Abstract
Here we present a new methodology for chemical polishing of microchannels in polycarbonate (PC). Tuning the time of exposition and the concentration of ammonia, the roughness arising from the micromachining process can be significantly reduced or completely removed while preserving the structure of microchannels. Besides smoothing out the surface, our method modifies the wettability of the surface, rendering it hydrophobic. The method increases the optical transparency of microchannels and eliminates undesired effects in two-phase microfluidic systems, including wetting by aqueous solutions and cross-contamination between aqueous droplets that could otherwise shed satellites via pinning.
Highlights
Progress in microfluidics has been directly reliant on the access to facile methods for microfabrication
In this paper we describe a simple method that enables polishing of the surfaces of polycarbonate microchannels altered after assembly of the device
We present the comparison of the known in the literature methods of polycarbonate polishing and hydrophobization with the proposed methodology (Table 1)
Summary
Progress in microfluidics has been directly reliant on the access to facile methods for microfabrication. Parts of originally flat, and typically smooth material are removed mechanically with a spinning milling bit. The roughness of PC microchannels depends on the size of the used cutter and can be tamed under 1 μm for cutters of diameter between 0.1 and 3 mm [2]. Such roughness is typically undesired, because it decreases the optical transparency of the walls of the microchannels, may cause increased slip at the walls, as compared to the smooth microchannels [3]. The most important effect is in the rough edges causing pinning of the liquid-liquid interface of a passing droplet, making it more difficult to control the flow and to avoid the wetting of the walls by the droplet liquid, and potentially leading to cross-contamination between droplets [4]
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