This paper reports a method for spatially directed, self-assembled pore formation in poly-dimethylsiloxane (PDMS) that results in through-membrane pores only at desired locations. This method is based on bubble generation in uncured PDMS and subsequent bubble motion towards a hot region in a microfabricated chip containing a heater device due to thermocapillary effect. Pore formation in straight-line and semi-circular shapes is demonstrated. Coupled physics behind the pore formation and alignment process is described. Results show that the mechanism of pore formation can be controlled by changing the microheater temperature.

Poly-dimethylsiloxane (PDMS) is a well-known soft polymer with applications in a wide variety of research fields. PDMS is a particularly attractive material for miniaturized bioanalytical systems because of its biocompatibility, gas permeability, chemical inertness and the ability to reproduce miniature features such as microchannels in PDMS. This paper describes a technique to obtain through-membrane pores in thin PDMS membranes. This is based on thermocapillary effect in a MEMS-based microheater device made on a glass substrate. Uncured PDMS is poured on a microheater device that has been coated with a hydrophilic substrate such as poly-ethylene oxide (PEO). Upon heating, PEO evaporates and form gas bubbles in PDMS. The gas bubbles are attracted towards the hot region of the microheater device. The bubbles eventually self-assemble along the hottest isotherm, which in this case is the microheater line. In this manner, self-assembled pores in the desired pattern are obtained. Experiments conducted at different temperatures and PDMS thicknesses throw light on the physical phenomena behind this process and demonstrate the trade-off between PDMS curing rate and bubble escape rate. Results presented in this work are expected to aid in the design of novel PDMS-based membranes for filtration, separation and concentration.