Bulletin Spring‧Summer Autumn‧Winter 1999

Intel l igent Gels Wherein Lies Their Intelligence? Another State of Matter Mos t people are familiar w i t h the three states of matter: solid, l i q u i d and gas. Ac t ua l l y, there are many more exotic states, and one t ask of ma t e r i a l sc i en t i s ts is t o t r y t o understand their structure and properties, and derive use f u l applications f r om such understanding. One exotic state of matter is gels. They are not quite solid; neither are they l i qu i d. Examples include jello, hair-styling gels, sea cucumbers and soft contact lenses. Dr. Wu Ch i of the Department of Chemistry has been wo r k i n g on polyelectrolyte gels. Polyelectrolyte Gels Most c ommo n molecules are f a i r ly small, consisting of on l y a f ew atoms. For example, the oxygen molecule consists of on ly t wo oxygen atoms; the water molecule consists of t w o h y d r o g en atoms a nd one oxygen atom. Macromolecules, or huge molecules, also exist. They consist of tens of thousands, e v en m i l l i o n s of a t oms i n one s i ng l e molecule. The typical structure is a long chain of ca r bon a t oms, on w h i c h va r i ous side g r oups are attached. I f o n l y h y d r ogen is added, one can get polyetheylene, a familiar soft plastic; w i t h other side groups, one can get, for example, nylon. Polyelectrolytes are a special k i nd of macromolecules; i n these, many of the side groups can easily become charged b y gaining or losing electrons. By developing branches and intermolecular connections (called cross-linking) these macromolecules can f o rm a three- dimensional ne two r k (Fig. 1). The networks can collapse into rather tight structures (like jello powder before water is added); but i f water is added to fill up the space between the ne two r k, it can swell up and f o rm gels. The interaction between water and the po l ymer networks determines the swelling and sh r i nk i ng of a given polyelectrolyte gel. Research 13