Comb interfaces

Fig. 6.1.6 Equivalent circuit for parallel-plate style comb interface...

Branched chains may have an important role in interfacial phenomena. Ger-sappe et al. [192] studied the behavior of combs constituted by backbones of A monomers and branches, or teeth , of B units at the interface between immiscible A and B monomers. These teeth are more preferentially located at the interface than the equivalent units in linear chains. 

P.G. Triay, I.R. Hobart, D.E. Meijer, A. (1992) EXAFS spectroscopic study of neptu-nium(V) sorption at the a-FeOOH/water interface. Environ. Sci. Technol. 26 376-382 Combes, J.M. Manceau, A. Galas, G. (1986) Study of the local structure in poorly ordered precursors of iron oxi-hydroxides. J. Physique 47 697-701... 

A very sharp liquid-gel interface will be visible when the gel has polymerized. This should be visible within 10 to 20 min. The gel should be fully polymerized after 1 to 2 hr. In general, stacking gels should be cast just before use. However, the complete gel can be stored overnight at 4°C, with little effect on resolution, if covered with the comb in place. 

Wang, T. Cohen, J. Kassel, D. B. Zeng, L. 1999. A multiple electrospray interface for parallel mass spectrometric analyses of compound libraries. Comb. Chem. High Throughput Screen, 2,327-334. 

Certain comb-type silicone surfactants have been shown to stabilize emulsions in the presence of salts, alcohol and organic solvents that normally cause failure of emulsions stabilized using conventional hydrocarbon surfactants and a study by Wang et al. [66,67] investigated the cause of this stability. Interaction forces due to silicone surfactants at an interface were measured using AFM. Steric repulsion provided by the SPE molecules persisted up to an 80% or higher ethanol level, much higher than for conventional hydrocarbon surfactants. Nonionic hydrocarbon surfactants lose their surface activity and ability to form micelles in... 

D. Schaumloffel, A. Prange, A new interface for combing capillary electrophoresis with inductively coupled plasmaDmass spectrometry, Fresenius J. Anal. Chem., 364 (1999), 452D456. 

Procedure. Follow the proportions in Table II. Mix and pour into a sealed gel former immediately. Leave room for a short upper stacking gel. With a fine pipette, layer a small amount of 0.1% SDS solution on top of the unpolymerized gel to give a flat surface and to remove bubbles. As the gel polymerizes the water interface will become indistinct and then will reappear as the gel sets. Pour off the water and add the upper gel. Immediately insert the comb for well formation. Upper stacking gels usually shrink slightly as they polymerize. Mount the gel in a vertical apparatus. Make sure the running buffer contacts both upper and lower surfaces of the gel. 

These inerts are mostly polymeric or oligomeric in nature and can be both nonionic and anionic. They have multiple binding / interaction sites to the interface, so that a displacement becomes improbable. Several materials have been made available to the industry [6d,ej. The chemistries range from sulfonic condensates (Morwet) or lignin sul-phonates (Reaxx) to EO-PO-block copolymers (Pluronics), comb graft polymers, acrylate based copolymers or various other block copolymers. 

Surface analytical techniques. A variety of spectroscopic methods have been used to characterize the nature of adsorbed species at the solid-water interface in natural and experimental systems (Brown et al, 1999). Surface spectroscopy techniques such as extended X-ray absorption fine structure spectroscopy (EXAFS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) have been used to characterize complexes of fission products, thorium, uranium, plutonium, and uranium sorbed onto silicates, goethite, clays, and microbes (Chisholm-Brause et al, 1992, 1994 Dent et al, 1992 Combes et al, 1992 Bargar et al, 2000 Brown and Sturchio, 2002). A recent overview of the theory and applications of synchrotron radiation to the analysis of the surfaces of soils, amorphous materials, rocks, and organic matter in low-temperature geochemistry and environmental science can be found in Fenter et al (2002). 

The phenomenon of flyaway is a result of charge repulsion between hair fibers, which makes hair hard to comb or to keep in place. This problem occurs when hair is combed or brushed, particularly at low humidity. The generation of static charges is due to an unequal transfer of charges across the interface between materials in contact. 

Many different arrangements are used for capacitive sensing. Parallel-plate type interfaces sense variations of the plate spacing, z. Conversely, overlap type interfaces such as combs detect variations of the effective capacitor area. The two approaches and combinations thereof differ in sensitivity, displacement range, electrostatic force, and electrical spring constant generated. 

The sections below describe three representative capacitive interfaces. The single-ended parallel-plate style is used in inertial and pressure sensors where fabrication constraints preclude a complementary design. Many microfluidic applications, such as particle sorting or fluid level detection, and proximity sensors fall into this category also. Section 6.1.2.3 describes the advantages of complementary interfaces. The last section is devoted to comb style sensors. 

Lateral combs exploit variation in electrode overlap rather than spacing. Fig. 6.1.7 shows a typical arrangement. A differentia interface can be realized with combs on either side of a mechanical structure. Since the structure moves in the direction of the fingers, displacements in lateral combs are not limited by the gap between electrodes. 

The penalty for using lateral combs is reduced sensitivity compared to parallel-plate type interfaces for a given spacing x... 

Since, in most cases, the nominal overlap Xo is much larger than the displacement x, parallel-plate interfaces have considerably larger sensitivity. Lateral combs are most often used for actuation where large range is required or in electromechanical oscillators, where the position-dependence of the negative spring of parallel-plate interfaces introduces nonlinearity [13]. Parallel-plate structures are usually preferred for maximum displacement resolution. 

The same group has also presented Monte Carlo calculations on the compati-bilizing effect of comb copolymers [328]. Their interfacial behavior was compared with that of linear multiblock copolymers. By varying the numbers and lengths of the teeth it was demonstrated that combs with fewer and longer teeth localize themselves easier at the interface between two homopolymers, of the same nature as the backbone and teeth, than combs with a larger number of shorter teeth. In... 

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