5,926 research outputs found
Manipulation of Spherical Droplets on a Liquid Platform Using Thermal Gradients
In the recent years, there has been a growing interest in droplet-based
(digital) microfluidics for which, reliable means of droplet manipulation are
required. In this study we demonstrate thermal actuation of droplets on liquid
platforms, which is ideal for biochemical microsystems and lab-on-chip
applications because droplets can be transported with high speed, good control
and minimal thermal loading as compared to using conventional solid substrates.
In addition, other disadvantages of using solid surfaces such as evaporation,
contamination, pinning, hysteresis and irreversibility of droplet motion are
avoided.
Based on the theoretical development and measurements, a silicon-based
droplet transportation platform was developed with embedded Titanium micro
heaters. A shallow liquid pool of inert liquid (FC-43) served as the carrier
liquid. Heaters were interfaced with control electronics and driven through a
computer graphical user interface. By creating appropriate spatio-temporal
thermal gradient maps, transport of droplets on predetermined pathways was
successfully demonstrated with high level of robustness, speed and reliability.
The video shows normal imaging of droplet manipulation accompanied by the
corresponding infrared thermal imaging showing the spatio-temporal temperature
maps and the outline of the drop as it moves towards hot spots.Comment: 63rd APS - Division of Fluid Dynamics - 201
Planar digital nanoliter dispensing system based on thermocapillary actuation
We provide guidelines for the design and operation of a planar digital nanodispensing system based on
thermocapillary actuation. Thin metallic microheaters embedded within a chemically patterned glass
substrate are electronically activated to generate and control 2D surface temperature distributions
which either arrest or trigger liquid flow and droplet formation on demand. This flow control is
a consequence of the variation of a liquidâs surface tension with temperature, which is used to draw
liquid toward cooler regions of the supporting substrate. A liquid sample consisting of several
microliters is placed on a flat rectangular supply cell defined by chemical patterning. Thermocapillary
switches are then activated to extract a slender fluid filament from the cell and to divide the filament into
an array of droplets whose position and volume are digitally controlled. Experimental results for the
power required to extract a filament and to divide it into two or more droplets as a function of
geometric and operating parameters are in excellent agreement with hydrodynamic simulations. The
capability to dispense ultralow volumes onto a 2D substrate extends the functionality of microfluidic
devices based on thermocapillary actuation previously shown effective in routing and mixing nanoliter
liquid samples on glass or silicon substrates
Microfluidic DNA amplification - a review
The application of microfluidic devices for DNA amplification has recently been extensively studied. Here, we review the important development of microfluidic polymerase chain reaction (PCR) devices and discuss the underlying physical principles for the optimal design and operation of the device. In particular, we focus on continuous-flow microfluidic PCR on-chip, which can be readily implemented as an integrated function of a micro-total-analysis system. To overcome sample carryover contamination and surface adsorption associated with microfluidic PCR, microdroplet technology has recently been utilized to perform PCR in droplets, which can eliminate the synthesis of short chimeric products, shorten thermal-cycling time, and offers great potential for single DNA molecule and single-cell amplification. The work on chip-based PCR in droplets is highlighted
Microfluidics: Fluid physics at the nanoliter scale
Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the PĂ©clet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world
Thermocapillary actuation of droplets on chemically patterned surfaces by programmable microheater arrays
We have designed a microfluidic device for the actuation of liquid droplets or continuous streams on a solid surface by means of integrated microheater arrays. The microheaters provide control of the surface temperature distribution with high spatial resolution. These temperature gradients locally alter the surface tension along droplets and thin films thus propelling the liquid toward the colder regions. In combination with liquophilic and liquophobic chemical surface patterning, this device can be used as a logistic platform for the parallel and automated routing, mixing and reacting of a multitude of liquid samples, including alkanes, poly(ethylene glycol) and water
Thermocapillary valve for droplet production and sorting
Droplets are natural candidates for use as microfluidic reactors, if active
control of their formation and transport can be achieved. We show here that
localized heating from a laser can block the motion of a water-oil interface,
acting as a microfluidic valve for two-phase flows. A theoretical model is
developed to explain the forces acting on a drop due to thermocapillary flow,
predicting a scaling law which favors miniaturization. Finally, we show how the
laser forcing can be applied to sorting drops, thus demonstrating how it may be
integrated in complex droplet microfluidic systems.Comment: Five pages, four figure
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