Polymer Gels, Materials That Combine Liquid and Solid Properties

Abstract

We are accustomed to thinking of matter as being in one of three states: solid, liquid, or gas. Nature, however, has provided us with a marvelous intermediate state, the gel. Industrial applications are just beginning to explore the advantageous gel properties as adhesive, superabsorber, damper, membrane, toner, catalyst support, etc. Gels are good adhesives since they combine the surface wetting property of liquids with the cohesive strength of solids. Strong adhesion and damping properties suggest gels as a binder in composite materials. For example, the car of the future may operate at a much reduced noise level due to a thin layer of gel in its body. Widespread technical applications have not yet materialized because, until recently, it was difficult to measure gel behavior. This has changed, and as a consequence, gels can now be manufactured with reproducible properties. What the many possible types of gelation processes have in common is that molecules connect into a three-dimensional network structure. Junctions between molecules form as chemical bonds (cross-links) or physical associations (such as crystalline or glassy domains, hydrogen bonds, etc.). The molecular architecture determines the gel properties in ways which have yet to be explored. Typical parameters are the monomer building block, molecular size, branching, chain stiffness, cross-link functionality, and solvent content.