| Abstract [eng] |
It is technologically important to create devices with the smallest possible volume, both for practical everyday use and for scientific research. Smaller geometry of devices esults in not only convenience but also a reduction of production price. Microfluidic systems are no exception. Controlling fluids in small capillaries is important in technologies such as lab-on-a-chip or soft robotics, so efforts are being made to find the most efficient and convenient way to control them, while eliminating moving parts that might fail or wear out in systems. This can be achieved by using electromagnetic forces with electrolytic solutions or liquid metals. Our work investigates the theoretical possibilities of motion actuation of liquid metal - mercury and liquid metal alloy - galinstane (68.5 % gallium, 21.5 % indium and 10.0 % tin), using Lorentz force and practical realization of a linear capillary motor . Experimental tests performed with a drop of mercury on copper and iron rails by applying a constant, theoretically estimated, electric current revealed the most important parameters of the system that stop the movement of the drop. As a result of ohmic thermal losses, there is a limitation of the magnitude of the electric current. Thus, to avoid the possibility of system failure due to exceeding the critical temperatures of the materials, which in the system is the boiling point of mercury at 357 °C, a pulsed electric current was used. By applying such electric current flow action, the movement of the droplet at a speed of 0.2-0.26 mm/s was achieved, but, as shown in the calculations, its speed is greatly influenced by even small irregularities in the channel, the angle of inclination of the channel, as well as friction against the channel walls. In practical tests, the movement of the droplet was achieved at much lower values of the electric current strength than the obtained theoretical values. The mismatch between theoretical and physical tests could have been influenced by inaccurately determined coefficients of friction of mercury with different solid materials, or a much more complicated mechanism of the appearance and variation of the frictional forces than foreseen in the assumptions. However, due to the observed electrical contact phenomena and the results of the calculations, it is believed that surface treatment, gas composition, and material compatibility and purity become the most important factor in ensuring controlled and favorable conditions for drop motion. |
