attempts have been made to modify PDMS in different ways. These methods include graft polymerization, chemical modification of poly-
mers, zeolite doping of polymers, and physical (or chemical) modification of formed membranes. For example, Chang et al. prepared composite membranes of silicone/PVDF by curing a copolymer of polysiloxane and phosphate ester. The porous PVDF substrate was previously plasma-grafted with a thin layer of silicone-compatible material. This multilayer membrane afforded high PV performance (separation factor of 31) and a permeation rate of 0.9 kg/(m2 h) at a 10 wt % ethanol feed concentration at room temperature.7 Field et al. modified cross- linked PDMS membranes by sequential introduction of two different side arm functional groups, −(CH2)3OC2H5 and −(CH2)3NMe2. Membranes containing 20% ethyl ether (in AEE membranes) and 10% dimethylamino (in AMI mem- branes) groups produced a high cresol flux (30% higher than that achievable using either AEE or AMI modified membranes) and a high separation factor (α = 50.4).8 Kashiwagi et al. prepared highly permselective membranes by surface treatment of thin poly(dimethylsiloxane) membranes with silane com- pounds containing octadecyl groups. An ethanol permselectiv- ity of 18.0 and a flux of 0.015 kg/(cm2 h) were obtained with these membranes.9 Clearly, modification of the PDMS membrane is significant for the improvement of PV perform- ance. Considering that the surface energy of CF3 (6 mJ/m2) is lower than that of other functional groups, the behavior of fluorosilane molecules may tailor the wetting properties of these membranes.
Received: March 16, 2013