Temperature Effects on the Shell Structure of Micelles Formed by A Polystyrene-Poly(ethylene oxide) Diblock Copolymer in Water

초록

Amphiphilic block copolymers undergo self-assembly to form a variety of micelle morphologies in both aqueous media and organic solvents. As new and advanced nanomaterials, multicompartment micelles attract researchers in both academic and application fields due to their potential applications in biomedicine, drug delivery, and biotechnology. The micelle morphology is tuned by molecular parameters, such as molecular weight and block copolymer composition, and solution parameters like copolymer concentration, solvent composition, temperature, and others. Temperature has been used as a tool to control the block copolymer self-assembly for several years. The determination and control of the sol-to-gel transition temperature in a reliable manner are quite important because the sol-to-gel transition temperature determines injectability, formulation temperature, and sterilization condition. Thus, the kinetics of gel formation is determined by sol-to-gel transition temperature. The temperature dependence of the shell structure of micelles formed by a deuterated polystyrene-poly(ethylene oxide) diblock copolymer (dPS-b-PEO) in heavy water were investigated with small-angle neutron scattering (SANS). SANS data were analyzed using a core-shell modeled with a structure factor for a hard sphere potential. The shell thickness were obtained from the fits to the SANS data. The shell thickness first decreased with increasing temperature, reached a minimum at some point and then increased with a further increase of temperature. These structural changes seemed to be due to the combined effects of the decrease in hydrophilicity of the PEO block and the increase in thermal motion of the PEO block with increasing temperature.