Layer-by-Layer Assembly of a pH-Responsive and Electrochromic Thin Film

Abstract

This paper summarizes an experiment on thin film fabrication with layer-by-layer (LbL) assembly that is appropriate for undergraduate laboratory courses. The purpose of this experiment is to teach students about self-assembly in the context of thin films, and to expose students to the concepts of functional polymeric coatings. Students dip coat both microscope slides and conductive glass with films containing polyaniline (PANi), a conducting polymer, and sulfonated polystyrene (SPS). Assembly of the film is characterized by visual inspection, UV/Vis spectroscopy, and conductance measurements with a handheld multimeter. Greencolored films with measurable conductance are apparent after two PANi layers. Subsequently, the students observe the pH-dependent optical properties of the films, and also determine the electrochromic performance of the films using spectroelectrochemistry. The feasibility of this experiment has been tested by inclusion into an undergraduate-level polymer science laboratory with third and fourth year students at the Massachusetts Institute of Technology.

Thin Functional Polymer Films by Electropolymerization

“…Corresponding electrosynthesized ICPs have shown potential applications in electrocatalysis, batteries, capacitors, sensors, biosensors, organic light-emitting diodes, organic solar cells, and electrochromic devices [7]. The principle of the last application, i.e., electrochromism, could be in fact an interesting and innovative approach to be used in undergraduate and graduate classes [8,9]. Explanation of the electrochemical doping/dedoping processes of ICPs can be easily managed by applying different potentials to polymer films, resulting in color changes of the deposits via a suited modification of their chemical and electronic structures [10,11,12,13,14].…”

Studies on the thermal properties and flammability of polyamide 6 nanocomposites surface-modified via layer-by-layer deposition of chitosan and montmorillonite

“…A distinct change can be observed at 950-1150 cm -1 , which corresponds to incorporation of polyelectrolytes onto polymeric substrates. As signals of virgin chitosan overlay with those of PA6 (symmetric and asymmetric stretching of NH 4 ? at 1540 and 1635 cm -1 , respectively; planar deformations of N-H and C-N stretching at 1540 cm…”

“…; scissoring vibrations of NH 4 ? at 1170 cm -1 ), LbL modification effects require a detailed study of the latter region.…”

“…Since then, many practical applications of this surface treatment method have been described, such as in electrochromic materials [3][4][5], controlled drug delivery [6,7], composites with barrier properties towards oxygen [8][9][10][11][12], antireflective [13] and waterproof coatings [14][15][16], and antibacterial materials [17][18][19]. In principle, LbL assemblies arise from alternative dipping of substrates in, most often, water-based solutions of polyelectrolytes, which makes this method eco-friendly.…”

Revamping a Classic Analytical Chemistry Laboratory Experiment to Improve Student Understanding of Chemical Analysis, Method Development, Validation, and Statistics

“…In addition to the common mechanical, electrical, and optical properties of all ICPs, polyaniline (PANI), initially called “aniline black”, has been a known material (Henry Letheby first observed the formation of a bluish-green precipitate on the anode during aniline electrolysis over a century ago) . Since aniline is a base, the proton is the best ion to be doped into polyaniline structures, which is one of the reasons that polyaniline has been shown to sensitively respond to pH change via proton doping and dedoping processes, allowing for its extended utilization as a class of both qualitative and quantitative pH sensing materials. − As shown in Figure , in its fully oxidized and reduced states, PANI is electrically insulating and referred to as pernigraniline base (PB) and leucoemeraldine (LB), respectively. An intermediate oxidation state containing an equal number of oxidized and reduced repeat units exists between these two extremes and is referred to as emeraldine base (EB).…”