Phase separation of polymeric gels - domain dilation vs. coarsening
Wei Hong (Iowa State University), Xiao Wang (Iowa State University)
Mechanics of Phase Transforming and Multifunctional Materials
Tue 9:00 - 10:30
CIT 219
Some polymeric gels may undergo a hydrophilic-hydrophobic phase transition when subject to certain change in environmental conditions (e.g. temperature). The morphology of the gel during and after the phase transition depends on the speed of change and on the size of the sample. For a small enough gel, or if the temperature is changed quasi-statically, the gel has enough time to expel excess solvent and shrink uniformly. When a macroscopic gel undergoes deep quenching, the solvent molecules do not have time to migrate out of the sample, and they nucleate solvent-rich zones, and the homogeneous gel separates into coexisting domains. Depending on the final condition, the coexisting domains may reach equilibrium (shallow quenching) or never reach equilibrium (deep quenching). The deep quenching process exhibits interesting morphology, and is very different from the regular spinnodal decomposition. Instead of coarsening (i.e. the growth of a domain by combining smaller domains of similar composition), a domain dilates by absorbing solvent from the surrounding domains. Such a process results in a foam-like structure which is never observed in regular spinnodal decomposition. The dilating domains grow indefinitely and will ultimately induce damage to the polymer network and permanently form a foam structure.