LCST PHASE SEPARATION BEHAVIOR OF SIMPLE ALKYL GALLATES BEARING SHORT OLIGOETHYLENE GLYCOL GROUP

Abstract

Simple alkyl gallates bearing short oligo(ethylene glycol) (OEG) chains exhibit lower critical solution temperature (LCST) phase separation in aqueous solution. The gallates synthesized in this study showed cloud points ranging from 24 to 56 °C, depending on the length of the alkyl chain in the ester, the length of the OEG groups, and the gallate concentration. Dynamic light scattering (DLS) showed that gallate aggregates were around 100 nm in size, forming micelle clusters below the cloud point, and abruptly extended to >2000 nm above the cloud point. Variable-temperature (VT) ¹H NMR showed splitting of the aromatic proton signals of the gallates above the cloud point, suggesting conversion of the micelle clusters into both monomeric gallate and large vesicular structures. These gallate aqueous solutions are materials capable of broadly adjusting the cloud point within the temperature range relevant to human living environments, rendering them promising candidates for application in the active layer of temperature-responsive smart windows.