報告題目：Phase transition and phase separation in polymeric gels
報告時間：6月5日（星期三）下午4:00-5：00
報告地點：玉泉校區教12-118
報 告 人：美國Iowa State University洪偉教授
報告簡介：
Phase transition in polymeric gels, as one of the key mechanisms for their stimuli responsiveness, has attracted great interest from both theoretical and practical aspects. Considering concurrent large deformation and mass transportation, we formulate a Ginzburg-Landau-type model for the phase separation of a thermo-sensitive gel. It is found that the morphology of a phase-separated gel is determined by its size and the temperature change. Allowing solvent to migrate out of the gel within a short period of time, a relatively small gel can shrink uniformly above the critical temperature. When heated quickly above the critical temperature, a large gel may develop heterogeneous structures by nucleating solvent-rich domains inside. For a small temperature change (shallow quenching), the formation of equilibrated coexisting phases is thermodynamically possible, and the morphology of phase separated gel is controlled by regular coarsening. For a large temperature change (deep quenching), the gel undergoes a unique process of domain dilation, resulting in a spongy structure of out-of-equilibrium domains. The phase-field model simulates the evolution process of a phase-separating gel, and reveals that the dilation process is a consequence of the competing demixing thermodynamics and the large-deformation kinematics. The model may explain the formation of similar structures in other systems, and the methodology can also be applied to the structural evolution of other soft materials.
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