Applied Surface Science, Volume 268, 1 March 2013, Pages 450-457.
Lukas Baumann, Dirk Hegemann, Damien de Courten, Martin Wolf, René M. Rossi, Wolfgang P. Meier, Lukas J. Scherer
Empa, Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St.Gallen, Switzerland &
University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland &
Division of Neonatology, University Hospital Zurich, Frauenklinikstrasse 10, 8091 Zurich, Switzerland &
ETH Zurich, Ramistrasse 101, 8092 Zurich, Switzerland
To tune the permeability resistance of porous polycarbonate (PC) membranes for caffeine, their surfaces were plasma modified with different monomers in a grafting from process. These coatings provided characteristic surface hydrophilicities. It was found that membranes with more hydrophilic surfaces have lower resistances to let caffeine pass through than membranes with hydrophobic surfaces. Additionally, it was possible to post-modify a poly(2-aminoethyl methacrylate) (AEMA) coated PC membrane with octanoic acid (Oct) under mild conditions. This post modification allowed transforming a slightly hydrophilic PC-AEMA membrane with a moderate permeability resistance into a hydrophobic PC-AEMA-Oct membrane with a high permeability resistance. Overall, it was possible to tune the PC membrane resistance for caffeine in a range from 5100 up to 15,100 s/cm.
The tuning of the membrane surface is important to adjust the membrane characteristics to the desired application. We propose in this paper a straightforward method how to change the surface tension of the membrane without changing the bulk characteristics of the membrane. Since the surface hydrophilicity has a direct influence to the permeability resistance of the membrane towards aqueous solutions, the permeability rate can be tuned using the proposed plasma-induced process. The power of this work was demonstrated in another work showing that the membrane resistivity can be triggered by light (ACS Appl. Mater. Interfaces, 2013, 5 (13), pp 5894–5897).