Coarsening Effects on Microstructure Formation in Isopycnic Polymer Solutions and Membranes Produced via Thermally Induced Phase Separation

Abstract

The phase separation of isopycnic polystyrene-diethyl malonate solutions has been studied by investigating the microstructure of polymer membranes. Polymer solutions underwent spinodal decomposition and coarsening via a thermally induced phase separation procedure, and supercritical CO2 extraction was employed to remove solvent, resulting in microporous membranes. At relatively short coarsening times, the coarsening rate of the cell size can be expressed as a power law in time with the exponent increasing with increasing quench depth; for deep quenches, the growth rate has an exponent of Vs in agreement with the classic theories for coarsening by Ostwald ripening or coalescence. At longer coarsening times, there was a crossover to a much faster growth rate, yielding an exponent of 1.0 independent of phase separation temperature, consistent with expectations for the hydrodynamic flow mechanism of coarsening suggested by Siggia. This is the first experimental confirmation of the evolution of the coarsening mechanism from one mechanism with a growth rate consistent with Ostwald ripening or coalescence to a second mechanism with a faster growth rate. Comparisons were also made to coarsening observed in nonisopycnic/low-viscosity polystyrene-cyclohexane systems where strong gravitational effects dominate the phase separation process at relatively short times and crossover effects cannot be observed.

Kinetic studies of thermally induced phase separation in polymer-diluent system

“…33 The domain size S was measured by optical microscopy, 25,33 light scattering, 24,26,28,29 and electron microscopy. 27,30,31,32 S was generally correlated to the time t with a scaling relation as follows:…”

Micro- and ultrafiltration film membranes from poly(ether ether ketone) (PEEK)

“…The decreasing influence of temperature at lower PEEK concentrations shown in Figure 3(A) suggests that the phase-separation mechanism may be more strongly influenced by hydrodynamic flow which is independent of phase separation temperature. 27 Another important parameter affecting PEEK film membrane performance is the film pick-up …”

The development of a high-throughput/ combinatorial workflow for the study of porous polymer networks

“…10 Several general methods for creating porous polymers have been described. These methods include conventional foaming techniques involving a nonreactive gas, 11 emulsion-templating, 12,13 thermally induced phase separation, 14 chemically induced phase separation (CIPS), 15 selective degradation of block copolymers, 16 and molecular imprinting. 17 Relative to the other methods for producing porous polymer materials, CIPS probably provides the greatest versatility with respect to the range of materials that can be generated.…”