Mechanism of polymer particles formation during the soap-free emulsion terpolymerization of styrene - acrylic acid – N -(isopropyl acrylamide) for photonic crystals fabrication

Abstract This study presents the synthesis and characterization of a styrene (ST), acrylic acid (AA), and N-(isopropyl acrylamide) (NiPAM) terpolymer obtained by a soap-free emulsion process. The influence of AA/NiPAM ratio on the reaction mechanism and the reaction kinetics was investigated. Thus, the polymerization rate increases with the concentration of NiPAM in the substrate. The obtained polymer colloids permitted the fabrication of photonic crystals (PCs) in all four cases, regardless of the substrate composition. The structures were investigated by UV–vis, SEM, and optical microscopy. A micellar polymerization mechanism in the case of AA rich substrates and a heterogeneous mechanism for NiPAM rich substrates were ascertained using the UV–vis, DLS, TEM, and XPS analyses. As the NiPAM concentration increased in detriment to AA, the particle formation mechanism leads to the formation of two distinct types of polymer particles. The zeta (ζ) potential values confirmed the latexes stability in all cases. The LCST values situated in the range of 37−44 °C were determined by DSC analysis. The humidity responsive characteristics were evaluated as an application for the obtained PCs.