Multiple-phase behavior and its microscopic implication for 4-acrylamidosalicylic acid gel

Poly(4-acrylamidosalicylic acid) gels exhibited multiple-phase behavior dep ending on their histories in the parameter space of pH and temperature. Fou r different phases, denoted as phase091 (as-prepared), phase244 (swollen at high pH), phase064 (heat-treated), and phase233 (swollen at high pH after heat treatment) were clearly resolved, where the three digits denote their linear swelling ratios in percentage with respect to their sizes at prepara tion. Each phase was stable and did not change its swelling ratio with pH o r temperature as long as the values of pH or temperature were within limite d ranges. Transitions among different phases were discrete with hysteresis loops. The structure factors corresponding to these four phases were obtain ed by small-angle neutron scattering, which indicated the presence of chara cteristic structures depending on pH and temperature, particularly in the s hrunken state (i.e., phase064). (C) 2001 American Institute of Physics.