Membrane technology represents one of the most cost-effective and environmentally friendly separation techniques developed to date. However, performance of membranes is often limited by a tradeoff between the two key performance indicators, i.e., permeability and selectivity. The goal of this project is to fabricate isoporous membranes, i.e., those with uniform pore size. These membranes provide the highest selectivity but are known to be extremely hard to fabricate due to high production cost of these highly ordered structures. Even through a broad pore size is almost inevitable during the industrial fabrication, it is possible to narrow the pore size distribution during surface modification, which was demonstrated here using initiated Chemical Vapor Deposition (iCVD). iCVD is chosen because it is conformal and applicable to any kind of substrate: 2D or 3D, planar or nano-/micro-structured, etc. We hypothesize that it is possible to fabricate isoporous membranes by iCVD, because the rate of coating growth is proportional to the diameter of a nano/micro-pore, thus narrowing the pore size distributions. To test this hypothesis, Anodic Aluminum Oxide (AAO) membranes with pore sizes ranging from 80 nm to 160 nm with depth of 5 and 10 μm were prepared (using anodization) and surface-modified using iCVD. Coatings of poly(4-aminostyrene) [PAS] were deposited at various values of fractional saturation pressure (Pm/Psat, which represents monomer concentration at the surface). PAS bears primary amine groups, allowing further improvements of membrane selectivity by secondary functionalization. The shrinking of pore size distribution was only observed for membranes with pore sizes larger than 100 nm due to the dominance of initiator-controlled regime. While for the membranes with the average pore size of 80 nm, broadening of pore size distribution was observed due to an effect we termed initiator amplification. That fundamental insight, along with the novel membranes with narrowed pore size distribution, could transform the current understanding of CVD-based membrane modification/fabrication and improve many crucial separation processes including wastewater treatment and purifications in the pharmaceutical and manufacturing industries.

Initiated chemical vapor deposition enables narrowing pore size distribution for enhanced selectivity

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.