Effect of entanglements on temperature response of gel immobilized microgel photonic crystals

Abstract

We report here, an evidence of entanglements between polymer chains of thermo-responsive microgels with the immobilizing hydrogel, by studying the temperature dependent dynamics of the microgel-hydrogel composite. The dynamics measurements show a decrease in amplitude of microgel thermal vibrations with an increase in temperature in contrast to the expected amplitude increase, confirming the binding between microgel and hydrogel through the entanglement of their polymer chains. The consequences of these entanglements on the temperature dependence of diffraction of immobilized microgel crystals, across the volume phase transition (VPT) of microgels, have been studied using UV–vis spectroscopy. As an effect of entanglements in immobilized microgel crystals, it is found that the crystalline order (the Bragg diffraction) is retained above VPT with small increase in structural disorder (width of the Bragg diffraction peak). Entanglements restrict thermal motion of microgels leading to retention of crystalline order above the VPT. However, it induces local strain in lattice due to shrinking of microgels upon VPT leading to a small increase in structural disorder.