Many of the chemical substances we encounter every day were once part of a complex mixture. Isolating the individual components on an industrial scale often includes separation processes. For mixtures containing liquids, filtration is one of the most common separation methods. Achieving selective separation is challenging, and an ideal membrane requires nanoscale control of porosity. It should also be easily functionalized and prepared from commercially viable materials.
In their paper in Small, Suzana P. Nunes, Klaus-Viktor Peinemann, and co-workers from the King Abdullah University of Science and Technology in Saudi Arabia describe functionalized nanochannels formed by self-assembly of a hydrophobic block copolymer, poly(styrene-b-butadiene-b-styrene), synthesized by Nikolaos Hadjichristidis and his group.
Membranes were cast using solvents of different polarities, dried, and then swelled in different solvents. The membranes have a thin, ordered layer on the surface and a substructure with larger pores, making them especially suitable for filtration.
A thio-ene reaction allows the addition of hydrophilic thioglycolic acid to the membrane’s butadiene moieties, which is confirmed by X-ray photoemission spectroscopy. Casting thinner films onto a porous polyacrylonitrile support forms a well-ordered structure of self-assembled channels. Thioglycolic acid modification occurs evenly throughout the whole membrane, and the sulfur groups are located within the polybutadiene phase and are part of the interconnected nanochannel network.
Permeation is improved fivefold for water and twofold for methanol, for the modified over the unmodified membrane. As expected from carboxylic acid modification, 74% of methyl orange indicator and 100% of brilliant blue indicator are rejected with negligible membrane adsorption. In contrast, the membrane is highly permeable to neutral vitamin B12 and positively charged rhodamine B. Rejection of poly(ethylene glycol) indicates a mean pore size of 4.4 nm.
To find out about this versatile polymeric membrane, please visit the Small homepage.