Phase Transitions in Soft Matter

Soft matter physics has become a rapidly developing branch in condensed matter physics. This is certainly due to the fact that soft matter does play an important role not only in our daily life, but also in many technological applications.

Despite the fundamental role that soft matter plays in our lives, systematic investigations of its properties have been out of reach over many decades which is due to the intrinsic complexity of these systems. Only in recent years special experimental techniques in combination with new theoretical concepts have brought along - in a fruitful cooperation among soft condensed matter scientists - a deeper insight into the intriguing phenomena of these systems. Since typical soft matter particles are mesoscopic in size, they can be be investigated with experimental methods that are much simpler to handle than, for atomic systems: information is obtained directly in real space and particles can be moved in space nearly arbitrarily with optical squeezers.

During the past year we have in particular focused on ionic microgels. They are mesoscopically sized, covalently cross-linked polymer networks, their diameter s being in the range between 10 nm and 1 mm. Most microgels are based on poly(N-isopropylacrylamide) (PNIPAM) or related co-polymers that are cross-linked during emulsion polymerization, a process that can produce remarkably uniform particles. When the polymer chains comprising the microgels carry ionic groups on their backbones, the latter dissociate upon solution into an aqueous solvent, leading to charged or ionic microgels. Active interest in polyelectrolyte gels (to which microgels belong as a subgroup) remains to date, due to their ability to absorb large amounts of water and act as superabsorbers or drug delivery systems.