AA 2024-T3. Corros. Sci. 2017, 127, 230-239. (23) Snihirova, D.; Lamaka, S. V.; Cardoso, M. M.; Condeco, J. A. D.; Ferreira, H. E. C. S.; Montemor, M. D. pH-sensitive polymeric particles with increased inhibitor-loading capacity as smart additives for corrosion protective coatings for AA2024. Electrochim. Acta 2014, 145, 123-131. (24) Borisova, D.; Moehwald, H.; Shchukin, D. G. Mesoporous Silica Nanoparticles for Active Corrosion Protection. ACS Nano 2011, 5, 1939-1946. (25) Skorb, E. V.; Andreeva, D. V. Self-healing properties of layer-by-layer assembled multilayers. Polym. Int. 2015, 64, 713-723. (26) Njoku, D. I.; Cui, M. M.; Xiao, H. G.; Shang, B. H.; Li, Y. Understanding the anticorrosive protective mechanisms of modified epoxy coatings with improved barrier, active and selfhealing functionalities: EIS and spectroscopic techniques. Sci. Rep. 2017, 7.

60


Page 61 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(27) Marques, A. G.; Taryba, M. G.; Panao, A. S.; Lamaka, S. V.; Simoes, A. M. Application of scanning electrode techniques for the evaluation of iron-zinc corrosion in nearly neutral chloride solutions. Corros. Sci. 2016, 104, 123-131. (28) Gnedenkov, A. S.; Sinebryukhov, S. L.; Mashtalyar, D. V.; Gnedenkov, S. V., Localized corrosion of the Mg alloys with inhibitor-containing coatings: SVET and SIET studies. Corros. Sci. 2016, 102, 269-278. (29) Montemor, M. F.; Snihirova, D. V.; Taryba, M. G.; Lamaka, S. V.; Kartsonakis, I. A.; Balaskas, A. C.; Kordas, G.; Tedim, J.; Kuznetsova, A.; Zheludkevich, M. L.; Ferreira, M. G. S. Evaluation of self-healing ability in protective coatings modified with combinations of layered double hydroxides and cerium molibdate nanocontainers filled with corrosion inhibitors. Electrochim. Acta 2012, 60, 31-40. (30) Snihirova, D.; Lamaka, S. V.; Taryba, M.; Salak, A. N.; Kallip, S.; Zheludkevich, M. L.; Ferreira, M. G. S.; Motemor, M. F. Hydroxyapatite Microparticles as Feedback-Active Reservoirs of Corrosion Inhibitors. ACS Appl. Mater. Interfaces 2010, 2, 3011-3022. (31) Wang, W.; Li, W. H.; Fan, W. J.; Zhang, X. Y.; Song, L. Y.; Xiong, C. S.; Gao, X.; Liu, X. J. Accelerated self-healing performance of magnetic gradient coating. Chem. Eng. J. 2018, 332, 658-670. (32) Ding, C. D.; Xu, J. H.; Tong, L.; Gong, G. C.; Jiang, W.; Fu, J. J. Design and Fabrication of a Novel Stimulus-Feedback Anticorrosion Coating Featured by Rapid Self-Healing Functionality for the Protection of Magnesium Alloy. ACS Appl. Mater. Interfaces 2017, 9, 21034-21047. (33)Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (© 1994-2018 ACD/Labs) 61



Page 62 of 64

(34) Wyman, I. W.; Macartney, D. H. Host-guest complexations of local anaesthetics by cucurbit[7]uril in aqueous solution. Org. Biomol. Chem. 2010, 8, 247-52. (35) Khashab, N. M.; Trabolsi, A.; Lau, Y. A.; Ambrogio, M. W.; Friedman, D. C.; Khatib, H. A.; Zink, J. I.; Stoddart, J. F. Redox- and pH-Controlled Mechanized Nanoparticles. Eur. J. Org. Chem. 2009, 1669-1673. (36) Jeon, W. S.; Moon, K.; Park, S. H.; Chun, H.; Ko, Y. H.; Lee, J. Y.; Lee, E. S.; Samal, S.; Selvapalam, N.; Rekharsky, M. V.; Sindelar, V.; Sobransingh, D.; Inoue, Y.; Kaifer, A. E.; Kim, K. Complexation of ferrocene derivatives by the cucurbit[7]uril host: A comparative study of the cucurbituril and cyclodextrin host families. J. Am. Chem.Soc. 2005, 127, 1298412989. (37) Wang, T.; Sun, G.; Wang, M.; Zhou, B.; Fu, J. Voltage/pH-Driven Mechanized Silica Nanoparticles for the Multimodal Controlled Release of Drugs. ACS Appl. Mater. Interfaces 2015, 7, 21295-21304. (38) Yoon, J. A.; Kamada, J.; Koynov, K.; Mohin, J.; Nicolay, R.; Zhang, Y. Z.; Balazs, A. C.; Kowalewski, T.; Matyjaszewski, K. Self-Healing Polymer Films Based on Thiol-Disulfide Exchange Reactions and Self-Healing Kinetics Measured Using Atomic Force Microscopy. Macromolecules 2012, 45, 142-149. (39) Maia, F.; Yasakau, K. A.; Carneiro, J.; Kallip, S.; Tedim, J.; Henriques, T.; Cabral, A.; Venancio, J.; Zheludkevich, M. L.; Ferreira, M. G. S. Corrosion protection of AA2024 by sol-gel coatings modified with MBT-loaded polyurea microcapsules. Chem. Eng. J. 2016, 283, 1108-1117.

62


Page 63 of 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(40) Dalmoro, V.; dos Santos, J. H. Z.; Aleman, C.; Azambuja, D. S. An assessment of the corrosion

protection

of

AA2024-T3

treated

with

vinyltrimethoxysilane/(3-

glycidyloxypropyl)trimethoxysilane. Corros. Sci. 2015, 92, 200-208. (41) Vimalanandan, A.; Lv, L.-P.; The Hai, T.; Landfester, K.; Crespy, D.; Rohwerder, M. Redox-Responsive Self-Healing for Corrosion Protection. Adv. Mater. 2013, 25, 6980-6984. (42)Åslund, F.; Berndt, K.D.; Holmgren, A. Redox potentials of glutaredoxins and other thioldisulfide oxidoreductases of the thioredoxin superfamily determined by direct proteinprotein redox equilibria. J. Biol. Chem. 1997, 272, 30780-30786. (43) Zhang, J.; Li, X. L.; Wang, J. W.; Xu, W. C.; Duan, J. Z.; Chen, S. G.; Hou, B. R. Influence of Calcareous Deposit on Corrosion Behavior of Q235 Carbon Steel with Sulfate-Reducing Bacteria. J. Ocean Univ. China 2017, 16, 1213-1219. (44) Zuo, Y.; Zhou, B. N.; Tang, Y. M. Inhibition of AA 2024-T3 Corrosion in Alkaline NaCl Solution by Compound Sodium Dodecylbenzenesulfonate and Cerium Chloride. Int. J. Electrochem. Sci. 2017, 12, 11137-11149. (45) Zhu, Q. J.; Wang, K.; Wang, X. H.; Hou, B. R. Electrochemical impedance spectroscopy analysis of cold sprayed and arc sprayed aluminium coatings serviced in marine environment. Surf. Eng. 2012, 28, 300-305.

63



TSR-SNs can simultaneously respond to the pH changes and corrosion potential in the local micro-corrosive regions, enhancing the response sensitivity of SF-SHAC and accomplishing self-healing functionality. 129x49mm (300 x 300 DPI)


Page 64 of 64

Triple-Stimuli-Responsive Smart Nanocontainers Enhanced Self

Recommend Documents