Obtention of selective membranes for water and hydrophobic liquids by plasma enhanced chemical vapor deposition on porous substrates

In this work, the possibility of obtaining selective membranes for water and hydrophobic liquids by plasma enhanced chemical vapor deposition (PECVD) of hexamethyldisilazane (HMDS) or double layers of HMDS and n-hexane on porous substrates using a capacitive plasma reactor was investigated. The porous substrates used were paper filter, diatomite and polyester textiles. The films were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and contact angle measurements. The membranes obtained were characterized by the Cobb test. Their efficiency to separate hydrocarbon compounds from water was evaluated through filtration experiments and Karl–Fischer titration tests. The reagents used in the filtration experiments were: chloroform, n-hexane, n-heptane, ethyl ether, benzene and diesel. XPS analysis showed that Si, N, C and O were present at the surface of the film. C peak was dominant in the double layer film spectra. C–Hn, CH2, Si–H, Si–CH3, N–H, Si–CH2–Si, Si–N–Si and Si–C bonds were identified in both types of the films by ATR-FTIR. The relative intensities of the corresponding peaks in the two spectra were different. The XPS and FTIR results indicated that C was most likely present in a CHn form at the surface of double layer film. The average contact angles formed by drops of water on the film surface ranged from 135° to 155°. Water adsorption measured by Cobb test decreased from average values ranging from 300 to 9000 g m−2 (for nonmodified surfaces) to values ranging from 0 to 20 g m−2 (for treated surfaces). The Karl–Fischer titration indicated that between 90 and 1000 ppm (depending on the reagent used) of water remained in the hydrocarbon compound after filtration.