Prof. Dr. Axel Müller

Star polyelectrolytes (poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA)) with dual (temperature and pH) responsive properties were utilized to fabricate multi-responsive microcapsules via layer-by-layer (LbL) assembly. The LbL microcapsules are very robust and uniform, with higher stability and different internal structure compared with conventional microcapsules based on linear polyelectrolytes. Ionic strength in the polyelectrolyte solution during the microcapsule assembly process has significant influence on the thickness and permeability of microcapsules. With increasing pH, the permeability of microcapsules decreases, and the transition from “open” to “close” state for target molecules can be achieved within a narrow pH range (from pH 7 to 8). On the other hand, the overall size and permeability of the microcapsules decrease with increasing temperature (with a shrinkage of 54% in diameter at 60 ^oC compared with room temperature), thus allowing to reversibly load and unload the microcapsules with high efficiency. The organization and interaction of star polyelectrolytes within confined multilayer structure are the main driving forces for the responsiveness to external stimuli. The multi-responsive LbL microcapsules represent a novel category of smart microstructures as compared to traditional microcapsules with “one-dimensional” response to a single stimulus.