Hydrophilic amorphous crosslinked membranes with subnanometer pores prepared by plasma-enhanced chemical vapor deposition and their shape-selective alcohol permeation

Abstract

High-density crosslinked polymer membranes several tens of nanometers thick were prepared by chemical vapor deposition (CVD) of propylamine (PA). Analysis by various methods showed that the densely crosslinked PA-CVD membranes had a composition of C3.0H4.7N0.8O0.4, and contained amine, imine, vinyl, and carbonyl functional groups. Positron annihilation lifetime spectroscopy and alcohol-retention studies showed that the crosslinked membranes had pore sizes of 0.3–0.7 nm. Their porosity was about 10%, as estimated from water-absorption experiments. By appropriate choice deposition conditions, the average pore diameter could be selected, and the porosity could be tuned in the range 1–18%. A membrane with 0.56 nm pores showed a significant difference in the retention factors of C3 and C4 alcohols, for example, showing a 77% retention of tert-butanol, three times that of n-butanol. The thickness of PA-CVD membranes could be reduced to 10 nm, and the membrane showed a high retention performance for divalent ions, a resistance to pressures of more than 40 bars, and a water flux of up to 170 L m−2 h−1. This comprehensive investigation of the effects of the CVD parameters will permit tuning of the thickness, pore size, porosity, and density of the hydrophilic crosslinked membranes.