Correlation between swelling/shrinking behaviour and nanorheology of microgel particles

During the last decades microgels made of N-isopropylacrylamide (NIPAM) have attracted much interest since they can be easily transferred into multiresponsive entities. That makes them interesting as drug delivery systems but also for the fabrication of multiresponsive coatings. Via specific comonomers the thermoresponsive PNIPAM gels get pH sensitive and the charge and hydrophobicity can be tailored. PNIPAM gels show co-nonsolvency in water/alcohol mixtures which induces also a swelling/shrinking process. In order to induce fast volume phase transitions external triggers like light or magnetic fields are useful. Therefore optical switchable azo-surfactants, gold nano particles or magnetic nanoparticles are embedded within the gel.
All these different triggers induce a volume phase transition of the microgels which has an impact for actuatorics. An application might be a touch screen with haptic functionality. In order to use these microgels as actuators and for haptics one has to understand the correlation between the volume phase transition and the rheological properties of the microgel particles. The talk focuses on the effect of different synthetic parameters (cross-linker, charge, additives) and outer parameters like solvent composition on the nanorheology. Therefore static and dynamic force experiments with high spatial resolution were carried out. It turned out that there is no simple correlation between the volume of a microgel and its rheological parameters G’ and G’’.