Controlling DOPA adsorption via interacting with polyelectrolytes: layer structure and corrosion resistance

Ting Chen abc, Hui Yang *a, Ming Yang d, Fanghui Liu a, Jiazhong Wu e, Siyu Yang e and Jinben Wang a
aCAS Key Lab of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China. E-mail: yanghui@iccas.ac.cn
bUniversity of Chinese Academy of Sciences, Beijing 100049, P. R. China
cSchool of Materials Science and Energy Engineering, Foshan University, Foshan, Guangdong 528000, China
dInstitute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, P. R. China
eState Key Laboratory of Enhanced Oil Recovery, Research Institute of Petroleum Exploration and Development of PetroChina, Beijing 100083, P. R. China

Received 10th March 2020 , Accepted 24th April 2020

First published on 24th April 2020


Protein adsorption on polyelectrolyte (PE) surfaces has aroused intensive attraction, but there are still few investigations on tuning the protein adsorption at a solid surface by controllable layer structures and surface properties of PE adlayers. Furthermore, there is a lack of understanding regarding the correlation between molecular conformation and anticorrosion performance of composite materials. With this in mind, we synthesized a series of PEs and constructed 3,4-dihydroxy-L-phenylalanine (L-DOPA) adlayers on the PE surfaces, monitoring the whole adsorption process in situ. A highly charged cationic PE surface exhibits a low adhesion of DOPA molecules, leading to a loose structure, rough surface morphology, and strong solvation effects and, accordingly, this kind of multilayer provides a poor anticorrosion capacity. In comparison, amphiphilic and highly charged cationic PE surfaces are in favor of DOPA adsorption and the formation of compact and smooth multilayers due to cation–π and hydrophobic interactions between DOPA and PEs. Interestingly, one of the multilayers exhibits a remarkable enhancement of inhibition efficiency of about 460-fold compared with that of the bare substrate, which is much higher than that of other anticorrosion coatings reported previously. Our findings reveal the interaction mechanism between DOPA and PE surfaces to achieve the controllable adsorption of biomolecules, providing a promising way to optimize the layer structures to improve the anticorrosion capacity.


Introduction

Protein adsorption at the solid/liquid interface is an attractive topic in many important fields of biosensors, surface anticorrosion, drug delivery, and so forth.1–6 Controlling protein adsorption is indispensable for the development of surface anticorrosion, such as “green” coatings for corrosion protection as a promising candidate to replace traditional materials.7,8 Mussel adhesive proteins (MAPs) have attracted considerable attention due to their favorable adhesive ability and corrosion resistance, widely needed for industrial equipment,9,10 biomedical materials,11,12 and as protective coatings for sophisticated electronic apparatus.13,14 Previously, efforts were made to study the corrosion resistance of MAP composite coatings, for instance, CeO2 nanoparticles were added to protein adlayers, or poly(ethylene glycol) and fibronectin/heparin multilayers, to endow the surface with a compact structure, and the anti-corrosion efficiency was improved by a factor of 100–260, compared with that of Mefp-1 or bovine serum albumin (BSA) protein films on the substrate.15,16 A compact network microstructure has been shown to be a major factor in improving the corrosion resistance capability through prevention of the penetration of water to the substrate, and the protection efficiency of such composite films increased as the coating got thicker.17,18 For example, dihydroxyphenylalanine (DOPA), responsible for the adhesive capacity of MAPs, and its derivative adlayers have shown a 5-fold increase in inhibition efficiency (IE) compared with that of bare metal substrates, attributed to the strong adsorption at the solid surface via different interactions and resulting in the formation of a surface “shield”.19,20 When a self-assembled monolayer (SAM) was introduced as an adhesive interlayer between the DOPA coating and metal surface, the IE of the DOPA-SAM multilayer surface is enhanced 8–9-fold in comparison with that of the bare metal substrate. It is noteworthy that SAMs play an important role in the interaction with DOPA molecules and the adsorption conformation of multilayers, affecting the affinity and anticorrosion property of the composite coatings.21 When a polymer interlayer replaces the SAM, the IE of the protein-polymer nanocomposite films can be improved greatly to 70–200-fold compared with that of the bare metal substrate, attributed to the formation of perfectly compact and dense composite films induced by the rearrangement and crosslinking of protein molecules on the polymer surface.22–24 In our previous study, we found that rich aggregate films can be tuned via the adsorption of highly charged amphiphilic polyelectrolytes (PEs) at different concentrations, based on various interactions between PEs and oppositely charged substrates, such as electrostatic, hydrophobic, and charge-patch interactions.25,26 Furthermore, PE–DOPA multilayers with different kinds of adsorption conformations can be further formed on substrates through different interactions, such as electrostatic, hydrophobic or cation–π interactions between PE adlayers and DOPA molecules, which will result in a more compact and denser surface and a large enhancement of corrosion resistance. To date, there are only few investigations using PEs to tune inhibition efficiency between the DOPA adlayer and the metal substrate, although it is fundamentally important for understanding the correlation between molecular structure and anticorrosion behavior of organic multilayers and is practically valuable for designing novel eco-friendly protection materials.

In view of this, we prepared a series of highly charged cationic PEs, including poly-1,3-bis(N,N-dimethyl-N-octylammonium)-2-propylacrylate dibromide (denoted as PAGC8) with double cations and hydrophobic chains in each structural unit, polyacryloyloxyethyl-N,N-dimethyl-N-octylammonium bromide (denoted as PASC8) with a single cation and a hydrophobic chain in each structural unit, and polyacryloyloxyethyl-N,N,N-trimethylammonium chloride (denoted as PASC1) with a single cation in each structural unit. Based on different self-assemblies of PEs, tunable DOPA–PE multilayers were constructed via in situ monitoring techniques, showing a remarkable anticorrosion enhancement of 460-fold compared with that of the bare metal substrate. Our findings provide a new insight into the contribution of molecular conformation and layer structure to the anticorrosive function of composite materials.

Experimental section

Materials

Pyrene and deuterium oxide were purchased from J & K Chemical Technology. Acryloyl chloride, 1-bromooctane, ammonium persulfate, and ammonium iron(II) sulfate hexahydrate were purchased from Beijing Chemical Co. A DOPA solution at 5 mmol was prepared by dissolving the solid powder in NaCl/HCl solutions at a 1[thin space (1/6-em)]:[thin space (1/6-em)]1 volume ratio (pH = 5.5), stirring for 6 h and placing in a dark and cool place to avoid oxidation. All reagents except those especially mentioned were used without further purification and all solutions were prepared with Millipore Milli-Q grade water (pH = 7.0 and electrical resistivity is 18.2 MΩ cm) in this work.

Synthesis

Acryloyloxyethyltrimethyl ammonium chloride (abbreviated as ASC1, Scheme 1) was purchased from Beijing Chemical Co. Acryloyloxyethyl-N,N-dimethyl-N-octylammonium bromide (abbreviated as ASC8) was prepared by blending N,N-dimethylaminoethyl acrylate and 1-bromooctane overnight in acetone with a molar ratio of 1[thin space (1/6-em)]:[thin space (1/6-em)]1.2. A geminized cationic monomer of 1,3-bis(N,N-dimethyl-N-octyl ammonium)-2-propyl acrylate dibromide (abbreviated as AGC8) was prepared by reaction of acryloyl chloride with 1,3-bis(N,N-dimethyl-N-octyl ammonium)-2-hydroxylpropane dibromide (the monomer precursor, abbreviated as BHD-C8), in which BHD-C8 was synthesized by blending epoxypropane and dimethylamine in an ethanolic solution at a molar ratio of 1[thin space (1/6-em)]:[thin space (1/6-em)]5, and quaternized with 1-bromooctane. After recrystallization with acetone/diethyl ether repeatedly, the white solid powder of the monomer was obtained. The structure characterization was confirmed by 1H NMR spectra as shown in Fig. S1 (ESI). All three kinds of PEs, including PASC1, PASC8, and PAGC8, were prepared by free radical polymerization in an aqueous solution for 2 h, using ammonium persulfate and ammonium iron(II) sulfate hexahydrate as initiators. The molecular weight and polydispersity were determined by the GPC analysis system as shown in Table S1 (ESI).
image file: d0sm00420k-s1.tif
Scheme 1 Synthetic routes and structures of (a) PASC1, (b) PASC8 and (c) PAGC8 PEs.

In situ monitoring by the combined QCM-D and LSPR methods

To study the adsorption behavior of PEs and DOPA, a combined quartz crystal microbalance with dissipation (QCM-D) and a localized surface plasmon resonance (LSPR) setup that monitors the molecular adsorption processes in real-time was used, as shown in Fig. 1. Q-Sense QWM401 window module (Biolin Scientific AB, Sweden) and an Insplorion Acoulyte module (Insplorion AB, Gothenburg, Sweden) provide an optical connection between the QCM-D chamber and an Insplorion X-Nano optics unit. Dry mass (optical mass, excluding coupled solvent mass) can be evaluated from the LSPR response27,28 and wet mass (acoustic mass, including coupled solvent mass) can be evaluated from the QCM-D measurements,29,30 providing more information about structural changes upon molecular adsorption. A standard Q-Sense quartz crystal sensor was used in our study, upon which a thick silicon dioxide layer was fabricated on the top gold electrode with an average grain size of ∼25 nm (Fig. 1d), and the distributed nanostructures on the substrate can eliminate both far and near field coupling between adsorbates.31
image file: d0sm00420k-f1.tif
Fig. 1 (a) and (b) Overview of the combined QCM-D and LSPR instrument setup; (c) architecture of the modified QCM-D sensor chip with a SiO2 spacer layer coated on the top electrode; (d) 3D AFM image of the gold nanodisk array on the QCM-D sensors.

Critical aggregation concentration (CAC) values of different PEs were obtained from the steady-state fluorescence spectra using a spectrofluorometer (Hitachi F-4500, Japan). The concentrations for PASC8 are set as 35 mg L−1 (0.5 × CAC) and 140 mg L−1 (2.0 × CAC), and the concentrations for PAGC8 are set as 70 mg L−1 (0.5 × CAC) and 260 mg L−1 (2.0 × CAC) based on the CAC values (Fig. S2, ESI), and the similar low and high concentrations (70 mg L−1 and 140 mg L−1) of PASC1 were selected as well in this study. A series of PEs adsorbed onto the SiO2 coated sensor substrate were first monitored and after adsorption equilibrium, DOPA solutions were added at the same flow rate as that of PEs of 20 μL min−1. Changes in frequency (Δf) and dissipation (ΔD) were collected and the adsorbed mass was evaluated using the Voigt model for PEs or DOPA adsorption via the Q-tools software package (Biolin Scientific AB, Sweden), with layer densities of 1000 kg m−3 and 1200 kg m−3, respectively,32–34 fluid density of 1000 kg m−3, layer viscosity of 0.0005–0.1 kg ms−1, layer shear modulus of 103–105 Pa, and thickness of 10−10–10−6.35 In the LSPR, the measured signal (λmax) is the wavelength at which the extinction spectrum of the sensor exhibits a maximum, which is acquired by collecting light that was transmitted through the gold nanodisks. When a sample layer, i, is adsorbed on the sensor surface, the sensor response (Δλmax) will be quantitatively proportional to the change in optical mass (Δmdry), by the following equation:31,36

image file: d0sm00420k-t1.tif
wherein, the layer thickness, di, can be obtained using QCM-D; S0 is the bulk refractive index sensitivity of the sensor surface (60 nm per RIU); Lz is the characteristic decay length and is considered constant (30 nm); dni/dc is the refractive index-increment of the sample layer, and the value of polymer solution was chosen to be 0.13.37

Ex situ characterization

The molecular weight and polydispersity of PEs were determined using a Waters Breeze 1515 GPC analysis system (dimethylformamide, DMF). The surface topography was characterized in air through the AFM method in Peakforce tapping mode (FASTSCAN, Bruker Instruments, USA) using a silicon cantilever (Fastscan-B, Bruker Instruments, Germany). The value of Peakforce set-point was set at 1.065 nN, and 0.1 mol L−1 HCl solution was used as the corrosion solution in our studies. The water contact angles of different surfaces were obtained using a DSA 100 (Kruss DSA CA goniometer, Germany) drop shape analysis system and 3 μL of distilled water was used. Electrochemical corrosion measurements were performed in 0.1 mol L−1 HCl solution using a CHI602 workstation (Shanghai Chenhua Instruments Inc., China), with an Ag/AgCl electrode as the reference electrode, a platinum electrode as the counter electrode, and the sample as the working electrode. The data of Tafel curves were collected when the curve of “open-circuit potential-time (OCPT)” reached a steady state after samples were immersed in HCl solution for over 2 hours. Different surface morphologies before and after electrochemical corrosion measurements were characterized by using scanning electron microscopy (SEM, S-4800 JEOL, Japan).

Results and discussion

Controllable construction of DOPA–PE multilayers

Through the combination of QCM-D and LSPR measurements, the shifts in frequency, dissipation, and LSPR peak were collectively obtained as shown in Fig. 2 and Table S2 (ESI). Upon addition of PE solution, a rapid frequency decrease, dissipation increase, and LSPR peak increase can be observed in all three PE systems, suggesting a rapid transport and adsorption of PEs from the solution to the surface. And then an adsorption plateau appears due to the rearrangement of the preadsorbed molecules to maximize their contact and minimize their free energy. For PASC1, on the one hand, the little change in frequency and dissipation is obtained from QCM-D measurements, increasing from 1.6 Hz to 3.3 Hz and from 0.2 × 10−6 to 0.4 × 10−6 with the increase of PE concentration, corresponding to the wet mass of about 28.5 and 73.6 ng cm−2 (Fig. S3, ESI), respectively; on the other hand, Δλmax obtained from LSPR increases from 0.09 nm to 0.17 nm as the concentration is increased, corresponding to the dry mass of about 15.0 and 29.0 ng cm−2, respectively. For PASC8, the value of frequency and dissipation increases from 5.2 Hz to 15.0 Hz and from 0.4 × 10−6 to 1.3 × 10−6 with the increase of PE concentration, corresponding to the wet mass of about 206.0 and 409.6 ng cm−2, respectively; while Δλmax increases from 0.72 nm to 1.29 nm, corresponding to the dry mass of about 128.0 and 241.0 ng cm−2 as the concentration is increased. For PAGC8, the value of frequency and dissipation increases from 8.8 Hz to 18.0 Hz and from 0.4 × 10−6 to 1.7 × 10−6 with the increase of PE concentration, corresponding to the wet mass of about 336.0 and 519.0 ng cm−2, respectively; Δλmax increases from 0.89 nm to 1.37 nm, corresponding to the dry mass of about 164.0 and 270.0 ng cm−2 as the concentration is increased. Obviously, the increase of adsorbed mass for PASC8 and PAGC8 adlayers is slowing down gradually compared with that of PASC1 with a four-fold increase in concentration, and it is mainly attributed to the occupation of pre-adsorbed PEs on the substrate and the repulsion of hydrophobic chains of amphiphilic PEs to water molecules, hindering the adsorption of upcoming molecules and the increase of dry or wet mass.
image file: d0sm00420k-f2.tif
Fig. 2 (a) Schematic illustration of the proposed models for PE adsorption onto silica surfaces; QCM-D frequency, dissipation shifts and LSPR peak shifts as a function of time for (b) PASC1, (c) PASC8 and (d) PAGC8 adsorption at pH 7.0 and without salt.

Fig. 3a shows almost linear trends with a small change in energy dissipation per frequency change in the presence of PASC1, suggesting that the PE chains adsorb randomly on the surface and there are nearly no rearrangements of them attributed to the electrostatic interactions of the PE−surface, while the curves of ΔD vs. Δf plots of PASC8 and PAGC8 can be divided into two regimes (Fig. 3b, c and Table S3, ESI). For PASC8, the first regime shows a large shift in frequency and a small shift in dissipation, suggesting a rapid adsorption of PEs and a formation of rigid adlayers, while in the second regime, the frequency decreases slowly and dissipation increases rapidly, suggesting a rearrangement process of preadsorbed molecules through a complex balance of different forces, such as PE–surface and PE aggregate–surface interactions, exhibiting the formation of a compact and dense adlayer, and PAGC8 shows a similar trend. Moreover, PAGC8 presents a larger shift in frequency and dissipation than that of PASC8, implying an existence of rearrangements to a larger extent. From the difference between wet mass and dry mass, the relative water content (RWC) of PE adlayers can be calculated though the equation: [(mwetmdry)/mwet] × 100%.38 RWC of PASC1 adlayer is about 47.4 and 60.6 wt% as the concentration is increased, which is similar with the water contents of cationic polymer PMETAC (∼57.5%) and other polymers,39,40 while the water content decreases to about 37.0 and 41.2 wt% in the case of PASC8, and to about 51.2 and 47.7 wt% in the case of PAGC8 at 0.5 × CAC and 2.0 × CAC respectively, as shown in Fig. 4. The contact angle increases from 11.9° for a fresh silica surface to 25.2°∼36.0° for the PASC1 surface, and increase to 37.7°–49.2° for the PASC8 surface and 47.5°–56.7° for the PAGC8 surface, respectively (Fig. 4 and Fig. S4, ESI). In the case of the PASC1 adlayer without hydrophobic chain structures, the water content is higher and the PE surface is more hydrophilic than that of amphiphilic PE adlayers, such as PASC8 and PAGC8, in which hydrophobic chains participate in the molecular aggregation at the surface through hydrophobic interaction and weaken the electrostatic repulsion between cationic head groups, resulting in the repelling of water molecules and leading to a lower water content with a higher hydrophobic property.


image file: d0sm00420k-f3.tif
Fig. 3 ΔD–Δf plots of (a) PASC1, (b) PASC8, and (c) PAGC8 at different concentrations.

image file: d0sm00420k-f4.tif
Fig. 4 Water content and contact angles of different PE adlayers on substrates.

With the introduction of DOPA to the PASC1 surface, both the frequency and dissipation values change slowly, leading to a small wet mass of DOPA being about 440.3 and 638.3 ng cm−2 at low and high concentrations (Fig. 5a, b, Fig. S5 and Table S4, ESI), while the dry mass estimated from ellipsometry is about 373.5 and 490.5 ng cm−2, respectively. The wet mass increases to 1225.5 and 1792.6 ng cm−2 in the case of the PASC8 surface, and goes to 1334.1 and 2095.9 ng cm−2 in the case of the PAGC8 surface at 0.5 × CAC and 2.0 × CAC, with the dry mass increasing from 783.0 and 1368.2 ng cm−2 to 922.5 and 1651.5 ng cm−2, respectively. It can be seen that both the amphiphilic PE adlayers favor the DOPA adsorption, especially for the PAGC8 adlayer, because there are abundant interactions between DOPA and PE molecules such as hydrophobic and cation–π interactions. In comparison, the PASC1 adlayer inhibits the DOPA adsorption to some extent, due to the formation of a hydration layer via cationic hydration of quaternary ammonium-type cations and resulting in a physical barrier to prevent direct contact between DOPA and the modified surface (Fig. 5c). The water contents of DOPA adlayers adsorbed on the PASC1 surface are about 36.1 and 23.7 wt% as the concentration is increased, while the water content increases to about 36.1 and 23.7 wt% in the case of PASC8, and to about 30.9 and 21.2 wt% in the case of PAGC8 at 0.5 × CAC and 2.0 × CAC, respectively.


image file: d0sm00420k-f5.tif
Fig. 5 (a) Shifts in frequency and dissipation for the adsorption of DOPA on different surfaces at pH 5.5 and without salt; (b) QCM-D mass of DOPA adsorbed films on different surfaces; (c) schematic illustrations of DOPA adsorption on different PE surfaces.

A uniform and smooth surface topography can be observed for all PE adlayers (Fig. 6a–c), with an average root mean-square roughness (RMS) in a range of 1.50–2.30 nm, indicating that PEs randomly distribute in a form of closely packed nanoaggregates. After DOPA adsorption, a series of DOPA–PE multilayers form at the surface with RMS values of 1.11–1.51 nm (Fig. 6a′–c′), in which a smoother surface morphology is shown compared with that of the PE adlayers and the DOPA-PAGC8 surface is the most homogeneous.


image file: d0sm00420k-f6.tif
Fig. 6 AFM images of PE surfaces in air for: (a) PASC1 at 140 mg L−1, (b) PASC8 at 2.0 × CAC and (c) PAGC8 at 2.0 × CAC; AFM images of DOPA–PE multilayers in air for: (a′) PASC1 at 140 mg L−1, (b′) PASC8 at 2.0 × CAC and (c′) PAGC8 at 2.0 × CAC.

Anticorrosion behavior

Dynamic chemical corrosion studies are performed in the case of DOPA adlayers constructed on a bare substrate; PASC1, PASC8, and PAGC8 adlayers show increases of 23.3, 16.0, 7.1, and 4.3 Hz in frequency, respectively, after the introduction of strong acid solution (Fig. 7a). A rapid desorption and a serious decomposition process appear in the case of the DOPA adlayer (referring to the DOPA adlayer on the bare substrate) and DOPA-PASC1 multilayer, due to the cleavage of chemical bonds of the DOPA crosslinker during the harsh attack of acid molecules.41,42 DOPA-PASC8 and DOPA-PAGC8 multilayer surfaces show a slight removal process, especially for the latter one exhibiting the lowest desorption amount in the four cases. Corrosion current (Icorr) of the bare substrate, PE adlayer surfaces, DOPA adlayer surface, and DOPA–PE multilayer surfaces in acid solution are presented in Fig. 7b, obtained from the typical potentiodynamic polarization curves (Fig. S7 and Table S5, ESI). Compared with the bare substrate, Icorr decreases from 60.39 μA cm−2 to a range of 2.80–2.99 μA cm−2 after PE modification, and further decreases to a range of 0.13–0.34 μA cm−2 after DOPA assembly. In particular, an ultralow Icorr of 0.13 μA cm−2 with the introduction of PAGC8 interlayer is obtained (inset graph in Fig. 7b), resulting in a remarkable enhancement of IE of about 460-fold compared with that of the bare substrate.
image file: d0sm00420k-f7.tif
Fig. 7 (a) Frequency shifts of DOPA desorbed from different surfaces at exposure of 0.1 mol L−1 HCl solution; (b) corrosion current obtained from potentiodynamic polarization curves for different surfaces, and the inset shows changes of corrosion current for the different DOPA-multilayer surfaces.

Different from the smooth and clean morphology of all the modified surfaces (Fig. 8a–d), a large amount of corrosion cracks is observed on the DOPA adlayer and the DOPA-PASC1 multilayer surfaces after immersion in acid solution (Fig. 8a′ and b′), which is similar to the surface morphology of polydopamine film or polymer–protein multilayers on the substrate before and after corrosion,15,43 while for the DOPA-PASC8 and DOPA-PAGC8 multilayer surfaces, they maintain relatively smooth features without obvious corrosion cracks (Fig. 8c′ and d′), indicating an increasing anticorrosion order: DOPA surface < DOPA-PASC1 surface < DOPA-PASC8 surface < DOPA-PAGC8 surface. For the DOPA adlayer formed on the bare substrate, a complex conformation with the aromatic ring lying parallel or orienting perpendicular to the surface leads to a loose layer structure with a poor anticorrosion capacity (Fig. 8e).35,44 For the PASC1 surface, the strong solvation effect hinders the adhesion of DOPA and the fluctuant surface morphology generates a loose multilayer, showing a limited anticorrosion property as well, while for PASC8 and PAGC8 surfaces, DOPA adsorption is greatly enhanced and a compact and dense layer structure forms, due to the strong cation–π and hydrophobic interactions between DOPA molecules and cationic PEs, in favor of the subsequent controlled intermolecular interactions between DOPA molecules on the smooth surface with a preferentially flat conformation, presenting a remarkable corrosion resistance efficiency.


image file: d0sm00420k-f8.tif
Fig. 8 SEM images of DOPA–PE multilayers formed on (a) bare substrate, (b) PASC1 at 140 mg L−1, (c) PASC8 at 2.0 × CAC and (d) PAGC8 at 2.0 × CAC surfaces before corrosion; (a′) (b′), (c′) and (d′) correspond to the surfaces after acid corrosion. (e) Schematic illustrations of anticorrosion mechanisms of different DOPA–PE multilayers.

In short, the adsorbed mass and the layer structure of DOPA on the substrate can be tuned by different kinds of PE interlayers, which serve as an intermediate layer that bridges DOPA and the substrate with rich aggregation behaviors and adsorption conformations. These kinds of DOPA–PE multilayers are imparted as a reinforced “shield” against acid corrosion, providing a promising strategy for the design of safe and effective materials for anticorrosion.

Conclusion

In this study, a series of DOPA–PEs multilayers have been constructed and the molecular conformation as well as the surface properties have been investigated through QCM-D, LSPR, AFM, CA, and electrochemical corrosion measurements. The PASC1 surface exhibits a reduction of DOPA adhesion, due to the water solvation effect and fluctuant surface morphology, endowing the multilayer with a limited corrosion resistance, while both PASC8 and PAGC8 surfaces, possessing high charge density and amphiphilicity, favor the DOPA adsorption through cation–π and hydrophobic interactions of DOPA–PE and the formation of smooth, compact, and dense multilayers, showing a high corrosion resistance efficiency. As a result, the adsorbed mass and molecular conformation of DOPA can be tuned by introducing PE interlayers, and the correlation between the layer structure and the anticorrosion performance of the DOPA–PE multilayers on the substrate is revealed. The results provide guidance for the design of green anticorrosion materials via selecting PEs that bridge an organic compound and a metal interface.

Conflicts of interest

The authors declare no competing financial interest.

Acknowledgements

This work was funded by the National Natural Science Foundation of China (21872152 and 21603240), the Important National Science and Technology Specific Project of China (2017ZX05013-003 and 2016ZX05025-003-009), the Strategic Priority Research Program of CAS (XDB22030102), and the Guangdong Basic and Applied Basic Research Foundation (2019A1515110370). We thank Dr David Johansson from the Sweden Insplorion AB for the help with the LSPR measurements. We thank Dr Min Wang from the Biolin Scientific AB for the help with the QCM measurements.

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Footnote

Electronic supplementary information (ESI) available. See DOI: 10.1039/d0sm00420k

This journal is © The Royal Society of Chemistry 2020