Rheological and optical response of hydroxypropyl methylcellulose under variable temperatures for optical switching based on thermo‐optical effect

This work is devoted to investigate novel aspects of the rheological and optical response of hydroxypropyl methylcellulose (HPMC) as a result of temperature variations from 308.15 to 338.15 K. First, new insights on correlation between the solution flow behavior and the film thickness uniformity, under distinct temperatures, are established. Then, the HPMC film is examined from the point of view of some basic surface parameters describing the surface morphology, such as root mean square roughness, surface area ratio, texture direction index, kurtosis, skewness and surface bearing index. The refraction properties of HPMC are reported for the first time as a function of wavelength and temperature. The changes in the optical dispersion parameters as a function of temperature increase reveal the reduction of strength of interband optical transitions from 15.147 to 14.086 eV and a smaller band gap from 6.475 to 6.137 eV. The latter is caused by temperature‐induced dilatation of the polymer lattice and its effect on the electron–lattice interactions. The thermo‐optic coefficient of HPMC is found to be larger than that of other polymers, while its dependence on the wavelength is small, varying from −2.03 × 10−4 K−1 at 489 nm to −2.31 × 10−4 K−1. The resulted properties are corresponding to the demands imposed for materials used in optical switching based on thermo‐optical effect.