Superhydrophobic oleophobic PDMS-silica nanocomposite coating

In general, most of the artificial superhydrophobic surfaces are oleophilic. These surfaces can be rendered oil repellent by introducing low-surface-energy fluoroalkyl groups on the surface. In the present study, superhydrophobic polydimethylsiloxane (PDMS)-silica nanocomposite coating was converted from oleophilic to oleophobic state by applying fluoroalkylsilane (FAS) layers as topcoat. The effect of fluoroalkyl groups on the wettability and surface morphology was studied. It was found that there was a difference in the wettability behavior obtained by hydrolyzed and unhydrolyzed FAS. The oil contact angle (oil CA) was higher after the treatment of PDMS-silica coating with hydrolyzed FAS than that obtained with unhydrolyzed FAS. However, water contact angle (water CA) decreased as the number of passes of hydrolyzed FAS increased, whereas water CA was not affected by applying same number of passes of unhydrolyzed FAS. The surface morphology was characterized by field emission scanning electron microscopy and 3D profilometry. Surface chemical composition was determined by energy dispersive X-ray spectrometery (EDX) and X-ray photoelectron spectroscopy (XPS). EDX and XPS analysis indicated significantly higher fluorine content on the surface for coating with hydrolyzed FAS. The superhydrophobic phenomenon of the FAS-modified surface was analyzed with Cassie and Wenzel mechanisms.