Guang-Way Jang

Thermal transitions and mechanical properties of films of chemically prepared polyaniline

The mechanical and thermal properties of the solution-cast films of chemically prepared polyaniline have been studied by means of dynamic mechanical analysis (d.m.a.), differential scanning calorimetry (d.s.c.) and thermogravimetric analysis (t.g.a.). The glass transition temperature (Tg) of the polyaniline films in emeraldine base form was determined and characterized for the first time to be in the range of ∼ 105–220°C for the films containing ∼ 16-0% of 1-methyl-2-pyrrolidinone (NMP) residual solvent, respectively, from a decrease in the storage modulus in d.m.a. and from d.s.c. studies. Depending on the content of NMP, the thin films of polyaniline have a storage modulus of ∼ 200 MPa-2 GPa at temperatures below Tg. Other thermal transitions and reactions in the temperature range of ∼ 25–500°C are also characterized by infra-red spectroscopy, X-ray diffraction and cyclic voltammetry and are discussed in relation to the mechanical properties of polyaniline.

Monitoring the chemical polymerization of aniline by open-circuit-potential measurements

Abstract We present the first open-circuit-potential (OCP) study of the chemical polymerization of aniline in the presence of various aromatic additives and demonstrate the feasibility of monitoring the polymerization rate by the OCP technique. With (NH4)2S2O8 as oxidant, there are three stages in the OCP-reaction time plots. The time (t1 + t2) needed for completion of the first two stages is inversely related to the rate of polymerization. The presence of p-aminodiphenylamine, N,N′-diphenylhydrazine, benzidine and p-phenylenediamine reduces the t1 + t2 value and therefore increases the rate of polymerization. In contrast, the presence of p-hydroquinone increases the t1 + t2 value and thus reduces the polymerization rate. These preliminary results are consistent with the kinetics and mechanism of the electrochemical polymerization of aniline.

Large‐Area Electrochromic Coatings Composites of Polyaniline and Polyacrylate‐Silica Hybrid Sol‐Gel Materials

A low-cost technique for fabricating large-area electrochromic coatings is described. Polyaniline was incorporated into polyacrylate-silica hybrid sol-gel networks using suspended particles or solutions. A solution of polyaniline and poly[methyl methacrylate-co-3-(trimethoxysilyl)propyl methacrylate] can be spray- or brush-coated on transparent indium-tin oxide substrates to form robust electrochromic coatings. Silane functional groups on the polyacrylate chain act as coupling and cross-linking agents to improve surface adhesion and mechanical properties of the resulting composite coatings. These coatings showed reversible transparent to green color change when polarized at potentials between {minus}0.4 and +0.4 V vs. Ag/AgCl in a 0.2 M LiClO{sub 4}/acetonitrile electrolyte solution. The cycle lifetimes of polyaniline films were improved by incorporating the polymer in the polyacrylate-silica matrix. Electrochromic switching was demonstrated for the composite coatings in large-area all-solid-state devices.

Emission Mössbauer studies of the Y−Ba−Cu(57Co)−O system

During the usual thermal treatment of the superconducting YBa2Cu3O7 compound, cobalt and iron substitute predominantly at the Cu(1) site as shown by neutron and X-ray diffraction. EXAFS, and IR studies. A sequence of thermal treatments permits reversible cycling of cobalt-57 between the two copper sites. This allows us to micro-probe both the chain and the sheet site with varying degree of oxygen content.