| Abstract: | We present a survey over recent studies of the volume transition in colloidal core-shell particles composed of a solid poly(styrene) core and a shell of a thermosensitive crosslinked polymer chains. The thermosensitive shell is built up from poly(N-isopropylacrylamide) chains (PNIPA) crosslinked by N,N′-methylenbisacrylamide (BIS). In addition, particles containing acrylic acid (AA) as comonomer have been synthesized and investigated. The volume transition of these particles have been studied by dynamic light scattering (DLS) and by small-angle X-ray scattering (SAXS). In all cases analyzed so far the volume transition was found to be continuous. This finding shows that the core-shell microgels behave in a distinctively different manner than ordinary thermosensitive gels: The crosslinked chains in the shell are bound to a solid boundary independent of temperature. The spatial constraint by this boundary decreases the maximum degree of swelling but also prevents a full collapse of the network above the volume transition. |
