Surface wettability and stability of chemically modified silicon, glass and polymeric surfaces via room temperature chemical vapor deposition

Abstract

Wettability of surfaces used in microdevices, either on the fabrication of fluidic passages or integration of sensing and actuating elements can impact the flow. The easiness of fabrication may dictate the materials and processes to use, that can subsequently have their surface wettability spatially controlled. The work reports surface wettability modification (SWM) by room temperature chemical vapor deposition (CVD) with HMDS (hexamethyldisilazane) and FDTS (perfluorodecyltrichlorosilane) on flat surfaces of silicon (Si), glass, SU-8 photoresist and PDMS (polydimethylsiloxane). The effect of SWM has been evaluated by the measurement of contact angles (CA) of 6 μL droplets of deionized water and phosphate-buffered saline buffer (PBS). Time of surface exposure and evolution of CA after modification have been investigated for each pair surface/fluid. The time of surface activation with HMDS or FDTS and the chemical affinity of these to the surface are seen to govern the efficiency of surface coverage and consequently the efficiency and stability of SWM. For both HMSD and FDTS SWM, hydrophilic surfaces (glass and Si) became more hydrophobic (CA rising from 20° up to ˜70°) while SU-8 hydrophobic surfaces became more hydrophilic (CA decreasing from 120° down to ˜100°) upon 30 min activation. PDMS surfaces shows no relevant SWM after activation with HMDS nor with FDTS. SWM of Si surfaces has remained irreversible following CVD exposure (HMDS and FDTS) for at least 65 h.