The gel that memorizes phases

A poly(4-acrylamidosalicylic acid) gel exhibits multiple phases as characte rized by distinct degrees of swelling; the gel can take one of four differe nt swelling values, but none of the intermediate values. The multiple phase behavior appears as a result of the combination of hydrogen bonding and hy drophobic interaction between polymer segments. The gel has remarkable memo ry: The phase behavior of the gel depends on whether the gel has experience d the most swollen phase or the most collapsed phase in the immediate past. The information is stored and reversibly erased in the form of a macroscop ic phase transition behavior. These phenomena are explained by a mean field theory where the number of hydrogen bonds is added to the equation of the state of a gel. (C) 2000 American Institute of Physics. [S0021-9606(99)5084 8-9].