There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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 Peclet 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.

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Microfluidics: Fluid physics at the nanoliter scale

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Colloidal particles act in many ways like surfactant molecules, particularly if adsorbed to a fluid–fluid interface. Just as the water or oil-liking tendency of a surfactant is quantified in terms of the hydrophile–lipophile balance (HLB) number, so can that of a spherical particle be described in terms of its wettability via contact angle. Important differences exist, however, between the two types of surface-active material, due in part to the fact that particles are strongly held at interfaces. This review attempts to correlate the behaviour observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.

Particles as surfactants—similarities and differences

Thank you for reading principles of optics electromagnetic theory of propagation interference and diffraction of light. As you may know, people have search hundreds times for their favorite novels like this principles of optics electromagnetic theory of propagation interference and diffraction of light, but end up in harmful downloads. Rather than enjoying a good book with a cup of coffee in the afternoon, instead they are facing with some infectious bugs inside their computer.

Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

We present the results of investigations of high-speed drainage of a thin film confined between a microscopic colloidal probe and a substrate performed with a new atomic force microscope-related setup. Theoretical calculations are used to formulate the governing equation (force balance) for instantaneous deflection of a cantilever spring, which is due to both concentrated forces acting on a colloidal probe and viscous drag force on a cantilever itself. The suggested way to subtract the latter contribution allows design of a lubrication experiment. Two pairs of interacting solids, characterized by different wettability and smoothness, immersed into water−electrolyte solutions have been studied. Results for hydrophilic silica surfaces are in excellent agreement with the Reynolds theory of hydrodynamic lubrication. Faster drainage of a thin film confined between hydrophobic rough polystyrene surfaces is consistent with the theory of film drainage between slippery surfaces. The slip lengths are found to be of...

Dynamic effects on force measurements. 2. Lubrication and the atomic force microscope

We report results of investigations of a high-speed drainage of thin aqueous films squeezed between randomly nanorough surfaces. A significant decrease in the hydrodynamic resistance force as compared with that predicted by Taylor's equation is observed. However, this reduction in force does not represent the slippage. The measured force is exactly the same as that between equivalent smooth surfaces obeying no-slip boundary conditions, but located at the intermediate position between peaks and valleys of asperities. The shift in hydrodynamic thickness is shown to be independent of the separation and/or shear rate. Our results disagree with previous literature data reporting very large and shear-dependent boundary slip for similar systems.

/pdf/surface-roughness-and-hydrodynamic-boundary-conditions-2pkq3xg2uj.pdf

Surface roughness and hydrodynamic boundary conditions

The lubricating behavior of the weakly charged short-side-chain glycoprotein mucin “Orthana” (Mw = 0.55 MDa) has been investigated between hydrophobic and hydrophilic PDMS substrates using soft-contact tribometry. It was found that mucin facilitates lubrication between hydrophobic PDMS surfaces, leading to a 10-fold reduction in boundary friction coefficient for rough surfaces. The presence of mucin also results in a shift of the mixed lubrication regime to lower entrainment speeds. The observed boundary lubrication behavior of mucin was found to depend on the bulk concentration, and we linked this to the structure and dynamics of the adsorbed mucin films, which are assessed using optical waveguide light spectroscopy. We observe a composite structure of the adsorbed mucin layer, with its internal structure governed by entanglement. The film thickness of this adsorbed layer increases with concentration, while the boundary friction coefficient for rough surfaces was found to be inversely proportional to the...

Viscous boundary lubrication of hydrophobic surfaces by mucin.

We study the interaction between hydrophobized silica surfaces of defined contact angle in water using an AFM-related force measuring device. In all cases the attraction between surfaces leads to a...

Gleb E. Yakubov

Papers

Dynamic effects on force measurements. 2. Lubrication and the atomic force microscope

Surface roughness and hydrodynamic boundary conditions

Viscous boundary lubrication of hydrophobic surfaces by mucin.

Interaction Forces between Hydrophobic Surfaces. Attractive Jump as an Indication of Formation of "Stable" Submicrocavities

Influence of ionic strength changes on the structure of pre-adsorbed salivary films. A response of a natural multi-component layer.