Biomimetic Polyelectrolytes Based on Polymer Nanosheet Films and Their Proton Conduction Mechanism

Abstract

We report a biomimetic polyelectrolyte based on amphiphilic polymer nanosheet multilayer films. Copolymers of poly(N-dodecylacrylamide-co-vinylphosphonic acid) [p(DDA/VPA)] form a uniform monolayer at the air−water interface. By depositing such monolayers onto solid substrates using the Langmuir−Blodgett (LB) method, multilayer lamellae films with a structure similar to a bilayer membrane were fabricated. The proton conductivity at the hydrophilic interlayer of the lamellar multilayer films was studied by impedance spectroscopy under temperature-and humiditycontrolled conditions. At 60 °C and 98% relative humidity (RH), the conductivity increased with increasing mole fraction of VPA (n) up to 3.2 × 10 −2 S cm −1 for n = 0.41. For a film with n = 0.45, the conductivity decreased to 2.2 × 10 −2 S cm −1 despite the increase of proton sources. The reason for this decrease was evaluated by studying the effect of the distance between the VPAs (l VPA ) on the proton conductivity as well as their activation energy. We propose that for n = 0.41, l VPA is the optimal distance not only to form an efficient two-dimensional (2D) hydrogen bonding network but also to reorient water and VPA. For n = 0.45, on the other hand, the l VPA was too close for a reorientation. Therefore, we concluded that there should be an optimal distance to obtain high proton conductivity at the hydrophilic interlayer of such multilayer films.

Progress on highly proton-conductive polymer thin films with organized structure and molecularly oriented structure

“…(d) Model of distance of each acidic group for high proton conduction. Reprinted with permission from Tsukamoto et al [16]. Copyright 2019 American Chemical Society.…”

“…This in-plane conductivity is considerably high as a weak acid source of carboxylic acid. It is noteworthy that they assessed the proton conduction mechanisms both theoretically and experimentally using a model of 2D hydrogen-bonding networks in a confined space prepared using Langmuir-Blodgett method (Figure 1(d)) [14][15][16]. Recently, Winey and co-workers proposed a new but simple polymer design for producing the organizing structure with proton conduction channels [17,18].…”

Monolayer nanosheets formed by liquid exfoliation of charge-assisted hydrogen-bonded frameworks

“…A range of self-assembled peptides, and block-co-polymer-based nanosheets have also been reported. [30][31][32][33] All of these nanosheets are based on relatively weak hydrogen-bonding interactions in combination with hydrophobic aromatic or aliphatic groups which in most cases drive nanosheet formation through the hydrophobic effect. 34,35 These nanosheets have also all been formed "bottom-up" through dynamic self-assembly processes in solution.…”

Interfacial and Internal Proton Conduction of Weak-acid Functionalized Styrene-based Copolymer with Various Carboxylic Acid Concentrations

“…The hydrophilic functional groups reportedly induce proton-conducting pathways from interaction between hydrophilic residues of polymer and water molecules. [4][5][6][7][8][9] Many studies have published proton transport improvement in an anhydrous state using acid-base combinations of proton conductors. [10][11][12][13][14][15][16] In this system, proton donors are acid groups with low pK a values because protons are readily dissociated.…”