Authors: C. Narayanan and D. Lakehal
Affilation: ASCOMP, Switzerland
Pages: 493 - 496
Keywords: contact angle, filling, level sets, multiphase
We present a new dynamic contact angle model applied to the filling<br>problem in microfluidic devices. The level-set method is used for<br>interface capture. Several attempts have been made in the past decades to model contact--line dynamics within the continuum fluid dynamics framework. Generally, ad--hoc models are used where contact angles are prescribed based on front velocities and criteria for advancing and receding scenarios. The model presented in this study is based on the molecular dynamics description of the contact--line, such that it does not require the specification of ad--hoc contact angles. Figure 1 presents a simulation of return to equilibrium of a wetting liquid (initial contact angle: $150^o$,<br>equilibrium $60^o$.<br>Bubble entrapment is an common problem in the design of microfluidic devices. Occurrence of these bubbles can be avoided through careful design of the chip geometry, control of the filling process, and selection of material properties (hydrophobic or hydrophilic). Simulation of casting of prepolymers on to a master to create stamps for microcontact processing is shown in Fig. 1. The simulation shows that the properties of the polymer and flow rates have to adjusted to avoid bubble entrapment. The paper will present further applications of the level-set, dynamic contact model to filling problems in micro--devices.