Use of HMDS/hexane double layers for obtaining low cost selective membrane

Abstract

Sheets of paper commonly used for filtration were coated with double layers of HMDS (hexamethyl disilazane) and n-hexane using a low pressure plasma reactor. The organic compounds formed a thin film with very good adhesion to the substrate; the process produced water-repellent surfaces, with apparent water-contact angles higher than 100° and water adsorption around 15 g/m 2 . The paper porosity was not altered, indicating that the depositions were conformal. Preliminary tests to investigate the possibility of using the modified paper as a selective membrane for separation of water and organic-polar and non-polar compounds of different chain length were conducted. The non-polar compounds tested were: n-hexane, cyclohexane, heptane, dodecane, benzene and poly(dimethylsiloxane). The polar organic liquids were ethanol, 2-propanol, carbon tetrachloride, acetophenone and phenol. Three types of behaviour were observed: (a) in the case of water/non-polar mixture, the non-polar compound passed through the modified paper whereas water did not; (b) in the case of acetophenone, phenol and carbon tetrachloride, neither the water nor the polar compound percolated through the modified paper; (c) in the case of water/2-propanol or ethanol solution, it was observed that a minimum concentration of alcohol was necessary in order for both the alcohol and water to percolate through the paper; in this case the alcohol percolates first, followed by water.