Block Copolymer-Directed Self-Assembly and Non-Solvent-Induced Phase Separation (SNIPS) Derived Porous Functional Materials for Advanced Separations and Energy

Membrane materials with an asymmetric structure can allow for high flux and pore accessibility, but also large surface area. These characteristics could potentially improve device performance in the areas of separations, catalysis, and energy conversion and storage devices. However, creating asymmetric structures from a bottom-up approach remains a challenge due to the complexity of understanding and controlling the underlying non-equilibrium phenomena.

One method for creating asymmetric structures is by pushing equilibrium block copolymer self-assembly to kinetic non-equilibrium. This will provide a versatile platform for creating materials with highly tunable morphologies and length scales on the order of tens of nanometers. At the same time, it will allow for a pathway to make porous materials with high pore accessibility, high specific surface area, and periodic ordering.

One example of non-equilibrium block copolymer-directed assembly is the self-assembly and non-solvent induced phase separation (SNIPS) process. In the SNIPS process, asymmetric porous polymer membranes can be made in which a concentration gradient and subsequent non-solvent induced “freezing in” of the structure creates a mesoporous surface layer atop a macroporous support structure. This structure provides an increased flux, yet retains the high separation resolution due to the block copolymer-derived pore uniformity in the top surface layer.

This technique has been used to create not only various polymeric materials, but recently also a variety of other functional materials. For example, the co-assembly of block copolymer and organic additive has allowed for the creation of graded, hierarchically porous all-organic hybrid materials. Subsequent heat-treatment at 1100C under inert gas produces amorphous hierarchically macro- and mesoporous carbon materials with graded porosity from the top surface layer to the support structure. Both materials characterization via such techniques as small-angle x-ray scattering as well as applications will be discussed.