(721i) In vitro and silico Characterization of Grafted Hydrophobic Brush Membranes

Authors: 
Sorci, M., Rensselaer Polytechnic Institute
Keating, J. J., Rensselaer Polytechnic Institute
Setaro, A., Rensselaer Polytechnic Institute
Underhill, P. T., Rensselaer Polytechnic Institute
Belfort, G., Rensselaer Polytechnic Institute
Tethered polymers have been implemented in several engineering/biomedical applications to stabilize colloids, to reduce friction between surfaces, to design novel fluidic devices, to fractionate proteins, etc. The Belfort’s lab is currently working on a new class of selective brush membranes, where a selective layer comprising “hydrophobic brushes” is grafted onto a non-selective permeable membrane.

The membranes were synthesized by graft-induced polymerization of hydrophobic vinyl monomers onto poly(ether sulfone) nanofiltration support membranes. The novel grafting method is based on the combination of atmospheric pressure plasma treatment and Activators Regenerated by Electron Transfer (ARGET) with Atom Transfer Radical Polymerization (ATRP). Several hydrophobic vinyl monomers were tested to investigate the effect of chain length, the presence of linear versus branched chains, etc. Membranes were characterized by ATR-FTIR (chemistry) and AFM (morphology, roughness, hydrophobicity). To gain a better understanding of the selective layer properties, the hydrophobic brush layer was grafted onto silica surfaces, following the same ARGET-ATRP method. Surfaces were characterized by a multitude of additional techniques: XPS (atomic composition and heterogeneity), Ellipsometry, AFM and DLS (thickness), QCM-D (polymerization reaction and layer viscoelasticity), ToF-SIMS (brush layer density). Complementary atomistic simulations have been used to quantify how polymers at different grafting densities used in the brush interact with the solvent (aqueous/organic mixture).

The novelty here is the use of hydrophobic brush-like structures as a selective skin or dense layer attached to a non-selective support membrane. However, if this new class of hydrophobic brush membranes is to reach its full potential, it is critical that we determine how it selects for one species (e.g. isobutanol) over another (e.g. water). Thus, we need to know how brush microstructural properties, chemistry and solution conditions influence the properties and eventually the filtration performance of the selective brush layer. This knowledge will allow structure-by-design for the first time.