Correlated Morphological Changes in the Volume Temperature Transition of Core–Shell Microgels

Abstract

PVCL and PNIPMAAm core–shell components in microgel particles are shown to have different volume phase temperature transition behavior than the respective homopolymer microgel particles due to confinement effects. A combination of dynamic light scattering (DLS) data that gives access to the temperature dependence of hydrodynamic radius and modified Flory–Rehner theory in the presence of networks confinement allowed obtaining information about correlated morphological changes of components inside of core–shell microgels. The core–shell components individual temperature behavior is analyzed by modifying the Flory–Rehner transition theory in order to account for core–shell morphology and the existence of an interaction force between core and shell. Describing the dependence on temperature of the radial scale parameter, the ratio between the radius of the core and the hydrodynamic radius, we gain access to the swelling behavior of the core and shell components irrespective of the swelling behavior of the total hydrodynamic radius. Furthermore, the theoretical description of volume phase temperature transition permits the development of scenarios for the correlated changes in the core and shell radial dimensions for the two microgels with reversed morphologies. The fact that the theoretical model is appropriate for the treatment of core–shell microgels is proved a posteriori by obtaining a temperature dependence of the components that is in accordance with the expected physical behavior. Novel core–shell microgel systems of PVCL (poly(N-vinylcaprolactam))-core/PNIPMAAm (poly(N-isopropylmethacrylamide))-shell and PNIPMAAm-core/PVCL-shell, with a double volume phase temperature transition due to the thermoresponsive components, were used for this study.