Physics

Organic chemistry

Polymer chemistry

Asymmetry

Membrane

Glass transition

Phase transition

Engineering

Chemical physics

Composite material

Chemistry

Materials science

Phase (matter)

Quantum mechanics

Spinodal

Spinodal decomposition

Chemical engineering

Polymer

Biochemistry

Microstructure

Thermodynamics

ACS Macro Letters

We report the first simulations of nonsolvent-induced phase separation (NIPS) that predict membrane microstructures with graded asymmetric pore size distribution. In NIPS, a polymer solution film is immersed in a nonsolvent bath, enriching the film in nonsolvent, and leading to phase separation that forms a solid polymer-rich membrane matrix and polymer-poor membrane pores. We demonstrate how mass-transfer-induced spinodal decomposition, thermal fluctuations, and glass-transition dynamics-implemented with mobility contrast between the polymer-rich and polymer-poor phases-are essential to the formation of asymmetric membrane microstructures. Specifically, we show that the competition between the propagation of the phase-separation and glass-transition fronts determines the degree of pore-size asymmetry. We also explore the sensitivity of these microstructures to the initial film composition, and compare their formation in 2D and 3D.

Mechanisms of Asymmetric Membrane Formation in Nonsolvent-Induced Phase Separation