Capillary osmosis

Relatively Important is the phenomenon of dijfusiophoresis and its counterpart plug or capillary osmosis. For both the driving force is a concentration gradient, either of an electrolyte or of a non-electrolyte. Consider for instance fig. 4.40. The presence of the gradient leads to at least an (osmotic) pressure gradient p(0) around the particle in the double layer. Moreover, by specific adsorption it can also lead to concentration polarization and x" may depend on 9. In this way driving forces are established to induce the particle to move. 

Diffuslophoresis is the counterpart of electrophoresis in that In the former case a concentration gradient is applied, it leads to polarization and motion in the latter case an electric field Is applied, which leads to concentration polarization and motion. When the particles are immobile, as in a porous plug, or when the concentration gradient is applied over a charged capillary the liquid starts to move. This leads to plug or capillary osmosis, the counterpart of electro-osmosis in plugs or capillaries. 

Diffuslophoresis was discovered by Deryagln et al. and is now well established - Good experimental verifications are avallable and this can also be said of capillary osmosis The phenomenon has also received wide practical application, for instance in the deposition of colloidal particles where the driving concentration gradient Is caused by surface (or electrode) reactions. 

Dijfusiophoresis. It is the motion of the suspended particles under the action of an externally applied concentration gradient of the electrolyte solution (or a gradient of solvent composition) that constitutes the dispersion medium. The presence of this macroscopic concentration gradient induces a local gradient of electric potential in the vicinity of the particle thus provoking its motion. The reciprocal phenomenon of diffusiophoresis is termed capillary osmosis the concentration-gradient-induced electric field sets the liquid in the vicinity of the double layer into motion. 

Boris Vladimirovich Derjaguin (1902-1994). .. was a Russian chemists and physicist whose work is tightly connected with the development of the modem science of colloids and surfaces. Most prominent is his theory on colloidal stability, now known as DLVO theory, which he developed together with Landau and independently from Verwey and Overbeek. Additionally, he examined the adhesion and friction of solid bodies, developed the theory of capillary osmosis, started investigation into foam stability, worked on the direct measurements of molecular attraction, and contributed to the theory of electrokinetic phenomena. 

Self-filling / capillary osmosis Protein PDMS ... 

Reverse osmosis models can be divided into three types irreversible thermodynamics models, such as Kedem-Katchalsky and Spiegler-Kedem models nonporous or homogeneous membrane models, such as the solution—diffusion (SD), solution—diffusion—imperfection, and extended solution—diffusion models and pore models, such as the finely porous, preferential sorption—capillary flow, and surface force—pore flow models. Charged RO membrane theories can be used to describe nanofiltration membranes, which are often negatively charged. Models such as Dorman exclusion and the... 

Electroosmotic flow in a capillary also makes it possible to analyze both cations and anions in the same sample. The only requirement is that the electroosmotic flow downstream is of a greater magnitude than electrophoresis of the oppositely charged ions upstream. Electro osmosis is the preferred method of generating flow in the capillary, because the variation in the flow profile occurs within a fraction of Kr from the wall (49). When electro osmosis is used for sample injection, differing amounts of analyte can be found between the sample in the capillary and the uninjected sample, because of different electrophoretic mobilities of analytes (50). Two other methods of generating flow are with gravity or with a pump. 

Hollow Fiber-Capillary Hollow Fiber reFers to verv small diameter membranes. The most siiccessFiil one has an outer diameter oF onlv 93 jlrn and is used For reverse osmosis, (iapillarv membranes are larger-diarneter membranes used For liquid separations. The distinction betw een them has blurred to the point where there is a virtual... 

A. E. Yaroshchuk, S. S. Durkhin. Phenomenological theory of reverse osmosis in macroscopically homogeneous membranes and its specification for the capillary charged model. J Memb Sci 79 133, 1993. 

Water has the highest surface tension (75 dyne/cm) of ail common liquids (except mercury). Together, surface tension and density determine how high a liquid rises in a capillary system. Capillary movement of water plays a prominent role in the life of plants. Lastly, consider osmosis, the bulk movement of water in the direction from a dilute aqueous solution to a more concentrated one across a semipermeable boundary. Such bulk movements determine the shape and form of living things. 

Shale stability is an important problem faced during drilling. Stability problems are attributed most often to the swelling of shales. It has been shown that several mechanisms can be involved [680,681]. These can be pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alterations. Three processes contributing to the instability of shales have to be considered [127] ... 

Introduction of a water-soluble ionic substance into the vascular system results in an increase in the number of particles in the bloodstream as the contrast substance dissolves. The body possesses several internal regulation systems and, when perturbed by an injection, attempts to restore the concentrations of substances in the blood to their normal or preinjection levels. To re-equilibrate the system, water from the cells of surrounding body tissue moves into the blood plasma through capillary membranes. This transfer of water is an example of osmosis, the diffusion of a solvent (water) through a semipermeable membrane (the blood vessels) into a more concentrated solution (the blood) to equalize the concentrations on both sides of the membrane. To accommodate the increase in... 

Factors Affecting Ionic Migration. Effect of Temperature. pH and Ionic Strength. Electro-osmosis. Supporting Medium. Detection of Separated Components. Applications of Traditional Zone Electrophoresis. High-performance Capillary Electrophoresis. Capillary Electrochromatography. Applications of Capillary El ectrochromatography. ... 

Figure 1. Schematic of preferential sorption-capillary flow mechanism for reverse-osmosis separations of sodium chloride from aqueous solutions...

The preferential sorption-capillary flow mechanism of reverse osmosis does that. In the NaCl-H20-cellulose acetate membrane system, water is preferentially sorbed at the membrane-solution Interface due to electrostatic repulsion of ions in the vicinity of materials of low dielectric constant (13) and also due to the polar character of the cellulose acetate membrane material. In the p-chlorophenol-water-cellulose acetate membrane system, solute is preferentially sorbed at the interface due to higher acidity (proton donating ability) of p-chlorophenol compared to that of water and the net proton acceptor (basic) character of the polar part of cellulose acetate membrane material. In the benzene-water-cellulose acetate membrane, and cumene-water-cellulose acetate membrane systems, again solute is preferentially sorbed at the interface due to nonpolar... 

Consider that a potential difference is applied across a glass capillary tube filled with an electrolytic solution (Fig. 6.134). What would one expect Of course, one would expect a current to flow through the capillary according to Ohm s law. In practice, however, a remarkable and unexpected phenomenon is observed. In addition to the current, the solution itself begins to flow—the phenomenon of electro-osmosis. Liquid flow is generally associated with the application of a pressure gradient, but in this case it appears that a potential difference is doing the job normally achieved by a pressure difference. 

Electro-osmosis in a capillary. In the local model of the previous section we assumed for the flow rate v the phenomenological generalized Darcy s law (6.3.3a) with constant coefficients. 

As is evident from the major difference between the GFR and the rate of urine production, the majority of the water in the filtrate is reabsorbed into the blood in the capillaries, by osmosis through the wall of the tubule and the interstitial fluid. This reabsorption of water occurs mostly in the proximal tubule, although some is also reabsorbed in the distal tubule and collecting duct. 

HOLLOW-FIBER MEMBRANES. A hollow-fiher membrane is a capillary having an inside diameter of - inn and an outside diameter < I mm and whose wall functions as a semipermeahlc membrane. The fibers can he employed singly or grouped into a bundle which may contain tens of thousands of fibers and up to several million libers as in reverse osmosis (Fig. 11. In most eases, hollow fibers are used as cylindrical membranes that permit selective exchange of materials across (heir walls. However, they can also he used as containers to effect the controlled release of a specific material, or as reactors to chemically modify a permeate as il diffuses through a chemically activated hollow-liher wall. e g., loaded with immobilized enzyme. 

The semipermeable membrane proposed for the demineralization of sea water is based on H. L. Calendar s theory that osmosis takes place through the membrane as vapor, condensing at the opposite membrane surface. The actual membrane being used consists of two sheets of untreated cellophane separated by a water-repellent powder, such as a silicone-coated pumice powder. The vapor gap is maintained by an air pressure in excess of the pressure on the sea water and the cellophane sheets support the capillary surfaces, which will withstand pressures up to 1500 p.s.i. A number of successful experiments are reported with over 95% desalinization. The present effort is directed toward obtaining reproducible experimental results and better methods of fabricating the vapor gap. 

This leaves arrangement C, Table I, in which the narrow air gap functions as a semipermeable membrane, as the most promising. The choice of material with capillaries small enough to support the pressure necessary for reverse osmosis of sea water is a research project in itself. 

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