Significant Enhancement of the hydrophilicity and ageing behavior of COC-based microfluidic devices by graphene oxide thin layer deposition surface modification

Several materials are used in the fabrication of microfluidic devices. Recently, the fabrication of these devices has relied on polymer-based material such as cyclic olefin copolymer (COC) [1-3]. This attention is related to its characteristics that make fabrication faster, easier, and cheaper through the use of soft lithography in comparison to other materials such as silicon and glass devices [1, 2]. Furthermore, COC has other desirable features such as being biologically inert, optically transparent, non-flammable, low-cost materials and non-toxic[2]. Therefore, it becomes an alternative material for different micro-manufacturing models. However, COC has some limitations, which limit its full application. Unlike silicon or glass substrates, COC is hydrophobic, which makes it not suitable for representing hydrophilic microchannels[1-3]. The surface of the microchannel can be modified to be hydrophilic to ensure that the channel walls are completely wetted so that it can be used for selective applications. Graphene oxide is one of the most interesting materials in research today due to its superior properties. In this study, different concentrations of graphene oxide (GO) were used to improve the hydrophilicity of the COC surface, thereby enhancing the wettability of its patterned microchannels. Argon-oxygen plasma was used to improve the adhesion between GO and COC surface. Plasma power of 30W with exposure times from 5min to 2hrs were carried out. A comprehensive study on the influence of plasma exposure time, GO and ageing on the surface properties of COC surface was carried out using different characterization techniques including Scan electron microscopy (SEM), Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). The hydrophilicity of COC was evaluated by measuring the water contact angle of the COC surface with and without GO deposition. As the GO concentration increased, a decrease in contact angle was observed, which confirmed the ability to enhance the wettability of the COC surface. The results also show that, compared with COC treated with plasma alone, COC coated with different concentrations of GO can effectively reduce the aging effect.