Viscoelastic behavior of tungstic acid gel during the gelation process

Abstract

This chapter provides the understanding of Tungstic acid which is a kind of transition metal hydroxide exhibits electrochromism and photochromism. In the gelation process, a colloidal solution becomes a solid (gel) by the formation of a network in which solvents are captured; the composite structure determines the characteristics of the gels. Such a solidification process leads to change in the viscoelasticity of the network of the gel. However, conventional viscoelastic measurements (such as ultrasonic methods) could not detect such changes which occur during the sol–gel transition because of the majority of the solvent which may not suffer much change. This chapter investigates the viscoelastic properties of tungstic acid during the gelation process by observing surface waves and rotational resistivity of cylindrical probe. Around gelation point, marked changes are observed in the surface wave velocity and amplitude. From the dispersion relations of the surface wave in the sol and gel states, it was found that the surface tension wave drastically changes to the Rayleigh wave at gelation point. These experimental results agree qualitatively with the theoretical results of viscoelastic model. At the end change in the real elastic modulus near the gelation point is emasure for the comparison of the experimental results with theoretical results. From the preliminary experimental results, real elastic modulus probably emerge at the gelation point.