Abstract

Modification of Polymer Based Microfluidic Chip via Plasma and UV Induced Surface Grafting Techniques

Tao Zhang, Scientist, Singapore Institute Of Manufacturing Technology

Recently, polymer-based microfluidic devices become more and more popular because of their outstanding properties such as low cost and easily generated channels. However, most polymeric materials have pristine surfaces with low surface energies, and are hydrophobic rather than hydrophilic, which leads to problems such as high flow resistance and even bubbles in thin channels, high operation pressure and high device complexity. Our group has developed superhydrophilic and UV responsive polymer-based microfluidic chips for reduction of flow resistance, bubble elimination and control of fluid flow without increasing device complexity. In our approach, polymer substrates, including cyclic olefin copolymer (COC), polycarbonate (PC) and poly methyl methacrylate (PMMA), are first activated by oxygen plasma treatment and then a porous grafting layer is generated on the polymer substrate with designed surface properties by UV initiation. For example, superhydrophilic surface (water contact angle less than 5 degrees) can be achieved by choosing certain monomer mixture. By choosing another UV-sensitive monomer mixture, the surface water contact angles of treated substrates can switch reversibly between superhydrophilicity (0 degrees) and hydrophobicity (104 degrees), triggered by different wavelength of UV illumination. The treatment approach can be carried out at room temperature in atmosphere within 10 minutes, which makes our approach easy to scale-up at relatively low cost. Chemical bonds form between the coated layer and the substrates, which generates very high adhesive strength between the two layers. Last but not least, the transparency of the treated substrate is not affected compared with pristine substrate, which is important for many microfluidic applications.