Synthesis and characterization of solvent-invertible amphiphilic hollow particles.

Previous researches on solvent-dependent polymer systems mainly focus on amphiphilic invertible polymers (AIPs), which are capable of forming solvent-dependent micellar or inverse micellar assemblies. However, polymer particles that are invertible in response to solvent polarity are almost unexplored. In this paper, we report a new type of invertible hollow polymer (IHP) particle that is comprised of polyethylenimine-g-poly(methyl methacrylate) (PEI-g-PMMA) copolymer. The amphiphilic PEI-g-PMMA hollow particles were first prepared through synthesis of well-defined PEI/PMMA core-shell particles, followed by removal of PMMA homopolymer from the core. The resulting IHP particles can be stably dispersed in both nonpolar solvent and water. We have investigated the morphology and surface property of the particles in both dichloromethane (DCM) and water using transmission electron microscopy, water contact angle measurement, and X-ray photoelectron spectroscopy analysis to gain insight into this unique particle dispersibility. Sustainability of the solvent-invertible property was carefully studied through repeated treatment of the IHP particles in DCM or water for up to six cycles. Solvent-dependent property of the dry films formed by IHP particles was also investigated through water contact angle measurement. Increasing water content on the DCM-treated IHP particle film could reduce the water contact angle from 94° to 51°. Our results demonstrate that the amphiphilic hollow particles are a new type of polymer design for smart materials that are invertible in response to nonpolar and aqueous media in both dispersed and solid states.