Shyam P. Maheswari

Electrochromism of Polyaniline: An In Situ FTIR Study

Electrochromic thin films of polyaniline were prepared by electropolymerization of aniline from an acidic aqueous solution on platinum and conducting glass surfaces. An in situ FTIR spectroelectrochemical technique was used to investigate structural changes of the film during oxidation and reduction. Coloring (oxidation) and bleaching (reduction) of the film were shown to be associated with the deprotonation and protonation of the film. It was detected that the N‒H stretching band around 2970 cm−1 decreased as the film was gradually oxidized.

In Situ Infrared Spectroscopic Study of the Electrochromic Reactions of Tungsten Trioxide Films

This paper reports on thin WO{sub 3} films which are transparent in the oxidized state and colored in the reduced state. These changes in optical properties are associated with compositional variations of the material. Changes in vibrational intensities of W{double bond}O, W{emdash}O, and W{double bond}O{emdash}H bonds in the electrochromic WO{sub 3} film were detected by an in situ FTIR technique at various stages of reduction (coloration). The absorbance due to O{emdash}H stretching and bending vibrations was found to increase during the electrochemical reduction of the film, indicating the incorporation of water into the film along with the formation of H{sub x}WO{sub 3} bronze during coloration. The absorbance due to W{double bond}O vibration decreased while that due to W{emdash}O vibration increased during reduction. These observations suggest that during the coloration process W{double bond}O bonds break and new W{emdash}O bonds form in the film, and thus, provide direct evidence for the electrochromic reaction. O{sub 2}W{double bond}O + xH{sup +} + xe{sup {minus}} {leftrightarrow} O{sub 2}W{emdash}O{emdash}H{sub x}.

Effect of Temperature on a Complementary WO 3 ‐ Prussian Blue Electrochromic System

An electrochromic device consisting of a cathodically coloring tungsten trioxide film and an anodically coloring Prussian blue (PB) film may find use in automotive «smart windows.» These windows have prospects for reduction of solar heat load on air conditioning systems and privacy applications in automobiles. Such windows must have good stability at elevated temperatures. The thermal stability and electrochromic switching performance of a complementary WO 3 -PB device is reported over the temperature range of 25 to 80 o C. The device showed good thermal stability up to 80 o C

Electrochromic characteristics of a complementary tungsten trioxide/Prussian blue cell

Optically switchable electrochromic materials are of importance in the automobile industry for the control of solar heat load, glare reduction, and privacy applications. A complementary electrochromic cell consisting of a cathodically colouring tungsten trioxide (WO3) film, an anodically colouring Prussian blue (PB) film, and a Li+ conducting polymer electrolyte was made. Cycling characteristics and colouration efficiency of the cell at various stages of cycling were evaluated. It was shown that the complementary cell requires less energy for operation compared to cells with a single film. The WO3/PB was cycled up to 1300 times. A gradual decrease in the contrast between the coloured and the bleached states upon cycling was observed during the first 400 cycles. The colouration efficiency of 102 cm2C−1 at the first cycle decreased to 67 cm2C−1 after 387 cycles. The cause of degradation is attributed to the lack of K+ ions available to PB film.

An Electrochemical Technique for Characterizing Metal-Lubricant Interfacial Reactions

An AC impedance technique, in combination with an electrical property cell, was employed to measure the electrical resistance and capacitance of lubricants. A comparison of the combined surface coating plus bulk fluid resistance and capacitance values measured for different additives blended in mineral oil, demonstrated that different metal-lubricant interaction mechanisms occur. The electrical measurements indicated that additives such as the mixed alkyl acid orthophosphate (acid phosphate) reacted with the cast iron electrodes to firm reaction films, whereas oleic acid was absorbed on the electrodes. Although the implied reactivity from electrical measurement for N-oleyl-1-1,3 diaminopropane (fatty amine) is comparable to that for acid phosphate, no reaction film for the former was detected by elemental analysis. Presented at the 41st Annual Meeting in Toronto, Ontario, Canada May 12–15, 1986

The nature of electrochemical reactions between several zinc organodithiophosphate antiwear additives and cast iron surfaces

This printing supersedes the publication in the July, 1988 Tribology Transactions pages 382-390 in which Fig. 16 and Table 5 were omitted along with the Discussion and Closure. The electrochemical reactivities of four commercial zinc organodithiophosphate (ZDP) antiwear additives, each blended with a common mineral oil, were measured during thermal decomposition tests. The results imply that electrochemical reactions between the decomposition products of ZDP and the electrode surfaces produce surface coatings on cast iron electrodes. This observation suggests that electrochemical methods might be useful tools for understanding the mechanism by which ZDPs reduce wear. The electrochemical reactivity of the blends was proportional to the thickness of surface coatings formed on the electrodes at the end of the test, and inversely proportional to the ZDPs decomposition temperatures. The effects of oxygen, oleic acid concentration, and surface coating on the electrochemical reactivity were measured. Presented ...

AC Impedance Measurements of the Resistance and Capacitance of Lubricants

An AC impedance technique in combination with a thin-film (12 μm) cell was employed to separately meusure the electrical resistance and capacitance of electrode-lubricant interfaces and bulk lubricant layers. In this study, three different additives were investigated by measuring the AC impedance spectrum of each additive mixed separately with a commercially available mineral oil. These additives were oleic acid, N-oleyl-1,3 diaminopropane (fatty amine), and mixed alkyl acid orthophosphute (acid phosphate). For lubricants containing 2 mass percent of an acid phosphate or fatty amine, the capacitance of the electrode-lubricant interface, Ci, and the capacitance and resistance of the bulk lubricant layer, Co and Ro, respectively, were evaluated separately from the AC impedance spectra. The lower limit of the resistance of the electrode-lubricant interface, Ri, was aDo estivnated. For additives, such as oleic acid, which physically adsorbs on the electrodes, the resistance and capacitance of the electrode-lu...

Electrochromic aspects of phosphotungstic acid

Abstract The electrochromic behavior of phosphotungstic acid (PWA) was investigated. A fluorine-doped tin oxide coated glass substrate was used for this work. In-situ measurements of optical absorbance under controlled electrochemical conditions showed that phosphotungstic acid can be colored and bleached by electrochemical oxidation and reduction. The coloration efficiency of PWA in an aqueous solution was found to be 16.8 cm2/C. This is lower than that observed with WO3 films presumably due to continuous dissolution of the reduced species. The diffusion coefficient of phosphotungstate anions [PW12O40]−3 was found to be 2.8×10 −5 cm 2 / s . The results indicate that PWA has desirable properties for use as an electrochromic material.

SILANIZED POLYANILINE AS AN ELECTROCHROMIC MATERIAL

An electrochromic film of polyaniline was electropolymerized from an acidic aqueous solution on a fluorine-doped, SnO 2 -coated glass precoated with an aniline derivative of a silane compound. The silane layer acted as a coupling agent to improve the surface adhesion of the electrochromic polyaniline film. The silanized polyaniline was found to possess good electrochromic properties, becoming blue upon electrochemical oxidation and near transparent upon reduction. The aging characteristics of the polyaniline film were found to be improved upon silanization

Metallo-organic deposition of tungsten oxide films from alkylammonium tungstate solutions

This paper describes a simple and inexpensive metallo-organic deposition (MOD) process for forming electrochromic tungsten oxide (WO3) films on glass. The thin films of WO3 were made by air firing (500–700°C) films from xylene/2-propanol solutions of bis-(di-n-octylammonium) tetratungstate, [(n-C8H17)2NH2]2[W4O13]. The process coats glass with undoped films ranging in colour from faint yellow to dark brown, and can be used to make gradients of these colours. The colour is determined by the firing parameters and results from residual carbon and tungsten suboxides in the film due to incomplete firing. Increased firing temperatures or longer firing times removes the carbon and produces films with higher crystallinity. Electrochemical doping with acid (H+) switches the colour gradient films to a uniformly blue colour.