Capillary Introduction of Polydimethylsiloxane to Microchannels

Capillary microfluidics employs surface tension to manipulate liquids without requiring peripheral equipment, rendering it a convenient and robust approach for managing complex microfluidic circuits. However, most capillary microfluidics are applied only to aqueous solution introduction. This study introduces the capillary introduction of a mixture of black ink and a prepolymer liquid of polydimethylsiloxane (black PDMS liquid). The behavior of the black PDMS liquid during capillary introduction was investigated in straight, open-ended PDMS microchannels. The surface tension of the liquid was determined using the pendant drop method as 20.9±0.1 mN/m. The contact angle of the black PDMS liquid on the solidified PDMS plate surface was measured from liquid flow images, revealing a dependence on the liquid flow velocity. A simplified flow model was proposed, assuming that the viscosity of the black PDMS liquid depended on its velocity and the viscosity was dependent on the shear rate to the power of -0.682. Building on the fundamental aspects of capillary flow, the introduction of black PDMS liquid into the patterned microchannel was successfully realized. This fundamental knowledge of the capillary introduction of PDMS liquid is expected to facilitate advancements in microsystems with specific patterns and applications.