Abstract: Filling of liquid samples is realized in a microfluidic device with applications including analytical systems, biomedical devices, and systems for fundamental research. The filling of a disk-shaped polydimethylsiloxane (PDMS) microchamber by liquid is analyzed with reference to microstructures with inlets and outlets. The microstructures are fabricated using a PDMS molding process with an SU-8 mold. During the filling, the motion of the gas-liquid interface is determined by the competition among inertia, adhesion, and surface tension. A single ramp model with velocity-dependent contact angles is implemented for the accurate calculation of surface tension forces in a three-dimensional volume-of-fluid based model. The effects of the parameters of this functional form are investigated. The influences of non-dimensional parameters, such as the Reynolds number and the Weber number, both determined by the inlet velocity, on the flow characteristics are also examined. An oxygen-plasma-treated PDMS substrate is utilized, and the microstructure is modified to be hydrophilic. Flow experiments are conducted into both hydrophilic and hydrophobic PDMS microstructures. Under a hydrophobic wall condition, numerical simulations with imposed boundary conditions of static and dynamic contact angles can successfully predict the moving of the meniscus compared with experimental measurements. However, for a hydrophilic wall, accurate agreement between numerical and experimental results is obvious as the dynamic contact angles were implemented.
Keywords: microfluidics; dynamic contact angle; gas-liquid interface; surface tension; filling process
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Chen, J.J.; Liao, S.C.; Liu, M.H.; Lin, J.D.; Sheu, T.S.; Miao, M., Jr. Surface Tension Flows inside Surfactant-Added Poly(dimethylsiloxane) Microstructures with Velocity-Dependent Contact Angles. Micromachines 2014, 5, 116-138.
Chen JJ, Liao SC, Liu MH, Lin JD, Sheu TS, Miao M, Jr. Surface Tension Flows inside Surfactant-Added Poly(dimethylsiloxane) Microstructures with Velocity-Dependent Contact Angles. Micromachines. 2014; 5(2):116-138.
Chen, Jyh J.; Liao, Shih C.; Liu, Mao H.; Lin, Jenn D.; Sheu, Tsung S.; Miao, Ming, Jr. 2014. "Surface Tension Flows inside Surfactant-Added Poly(dimethylsiloxane) Microstructures with Velocity-Dependent Contact Angles." Micromachines 5, no. 2: 116-138.