Construction of Compact Polyelectrolyte Multilayers Inspired by

Subscriber access provided by ECU Libraries

Article

Construction of Compact Polyelectrolyte Multilayers Inspired by Marine Mussel: Effects of Salt Concentration and pH as Observed by QCM-D and AFM Weina Wang, Yisheng Xu, Sebastian Backes, Ang Li, Samantha Micciulla, A. Basak Kayitmazer, Li Li, Xuhong Guo, and Regine von Klitzing Langmuir, Just Accepted Manuscript • Publication Date (Web): 23 Mar 2016 Downloaded from http://pubs.acs.org on March 23, 2016

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.

Langmuir 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 33

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

Langmuir

Construction of Compact Polyelectrolyte Multilayers Inspired by Marine Mussel: Effects of Salt Concentration and pH as Observed by QCM-D and AFM Weina Wang1,2, Yisheng Xu,1* Sebastian Backes2, Ang Li1, Samantha Micciulla2, A. Basak Kayitmazer3, Li Li1, Xuhong Guo1,4* and Regine von Klitzing2* 1

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China

2

Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Strasse des 17. Juni 124, D-10623 Berlin, Germany

3

Chemistry Department, Bogazici University, Bebek, Istanbul 34342, Turkey

4

Engineering Research Center of Materials Chemical Engineering of Xinjiang Bintuan, Shihezi University, Xinjiang 832000, China

*

To whom correspondence should be addressed. E-mail: [email protected] (Yisheng Xu)，[email protected] (Xuhong Guo) and [email protected] (Regine von Klitzing) 1

ACS Paragon Plus Environment

Langmuir

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: Biomimetic multilayers based on Layer-by-Layer (LbL) assembly were prepared as functional films with compact structure by incorporating the mussel-inspired catechol crosslinking. Dopamine modified poly(acrylic acid) (PAADopa) was synthesized as a polyanion to offer electrostatic interaction with the pre-layer polyethyleneimine (PEI) and consecutively crosslinked by zinc to generate compact multilayers with tunable physicochemical properties. In-situ layer-by-layer growth and crosslinking were monitored by Quartz Crystal Microbalance with Dissipation (QCM-D) to reveal the kinetics of the process and the influence of Dopa chemistry. Addition of Dopa enhanced the mass adsorption and led to the formation of a more compact structure. An increase of ionic strength induced an increase in mass adsorption in the Dopa-crosslinked multilayers. This is a universal approach for coating of various surfaces such as Au, SiO2, Ti and Al2O3. Roughness observed by AFM in both wet and dry conditions was compared to confirm the compact morphology of Dopa-crosslinked multilayers. Due to the pH sensitivity of Dopa moiety, metal-chelated Dopa groups can be turned into softer structure at higher pH as revealed by reduction of Young’s modulus determined by MFP-3D AFM. A deeper insight of the growth and mechanical properties of Dopa-crosslinked polyelectrolyte multilayers was addressed in the present study. This allows a better control of these systems for bioapplications.

Keywords: LbL films, PAADopa, zinc crosslinking, compact structure, pH turned

2


Page 2 of 33

Page 3 of 33

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

Langmuir

1. Introduction Polyelectrolyte multilayers can be self-assembled and self-organized from sequential deposition of oppositely charged polymers onto charged surfaces in aqueous solutions.1-3 The layer-by-layer deposition offers a variety of surface modification possibilities by tuning of the thickness, no limits of template shape, incorporating functional groups to control macroscopic properties and form hierarchical structures which allows generation of compartments like for cascade reactions.4 This technique has become one of the most prominent surface engineering strategies in materials science and shows great potential in many applications such as antifouling,5-7 electronic or optical devices8 and biomedical applications9-12 including drug delivery, biosensors,13 biomimetics, and tissue engineering.14,15 One driving force of the multilayer assembly for strong polyelectrolytes is assumed to be the electrostatic attraction, for weak polyelectrolytes is assumed to be weak

interactions including

hydrogen

bonding

and

hydrophilic/hydrophobic

interaction.16 For example, in the case of poly(acrylic acid) PAA the ionization is very sensitive to local environment, therefore the molecular organization, composition and surface properties could possibly be controlled by external parameters such as salt concentration and pH.15,17 Interestingly, some divalent ions like Zn2+ could induce formation of surface patterns on PAA containing films by forming complexes.16 However, for practical applications especially under harsh environment (eg. high salt concentration and pH), controllable film morphology, structure and mechanical properties are desired. One possible method to improve these physicochemical 3


Langmuir

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

properties is to introduce functional groups to help build robust films with tunable properties. Mimicking structures and functions from natural organisms has recently been a hot research topic due to the superior mechanical and biological properties compared to synthetic materials.9,18,19,36-39 Mussel-inspired surface chemistry provides a solution for creating robust LbL films because of its several virtues. First, it has universal modification capability on varied surfaces due to the highly active catechol groups, which are contained in mussel foot proteins (mfps). The highest content is up to ~30% from foot protein5 of the common blue mussel(M. edulis)showing highest adhesion.20 In addition, catechol groups can be coordinately crosslinked by metal ions21,22,40 such as Fe,Mn,Ti,Zn and Ca41 and covalently crosslinked under basic environment getting oxidized automatically.15,23,24 However, only the moderate crosslinker Zn forms fluidic and coacervate-like complexes with PAADopa at low pH conditions.25 This crosslinking structure makes the film become much more compact and significantly increases its mechanical strength.Finally, the surface adhesion at the organic-inorganic interface is stronger due to the presence of catechol groups. Therefore, in this work Dopa modified PAA was synthesized with 30% grafting ratio25 as a biomimetic polyanion. Linear polyethylenimine (PEI) was used as a precursor layer on substrate to provide a positively charged layer for self-assembly of multilayers. Crosslinking is a strategy to form more compact multilayers with controllable physicochemical properties.26

4


Page 4 of 33

Page 5 of 33

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

Langmuir

The crosslinked multilayers building under different salt concentrations were analyzed in-situ by QCM-D along with AFM to verify crosslinked Dopa effects on structure and multilayer morphology for further applications in hydrophilic modification on varied surfaces (eg. Au, Al2O3, Ti, SiO2). The nature of crosslinking should be coordination between catechol of PAADopa and zinc ions and electrostatic interactions between zinc and carboxylate groups (Scheme 1). At alkaline pH, the chelation is dominant forming strong crosslinking structure.41,42 Although at acidic pH both chelation and electrostatic interactions become weaker, they are still stronger than those of the system without zinc and help to form a compact structure when PAADopa interacts with PEI.

Scheme 1. Mussel Inspired Metal-Catecholate Crosslinking Mechanisms at different pHs.

Although covalent crosslinking multilayers of PAADopa and PEI has been reported,15 this is the first time that their repeated building-up and the divalent metal chelating process were investigated in-situ by QCM-D and ex-situ by AFM. This work addresses study of how metal chelated Dopa groups influence the mass and structure 5


Langmuir

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

changes during multilayer building process and how salt concentration affects this system. We expect that such QCM-D study, complemented with AFM observation, could enhance the understanding of LbL formation and crosslinking effects of this effective multilayer system which could be an ideal candidate for bioapplications.

2. Experimental section 2.1 Materials All water used for solutions was purified (≥18.0 MΩ•cm) by a Millipore water purification system using Gamma gold Millipore (0.22 µm, Merck KGaA, Darmstadt, Germany). PAADopa was synthesized by reaction of amidation as described in our previous work.25,27 Linear polyethyleneimine, (PEI, Mw = 25000 g mol-1), Zinc chloride (ZnCl2) were purchased from Sigma Aldrich. NaCl (purity＞99.5%) was from Fluka (Thomas Scientific). Other chemicals and solvents were purchased from Sigma-Aldrich (Germany) unless noted otherwise. All reagents were used without further purification.

2.2 Polyelectrolyte multilayer preparation Silicon wafers (test grade n-type) were treated with fresh piranha solution (30% H2O2: 98% H2SO4 =1:1 v/v) for 30 min, followed by abundant amount of Milli-Q water and finally dried with N2 stream. The multilayers were built in an alternate way dipping automatically by a Dipping Robot. The freshly cleaned silicon substrates 6


Page 6 of 33

Page 7 of 33

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

Langmuir

(10×40 mm2) were immersed in PEI (0.5 g/ml), PAADopa (1 mg/ml, 3.5 mM of Dopa) and Zn2+ (10.5 mM) solutions for 15 min to build the positive, negative and crosslinked layers on top. Before adsorption of the next layer, substrates were rinsed continuously in two rinsing baths (60 s for each). These adsorption and rinsing processes were repeated until reaching the desired number of layers. PEI/PAADopa-Zn multilayers with the cycle deposition of n times are noted as (PEI/PAADopa-Zn)n. The final multilayers were dried with N2 stream after assembly. Multilayers made at pH 4 were further immersed in phosphate buffer at pH 8.5 to obtain the pH turned multilayers.

2.3 Quartz crystal microbalance with dissipation (QCM-D) Quartz crystal microbalance with dissipation (QCM-D, Q-Sense E1, Sweden) was introduced to study real-time frequency and dissipation changes after excitation of the freely oscillating quartz crystal. Briefly, the crystal carrying two gold electrodes was fixed inside the chamber and brought to vibrate at the resonance frequency. The resulting changes in frequency (∆f) and dissipation (∆D) were monitored as a function of time and they were recorded at the fundamental frequency of quartz (4.95 MHz for

AT cut quartz sensors) and its 3rd, 5th, 7th, 9th, 11th and 13th overtones. Herein, the 5th, 7th, 9th and 11th overtones were shown in the results. The changes of adsorbed mass are reflected by ∆f, since the coupling of mass to the crystal causes the decrease of its oscillation frequency due to the enhanced inertia.35 Besides, viscoelastic properties of molecular layers are reflected by ∆D since the dissipation changes are related to the 7


Langmuir

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

decay rate of the oscillation amplitude by turning off the driving voltage responsible for the sensor oscillation. Different QCM-D crystals were purchased from Q-Sense (Sweden), they were coated with Silicon dioxide (QSX 303, thickness of SiO2 layer is 50 nm), Gold (QSX301, thickness of Au layer is 100 nm), Aluminum oxide (QSX309, thickness of Al2O3 layer is 100 nm) and Titanium (QSX310, thickness of Ti layer is 120 nm) respectively. Prior to adsorption, different cleaning methods were used. The Au-coated quartz crystal was cleaned by the mixture liquid of NH3: H2O2: H2O (1:1:5, v/v) for 10 min at 75°C. SiO2 and Al2O3-coated crystals were immersed in fresh sodium dodecyl sulfate (SDS) solution for 30 min at room temperature. The Ti-coated crystal was immersed in 1% Hellmanex II (Hellma Analytics, Germany) for 30 min at room temperature. Crystals coated with SiO2, Au and Al2O3 layers were rinsed with excess Milli-Q water and dried with a N2 stream. Ti-coated crystals were further sonicated in 99% ethanol for an extra 10 min, rinsed well with Milli-Q water and dried with N2. Finally, all crystals were treated in a preheated plasma cleaner (Femto, Diener electronic Plasma-Surface-Technology, Germany) for 10 min. The freshly cleaned crystal was then immediately fixed into the chamber (volume of flow channel: 100 µL, volume above the crystal: ~ 40 µL) and pumped with acetic acid buffer (pH 4, with/without 0.6 M NaCl) at a flow rate of 0.1 mL/min before experiments. After thorough equilibration of the baseline for at least three hours, the alternate PEI, PAADopa, Zn (or PEI, PAA, Zn as Parallel sample) adsorption-rinse cycle was repeated to build multilayers on the crystal. The adsorption/rinse time was set up to 15 8


Page 8 of 33

Page 9 of 33

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

Langmuir

and 10 min respectively to reach the equilibration states. All the experiments were carried out at 25°C in a stop-flow method changing injected solutions.

2.4 Atomic force microscopy (AFM) Roughness images of multilayers both in air and in buffer were measured by scanning force microscopy (SFM). All measurements were carried out using an MFP-3D AFM (Asylum Research, Oxford Instruments) with OMCL-AC240TS tips (Olypmus) in air and HQ: NSC18/CR-AU tips (Mikromash) in solution. Imaging was done in intermittent contact mode. The roughness was obtained from 5 µm x 5 µm scans. From these scans, five 1 µm x 1 µm squares were picked, from which the root mean square roughness (RMS) was calculated and averaged using the Asylum Research Software. The Young's modulus of PEI/PAADopa-Zn multilayers at different pHs (pH 4 and pH 8.5) was determined using the MFP-3D AFM. Instead of a sharp tip, a silica microsphere with a radius of 3.35 µm (Bangs Laboratories, Inc., USA) was glued to HQ: NSC35/ TIPLESS/ no Al cantilevers (Cantilever B, MikroMasch). Therefore a two-component epoxy adhesive (UHU plus endfest 300, UHU GmbH, Buehl, Germany) was used. The cantilevers were moved with a micromanipulator so that their far end was brought in contact with the glue. Afterwards, an individual silica microsphere could be picked up. The prepared cantilevers were left for at least 12 hours and cleaned in an air plasma chamber for 20 min before use. Before the measurement the cantilever 9


Langmuir

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

deflection (inverse optical lever sensitivity, InvOLS) was calibrated on a hard surface and the exact spring constant was determined by the thermal noise method, which is a built-in procedure in the MFP-3D instrument. The reference spring constant of the cantilever is given as 16 N/m. Force maps consisting of 144 force curves at a velocity of 1 µm/s were recorded for each sample. Only the approach curves were evaluated with the Asylum Research software using the Hertz model to obtain the Young's modulus. For the analysis only the part of the force curve up to 10-20% indentation was used.

2.5 Contact angle measurements Static contact angle measurements were performed with a contact angle goniometer (Data Physics Instruments, Germany) in the method of sessile drop and images were handled with the software SCA 20 (Dataphysics, version 3.12.11). The substrate was placed on a platform surrounded by Milli-Q water inside a sealed transparent cuvette (length of 28 mm, TH.GEYER) to minimize the influence of evaporation. The whole process was performed at room temperature and recorded automatically. At least ten measurements beginning from the well equilibrated state were averaged to obtain reliable results. FT-IR spectra were obtained with a Nicolet 6700 instrument (Nicolet Instrument, Thermo Company, USA) over the wavelength range of 4000-1160 cm-1. The PAADopa-Zn powder dried from solutions with pH 4 was ground with KBr uniformly and then pressed to a standard disk for measurement.

10


Page 10 of 33

Page 11 of 33

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

Langmuir

3. Results and discussion Firstly, PEI/PAA-Zn and PEI/PAADopa-Zn multilayers assembly are presented to study process kinetics in-situ and the effect of the existed Dopa units on crosslinking during the multilayer assembling. Secondly, the salt effect on PEI/PAADopa-Zn multilayers building process was investigated. Then, the result is further applied on hydrophilic modification of crystals with different surfaces (eg. Au, Ti, Al2O3 and SiO2 coated crystals). Finally, the effect of pH on crosslinked structural and mechanical properties of PEI/PAADopa-Zn multilayers was studied.

3.1 Dopa effect on multilayer building Quartz crystal microbalance with dissipation (QCM-D) is a type of high sensitivity mass sensing device. Its sensitivity can be characterized by either frequency shift or dissipation shift. Herein, QCM-D was applied to examine real-time frequency and dissipation changes during the multilayer preparation. The linear Sauerbrey relation was applied for calculating adsorbed mass (∆m = C×∆f, where ∆f is the overtone-normalized frequency change obtained directly from the test data, C is the mass sensitivity of the quartz crystal with a value of -17.7 ng•cm-2•Hz-1, ∆m is the mass change). The changes of adsorbed mass are reflected by ∆f since the oscillation frequency of the sensor is dependent on the mass coupled to its surface. Meanwhile, viscoelastic properties of molecular layers are reflected by ∆D which is related to the decay rate of the oscillation amplitude when the driving potential is turned off.28,29 11


Langmuir

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

Generally, multilayers showing frequency shifts which are independent on the overtone number are assumed to be rigid.17 In the experiments, for every layer construction PEI acted as pre-layer adsorbed onto the surface of gold crystal, providing a positively charged layer. Two anionic polymers PAA and PAADopa were used, and different overtones were examined to understand the effects of Dopa during the deposition in the presence of “crosslinker” zinc. As shown in Figure 1, the repeated mass increments demonstrate the successful multilayer building and different growth behaviors.

12


Page 12 of 33

Page 13 of 33

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

Langmuir

Figure 1. Shifts of mass and dissipation as a function of time for multilayers assembly of (a, a′) (PEI/PAA-Zn)1-4, (b, b′) (PEI/PAADopa-Zn)1-4, (c, c′) (PEI/PAA-Zn)8 and (d, d′) (PEI/PAADopa-Zn)8. Injection of cationic PEI solution (black arrows) continued for 15 min and followed by rinsing (blue arrows) for 10 min before the depositions of the following anionic PAA (or PAADopa) and the sequent crosslinker Zn2+. These crosslinked layer pairs were considered as one layer (dashed lines). Arrows point to increasing overtone number (5th, 7th and 9th) in (c, c′) and (d, d′)

In the case of non-Dopa system (Figure 1a), a typical deposition feature is noticed, namely that the mass uptake systematically increases after sequential flows of PEI, PAA, and Zn2+. More in detail, during the first four layer building, the initial adsorption is fast and requires ~10 min to reach a relatively constant value. After rinsing with the background buffer solution, the adsorbed mass of PEI, PAA and Zn decreased, accompanied by the decreased dissipation with structure changes from soft, hydrated into a more condensed type (Figure 1a′). Interestingly, the further flow of PEI on top of the first layer strongly increased the mass adsorption of polymer but also a strong mass loss is measured during rinsing. The sudden increase of the mass is likely related to the layer swelling, which might occur during polyelectrolyte adsorption due to the formation of a soft and highly hydrated layer as shown from the spikes of dissipation (Figure 1a′) indicating a highly swollen structure. Upon rinsing, the weakly bound PEI can be washed off and the following addition of PAA accelerated the dehydration process to form a relatively condensed structure, as reflected by the 13


Langmuir

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

sudden drop of mass and dissipation. After one layer deposition, the adsorption of PAA contributes less to the mass uptake. This is probably due to the water extrusion from the layer upon the complexation between PEI and PAA, which results unstable complexes with weak electrostatic interactions on top of layer (will be shown later in Figure 2a and a′). Furthermore, it seems that the addition of zinc resulted in a higher mass increase, due to the easier diffusion of zinc ions into both parallel and vertical directions after removal of complexes barrier. For structural changes, zinc ions might not contribute more because of the formed condensed structure (Figure 1a′ and 1c′). In contrast to the non-Dopa multilayers, modification of PAA backbone with Dopa groups generally eliminates the loosely adsorbed layers as most of the dissipation “spikes” disappeared during the adsorption (Figure 1b′ and 1d′). This is presumably because that higher adsorption of PAADopa offers more hydroxyl groups as interactive sites to form coordination with zinc ions (evidence for catechol-Zn2+ coordination was given by IR as shown in Figure S1, Supporting Information)21,25,41,47 to form a more compact and stable network-like structure. This strong interaction between adjacent layers in addition to electrostatic complexation of polymers reduces the layer swelling. As a result, more efficient adsorption of PEI and PAADopa contributed to the increased mass uptake, which is three times higher than that of (PEI/PAA-Zn)8 (Figure 1c and d). In the case of PEI/PAADopa-Zn system, the splitting of dissipation at the beginning might suggest forming a less homogeneous internal structure. As the layer growth proceeds, this situation gets improved with more homogeneous structure. Another difference is the growth behaviors observed from mass changes during the 14


Page 14 of 33

Page 15 of 33

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

Langmuir

construction process of these two multilayers, as shown in Figure 1c and d. The construction of (PEI/PAA-Zn) multilayer changes from linear to exponential growth from the 6th deposition step onwards. In contrast, the (PEI/PAADopa-Zn) multilayer shows an exponential growth right from the beginning. It is well accepted that exponential growth is observed when at least one constituent diffuses in and out of the film during each deposition step of the bilayer.43-45 This exponential mass increase is probably due to the diffusion of polymer chains, which enhances the mass uptake of the multilayer. The topography of multilayer structures after QCM-D measurement was then scanned in buffer (pH4) by AFM after eight layers ofPEI/PAA-Zn and PEI/PAADopaZn (Figure 2a and b). For the non-Dopa multilayers (Figure 2a), the surface is porous and not uniform, where large complexes can be observed in wet state, while by changing the external condition such as the drying state, the large complexes probably shrink and become much smaller (Figure 2a′). This unstable structure is also consistent to the fluctuant dissipation shifts responded to external changes in Figure 1a′. In contrast, for the Dopa-contained multilayers scanned in wet state, the crosslinked layers form more stable and uniform surface structures. One possible reason is that during the multilayer building process, the addition of zinc solution may significantly reduce the mobility of adsorbed PEI polymer chains, forming a more compact layer. The other explanation is a similar mechanism as mentioned in previous work25 in which PAADopa and Zn2+ can quickly generate a viscous phase separation forming condensed crosslinked structure. Such crosslinking is due to the electrostatic 15


Langmuir

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

interaction between negatively charged PAADopa and positive Zn2+ chelated with catechol groups from another PAADopa chain. In general, this compact structure is superior for film growth and more efficient mass adsorption.

Figure 2. AFM phase images of the surfaces (5×5µm2) after adsorption of 8 crosslinked polyelectrolyte layer pairs. (a and a′): (PEI/PAA-Zn)8 and (b and b′): (PEI/PAADopa-Zn)8. Measurements were performed in buffer at pH 4 (a and b) and at dry state (a′ and b′).

3.2. Salt effect on multilayer building The constructed films are usually exposed to a variety of environmental 16


Page 16 of 33

Page 17 of 33

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

Langmuir

conditions in common applications. Since polyelectrolyte multilayers are sensitive to external parameters, the salt effects were investigated on the multilayer adsorption processes to mimic the situation in the sea. Salt concentration up to 0.6 M NaCl is defined as model seawater.7 Multilayers were prepared at the same polymer or Zn2+ concentration but different salt content to examine the structural variations of the films.

Figure 3. In-situ analysis of (PEI/PAADopa-Zn)2 multilayers assembly from aqueous solution with (a) no NaCl, (b) 0.1 M NaCl and (c) 0.6 M NaCl, rinsing medium is the background buffer (pH 4), overtone numbers 5th, 7th, 9th and 11th are shown. (d) Comparison of equilibrium mass of adsorption and rinsing processes with different concentration of NaCl. Dashed lines indicate the end of a complete layer.

As seen in Figure 3, an increase of salt concentration leads to higher mass uptake 17


Langmuir

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 water in all adsorption steps, and the entire structure is still compact after rinsing. When 0.1 M NaCl was added (Figure 3b), a new behavior of PEI occurred during the second deposition. The mass uptake increases greatly accompanied by the increased dissipation even during the rinsing step which indicates a quick hydration process due to the loose structure of PEI layer. When the concentration of NaCl was increased to 0.6 M (Figure 3c), higher dissipation and more negative frequency indicate a stronger layer swelling compared to that rinsing with 0.1 M NaCl. Furthermore, during rinsing the equilibration of PEI layer is much slower. The PEI layer is sensitive to the ionic strength of the rinsing medium. This is due to the charge screen on the polymer chain leading to stronger chain coiling and higher extrinsic charge compensation (higher mobility).47 Therefore, in our case, PEI can diffuse more easily inside the multilayer structure, but the phenomenon is less prominent for the case with much lower ionic strength. In Figure 3d, the mass changes of adsorption and rinsing processes are presented. By adding NaCl, a higher mass increment is observed. After rinsing, there is a slight mass decrease as the loosely bound polymers were washed away except the PEI layer. This may be caused by the screened charges forming a coiled layer with a reduced number of contact points between polymer chains which is favorable for hydration.17,30,31 After assembly of (PEI/PAADopa-Zn)8 multilayers with 0.6 M NaCl during adsorption, QCM crystal surfaces were scanned by AFM in wet state at pH 4 (Figure 4a and a′). Compared to the films assembled without addition of NaCl (Figure 2b and b′), the crosslinked surface with 0.6 M NaCl is rougher (rms 35.6 nm in dry state and 18


Page 18 of 33

Page 19 of 33

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

Langmuir

44.4 nm in wet state). The crosslinked coils on the surface (Figure 4 a) may be the reason for the dissipation spike of PEI as seen from QCM-D measurement (Figure 3c). After drying process, the surface morphology (Figure 4a′) remains similar, indicating the stable structure.

Figure 4. AFM phase images of the surfaces (5×5µm2) after adsorption of 16 crosslinked polyelectrolyte layers (PEI/PAADopa-Zn)8 deposited from solutions with 0.6M NaCl added. (a) Performed in wet at pH 4; (a′) Performed in dry state.

Dopa-containing materials are great candidates for coating on different types of surfaces. It is interesting to apply these polyelectrolytes on modification of different surfaces especially under high ionic strength to investigate whether the structure is robust

enough

to

form

multilayers

under

harsh

environments.

Herein,

PEI/PAADopa-Zn multilayers were assembled on Ti, Al2O3, SiO2, and Au crystals in 0.6 M NaCl as shown in Figure 5a-d, respectively. In general, the trends of mass changes are similar. Increased mass (more negative frequency) during adsorption and decreased mass (less negative frequency) during rinsing were observed. 19


Langmuir

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. Frequency and dissipation shifts for (PEI/PAADopa-Zn)2 multilayers on (a) Ti, (b) Al2O3, (c) SiO2, and (d) Au crystals. All solutions are prepared in buffer with 0.6 M NaCl added, rinsing with NaCl-free buffer. Overtone numbers 5th, 7th, 9th and 11th are shown sequentially. Black arrow indicates the injection of polymer liquid, blue arrow shows the beginning of rinsing with background buffer.

However, a different trend (shown in Figure 6) is that for PEI, the mass uptake exhibits continuously increasing during both adsorption and rinsing, indicating the loosely packed structure of PEI which can become hydrated quickly due to the charge screening along the polyanion chains.32 Therefore it can be concluded that the swelling properties and growth mechanism of PEI/PAADopa-Zn multilayers are mostly independent on the underneath substrate due to the formation of dense multilayers 20


Page 20 of 33

Page 21 of 33

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

Langmuir

(Figure S2, Supporting Information).

Figure 6. Comparison of deposited mass for (PEI/PAADopa-Zn)2 multilayers on Au, Al2O3, Ti and SiO2 crystals.

Static water contact angle was introduced to evaluate these Dopa-containing coatings as shown in Figure 7. As expected, the contact angles of (PEI/PAADopa-Zn)2 modified Au, Al2O3, Ti and SiO2 crystals are around 20° due to the existence of hydrophilic groups such as catechol or carboxylic acid groups on the surface. The result is consistent with the studies of other catechol-contained coatings.33,34 Surface morphologies of these crystals are shown in Figure S2. For crystals with higher mass uptake (Au and SiO2), larger crosslinked complexes on surface are formed, which confirms the assumption that the final multilayer structure arises from the formation of crosslinked aggregates of PAADopa-Zn complexes. These aggregates ultimately grow 21


Langmuir

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 completely cover the surface after further deposition. In general, the crosslinked network is still compact and stable on different types of surfaces suggesting effective and universal coating by using Dopa-inspired multilayer films.

Figure 7. Contact angle of different bare and PEI/PAADopa-Zn (0.6 M NaCl during adsorption) coated Au, Al2O3, Ti and SiO2 crystals.

3.3. pH effect on mechanical property of multilayers In previous studies, pH was found to have a strong influence on Dopa-crosslinking chemistry40,41,46 including coordinate with metal ions and covalent crosslinking through oxidation. The coordinate bonds are commonly considered to be comparable to, but weaker than covalent bonds.41 By increasing pH, the complexation becomes stronger between catechols and Zn ions.42 22


Page 22 of 33

Page 23 of 33

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

Langmuir

The mechanical properties of (PEI/PAADopa-Zn)12 multilayers were analyzed by MFP-3D AFM. The nano-indentation was performed on 144 positions of one sample and repeated for at least three times. The obtained force curves were then fitted with Hertz model for contact mechanics to obtain the Young’s Modulus (Figure S3). Thickness measurements were performed (not shown) to ensure the indentation depth during the mechanical test is below the range of film thickness in order to obtain effective data.

Figure 8. Force-depth data acquired during nanoindentation of (PEI/PAADopa-Zn)12 multilayers formed at pH 4 and 8.5. Young’s moduli for (PEI/PAADopa-Zn)12 multilayers at pH 4 and 8.5 after fitting with Hertz model for contact mechanics. The inset shows force-depth responses acquired during nanoindentation of multilayers in buffer at pH 4 (red) and 8.5 (blue). The lines are representative fitting curves using Hertz model to extract a corresponding Young’s modulus.

23


Langmuir

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

At pH 4, the average elastic modulus of (PEI/PAADopa-Zn)12 multilayers (Figure 8) is as high as 12.21 MPa. The reason for such high stiffness might be that PEI group was able to complex with Zn2+ which may facilitate the electrostatic interaction with free carboxylate groups of PAA.16 In addition, at low pH, the coordinate crosslinking of PAADopa-Zn induced more interactions among the free carboxylate groups of PAA25 and amine groups PEI causing extremely compact structure. This high stiffness is consistent with the results from QCM experiments, where extremely low dissipation was observed in Figure 1b′ and 1d′. By increasing pH the coordinate interactions are strengthened along with auto-oxidation in air. However, unlike the overall covalent intermolecular interactions or the strong coordinate crosslinking with oxidative metal ions, herein the divalent zinc ions show weak coordination effects.25 At elevated pH of 8.5, a deeper degree of metal-chelating along with covalent intermolecular interactions were established. As a result, the pH triggered a higher hydration degree in the multilayers, and therefore they became much softer with a Young’s modulus of 0.93 MPa (Figure 8) compared to the multilayer without Zn2+ (2.13 MPa at pH 7.415). Such pH response is not detected in the system without Dopa content (data not shown).

4. Conclusions In this study, zinc crosslinking approach was introduced to assemble compact multilayers. In-situ analysis of crosslinked multilayers were recorded by QCM-D and 24


Page 24 of 33

Page 25 of 33

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

Langmuir

Dopa chemistry was introduced in multilayer assembling leading to higher mass uptake and more compact structure compared to the multilayers without Dopa. Higher ionic strength induced higher mass uptake in the crosslinked multilayers and it was shown the possibility to modify various surfaces, such as Au, SiO2, Ti, and Al2O3 obtaining similar layer properties. Different surface morphologies in wet and dry conditions were compared with AFM analysis. Furthermore, in the presence of divalent ions Zn2+, Dopa containing multilayers can be turned by pH from hard to soft materials, as revealed by the change of Young’s modulus determined by MFP-3D AFM. Such Dopa containing multilayers with tunable mass uptake, surface morphology and stiffness represent an efficient and universal approach for surface modification, especially for designing physicochemical controlled films for bioapplications.

Supporting Information FT-IR spectra of PAA, PAADopa and PAADopa-Zn (Figure S1). AFM height images of (PEI/PAADopa-Zn)2 multilayers (with 0.6 M NaCl during adsorption) adsorbed on different crystals, Au, SiO2, Al2O3 and Ti (Figure S2). Force-depth data acquired

from

MFP-3D

AFM

measurements

during

nanoindentation

(PEI/PAADopa-Zn)12 multilayers formed at pH 4 and 8.5 (Figure S3).

Acknowledgments 25


of

Langmuir

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

Yisheng Xu and Xuhong Guo acknowledge the financial support from the National Natural Science Foundation of China (No. 51273063, 21476143, and 21306049), the Fundamental Research Funds for the Central Universities, the higher school specialized research fund for the doctoral program (222201313005 and 222201314029), 111 Project Grant (B08021)，the Open Project of State Key Laboratory of Chemical Engineering (SKL-ChE-14C01), Innovation Program of Shanghai Municipal Education Commission (15ZZ030) and Firmenich. Weina Wang acknowledges the China Scholarship Council and Technische Universität Berlin for Financial support. Samantha Micciulla and Sebastian Backes acknowledge Technische Universität Berlin for Financial support.

References (1) Decher, G.; Hong, J. D. and Schmitt, J. Buildup of ultrathin multilayer films by a self-assembly process: III. Consecutively alternating adsorption of anionic and cationic polyelectrolytes on charged surfaces. Thin Solid Films 1992, 210, 831835. (2) Decher, G. Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites. Science, 1997, 277, 1232-1237. (3) Hammond, P.T. Recent explorations in electrostatic multilayer thin film Assembly. Curr. Opin. Colloid Interface Sci. 2000, 4, 430-442.

26


Page 26 of 33

Page 27 of 33

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

Langmuir

(4) von Klitzing, R. Internal structure of polyelectrolyte multilayer assemblies. Phys. Chem. Chem. Phys. 2006, 8, 5012-5033. (5) Dalsin, J. L. and Messersmith, P.B. Bioinspired antifouling polymers. Mater. Today 2005, 8, 38-46. (6) Chen, L.; Therien-Aubin, H.; Wong, M. C. Y.; Hoek, E. M. V. and Ober, C. K. Improved antifouling properties of polymer membranes using a 'layer-by-layer' mediated method. J. Mater. Chem. B 2013, 1, 5651-5658. (7) Wilke, P.; Helfricht, N.; Mark, A.; Papastavrou, G.; Faivre, D. and Börner, H. G. A Direct Biocombinatorial Strategy toward Next Generation, Mussel-Glue Inspired Saltwater Adhesives. J. Am. Chem. Soc. 2014, 136, 12667-12674. (8) Wu, A.; Yoo, D.; Lee, J.-K. and Rubner, M. F. Solid-State Light-Emitting Devices Based on the Tris-Chelated Ruthenium (II) Complex: 3. High Efficiency Devices via a Layer-by-Layer Molecular-Level Blending Approach. J. Am. Chem. Soc. 1999, 121, 4883-4891. (9) Tang, Z.; Wang, Y.; Podsiadlo, P. and Kotov, N. A. Biomedical Applications of Layer-by-Layer Assembly: From Biomimetics to Tissue Engineering. Adv. Mater. 2006, 18, 3203-3224. (10) Ji, J.; Fu, J. and Shen, J. Fabrication of a Superhydrophobic Surface from the Amplified Exponential Growth of a Multilayer. Adv. Mater. 2006, 18, 1441-1444. (11) Wang, Y.; Joshi, P. P.; Hobbs, K. L.; Johnson, M. B. and Schmidtke, D. W. Nanostructured Biosensors Built by Layer-by-Layer Electrostatic Assembly of Enzyme-Coated Single-Walled Carbon Nanotubes and Redox Polymers. Langmuir 27


Langmuir

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

2006, 22, 9776-9783. (12) Boudou, T.; Crouzier, T.; Ren, K.; Blin, G. and Picart, C. Multiple Functionalities of Polyelectrolyte Multilayer Films:New Biomedical Applications. Adv. Mater. 2010, 22, 441-467. (13) Rubianes, M.D. and Strumia, M.C. Polyethylenimine Functionalized with Dopamine: Characterization and Electrocatalytic Properties. Electroanal. 2010, 22, 1200-1206. (14) Hsu, B.B.; Hagerman, S. R.; Jamieson, K.; Veselinovic, J.; O’Neill, N.; Holler, E.; Ljubimova, J. Y. and Hammond, P. T. Multilayer Films Assembled from Naturally-Derived Materials for Controlled Protein Release. Biomacromolecules 2014, 15, 2049-2057. (15) Min, Y. and Hammond, P. T. Catechol-Modified Polyions in Layer-by-Layer Assembly to Enhance Stability and Sustain Release of Biomolecules: A Bioinspired Approach. Chem. Mater. 2011, 23, 5349-5357. (16) Cao, M.; Wang, J. and Wang, Y. Surface Patterns Induced by Cu2+ Ions on BPEI/PAA Layer-by-Layer Assembly. Langmuir 2007, 23, 3142-3149. (17) Liu, X.; Goli, K. K.; Genzer, J. and Rojas, O. J. Multilayers of Weak Polyelectrolytes of Low and High Molecular Mass Assembled on Polypropylene and Self-Assembled Hydrophobic Surfaces. Langmuir 2011, 27, 4541-4550. (18) Lee, H.; Dellatore, S. M.; Miller, W. M. and Messersmith, P. B. Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science 2007, 318, 426-430. (19) Faure, E.; Falentin-Daudré, C.; Jérôme, C.; Lyskawa, J.; Fournier, D.; Woisel, P. 28


Page 28 of 33

Page 29 of 33

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

Langmuir

and Detrembleur, C. Catechols as versatile platforms in polymer chemistry. Prog. Polym. Sci. 2013, 38, 236-270. (20) Bandara, N.; Zeng, H. and Wu, J. Marine mussel adhesion: biochemistry, mechanisms, and biomimetics. J. Adhes. Sci. Technol. 2013, 27, 2139-2162. (21) Waite, J.H.; Andersen, N. H.; Jewhurst, S. and Sun, C. Mussel Adhesion: Finding the Tricks Worth Mimicking. J. Adhesion 2005, 81, 297-317. (22) Karabulut, E.; Pettersson, T.; Ankerfors, M. and Wagber, L. Adhesive Layer-byLayer Films of Carboxymethylated Cellulose Nanofibril–Dopamine Covalent Bioconjugates Inspired by Marine Mussel Threads. ACS Nano 2012, 6, 4731-4739. (23) Ahn, B.K.; Lee, D. W.; Israelachvili, J. N. and Waite, J. H. Surface-initiated self-healing of polymers in aqueous media. Nat Mater Letter 2014, 13, 867-872. (24) Wei, Q.; Achazi, K.; Liebe, H.; Schulz, A.; Noeske, Paul-Ludwig, M.; Grunwald I. and Haag R. Mussel-Inspired Dendritic Polymers as Universal Multifunctional Coatings. Angew. Chem. Int. Edit. 2014, 53, 11650-11655. (25) Wang, W.; Xu, Y.; Li, A.; Li, T.; Liu, M.; von Klitzing, R.; Ober, C. K.; Kayitmazer A. B.; Li L. and Guo X. Zinc induced polyelectrolyte coacervate bioadhesive and its transition to a self-healing hydrogel. RSC Advances 2015, 5, 66871-66878. (26) Alves, N.M.; Picart, C. and Mano, J.F. Self Assembling and Crosslinking of Polyelectrolyte Multilayer Films of Chitosan and Alginate Studied by QCM and IR Spectroscopy. Macromol. Biosci. 2009, 9, 776-785. (27) Guo, X.; Abdala, A. A.; May, B. L.; Lincoln, S. F.; Khan, S. A. and Prud’homme, 29


Langmuir

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

R. K. Rheology control by modulating hydrophobic and inclusion associations in modified poly(acrylic acid) solutions. Polymer 2006, 47, 2976- 2983. (28) Höök, F.; Rodahl, M.; Kasemo, B. and Brzezinski, P. Structural changes in hemoglobin during adsorption to solid surfaces: Effects of pH, ionic strength, and ligand binding. Proc. Natl. Acad. Sci. USA. 1998, 95, 12271-12276. (29) Rodahl, M.; Höök, F. and Kasemo, B. QCM Operation in Liquids: An Explanation of Measured Variations in Frequency and Q Factor with Liquid Conductivity. Anal. Chem. 1996, 68, 2219-2227. (30) Dodoo, S.; Steitz, R.; Laschewsky, A. and von Klitzing, R. Effect of ionic strength and type of ions on the structure of water swollen polyelectrolyte multilayers. Phys. Chem. Chem. Phys. 2011, 13, 10318-10325. (31) Sukhishvili, S. A.; Kharlampieva, E. and Izumrudov, V. Where Polyelectrolyte Multilayers and Polyelectrolyte Complexes Meet. Macromolecules 2006, 39, 8873-8881. (32) Dodoo, S.; Balzer, B.; Hugel, T.; Laschewsky, A. and von Klitzing, R. Effect of Ionic Strength and Layer Number on Swelling of Polyelectrolyte Multilayers in Water Vapour. Soft Mater. 2013, 11, 157-164. (33) Wei, Q.; Becherer, T.; Noeske, Paul-Ludwig, M.; Grunwald, I. and Haag, R. A Universal Approach to Crosslinked Hierarchical Polymer Multilayers as Stable and Highly Effective Antifouling Coatings. Adv. Mater. 2014, 26, 2688-2693. (34) Wei, Q.; Becherer, T.; Mutihac, R. C.; Noeske, Paul-Ludwig, M.; Paulus, F.; Haag, R. and Grunwald, I. Multivalent Anchoring and Cross-Linking of Mussel30


Page 30 of 33

Page 31 of 33

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

Langmuir

Inspired Antifouling Surface Coatings. Biomacromolecules 2014, 15, 3061-3071. (35) Rodahl M. and Kasemo B. On the measurement of thin liquid overlayers with the quartz-crystal microbalance. Sens. Actuators A-Phys. 1996, 54, 448-456. (36) Longo, J.; Garnier, T.; Mateescu, M.; Ponzio, F.; Schaaf, P.; Jierry, L. and Ball, V. Stable Bioactive Enzyme-Containing Multilayer Films Based on Covalent Cross-Linking from Mussel-Inspired Adhesives. Langmuir 2015, 31, 1244712454. (37) Maerten, C.; Garnier, T.; Lupattelli, P.; Chau, N. T. T.; Schaaf P.; Jierry, L and Boulmedais F. Morphogen Electrochemically Triggered Self-Construction of Polymeric Films Based on Mussel-Inspired Chemistry. Langmuir 2015, 31, 13385-13393. (38) Lee, H.; Lee, Y.; Statz, A. R.; Rho, J.; Park, T. G. and Messersmith P. B. Substrate-Independent Layer-by-Layer Assembly by Using Mussel-AdhesiveInspired Polymers. Adv. Mater. 2008, 20, 1619-1623. (39) Podsiadlo, P.; Liu, Z.; Paterson, D.; Messersmith, P. B. and Kotov N. A. Fusion of Seashell Nacre and Marine Bioadhesive Analogs: High-Strength Nanocomposite by Layer-by-Layer Assembly of Clay and L-3,4-Dihydroxyphenylalanine Polymer. Adv. Mater. 2007, 19, 949-955. (40) Holten-Andersen, N.; Jaishankar, A.; Harrington, M. J.; Fullenkamp, D. E.; DiMarco, G.; He, L.; McKinley, G. H.; Messersmith, P. B. and Lee, K. Y. C. Metal-coordination: using one of nature's tricks to control soft material mechanics. J. Mater. Chem. B. 2014, 2, 2467-2472. 31


Langmuir

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

(41) Xu, Z. Mechanics of metal-catecholate complexes: The roles of coordination state and metal types. Sci. Rep.-UK. 2013, 3, 2914. (42) Sever, M. J. and Wilker, J. J. Visible absorption spectra of metal-catecholate and metal-tironate complexes. Dalton T. 2004, 1061-1072. (43) Picart, C.; Lavalle, P.; Hubert, P.; Cuisinier, F. J. G.; Decher, G.; Schaaf, P. And Voegel, J.-C. Buildup Mechanism for Poly(l-lysine)/Hyaluronic Acid Films onto a Solid Surface. Langmuir 2001, 17, 7414-7424. (44) Picart, C.; Mutterer, J.; Richert, L.; Luo, Y.; Prestwich, G. D.; Schaaf, P.; Voegel, J.-C. and Lavalle, P. Molecular basis for the explanation of the exponential growth of polyelectrolyte multilayers. Proc. Natl. Acad. Sci. USA. 2002, 99, 12531-12535. (45) Lavalle, P.; Picart, C.; Mutterer, J.; Gergely, C.; Reiss, H.; Voegel, J.-C.; Senger, B. and Schaaf, P. Modeling the Buildup of Polyelectrolyte Multilayer Films Having Exponential Growth. J. Phys. Chem. B 2004, 108, 635-648. (46) Wu, J.; Zhang, L.; Wang, Y.; Long, Y.; Gao, H.; Zhang, X.; Zhao, N.; Cai, Y. and Xu J. Mussel-Inspired Chemistry for Robust and Surface-Modifiable Multilayer Films. Langmuir 2011, 27, 13684-13691. (47) Hong, L. and Simon, J. D. Insight into the Binding of Divalent Cations to Sepia Eumelanin from IR Absorption Spectroscopy. Photochem. Photobiol. 2006, 82, 1269.

32


Page 32 of 33

Page 33 of 33

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

Langmuir

TOC graphic:

Construction of Compact Polyelectrolyte Multilayers Inspired by Marine Mussel: Effects of Salt Concentration and pH as Observed by QCM-D and AFM

33


Construction of Compact Polyelectrolyte Multilayers Inspired by

Recommend Documents