Permeability of small molecules through vapor deposited polymer membranes

Free-standing, thin films of poly(2-hydroxyethyl methacrylate), p(HEMA), membranes deposited by initiated chemical vapor deposition (iCVD) technique are presented. Systematic studies of permeation of model dye molecules through these free-standing thin films are performed and effects of process parameters on the permeability and selectivity of the membranes synthesized using an all-dry process are demonstrated for the first time. Permeation studies of model dye molecules show that the diffusion of large dye molecules through the membrane is faster than the smaller dye molecules, due to loss of conformation entropy. Mesh sizes of the membranes are controlled by tuning the crosslink ratio of the polymer and diffusion coefficients of alizarin yellow model dye molecules are obtained as 0.44 x 10(-7) and 1.71 x 10(-7) cm(2)/s for high and low crosslinked membranes, respectively. Selectivity of the membranes is also demonstrated by the permeation studies of dyes with similar sizes but different polarities and the permeability coefficient of the hydrophilic dye is observed to be 30 times larger than that of the hydrophobic dye of similar size. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42453.