Thermocapillary effect of a liquid plug in transient temperature fields.

Abstract

In this paper we present the theoretical and experimental results of thermocapillary effects of liquid plugs in a long capillary, which is exposed to a transient temperature gradient. A one-dimensional analytical model is formulated for the dynamic behavior of a liquid droplet, which is driven by the thermocapillary effect under a transient temperature field. The thermocapillary actuation concept can be used for liquid transport in microfluidics. In microfluidic applications, the temperature field is often induced by the activation of integrated heaters. The generated temperature field and temperature gradient drive a liquid droplet according to the temperature-dependent surface tension. In the initial stage, the transient temperature gradient spreads in the capillary wall much slower than the droplet itself, and thus leads to an interesting behavior of droplet motion as described in this paper. Experiments were carried out for liquid droplets with different viscosities in long glass capillaries with different radii. The capillaries are exposed to a resistive heater at one of its ends. The analytically predicted behavior of the droplet motion agrees qualitatively well with the measurement.