Dipolar thermocapillary motor and swimmer (original) (raw)
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Thermocapillarity in Microfluidics—A Review
Micromachines, 2016
This paper reviews the past and recent studies on thermocapillarity in relation to microfluidics. The role of thermocapillarity as the change of surface tension due to temperature gradient in developing Marangoni flow in liquid films and conclusively bubble and drop actuation is discussed. The thermocapillary-driven mass transfer (the so-called Benard-Marangoni effect) can be observed in liquid films, reservoirs, bubbles and droplets that are subject to the temperature gradient. Since the contribution of a surface tension-driven flow becomes more prominent when the scale becomes smaller as compared to a pressure-driven flow, microfluidic applications based on thermocapillary effect are gaining attentions recently. The effect of thermocapillarity on the flow pattern inside liquid films is the initial focus of this review. Analysis of the relation between evaporation and thermocapillary instability approves the effect of Marangoni flow on flow field inside the drop and its evaporation rate. The effect of thermocapillary on producing Marangoni flow inside drops and liquid films, leads to actuation of drops and bubbles due to the drag at the interface, mass conservation, and also gravity and buoyancy in vertical motion. This motion can happen inside microchannels with a closed multiphase medium, on the solid substrate as in solid/liquid interaction, or on top of a carrier liquid film in open microfluidic systems. Various thermocapillary-based microfluidic devices have been proposed and developed for different purposes such as actuation, sensing, trapping, sorting, mixing, chemical reaction, and biological assays throughout the years. A list of the thermocapillary based microfluidic devices along with their characteristics, configurations, limitations, and improvements are presented in this review.
Thermo-capillarity in microfluidic binary systems via phase modulated sinusoidal thermal stimuli
Physics of Fluids, 2022
In this article, we have explored the theoretical aspects of thermo-capillarity driven hydrodynamics at the interface of an immiscible binary-fluid system within a microfluidic domain. The top and bottom walls of the microfluidic confinement are exposed to sinusoidal thermal stimuli with different mean values, wave numbers, and phase differences. We explore the influence of different governing parameters on the thermal and hydrodynamic transport due to interfacial thermo-capillarity and within the constituent fluids. To this end, we deduce the full solutions for the temperature field, hydrodynamics, and the interfacial deformation characteristics in an analytical framework, by appealing to the assumption of the creeping flow (vanishingly small Reynolds, Marangoni, and Capillary number regime) and nearly un-deformed interface. Complicated spatial distribution of the isotherms is generated across the fluids, leading to spatially varying thermal gradients across and along the interface...
Manipulation of a droplet in a planar channel by periodic thermocapillary actuation
Journal of Micromechanics and Microengineering, 2008
Thermocapillary manipulation of a droplet in a planar microchannel with periodic actuations has been demonstrated by both theoretical simulation and experimental characterization. The driving temperature gradients are provided by four micro heaters embedded in the boundaries of the planar channel. The temperature distributions corresponding to the periodic actuations are calculated, and are coupled to the droplet through the surface tensions which drive the droplet. The results show that the droplet will be driven to move along closed loops whose patterns can be designed and controlled by the periodic heating schemes and actuation frequencies. Qualitative agreement between the simulation and experimental observation, in terms of the temperature distributions and droplet moving tracks, has been obtained.
Long-range electrothermal fluid motion in microfluidic systems
International journal of heat and mass transfer, 2016
AC electrothermal flow (ACEF) is the fluid motion created as a result of Joule heating induced temperature gradients. ACEF is capable of performing major microfluidic operations, such as pumping, mixing, concentration, separation and assay enhancement, and is effective in biological samples with a wide range of electrical conductivity. Here, we report long-range fluid motion induced by ACEF, which creates centimeter-scale vortices. The long-range fluid motion displays a strong voltage dependence and is suppressed in microchannels with a characteristic length below ~300 μm. An extended computational model of ACEF, which considers the effects of the density gradient and temperature-dependent parameters, is developed and compared experimentally by particle image velocimetry. The model captures the essence of ACEF in a wide range of channel dimensions and operating conditions. The combined experimental and computational study reveals the essential roles of buoyancy, temperature rise, an...
18th IEEE International Conference on Micro Electro Mechanical Systems, 2005. MEMS 2005.
We report a phenomenon in which a micromachined heat source placed less than 50 µm above the surface of a liquid drives a high-speed doublet flow pattern with linear velocities reaching nearly 5 mm/sec and rotational velocities up to 1200 rpm. Tests were performed on a 50-100 µmthick layer of water containing 3 µm polystyrene beads for flow visualization. The thermal source is a polyimide cantilever with an integrated heater near the tip, operated with input powers ranging from 0-32 mW. It has no moving parts and does not contact the liquid. The speed of the doublet flow scales with input power as well as liquid temperature, and is inversely related to the air gap between the heater and liquid surface. The orientation of the doublet flow can be reversed by changing the angle of the cantilever. A one-dimensional array of probes used in the same manner generates a linear flow pattern.
Lab on a Chip, 2010
We report a novel method for bubble or droplet displacement, capture and switching within a bifurcation channel for applications in digital microfluidics based on the Marangoni effect, i.e. the appearance of thermocapillary tangential interface stresses stemming from local surface tension variations. The specificity of the reported actuation is that heating is provided by an optimized resistor pattern (B. Selva, J. Marchalot and M.-C. Jullien, An optimized resistor pattern for temperature gradient control in microfluidics, J. Micromech. Microeng., 2009, 19, 065002) leading to a constant temperature gradient along a microfluidic cavity. In this context, bubbles or droplets to be actuated entail a surface force originating from the thermal Marangoni effect. This actuator has been characterized (B. Selva, I. Cantat, and M.-C. Jullien, Migration of a bubble towards a higher surface tension under the effect of thermocapillary stress, preprint, 2009) and it was found that the bubble/droplet (called further element) is driven toward a high surface tension region, i.e. toward cold region, and the element velocity increases while decreasing the cavity thickness. Taking advantage of these properties three applications are presented: (1) element displacement, (2) element switching, detailed in a given range of working, in which elements are redirected towards a specific evacuation, (3) a system able to trap, and consequently stop on demand, the elements on an alveolus structure while the continuous phase is still flowing. The strength of this method lies in its simplicity: single layer system, in situ heating leading to a high level of integration, low power consumption (P < 0.4 W), low applied voltage (about 10 V), and finally this system is able to manipulate elements within a flow velocity up to 1 cm s À1 .
Numerical Heat Transfer; Part A: Applications, 2021
The main objective of this paper is to numerically investigate the transient forward and backward thermocapillary motion of a water droplet in a microchannel occupied by the hexadecane oil. The top and bottom walls of the microchannel are kept at the ambient temperature. Two heat sources activated periodically are put on the front side and rear one of the droplet in a microchannel, respectively. When the heat source is activated, two vortices are formed inside a water droplet and the oil flow passes over the droplet in the microchannel. The forward and backward thermocapillary migration caused by two periodic heat sources results in the thermocapillary stress gradient along the fee interface which drives a water droplet to move to the cold side of the open channel. The mechanism of a droplet migration behavior is consistent with the previous experimental observation. The water droplet first accelerates rapidly, and then decelerates significantly at various intervals. The dynamic contact angle is significantly altered owing to the pressure change exerting on the hexadecane/water interface during the actuation process. The velocity of a water droplet is enlarged by a higher heating power and a larger microchannel height.
Thermophoresis: moving particles with thermal gradients
Soft Matter, 2008
Thermophoresis is particle motion induced by thermal gradients. Akin to other nonequilibrium transport processes such as thermal diffusion in fluid mixtures, it is both experimentally and theoretically a challenging subject. New insights stemming from careful experimental surveys and strict theoretical models have however shed light on the underlying physical mechanisms, enabling depiction of thermophoresis as a subtle interfacial effect. These recent advancements open up alluring perspectives to exploit thermophoresis as a novel tool in macromolecular fractionation, microfluidic manipulation, and selective tuning of colloidal structures.
Thermophoretically driven capillary transport in microfluidic channels
arXiv (Cornell University), 2017
Thermal gradient enhances nanoparticle deposition for a given nanofluid. The interplay between thermophoresis and diffusion governs particle migration. Thermal gradient and particle size enhance the rate of capillary transport. Optimum flow rates can be achieved for a given nanoparticle suspension.