Surface tension gradients induce Marangoni ﬂow, which can be exploited for ﬂuid transport. At the micron scale, these surface-driven ﬂows can be quite signiﬁcant. In this project, we use surface tension gradients to drive bulk ﬂuid ﬂows by introducing ﬂuid-ﬂuid interfaces along the walls of microﬂuidic channels. The gradients are induced through thermal energy, exploiting the temperature dependence of a ﬂuid-ﬂuid interface to generate thermocapillary ﬂow. We designed a biocompatible thermocapillary microchannel capable of being powered by solar irradiation. We demonstrated the ability of the system to replace bulky peripherals, like traditional syringe pumps, on a diagnostic microﬂuidic device that captures and detects leukocyte subpopulations within blood. In short, thermocapillary-driven microﬂuidic devices could be implemented for clinical assays at the point of care without the use of electricity.
The image above shows the design concept for thermocapillary-driven microﬂuidic channels.
(A) Schematic of the entire microﬂuidic channel with air pockets trapped along the side walls. The dashed rectangle represents the region depicted in (B).
(B) Microﬂuidic channel ﬁlled with water and air trapped all along the wall. The dashed rectangle represents the region depicted in the schematic in (C).
(C) Schematic of the inside of a microﬂuidic channel with water (blue) and air pockets (cyan). The dimensions of the cavities and channel are labeled.
(D) Schematic of the experimental setup with heating and cooling Q via thermoelectric (Peltier) modules. Scale bars represent (A) 10 mm, (B) 300 µm, and (C) 200 µm.