Swelling of cross-linked polystyrene beads in toluene

Ultraviolet light irradiation of PS microbeads can be used for controlling the solvent uptake and release upon exposure to its vapor. The irradiation leads to additional fracture and crosslinking of PS chains thus reducing the amount of solvent uptake significantly. Confocal fluorescence microscopy showed that this effect is pronounced in a shell of the PS microbeads having a thickness in the range of 1-2 mu m. In addition, this shell shows considerable fluorescence when excited between 300 nm and 500 nm that is attributed to lower molecular weight fragments of PS. Fluorescence correlation spectroscopy studies of small tracers diffusion in a microbead core have revealed that the swelling of the core is not altered by the UV exposure, and the UV crosslinking effects are limited to the shell only. Chemically and UV cross-linked PS beads keep their shapes even after numerous swelling cycles in saturated toluene vapors. (C) 2008 Elsevier B.V. All rights reserved.