Protective Coatings for Aluminum Alloy Based on Hyperbranched 1,4

Subscriber access provided by University of Newcastle, Australia

Article

Protective coatings for aluminum alloy based on hyperbranched 1,4-polytriazoles Elaine Armelin, Rory Whelan, Yeimy Mabel MartínezTriana, Carlos Aleman, M.G. Finn, and David Diaz Diaz ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b14174 • Publication Date (Web): 09 Jan 2017 Downloaded from http://pubs.acs.org on January 10, 2017

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 47

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

Protective coatings for aluminum alloy based on hyperbranched 1,4-polytriazoles

Elaine Armelina,b,*, Rory Whelanc, Yeimy Mabel Martínez-Triana,c Carlos Alemána,b, M. G. Finnd and David Díaz Díazc,e*

a Departament

d’Enginyeria Química, EEBE, Universitat Politè cnica de Catalunya, C/

Eduard Maristany, 10-14, Ed. I2, 08019, Barcelona, Spain. b Center

for Research in Nano-Engineering, Universitat Politè cnica de Catalunya, Campus Sud, Edifici C’, C/Pasqual i Vila s/n, 08028, Barcelona, Spain.

c Institut

für Organische Chemie, Universität Regensburg, Universitätsstr. 31, 93040, Regensburg, Germany.

d

School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, USA 30332 e

IQAC-CSIC, Jordi Girona 18-26, 08034, Barcelona, Spain.

*Corresponding authors: [email protected] and [email protected]

1 ACS Paragon Plus Environment


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

ABSTRACT Organic polymers are widely used as coatings and adhesives to metal surfaces, but aluminum is among the most difficult substrates because of rapid oxidative passivation of its surface. Poly(1,4-disubstituted 1,2,3-triazoles) made by copper-catalyzed azide-alkyne cycloaddition form strongly bonded interfaces with several metal substrates. In this work, a variety of alkyne and azide monomers were explored as precursors to anticorrosion coatings for a standard highstrength aluminum-copper alloy. Monomers of comparatively low valency (diazide and trialkyne) were found to act as superior barriers for electrolyte transfer to the aluminum surface. These materials showed excellent resistance to corrosive pitting due to the combination of three complementary properties: good formation of highly crosslinked films, as observed by FTIR and DSC; good adhesion to the aluminum alloy substrate, as shown by pull-off testing; and excellent impermeability, demonstrated by EIS.

Keywords: click chemistry, copper-catalyzed azide−alkyne cycloaddition, aluminum alloy, adhesion property, corrosion protection.


Page 2 of 47

Page 3 of 47

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


INTRODUCTION Poly(1,4-disubstituted 1,2,3-triazoles) were first reported by Finn and coworkers in 2004 to have high adhesive strength to metallic copper and copper alloy, and to be formed in situ from polyvalent azides and alkynes by the action of Cu(I) ions provided from the metal surface.1 This represented the first published application of the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction 2,3 to materials science. While many other uses for the CuAAC process in polymer and materials chemistry have emerged since,4-7 most studies with metal substrates have focused on the deposition of small-molecule triazole derivatives, rather than polymers, on copper, mild steel, and brass.8-12 Yet the CuAAC process presents an important opportunity for the development of polytriazole coatings for corrosion protection, for the following reasons. First, in the few additional studies of polytriazole-metal adhesion published by us

1,13,14,15

and

others, 16-18 the process of polytriazole formation on copper-containing surfaces was found to have the unusual property of leading to hyperbranched materials with glass transition temperatures significantly in excess of curing temperatures, suggesting that crosslinking may be promoted by the strongly exothermic nature of the azide-alkyne cycloaddition reaction.15,19 Second, 1,2,3-triazoles bind well to a variety of metals and are extraordinarily stable toward many potential decomposition processes. Moreover, poly(1,2,4-triazoles) have been used as protected coating towards corrosion of copper.10 Specifically, Takenouti and co-workers reported the formation of homogeneous and adherent polymer films by electro-oxidation of 3amino 1,2,4-triazole on a copper substrate in alkaline methanol solution.10 The protection of polyamino-1,2,4-triazole films obtained by different electropolymerization conditions was determined by electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl solutions. The best results showed 99% protection after one month immersion test. Later, Zheludkevich and coworkers

compared

the

1,2,4-triazole,

3-amino-1,2,4-triazole,

benzotriazole

and

2-

mercaptobenzothiazole as corrosion inhibitors for protection of the AA2024 aluminium alloy in neutral chloride solutions.20 This study demonstrated that all these compounds confer corrosion protection to the AA2024 alloy forming a thin organic layer on the substrate surface. Among 3 ACS Paragon Plus Environment


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

these inhibitors, benzotriazole and 2-mercaptobenzothiazole showed better corrosion protection by decreasing the rate of both the anodic and cathodic processes. Additionally, a number of different organic compounds such as imidazole derivatives,21,22 substituted bis- and mono-azo dyes,23 thiols,24 and inorganic salts (i.e., cerium salts)25,26 has been traditionally used to protect Al surfaces. Paints and coatings are an important component of the chemical industry,27 with architectural coatings accounting for the largest market share. Among well-established types of protective coatings, crosslinked epoxy-based resins (incorporating bisphenol A diglycidyl ether and hardener agents such as amines, amides, polyamineamides, and anhydride acids) claim the largest market share in both volume and value.27,28 Solvent- and water-borne formulations employ many additional additives and pigments, and they represent the most widely used primers on the protective coatings market. Their advantages include easy film formation at room temperature, short curing time, extraordinary stability toward weathering, and great resistance to chemical reagents. However, the use of toxic aromatic solvents and co-solvents for these materials, required in many applications, has led the research community to explore other network polymers for more eco-friendly coatings.29,30 Aluminum is a particularly difficult case since the well-known oxidative passivation of metallic Al makes it difficult to coat and to protect against pitting and corrosion. In most cases, coating requires aggressive depassivation or deoxidation cleaning treatments31-33 to eliminate the thin Al2O3 layer and alloying elements. Due to the ability of triazoles to interact with metal surfaces and the ease by which 1,2,3-triazoles can be formed in the presence of metallic copper,34 we decided to create and explore hyperbranched triazolyl coatings for aluminum−copper alloy. Among such alloys, a version having relatively high copper content (45%), known by the trade name AA2024-T3, is a widely used high strength material, with excellent mechanical and thermal properties for engineering applications. It also suffers from poor resistance to pitting corrosion,35,36 making protective coatings particularly useful in this case. 4 ACS Paragon Plus Environment

Page 4 of 47

Page 5 of 47

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


Our goal was to develop long-lasting and non-wettable organic coatings for easy deposition and protection of this aluminum alloy without need for exhaustive substrate pre-treatment or cleaning. Important parameters included film barrier properties, adhesion, and control over the electrochemistry of corrosion. Our initial studies therefore surveyed a variety of alkyne and azide monomers, CuAAC catalysts, and crosslinking conditions, evaluating the efficiency of surface protection in NaCl solution.

EXPERIMENTAL SECTION Materials. Unless otherwise stated, all chemicals were purchased from Sigma-Aldrich Co. Aluminum alloy samples, tradename AA2024-T3, of 5.01.4 cm2 dimension and 3 mm thickness were used as substrates for polytriazole formation. The alloy nominal composition is (in mass %): Cu = 3.8-4.9; Mg = 1.2-1.8; Mn= 0.3-0.9; Fe and Si= 0.5; Cr = 0.1; Zn = 0.15; Ti = 0.15, other elements = 0.15 and Al balance to 100%. Preparation of aluminum substrate for polytriazole deposition. The surfaces of the aluminum alloy substrates were prepared by polishing with silicon carbide paper up to grade #1200. After this they were thoroughly washed with distilled water, immersed in 0.05 M aqueous acetic acid (pH 3) for 5 min, washed with distilled water in a sonication bath for 5 min, dried under a hot air stream, and stored under vacuum before use.37 General procedure for the synthesis of linear and hyperbranched 1,4-polytriazoles. Monomers 1A-5A (azides) and 1B-6B (alkynes) were prepared as previously described.1,13,14 The structures of these monomers and polymer nomenclature appear in Scheme 1 and Table 1. All polytriazole materials were made with a slight excess of alkyne functional groups, achieved by using the following molar ratios, where A is azide and B is alkyne: [A2 + B3] = 1.5:1.05, [A2 + B4] = 2.0:1.05, [A3 + B2] = 1.5:1.55, [A3 + B3] = 1.0:1.05, [A3 + B4] = 2.0:1.5. Additionally, two Cu(I) catalysts (CuBF4•4CH3CN, designated catalyst A, and CuPF6•4CH3CN, catalyst B) were tested independently, both dissolved in acetonitrile (1.4 mg/100 L). Typically, solid monomers were dissolved in a minimum amount of CH3CN or THF (200-300 µL), and liquid monomers were 5 ACS Paragon Plus Environment


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

added neat. The two reagents were mixed in a small glass test tube and catalyst (dissolved in a minimum amount 50-100 L of acetonitrile) was then added and mixed in quickly. The resulting mixture was immediately deposited onto either high density polyethylene (100 × 80 × 4 mm3) or AA2024-T3 (50 × 15 × 3 mm3) flat plates as substrates and spread manually with the tip of the Pasteur pipette. Films were easily detached from the former for thermal characterization, whereas the alloy substrates were employed for corrosion, adhesion, and nanoindentation tests. The cast films were allowed to stand for 3 days at ambient temperature for slow organic solvent evaporation and uniform film formation, followed by post-curing heating in an oven at 110 ºC for 1.5 hours to ensure a high degree of crosslinking (Figure S1). The average thickness of the films formed in this way was 15.0 ± 5.6 µm in all cases, using 50-60 µL of initial solution deposited on the substrate.


Page 6 of 47

Page 7 of 47

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


Table 1. Molecular formulas of azides (Ax) and alkynes (Bx), with variable functionalities, and polymer abbreviations employed in this study.



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 8 of 47

Page 9 of 47

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


Scheme 1. Schematic representations of linear and hyperbranched poly(1,4-disubstituted 1,2,3-triazole)s by CuAAC click reactions of multifunctional azides (Ax) and alkynes (Bx).



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

Characterization. Monomers were characterized by 1H NMR and

Page 10 of 47

13C

NMR (300 MHz

Bruker AMX300 spectrometer operating at 300.1 MHz and 75.5 MHz, respectively; CDCl3 or DMSO-d6) and FTIR (Jasco 4100 spectrophotometer, coupled with an attenuated total reﬂection accessory, Specac model MKII Golden Gate Heated Single Reﬂection Diamond ATR, which allowed monitoring of crosslinking reactions). Cured polytriazoles films (approximately 8 mg in weight) were characterized by isothermal FTIR-ATR and triazole formation was monitored with dynamic FTIR-ATR from 30 °C to 200 °C, with a scan rate of 5 °C/min (Figure S2). Differential scanning calorimetry (DSC) at temperatures from -90 °C to 250-280°C was performed using a TA Instruments Q100 series instrument equipped with a refrigerated cooling system operating under nitrogen atmosphere. Dynamic mechanical thermal analyses (DMTA, 30–300 °C, heating of 10°C/min for the first heating and cooling scans) were carried out with a TA Instruments DMA Q800 analyzer. The glass transition temperature (Tg) of each cured sample was determined by the second heating scan (20°C/min). 1,4-Polytriazoles were isothermally cured in a Teflon mold at 110 °C for 1.5 h. Prismatic rectangular samples (30100.6 mm3) were analyzed by 3-point bending at a heating rate of 3 °C/min from 50 °C to 120 °C, using a frequency of 1 Hz and an oscillation amplitude of 20 µm. Thermogravimetric analysis (TGA) was carried out with a Q50 instrument (TA Instruments) from 30 °C to 600 °C at a heating rate of 10°C/min, under nitrogen atmosphere. Cryo-fractured surfaces of polytriazoles films were examined by scanning electron microscopy (SEM) using a Focus Ion Beam Zeiss Neon 40 instrument (Carl Zeiss, Germany), equipped with an energy-dispersive X-ray (EDX) spectroscopy system and operating at 5 kV. Samples were mounted on double-sided adhesive carbon discs and sputter-coated with a thin layer of carbon to enhance sample charging. Contact angle (CA) measurements were carried on with an OCA 15EC instrument (DataPhysics GmbH, Filderstadt) using the droplet sessile method at room temperature; ultrapure water was employed as solvent. For static contact angle (sCA) measurements, 0.5 μL droplets of liquid were dispensed on the respective surfaces, which were previously maintained in a desiccator for drying. Data were recorded after drop stabilization (30 10 ACS Paragon Plus Environment

Page 11 of 47

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


s) using SCA 20 software. CA values were obtained as the average of ten independent measures for each sample. sCA measurements were performed with solid films adhered to the aluminum alloy surface before and after 30 days of immersion in 0.05M aqueous NaCl. The hardness and elastic modulus of polytriazole films adhered to AA2024 substrates was measured using an MTS Nanoindenter XP instrument with calibrated Berkovich diamond tip (strain rate of 0.05 s-1 and 1000 nm of penetration depth of the tip). The results were analysed with the Oliver and Pharr method.37 For nano-hardness testing, coatings between 10 and 15 µm in thickness were used to avoid effects of the hardness of the underlying metal. The adhesion strength of polytriazoles coatings on AA2024 rectangular pieces (40263 mm3) was determined by pull-off test, according to UNE-EN-ISO 4624,38 using KN-10 (Neurtek S.A.) adhesion equipment. For dry adhesion the coated panels and dolly, 20 mm in diameter, were bonded using a two-component epoxy adhesive (AralditeTM). After 24 h of adhesive cure, a slot was cut around the dolly at the substrate boundary to avoid the effect of peripheral coatings. At least five independent measurements for each system were made, those with interfacial failure were considered and the minimum force to detach the coatings from substrate was recorded accordingly. A lack of reported error indicates samples that showed poor reproducibility in their mode of failure. Corrosion testing. Electrochemical impedance spectroscopy (EIS) was performed for permeability and corrosion protection studies. The experiments were conducted with an Autolab PGSTAT302N potentiostat-galvanostat, equipped with the ECD module (Ecochimie, The Netherlands). A three-electrode electrochemical cell arrangement was used, consisting of rectangular AA2024-T3 panels (30×10×2 mm3) with 0.785 cm2 of exposed area as working electrode, a saturated Ag|AgCl reference electrode, and a Pt wire as counter electrode. EIS analyses were carried out as a function of time in NaCl solution (0.05 M). All samples were kept in solution for 1 h to reach the open-circuit potential (Eocp). The amplitude of the EIS perturbation signal was 10 mV, the frequency ranged from 105 to 10−2 Hz taking 7 frequencies per decade. Two systems were considered: (i) bare alloy AA2024-T3, and (ii) alloy AA2024-T3 11 ACS Paragon Plus Environment


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 12 of 47

coated with polytriazole coatings obtained by click-chemistry polymerization and after postcuring as described above.

RESULTS AND DISCUSSION 1,4-Polytriazoles film forming properties and morphology The deposition of mixed monomers plus catalyst is a simple process, needing only 10-15 mg of polymer (delivered in 500 µL of a 100 g/mL solution) to cover 40.5 cm2 of metal surface (6 plates). The polymerization/crosslinking reaction was monitored via detection of azide consumption by IR spectroscopy (2100 cm-1), and the degree of crosslinking was assessed by thermal analyses. A slight excess of alkyne monomer (5×10-4mol %) was found to be required for the complete disappearance of azide groups (Figure 1). This is consistent with the report of Tang and co-workers that adhesion strength and the thickness of the interface between polymer and aluminum substrate (AA6063) increased with the use of excess of triyne monomer.16

20%

-  -

Figure 1. FTIR spectra of monomers 1A (red), 1B (blue), and polymer 1A21B3 (green) showing the main absorption bands for each compound. The lack of strong and sharp azide absorption band (2138 cm-1) in the polymer film is evidence that the crosslinking reaction was completed.


Page 13 of 47

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


Films prepared by CuAAC reactions were all transparent (from 10 to 30-40 m) due to their amorphous nature. However, films approximately 50 µm or greater in thickness, as well as those cured at temperatures greater than 110-120°C, were darker in color and somewhat less transparent (Figure S3). Monomers with two or more methylene groups in the main chain (for example, 1A21B3, 2A22B3 and 5A35B4) offered more flexible polymer films after curing than monomers with more aromatic rings or constrained linkages (tetrasubstituted sp3 carbon centers), such as 4A34B3 and 4A36B3. Interestingly, the use of bi-functional azide 3A with bi-, trior tetra-functional alkynes (3b, 4B, or 5B) gave powders or unstable materials rather than strong films, perhaps because of more crystalline phase formation (due to the presence of both hydrogen bonding donating and polar groups) or a unique cleavage pathway at high temperature (intramolecular attack of the central hydroxyl group on an amide linkage). Although some hyperbranched polytriazole films were obtained with these monomers (4A36B3 and 4A34B3), they were brittle. Moreover, the nature of the catalyst did not influence film formation or properties (crosslinking degree or corrosion protection), in spite of the fact that CuPF6 is less soluble in acetonitrile than CuBF4. Polytriazole systems are usually brittle rather than flexible, unless structural modifications with soft segments are introduced or they are copolymerized with non-rigid polymers such as polyurethanes or polysiloxanes.39-41 Thus, they behave as glassy thermosets. In order to check the brittleness of poly(1,4-disubstituted 1,2,3-triazole)s synthesized in this work, cryo-SEM was employed to observe transverse sections of the solid films. The surface of 1A21B3 was unique in showing fracture marks similar to those of natural rubber elastomeric films (Figure 2A).42 The other films (Figures 2B-F) appeared more similar to glassy epoxy thermosets,43 showing brittle regions characterized by extensive crack propagation.44 The greater flexibility of the 1A21B3 material is likely to result from the lesser degree of crosslinking and greater molecular spacing between triazoles provided by the linear 1A monomer.



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 14 of 47

Figure 2. SEM micrographs of cryofractured surfaces in the following materials cured for 3 days at RT and post-cured 1.5 h at 110 ºC: (A) 1A21B3, (B) 2A22B3, (C) 4A34B3, (D) 4A36B3, (E) 4A35B4, and (F) 5A35B4. The scale bar of inset micrograph is 200 nm.

Thermal characterization Differential scanning calorimetry (DSC, Figure 3A) showed large exothermic transitions from 70 ºC to 140-150 ºC on the first heating scan for all materials measured. These data suggest the existence of potentially complex dynamic curing processes at 10 °C/min, possibly involving additional triazole formation. At higher temperatures, sample 4A35B4 exhibited clear evidence of degradation (which was further confirmed by TGA analysis, see below), whereas 1A21B3 and 2A22B3 recovered to the original baseline after a devitrification step (Figure 3A, circle inset). Devitrification is a common phenomenon in non-isothermally cured crosslinked systems, as discussed in Supporting Information. Materials 4A34B3 and 5A35B4 showed intermediate behavior in the first heating scan, with multiple devitrification steps indicating heterogeneous 14 ACS Paragon Plus Environment

Page 15 of 47

crosslinking in the thermoset chains derived from the use of a tri-functional azide and a tri- or tetra-functional alkyne. This feature, as well as some degradation at higher temperatures, was also confirmed by TGA analysis.

Degradation

Devitrification

A)

B) Degradation

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 3. DSC of branched and hyperbranched polytriazoles synthesized: A) first and B) second heating curves. The second DSC heating scan (Figure 3B) in the calorimetry analysis showed clear T g behavior (at approximately 150 °C) for only 1A21B3 and 2A22B3, showing these materials to be fully cured. In contrast, no final glass transition temperature could be detected by DSC for the films 4A34B3, 4A35B4 or 5A35B4. Apparent decomposition at higher temperature may mask a glass transition, or these materials may have more complex cure behavior. In this case, dynamic



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 16 of 47

mechanical thermal analysis (DMTA) is often used for amorphous phase investigation in high T g polymeric materials. These data for sample 5A35B4 are shown in Figure S4. The Tg for this polytriazole is evidenced by the broadened glass transition region in the loss tangent (tan ) curve with two pronounced shoulders at about 110 ºC and 130 ºC. No rubbery state with a constant plateau was observed in storage modulus curve below 160 ºC. Additionally, this thermoset polymer did not exhibit any soft transition behavior above 110-140 ºC. Therefore, as expected, crosslinking behavior is highly dependent on the number of reactive functional groups present in the starting materials, and the well-cured polytriazole films have glass transition temperatures up to 30-40°C higher than the curing temperature (Tc 110°C), as previously observed for similar polymers.15,19 TGA analysis (Figure 4) showed 1A21B3 to be the most stable polytriazole material, with decomposition temperatures at approximately 398°C and 453°C; 2A22B3 and 4A34B3 were next with decomposition temperatures of approximately 340°C, with 2A22B3 showing only one decomposition step. In contrast, 4A35B4 and 5A35B4 (made with different catalysts) were the least stable and showed multiple several decay steps, assumed to be due to thermoset heterogeneity as discussed above with respect to the DSC data. All samples with the exception of 2A22B3 showed an initial mass loss of 2.2-2.7% at approximately 85°C, assigned to evaporation of acetonitrile solvent trapped in the polymer matrix (DTG1, derivative thermo-gravimetric temperature). We suggest that the second derivative peak (DTG2), observed at 242-253°C for most samples, corresponds either to the rupture of the ester linkage in the azide monomer unit (5B) or (for samples 4A34B3 and 5A35B4) to molecular cleavage of triazole oligomers that are not well crosslinked. We believe the highest decomposition temperatures of approximately 340 °C for 4A34B3 and 380-400 °C for 5A35B4 are related to the thermoset decomposition. Finally, all films gave a high percentage of char yield at 600 °C, probably due to the presence of inorganic copper catalyst and the presence of aromatic rings in the polymer chains. Char yield are often higher for compounds with more benzene and melamine derivatives than analogous polymers


Page 17 of 47

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


without aromatic rings. Table 2 summarizes the main thermal properties parameters, and Figure S5 shows TGA-DTG curves as a function of temperature.

Figure 4. TGA thermograms of the branched and hyperbranched polytriazoles films. Table 2. Thermal properties of poly(1,4-disubstituted 1,2,3-triazole) films studied here. Tg

DTG1

DTG2

Td,max

Char yield

(ºC)

(ºC)

(ºC)

(ºC)

(%)

1A21B3

150

84

-

398, 453

37

2A22B3

150

-

-

343

40

4A35B4

-

78

253

346, 413

35

4A34B3

177

100

---

338, 414

35

5A35B4-A

169

90

192, 242

380, 410

36

5A35B4-B

169

82

187, 242

385

35

SAMPLE

Wettability of polytriazoles coatings on AA2024 surface Five films were tested for aqueous surface wettability (water contact angle, WCA) after preparation and again after incubation in NaCl solution, with results shown in Table 3. Those



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 18 of 47

materials derived from alkynes 1B3, 2B3, and 4B3 gave rise to hydrophobic materials (WCA >90°), whereas 5B4 produced two films of more hydrophilic character (WCA near 90°). These alkyne building blocks are quite different from each other in their hydrogen bonding capability as well as overall polarity, so we suggest that the good degree of crosslinking (usually difficult to achieve with tetravalent monomers) is an important contributor. This is consistent with a previous report of a polytriazole coating by Kumar and co-workers,19 in which polar building blocks were also involved but apparently not present at the polymer surface. Both contact angle and SEM measurements (Figure 5) showed 1A21B3 to remain hydrophobic even after 30 days of immersion in NaCl solution (4A34B3 behaved similarly; data not shown). The polytriazole-coated surface was found to be quite smooth with no sign of corrosion after immersion, in contrast to the properties and transformation of the unprotected aluminum substrate. The increase in hydrophilic character in the latter is presumably due to the formation corroded pits the growth of aluminum oxide (white spots in the optical photograph and globular structures in the high magnification image). Wettability properties are also illustrated by a video in the Supporting Information. Other coatings, like 2A22B3 and 5A35B4, were less stable with respect to surface hydrophobicity, for reasons that will require further investigation to identify.


Page 19 of 47

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 5. Characterization of (A) bare alloy AA2024 and (B) alloy coated with 1A21B3, before and after immersion in NaCl solution for 30 days at room temperature. The value of water contact angle is shown above a representative SEM image for each case.

Table 3. Water contact angle (WCA) for AA2024 uncoated and coated with several polytriazoles films.

a)

SAMPLE

WCA (deg) a)

WCA (deg) b)

AA2024

84.1 ± 7.3

63.3 ± 19.1

1A21B3

95.5 ± 3.9

92,9 ± 5.1

2A22B3

95.8 ± 2.8

84.3 ± 1.3

4A35B4

89.1 ± 2.7

92.9 ± 5.1

4A34B3

96.6 ± 3.7

91.4 ± 1.7

5A35B4

88.3 ± 3.2

82.8 ± 2.1

Dry films. b) Dry films after 30 days of immersion in NaCl solution.



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 20 of 47

Characterization of corrosion resistance with increasing immersion time in NaCl solution Electrochemical impedance spectroscopy (EIS) was the technique chose to investigate the barrier properties of polytriazole films. The Nyquist plots depicted in the Figure 6 were fitted using an electrical equivalent circuit (EEC), depending on the impedance response for each case (Table S1, SI). The Nyquist plot for bare AA2024 immersed on NaCl 0.05M is mainly composed by a single time constant Rs(RpCdl), where Rs represents the ohmic resistance between the working and the reference electrodes; Rp is the polarization resistance and Cdl corresponds to the double-layer capacitance. The capacitance was replaced by a constant phase element (CPEdl) which describes the non-ideal capacitor when the phase angle is not -90°. After 30 days of metal bare corrosion, another electrical parameter appears, the Warburg impedance (W), related to the diffusion across the oxide layer (Figure S6). When the metal is protected with an organic polymer, it behaves as a semi-capacitive material, since most of the coating is nonconductive to ions. The Nyquist diagram of the 1A21B3 film shows two time constants at the beginning of the experiment (Figure 6A). The one at high frequency was attributed to the coating layer properties, while that at low frequencies was related to interfacial phenomena. The proposed EEC is given by Rs(CPEc [Rc·CPEdl]), where the CPEc and Rc represent the coating capacitance and coating resistance, respectively, and CPEdl corresponds to the capacitance of the metal/coating interface. Despite on Figure 6A the films from samples 2A22B3, 4A35B4, 4A34B3 and 5A35B4 seems to have greater coating resistance than that of 1A21B3, it can be observed, by enlarging the high frequency zone drawn on the figure A (Figure 6B), that 1A21B3 has the highest capacitive value followed by sample 2A22B3. By contrary, 4A35B4, 4A34B3 and 5A35B4 do not offer any barrier properties to the metal surface because their EEC correspond fundamentally to a highly porous polymer with three time constants detected at the beginning of the immersion time Rs(Rc CPEc)(Rct·CPEdl)(Rdif·CPEdif). Appearance of several time constants is an indication of undesirable corrosion phenomenon under the film, i.e. diffusion of ions from electrolyte and oxide layer. A 20 ACS Paragon Plus Environment

Page 21 of 47

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


schematic illustration of corrosion attack of unprotected and protected AA2024 surface can be seen in the Figure 7A.

Figure 6. A) Nyquist plots for AA 2024 panels covered with poly(1,4-disubstituted 1,2,3triazoles) at initial immersion time on NaCl 0.05M; B) Nyquist plot of the high frequency zone depicted on the figure above, showing the semi-circle corresponding to the coating resistance and coating capacitance. Lines represent the EEC fitting curves with parameters included on Tabla S1. 21 ACS Paragon Plus Environment


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 22 of 47

EIS can also be used to follow the corrosion potential (EOCP) stability with time, as shown in Figure 7B. The bare metal and metal covered with 4A35B3 and 5A35B4 showed the development of a more positive corrosion potential value after only 24 hours immersion, consistent with rapid entrance of liquid and deterioration of the metal surface. In contrast, coatings 1A21B3, 2A22B3, and 4A35B4 gave rise to slower increases in EOCP. Furthermore, after 20 days the bare metal as well as two of the former three coatings (4A34B3 and 5A35B4) failed to different degrees, showing significantly higher EOCP values and creating very rough surfaces formed by corrosion products that act as porous layers, facilitating the entry of ions and continued growth of the oxide layer. On the other hand, long protection against AA2024 corrosion was obtained with 1A21B3 and 2A22B3 coatings, which remain practically unaltered from 48 hours to 30 days. The rate of water uptake (), which is related to the electrolyte permeation across the film, was calculated according to equation (1) employing the capacitance results obtained from EIS experiments at 30 days: φ(t) =

𝑙𝑜𝑔 𝐶(𝑡)/𝑙𝑜𝑔 𝐶(𝑡=0) 𝑙𝑜𝑔 𝜀𝑟 (𝐻2𝑂)

Eq. (1)

where C(t) is the coating capacitance at immersion time t, C(t=0) is the initial coating capacitance, and r is the water permittivity (i.e. 80 at 25ºC).45 This formula is based on the following assumptions: (i) water is homogeneously dispersed; (ii) no water-polymer chemical interaction occurs; (iii) penetration of a low volume of water and no swelling of the matrix. The coating capacitance (CPEc) values for water uptake calculations were taken at a maximum frequency of the first semi-circle in the Nyquist plot, at room temperature for 30 days in NaCl 0.05M. As shown in the Figure 7C, polytriazole 1A21B3 is highly resistant to water penetration through the entire test period, whereas water absorption is low to moderate for 2A22B3 (after 3 days).


Page 23 of 47

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 7. A) Galvanic corrosion of AA2024 without protection (upper) and with poly(1,4disubstituted 1,2,3-triazoles), B) Corrosion potential evolution and C) Water uptake with immersion time for samples 1A21B3 and 2A22B3.



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 24 of 47

In conclusion, the AC impedance spectroscopy represents a powerful tool to observe passivation, corrosion, blistering and other phenomena occurring at the metal-coating interface. Additionally to the Figure 6, the Nyquist and Bode plots for all samples with increase immersion time are included in the supporting information. The former represents the combination of the electrolyte resistance and the interfacial impedance, whereas the latter represents the magnitude of impedance, expressed in log |Z|, the phase angle (in degrees) as well as their variation with frequency perturbation. Usually, in a high capacitive system the impedance from the Bode plot decreases when the coating absorbs water, but maintains a linear relationship with frequency. The slope does not change substantially and the phase angle remains at high values. As can be seen in the Figure S6, the protective behaviour of 1A21B3 coating (phase angle close to 70 degrees at high frequencies) was maintained with the greatest period of immersion time, proving that it is the most protective system compared to the others polytriazoles approached. Surface pretreatment, adhesion and mechanical properties Good crosslinking in thermoset films is an important requirement for effective barrier protection with polymer coatings; another is the need for good adhesion to the substrate46. We found that the mildly abrasive cleaning procedure applied to the metal surface before polytriazole deposition was essential for effective adhesion of the films to the AA2024 surface. We have also previously identified by backscattered SEM micrography and XPS analysis the presence of copper alloying intermetallic phases such as Al2CuMg, Cu3Mn2Al, and Al6(Cu, Fe, Mn), on similarly-pretreated AA2024 surfaces.36 While these multi-phase intermetallic particles have been shown to be responsible for the progression of corrosion failure on AA2024 in NaCl solutions47, they may well assist in adhesion in our case by engaging in strong interactions with triazole rings of the crosslinked polymer. Note also that the substrate composition can be important; for example, superior adhesion strength has been reported to aluminum substrates AA6163 (0.1% maximum Cu content)16 with A2B3 polytriazole adhesives and for AA7075 (1.2-


Page 25 of 47

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


1.6% Cu content)17 with either A4B2 or A4B3 polytriazole adhesives containing aromatic main groups. Adhesion strength to the AA2024 substrate was measured by peel testing, with results summarized in Figure 8 and Table 4. Coatings 1A21B3 and 2A22B3 performed the best (2.22-2.31 MPa), compared to moderate (1.5-1.0 MPa) and poor adhesion strength (0.31 MPa) of the more highly branched polytriazole systems. These results compared favorably with the adhesion properties of a standard sol-gel organosilane coating (regarded as having good adhesion properties, abrasion resistance, and chemical resistance)48 and a standard epoxy coating (which usually has excellent adhesion properties and chemical resistance)49. Cohesive rupture of the adhesive and dolly interface (classified as Y type)38 was observed for 1A21B3 and 2A22B3, whereas the other materials tested did not exhibit a consistent failure mode. The hardness of the polymer films directly deposited onto the AA2024 substrate was measured by nanoindentation (Figure 8B). The lowest values of elastic modulus and hardness were obtained for 1A21B3 – the film composed of the most flexible monomers, and which had the best adhesion and anticorrosion properties. Conversely, the most brittle and hard materials (such as 4A35B4) were the poorest coatings.



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 26 of 47

Figure 8. A) Pull-off adhesion values and B) Young’s modulus and hardness parameters of poly(1,4-disubstituted 1,2,3-triazole)s films adhered to AA2024 substrates before corrosion assays (dry state). In panel A, values lacking error estimates denote materials for which the failure mode varied among type Y, -Y and A/B. In those cases, only one sample with failure mode comparable to 1A21B3 and 2A22B3 (Y type) was considered. Table 4. Adhesion strength, elastic modulus and hardness values obtained for the polytriazole systems with the best film forming properties. SAMPLE

a)

Adhesion strength a) Young’s modulus b)

Hardness b)

(MPa)

(GPa)

(GPa)

1A21B3

2.22 ± 0.09

4.30 ± 0.22

0.33 ± 0.01

2A22B3

2.31 ± 0.68

5.80 ± 0.29

0.39 ± 0.01

4A35B4

0.37

7.90 ± 0.40

0.56 ± 0.01

4A34B3

1.00

6.30 ± 0.32

0.33 ± 0.02

5A35B4

0.31

6.40 ± 0.32

0.36 ± 0.07

Silane c)

1.58

-

-

Epoxy d)

0.63

-

-

Measured by pull-off testing. b) Young’s modulus and hardness were measured by nanoindentation. c) From reference 48. d) From reference 49.


Page 27 of 47

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


CONCLUSIONS Effective anticorrosion barrier coatings were developed using poly(1,4-disubstituted 1,2,3triazole)s as a consequence of their synergistic properties of adhesion and crosslinking. The strong interfacial interaction between organic coating and metal substrate was obtained with the help of copper-catalyzed azide−alkyne cycloaddition using the presence of copper alloying elements on the aluminum surface. The best anticorrosion and film forming properties on AA2024 surface were obtained with monomers of comparatively low functionality (A2B3 polytriazoles). Furthermore, the presence of several methylene groups on the azide compositions helped moderate the degree of crosslinking among polymer chains, offering a beneficial flexibility to the polymer film. Thus, the presence of bi-azide and tri-alkyne functionalities in poly(1,4-disubstituted 1,2,3-triazoles) coating has fulfilled the expected role by offering improved adhesion to the metal substrate and protective barrier properties at the film surface simultaneously. Deposition of 1,4-polytriazoles by click-chemistry is also an eco-friendly alternative that can be explored to replace other thermoset systems, like epoxies or organosilane, that requires large quantity of solvents and co-solvents for deposition onto metal surface and to protect it. This method may be particularly be attractive for applications in aerospace or other structures manufactured with AA2024 aluminum alloys that require good chemical resistance, toughness, flexibility, and retention of mechanical properties even at high temperatures.

ASSOCIATED CONTENT Supporting information: Figure S1−S6 representing the: physical aspect of polytriazoles films obtained after post-curing treatment, with their laboratory and abbreviation codes details; dynamic FTIR spectrum of 5A35B4 film; photographs of flexible and rigid films; DMA curves of 5A35B4 film; TGA and DTG curves of all samples; and Nyquist and Bode plots from EIS measurements of all samples; Table S1 with EIS fitting data. 27 ACS Paragon Plus Environment


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 28 of 47

Movie 1 showing the wettability of AA2024 surface after immersion in NaCl solution for few seconds (AA2024_ hydrophilic surface.MOV) Movie 2 showing the wettability of 1A21B3 polytriazole film surface after immersion in NaCl solution for few seconds (1A2_1B3_hydrophobic surface.MOV)

AUTHOR INFORMATION Corresponding authors: *To

whom

correspondence

should

be

addressed:

E-mail:

[email protected],

E-mail: david. [email protected]

Author Contributions: The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes: The authors declare no competing financial interest.

ACKNOWLEGMENTS This work has been supported by MICINN and FEDER funds (MAT2015-69367-R) and by University of Regensburg. E. Armelin acknowledges for mobility financial support given by “Salvador de Madariaga” program (PRX14/00627, MICINN). C. Alemán acknowledges the “ICREA Academia 2015” award for excellence in research, funded by the Generalitat de Catalunya. D. Díaz Díaz thanks the Deutsche Forschungsgemeinschaft (DFG) for the Heisenberg Professorship Award. The authors also thank Prof. X. Ramis from the Department of Heat Engines and Dr. E. Jiménez from Department of Materials Engineering (UPC) for their scientific support with DMTA and nano-indentation results, respectively.


Page 29 of 47

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


REFERENCES (1) Díaz, D. D.; Punna, S.; Holzer, P.; McPherson, A. K.; Sharpless, K. B.; Fokin, V. V.; Finn, M. G. Click Chemistry in Materials Synthesis. 1. Adhesive Polymers from CopperCatalyzed Azide-Alkyne Cycloaddition, J. Polym. Sci. A Polym. Chem. 2004, 42, 4392–4403. (2) Kolb, C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions, Angew. Chem. Int. Ed. 2001, 40, 2004–2021. (3) Rostovtsev, H V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. A Stepwise Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation” of Azides and Terminal Alkynes, Angew. Chem. Int. Ed. 2002, 41, 2596–2599. (4) Rutjes, F.; Fokin, V. V. Click Chemistry: In Chemistry, Biology and Macromolecular Science, J. Wiley & Sons, Weinheim, 2011. (5) Dervaux, B.; Du Prez, F. E. Heterogeneous Azide–Alkyne Click Chemistry: Towards Metal-Free End Products, Chem. Sci. 2012, 3, 959–966. (6) Espeel, P.; Du Prez, F. E. “Click”-Inspired Chemistry in Macromolecular Science: Matching Recent Progress and User Expectations, Macromolecules 2015, 48, 2–14. (7) Shi, Y.; Cao, X.; Gao, H. The Use of Azide–Alkyne Click Chemistry in Recent Syntheses and Applications of Polytriazole-based Nanostructured Polymers, Nanoscale 2016, 8, 4864–4881. (8) Qafasoui, W.; Blanc, C.; Pebere, N.; Srhiri, A.; Mankowski, G. Study of Different Triazole Derivative Inhibitors to Protect Copper Against Pitting Corrosion, J. Appl. Electrochem. 2000, 30, 959–966. (9) Negrón-Silva, G. E.; González-Olvera, R.; Angeles-Beltrán, D.; Maldonado-Carmona, N.; Espinoza-Vázquez, A.; Palomar-Pardavé, M. E.; Romero-Romo, M. A.; Santillan, R. Synthesis of New 1,2,3-Triazole Derivatives of Uracil and Thymine with Potential Inhibitory Activity against Acidic Corrosion of Steels, Molecules 2013, 18, 4613–4627. 29 ACS Paragon Plus Environment


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 30 of 47

(10) Trachli, B.; Keddam, M.; Takenouti, H.; Srhiri, A. Protective Effect of Electropolymerized 3-Amino 1,2,4-Triazole Towards Corrosion of Copper in 0.5 M NaCl, Corros. Sci. 2002, 44, 997–1008. (11) Cao, P. G.; Yao, J. L.; Zheng, J. W.; Gu, R. A.; Tian, Z. Q. Comparative Study of Inhibition Effects of Benzotriazole for Metals in Neutral Solutions As Observed with SurfaceEnhanced Raman Spectroscopy, Langmuir 2002, 18, 100–104. (12) Deng, Q.; Shi, H-W.; Ding, N-N.; Chen, B-Q.; He, X-P.; Liu, G.; Tang, Y.; Long, Y-T.; Chen, G-R. Novel Triazolyl Bis-amino Acid Derivatives Readily Synthesized via Click Chemistry as Potential Corrosion Inhibitors for Mild Steel in HCl, Corros. Sci. 2012, 57, 220–227. (13) Liu, Y.; Díaz, D. D.; Accurso, A. A.; Sharpless, K. B.; Fokin, V. V.; Finn, M. G.; Click Chemistry in Materials Synthesis. III. Metal-Adhesive Polymers from Cu(I)-Catalyzed Azide–Alkyne Cycloaddition, J. Polym. Sci. A Polym. Chem. 2007, 45, 5182–5189. (14) Accurso, A. A.; Delaney, M.; O’brien, J.; Kim, H.; Iovine, P. M.; Díaz, D. D.; Finn, M. G. Improved

Metal-Adhesive

Polymers

from

Copper(I)-Catalyzed

Azide–Alkyne

Cycloaddition, Chem. Eur. J. 2014, 20, 10710–10719. (15) Le Baut, N.; Díaz, D. D.; Punna, S.; Finn, M.G.; Brown, H. R. Study of High Glass Transition Temperature Thermosets Made from the Copper(I)-Catalyzed Azide-Alkyne Cycloaddition reaction, Polymer 2007, 48, 239–244. (16) Tang, Y.; Jim, C. K. W.; Liu, Y.; Ye, L.; Qin, A.; Lam, J. W. Y.; Zhao, C.; Tang, B. Z. Synthesis and Curing of Hyperbranched Poly(triazole)s with Click Polymerization for Improved Adhesion Strength, ACS Appl. Mater. Interfaces 2010, 2, 566–574. (17) Yanpeng, E.; Wan, L.; Huang, F.; Du, L. New Heat-resistant Polytriazole Adhesives: Investigation of Adhesion of Polytriazole Resins to Metals, J. Adhes. Sci. Technol. 2013, 27, 1767–1777.


Page 31 of 47

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


(18) Nicosia, C.; Huskens, J. Reactive Self-assembled Monolayers: From Surface Functionalization to Gradient Formation, Mater. Horiz. 2014, 1, 32–45. (19) Ramdas, M. R.; Kumar, K. S. S.; Nair, C. P. R. Synthesis, Structure and Tunable Shape Memory Properties of Polytriazoles: Dual-trigger Temperature and Repeatable Shape Recovery, J. Mater. Chem. A 2015, 3, 11596–11606. (20) Zheludkevich, M.L.; Yasakau, K.A.; Poznyak, S.K.; Ferreira, M.G.S. Triazole and thiazole derivatives as corrosion inhibitors for AA2024 aluminium alloy. Corros. Sci. 2005, 47, 3368–3383. (21) Popova, A.; Christov, M.; Raicheva, S.; Sokolova, E. Adsorption and inhibitive properties of benzimidazole derivatives in acid mild steel corrosion. Corros. Sci. 2004, 46, 1333–1350. (22) Khaled, K.F.; Amin, M. A. Electrochemical and molecular dynamics simulation studies on the corrosion inhibition of aluminum in molar hydrochloric acid using some imidazole derivatives. J. Appl. Electrochem. 2009, 39, 2553–2568. (23) Madkour, L.H.; Issa, R. M.; El-Ghrabawy, I. M. Kinetics of Substituted Bis- and Monoazo Dyes as Corrosion Inhibitors for Aluminium in Hydrochloric Acid and Sodium Hydroxide Solutions. J. Chem. Research 1999, 408–409. (24) Harvey, T.G.; Hardin, S.G.; Hughes, A.E.; Muster, T.H.; White, P.A.; Markley, T.A.; Corrigan, P.A.; Mardel, J.; Garcia, S.J.; Mol, J.M.C.; Glenn, A.M. The effect of inhibitor structure on the corrosion of AA2024 and AA7075. Corros. Sci. 2011, 53, 2184–2190. (25) Kozhukharov, S.; Kozhukharov, V.; Wittmar, M.; Schem, M.; Aslan, M.; Caparrotti, H.; Veith, M. Protective abilities of nanocomposite coatings containing Al2O3 nano-particles loaded by CeCl3. Prog. Org. Coat. 2011, 71, 198–205. (26) Kozhukharov, S.; Kozhukharov, V.; Wittmar, M.; Schem, M.; Aslan, M.; Caparrotti, H.; Veith, M. Protective ability of hybrid nano-composite coatings with cerium sulphate as 31 ACS Paragon Plus Environment


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 32 of 47

inhibitor against corrosion of AA2024 aluminium alloy. Prog. Org. Coat. 2012, 73, 95– 103. (27) Bhattacharya, A. The Protective Coatings Market: Growth Drivers, Eur. Coat. J. 2016, 07/08, 22–23. (28) Martí, M.; Molina, L.; Aleman, C.; Armelin, E. Novel Epoxy Coating Based on DMSO as a Green Solvent, Reducing Drastically the Volatile Organic Compound Content and Using Conducting Polymers As a Nontoxic Anticorrosive Pigment, ACS Sustain. Chem. Eng. 2013, 1, 1609−1618. (29) Fir, M.; Orel, B.; Surca Vuk, A.; Vilcnik, A.; Jese, R.; Francetic, V. Corrosion Studies and Interfacial Bonding of Urea/Poly-(dimethylsiloxane) Sol/Gel Hydrophobic Coatings on AA 2024 Aluminum Alloy, Langmuir 2007, 23, 5505−5514. (30) Montemor, M.F. Functional and Smart Coatings for Corrosion Protection: A Review of Recent Advances, Surf. Coat. Technol. 2014, 258, 17–37. (31) Liangliang, L.; Swain, G. M. Effects of Aging Temperature and Time on the Corrosion Protection Provided by Trivalent Chromium Process Coatings on AA2024-T3. ACS Appl. Mater. Interfaces 2013, 5, 7923−7930. (32) Xiangfeng, M.; Guoying, W.; Hongliang, G.; Yundan, Y.; Ying, C.; Dettinger, H. Anodization for 2024 Al Alloy from Sulfuric-Citric Acid and Anticorrosion Performance of Anodization Films, Int. J. Electrochem. Sci. 2013, 8, 10660−10671. (33) Joshi, S.; Fahrenholtz, W. G.; O’Keefe, M. J. Effect of alkaline cleaning and activation on aluminum alloy 7075-T6, Appl. Surf. Sci. 2011, 257, 1859–1863. (34) Díaz, D. D., Click Chemistry in Materials Synthesis: The Beginning, Macromol. Symp. 2015, 358, 10–20. (35) Vargel, C. in Corrosion of Aluminum; Sleeman, D., Ed.; Elsevier Ltd.: Oxford, U.K., 2004. 32 ACS Paragon Plus Environment

Page 33 of 47

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


(36) Torras, J.; Azambuja, D. S.; Wolf, J. M.; Aleman, C.; Armelin, E. How Organophosphonic Acid Promotes Silane Deposition onto Aluminum Surface: A Detailed Investigation on Adsorption Mechanism, J. Phys. Chem. C 2014, 118, 17724–17736. (37) Oliver, W.C.; Pharr, G.M. Measurement of Hardness and Elastic Modulus by Instrumented Indentation: Advances in Understanding and Refinements to Methodology, J. Mater. Res. 2004, 19, 3–20. (38) UNE-EN ISO 4624. Paints and varnishes - Pull-off test for adhesion. 2003, 1–19. (39) Priyanka, K. G.; Mishra, A. K.; Kantheti, S.; Narayan, R.; Raju, K. V. S. N. Synthesis of Triazole Ring-Containing Pentol Chain Extender and Its Effect on the Properties of Hyperbranched Polyurethane-Urea Coatings, J. Appl. Polym. Sci. 2012, 126, 2024–2034. (40) Kantheti, S.; Sarath, P.S.; Narayan, R.; Raju, K. V. S. N. Synthesis and Characterization of Triazole Rich Polyether Polyols Using Click Chemistry for Highly Branched Polyurethanes, React. Funct. Polym. 2013, 73, 1597–1605. (41) Sykam, K.; Donempudi, S. Novel Multifunctional Hybrid Diallyl Ether Monomer via Azide Alkyne Click Reaction as Crosslinking Agent in Protective Coatings, Polymer 2015, 62, 60–69. (42) González N., Custal M. A., Lalaouna S., Riba J-R., Armelin E., Improvement of Dielectric Properties of Natural Rubber by Adding Perovskite Nanoparticles, Eur. Polym. J. 2016, 75, 210–222. (43) Flores, M.; Fernández-Francos, X.; Jiménez-Piqué, E.; Foix, D.; Serra, A.; Ramis, X. New Epoxy Thermosets Obtained From Diglycidylether of Bisphenol A and Modified Hyperbranched Polyesters With Long Aliphatic Chains Cured by Diisocyanates, Polym. Eng. Sci. 2012, 52, 2597–2610. (44) Thermosets: Structure, Properties and Applications. Ed. Qipeng Guo. Woodhead Publishing, Oxford, 2012. 33 ACS Paragon Plus Environment


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 34 of 47

(45) Bonora, P. L.; Deflorian, F.; Fedrizzi, L. Electrochemical Impedance Spectroscopy as a Tool for Investigating Underpaint Corrosion, Electrochim. Acta 1996, 41, 1073–1082. (46) Yuan, X.; Yue, Z. F.; Chen, X.; Wen, S. F.; Li, L.; Feng, T. The Protective and Adhesion Properties of Silicone-Epoxy Hybrid Coatings on 2024 Al-alloy with a Silane Film as Pretreatment, Corros. Sci. 2016, 104, 84–97. (47) Zhang, X.; Hashimoto, T.; Lindsay, J.; Zhou, X. Investigation of the De-alloying behaviour of -phase (Al2Cu) in AA2024-T351 Aluminium Alloy, Corros. Sci. 2016, 108, 85–93. (48) Calabrese, L.; Bonaccorsi, L.; Caprì, A.; Proverbio, E. Effect of Silane Matrix on Corrosion Protection of Zeolite Based Composite Coatings, La Metallurgia Italiana, 2014, 6, 35–39. (49) Dalmoro, V.; Alemán, C.; Ferreira, C. A.; dos Santos, J.H.Z.; Azambuja, D. S.; Armelin, E. The Influence of Organophosphonic Acid and Conducting Polymer on the Adhesion and Protection of Epoxy Coating on Aluminium Alloy. Prog. Org. Coat. 2015, 88, 181–190.


Page 35 of 47

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


TABLE OF CONTENTS



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

ACS Paragon Plus Environment

Page 36 of 47

Page 37 of 47

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




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

20%

-  -

Figure 1


Page 38 of 47

Page 39 of 47

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


(B)

(A)

2 µm (C)

2 µm (D)

2 µm

2 µm (F)

(E)

2 µm

1 µm

Figure 2



Degradation

Devitrification

A)

B) Degradation

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

Page 40 of 47


Page 41 of 47

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




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

A)

B)

Page 42 of 47

Before immersion

After immersion

84.1º

63.3º

Smooth surface

Rough surface

10 µm

20 µm

95.5º

92.9º

Non-wettable surface

Non-wettable surface

20 µm


20 µm

Page 43 of 47

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


A)

B)



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

A)

WATER ACCESS

Page 44 of 47

CORROSION PRODUCT

GALVANIC CORROSION

PORE

Al2CuMg ANODIC ZONES

WATER ACCESS

LONG-LASTING PROTECTION

Polytriazole

A2

AA2024 Hydrophobic thermoset

B)

C)


B3

Page 45 of 47

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


A)



10

1,0

9

0,9

7.9

8

0,8

7 5.8

6 5 4

6.4

6.3

0,7

0.56

0,6 0,5

4.3

0.39 0.33

0.33

0.36

0,4

3

0,3

2

0,2

1

0,1

0

0,0 1A21B3

2A22B3

4A35B4

4A34B3


5A35B4

Hardness (GPa)

B) Young's modulus (GPa)

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

Page 46 of 47

Page 47 of 47

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


Table of Contents

Cu (I)

A2

4

1

B3

Without protection: Rough corrosion products

With polytriazole film: Homogenous and anticorrosive coating Click chemistry

Aluminum alloy 2024


Protective Coatings for Aluminum Alloy Based on Hyperbranched 1,4

Recommend Documents