CiteULike: weeks's microfluidics

Microfluidics: Fluid physics at the nanoliter scale

Todd Squires — 2006-01-16T15:14:37-00:00

Reviews of Modern Physics, Vol. 77, No. 3. (2005)

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 Péclet 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.

Continuous Particle Separation Through Deterministic Lateral Displacement

Lotien Huang — 2007-11-30T17:48:27-00:00

Science, Vol. 304, No. 5673. (14 May 2004), pp. 987-990.

We report on a microfluidic particle-separation device that makes use of the asymmetric bifurcation of laminar flow around obstacles. A particle chooses its path deterministically on the basis of its size. All particles of a given size follow equivalent migration paths, leading to high resolution. The microspheres of 0.8, 0.9, and 1.0 micrometers that were used to characterize the device were sorted in 40seconds with a resolution of [~]10nanometers, which was better than the time and resolution of conventional flow techniques. Bacterial artificial chromosomes could be separated in 10 minutes with a resolution of [~]12%. 10.1126/science.1094567

From Micro- to Nanofabrication with Soft Materials

Stephen Quake — 2007-09-27T08:45:33-00:00

Science, Vol. 290, No. 5496. (24 November 2000), pp. 1536-1540.

Soft materials are finding applications in areas ranging from microfluidic device technology to nanofabrication. We review recent work in these areas, discuss the motivation for device fabrication with soft materials, and describe applications of soft materials. In particular, we discuss active microfluidic devices for cell sorting and biochemical assays, replication-molded optics with subdiffraction limit features, and nanometer-scale resonators and wires formed from single-molecule DNA templates as examples of how the special properties of soft materials address outstanding problems in device fabrication.

Mechanism for clogging of microchannels

Hans Wyss — 2007-09-22T19:57:03-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 74, No. 6. (2006)

We investigate clogging of microchannels at the single-pore level using microfluidic devices as model porous media. The process of clogging is studied at low volume fractions and high flow rates, a technologically important regime. We show that clogging is independent of particle flow rate and volume fraction, indicating that collective effects do not play an important role. Instead, the average number of particles that can pass through a pore before it clogs scales with the ratio of pore to particle size. We present a simple model that accounts for the data.

Jamming, Two-Fluid Behavior, and “Self-Filtration” in Concentrated Particulate Suspensions

MD Haw — 2007-09-22T19:54:19-00:00

Physical Review Letters, Vol. 92, No. 18. (2004), pp. 185506-185506.

We study the flow of model hard-sphere colloidal suspensions at high volume fraction driven through a constriction by a pressure gradient. Above a particle-size dependent limit 0, direct microscopic observations demonstrate jamming and unjamming—conversion of fluid to solid and vice versa—during flow. We show that such a jamming flow produces a reduction in colloid concentration x downstream of the constriction. We propose that this "self-filtration" effect is due to a combination of jamming of the particulate part of the system and continuing flow of the liquid part, i.e., the solvent, through the pores of the jammed solid. Thus we link jamming in colloidal and granular media with a "two-fluid-like" picture of the flow of concentrated suspensions. Results are also discussed in the light of the original experiments of Reynolds on dilation in granular materials.

Experimental studies of the flow of concentrated hard sphere suspensions into a constriction

L Isa — 2006-06-07T11:46:33-00:00

Journal of Physics: Conference Series, Vol. 40, No. 1. (2006), pp. 124-132.

Interesting flow properties are observed when a concentrated suspension of colloidal particles flows into a geometrical constriction. We present here a description of two different experimental techniques used to study the pressure driven flow of dense suspensions of micron-sized hard spheres into glass capillaries. The first one involves the analysis of the driving pressure during the flow, the other one is based on fast confocal microscopy. Technical details are given, together with a selection of preliminary results.