RESUMEN
In this paper, we explore a concept and present the first experimental evidence to show that it is possible to form a stable liquid film and create lifting force at the interface via thermal gradient to minimize interfacial rubbing of surfaces and the associated wear. The approach is based on manipulating the flow behavior via thermocapillary, which describes how a liquid can be made to flow from warm to cold regions purely by inducing a thermal gradient. We show that liquid bridges between two parallel plates can be manipulated and stabilized under a combined effect of the thermocapillary flow and the Couette flow, which describes the motion of a viscous fluid between two parallel plates in a relative sliding motion. The equilibrium stage is confirmed under different experimental conditions of a thermal gradient, interfacial gap, liquid viscosity, and liquid bridge volume. A strategy is proposed to control liquid motion and create lifting force between two plates. A theoretical model is also presented to illustrate the principle of the equilibrium stage. Creating lifting forces at the interface offers a new thermo-hydrodynamic tool for manipulating liquids behavior. This approach has the potential for controlling liquid motion in mechanical components and nature.
RESUMEN
Selective laser sintering of metal nanoparticle ink is a low-temperature and non-vacuum technique developed for the fabrication of patterned metal layer on arbitrary substrates, but its application to a metal layer composed of large metal area with small voids is very much limited due to the increase in scanning time proportional to the metal pattern density. For the facile manufacturing of such metal layer, we introduce micropatterning of metal nanoparticle ink based on laser-induced thermocapillary flow as a complementary process to the previous selective laser sintering process for metal nanoparticle ink. By harnessing the shear flow of the solvent at large temperature gradient, the metal nanoparticles are selectively pushed away from the scanning path to create metal nanoparticle free trenches. These trenches are confirmed to be stable even after the complete process owing to the presence of the accompanying ridges as well as the bump created along the scanning path. As a representative example of a metal layer with large metal area and small voids, dark-field photomask with Alphabetic letters are firstly created by the proposed method and it is then demonstrated that the corresponding letters can be successfully reproduced on the screen by an achromatic lens.
RESUMEN
We consider the effect of a partially contaminated interface on the steady thermocapillary flow developed in a two-dimensional slot of finite extent. The contamination is due to the presence of an insoluble surfactant which is carried away by the flow and forms a region of stagnant surface. This problem, first studied in the classical theoretical paper by Carpenter and Homsy (1985, J. Fluid Mech. 155, 429), is revisited thanks to new experimental data. We show that there is a qualitative agreement between above theory and our experiments: two different regions simultaneously coexist on the surface, one of which is free from surfactant and subject to vigorous Marangoni flow, while the other is stagnant and subject to creeping flow with the surface velocity smaller about two orders of magnitude. We found, however, significant disagreement between theory predictions for the extent of a stagnant surface region and newly obtained experimental data. In this paper, we provide an explanation for this discrepancy demonstrating that the surface temperature distribution is far from suggested earlier. Another effect, not previously taken into account, is a possible phase transition experienced by the surfactant. We obtain a correct analytic solution for the position of the edge of the stagnation zone and compare it with the experimental data.
RESUMEN
Accurate control and precise positioning of opto-thermocapillary flow-addressed bubble microrobots are necessary for micromanipulation. In addition, micromanipulation using the simultaneous actuation of multiple microrobots requires a robust control system to enable independent motion. This paper demonstrates a hybrid closed-loop vision-assisted control system capable of actuating multiple microrobots simultaneously and positioning them at precise locations relative to micro-objects under manipulation. A vision-assisted grasp-planning application was developed and used to calculate the necessary trajectories of the microrobots to form cages around micro-objects. The location of the microrobots and the micro-objects was detected at the caging locations using a particle-tracking application that used image feedback for precise positioning. The closed-loop image feedback information enabled the position update of the microrobots, allowing them to precisely follow the trajectory and caging locations calculated by the grasp-planning application. Four microrobots were assigned to cage a star-shaped micro-object using the closed-loop control system. Once caged, the micro-object was transported to a location within the workspace and uncaged, demonstrating the micromanipulation task. This microrobotic system is well suited for the micromanipulation of single cells.
RESUMEN
HYPOTHESIS: Reducing particle contaminations on solid and delicate surfaces is of great importance in a number of industries. A new non-destructive method is proposed, which is based on the laser-induced thermocapillary effect for the removal of micron size particles from surfaces. The cleaning mechanism is related to the surface-tension-driven flows produced by the laser heating of thin layer of a cleaning liquid deposited onto a surface contaminated with particles. EXPERIMENTS: Focusing the laser irradiation into the line laser beam allowed using this method for a large-scale cleaning of surfaces. Hexadecane was used as a cleaning liquid to remove micron-sized polyethylene, Teflon, talc and Al2O3 particles from surfaces of welding glass, carbolite and soft magnetic disc using the line beam of the IR laser. FINDINGS: A good cleaning efficiency was achieved for cases of polyethylene and Teflon particles on both the complete wettable welding glass and the low-wettable soft magnetic disc, while in case of oleophilic talc and Al2O3 particles the effectiveness of the cleaning method was lower on all three substrates investigated. The thermal influence of the laser irradiation on substrates used was measured with infrared camera. It was shown that temperature in the irradiated area during the long-time heating increases insignificantly and cannot cause any damage of the substrate.
RESUMEN
Opto-thermocapillary flow-addressed bubble (OFB) microrobots are a potential tool for the efficient transportation of micro-objects. This microrobot system uses light patterns to generate thermal gradients within a liquid medium, creating thermocapillary forces that actuate the bubble microrobots. An interactive control system that includes scanning mirrors and a touchscreen interface was developed to address up to ten OFB microrobots. Using this system, the parallel and cooperative transportation of 20-µm-diameter polystyrene beads was demonstrated.