Influence of Used Polyvinyl Alcohol Grade on the Electrochromic Properties of Ni(OH)2-PVA Composite Films

Films based on nickel (II) oxides and hydroxides are used in electrochromic cells as one of the active materials that change their optical characteristics under the action of an electric current. Electrochemical deposition, due to which composite films of Ni(OH) 2 -polyvinyl alcohol (PVA) can be formed on the electrically conductive substrate, can become an alternative to expensive vacuum methods. The presented study is devoted to the study and improvement of the electrochemical method of deposition of Ni(OH) 2 -PVA electrochromic composite films. This study illustrates the influence of the grade of the used polyvinyl alcohol on the main qualitative characteristics of Ni(OH) 2 -PVA electrochromic composites. Four PVA grades have been used for the study: 17–99, 24–99, 30–99, and 30–88, which differ in the viscosity of solutions and the degree of hydrolysis. The deposition has been carried out by the electrochemical method in the presence of the listed grades of polymers dissolved in the electrolyte. As a result of the study, it has been shown that the properties of electrochromic films depend on the grade of PVA used. To a greater extent they depend on the degree of hydrolysis, and to a lesser extent – on the molecular weight of the polymer, expressed in terms of viscosity. Analysis of the data obtained makes it possible to assert that the degree of PVA hydrolysis has a greater effect on the final characteristics of the films than the viscosity of solutions. However, viscosity also affects the properties. Moreover, it has been found that there is some optimum for this value. In this case, in terms of the characteristics of the films obtained, the optimal PVA has been the one with an average viscosity (PVA 24-99) among polyvinyl alcohols of three grades with the same degree of hydrolysis. The results obtained make it possible to recommend the use of PVA with an average viscosity and a degree of hydrolysis of less than 99 %. Based on the literature data, assumptions have been made that allow explaining the results obtained by the change in the hydrophobicity of the film and the properties of the transparent SnO 2 :F layer on glass.