Polystyrene- block -poly(ethylene oxide) reverse micelles and their temperature-driven morphological transitions in organic solvents

摘要

Transmission electron microscopy (TEM) and light scattering (LS) experiments were conducted to study the micellar morphologies and the transformation process of Polystyrene-block-poly(ethylene oxide). The origin of morphological changes with temperature was also illustrated by the free energy calculation of micelles as a first approximation. 1,4-dioxane was chosen as the common solvent, and cyclohexane was selected as the selective solvent. At room temperature, spherical micelles are formed, and mixture of spherical micelles and cylindrical micelles are observed when the temperature decreased to 5°C. The PEO blocks are found to be slightly compressed in the core of the spherical micelle. Although the interfacial free energy is demonstrated to be the main driving force for the morphology transitions induced by decreasing temperature in this system, it is found that the reversible transformations when increasing to room temperature is not able to be observed in our experimental time range.