Gels – polymeric networks swollen with a substantial amount of solvent – represent a fascinating class of soft materials, with wide-ranging applications in fields as diverse as biomedicine, pharmaceutics, personal care products, foods, sensors, actuators, flexible electronics, oil recovery, and adhesives. Physical gels are held together by non-covalent interactions, which may be as specific as hydrogen bonds, or as general as solvophobic association of insoluble blocks. Among the attractive features of physical gels are reversibility, stimuli-responsiveness, and tunability of macroscopic properties. There are exciting opportunities to design new gel systems based on block copolymers, given the relative ease with which tailored architectures can be synthesized by modern controlled polymerization techniques.
In this talk two classes of physical gels will be highlighted. In one, the ability of ABC block terpolymers to form novel gel structures in water will be demonstrated, where blocks A and C are mutually immiscible and hydrophobic, while B is hydrophilic. In particular, the formation of hydrogels by sequential association (first A, then C) leads to a remarkably sharp gelation transition, at a relatively low polymer concentration. In the second system, gels formed by hydrogen bonding between the endblocks of a fully soluble ABA triblock and a separate, C homopolymer “crosslinker”, will be described. In this case the solvating medium is an ionic liquid, which affords access to a wide range of temperature and unprecedented rheological response.