No abstract

In the present study, simple models were proposed to predict the capillary-driven flow length in a surfactantadded poly(dimethylsiloxane) (PDMS) rectangular microchannel. Owing to the hydrophobic nature of PDMS, it is difficult to transport water in a conventional PDMS microchannel by means of the capillary force alone. To overcome this problem, microchannels with a hydrophilic surface were fabricated using surfactant-added PDMS. By measuring the contact angle change on the surfactant-added PDMS surface, the behavior was investigated to establish a simple model. In order to predict the filling length induced by the capillary force, the Washburn equation was modified in the present study. From the investigation, it was found that the initial rate-of-change of the contact angle affected the filling length. Simple models were developed for three representative cases, and these can be useful tools in designing microfluidic manufacturing techniques including MIcroMolding In Capillaries (MIMIC).

In the present study, a hot embossing process employing a hydrophilic polydimethylsiloxane (PDMS) mold was investigated considering the effect of the surface wettability of the mold on the replication quality of microfeatures. To turn the hydrophobicity of native PDMS into hydrophilicity, Silwet L-77 was employed as a surfactant in preparing a mold for a microcavity. Hot embossing experiments imprinting the microfeature onto thermoplastic sheets were performed with both a surfactant-modified mold and a native PDMS mold. A design of the experiment approach based on an orthogonal array was employed to investigate the effects of the relevant factors, including wettability and processing parameters. The characteristic dimensions of the hot-embossed microfeature were measured to evaluate the replication quality. The increased wettability of the PDMS mold surface was found to efficiently improve the replication quality of the microfeature. The major processing parameters of the hot embossing process, such as the embossing temperature, pressure, and time, were also investigated.