Membranes for Organic Solvent Nanofiltration Based on Preassembled Nanoparticles

A new class of organic solvent nanofiltration (OSN) membranes has been fabricated by assembling nanosized polymer particles with methacrylate moieties onto the surface of cross-linked polyimide ultrafiltration support membranes. Multiple layers of these nanoparticles create a separation film functionally similar to the top layer of an asymmetric OSN membrane. Nanoscale interstitial spaces formed between the particles serve as permeation channels. In principle, manipulating the size of the nanoparticles can be used to control the dimensions of the interstitial spaces through which permeation occurs. Two different sizes of nanoparticles, 120 nm and 300 nm, were used. As expected, membrane separation performance changed with the size of nanoparticles employed because of the changes in interstitial dimensions. Cross-linked polyimide ultrafiltration membranes prepared by phase inversion were coated with successive layers of nanoparticles by spin coating. After coating the nanoparticles were cross-linked by photo initiated free radical polymerization using ultraviolet light (365 nm wavelength). In addition to the size of the nanoparticles, the separation performance was also manipulated by changing the thickness of the nanoparticle layer. Membranes were characterized using scanning electron microscopy. The nanofiltration performance of these membranes was evaluated in solvents such as acetone and toluene. The molecular weight cutoff (MWCO) of the membranes was from 200 to 1,000 g.mol(-1) depending upon the nanoparticle diameter and thickness of the nanoparticle layer. Thus membranes with graded nanoscale porosities were successfully fabricated from interconnected nanoparticles providing control over membrane permeation performance.