Transparent and airtight silica nano- and microchannels with uniform tubular cross-section

Experimental results on a template-assisted technique to fabricate uniform nano- and microchannels are presented. Different template materials, polystyrene and poly(vinyl alcohol) electrospun and spider silk fibres were coated with silica. After calcination mechanically stable and transparent channels with uniform tubular diameter were obtained. The diameters ranged between 150 nm and 4 μm, depending on the size of the fibre template. By coating crossed fibres we prepared connected channel junctions that were solvent- and airtight. The channels and junctions remained tight even when applying a pressure above 3 bar as verified by laser scanning confocal microscopy. The flow of liquids in the channels was monitored and described by the Lucas–Washburn equation. We varied the viscosities and surface tensions of the liquids and measured the filling velocities over a distance of several millimeters as well as very close to the channel entrance. The late stage of capillary filling can be described well by the Lucas–Washburn equation. The early stage was slower than predicted. We attribute the delayed filling to the velocity dependence of the contact angle and modeled the filling behaviour by dynamic wetting theories.