Osmotic water flow

FIGURE 13.11 Red blood cells in solutions of different concentration (a) When the solute concentration of the surrounding fluid is equal to that within the cell, there is no net osmotic flow, and the red blood cell exhibits its typical shape, (b) When a cell is placed in pure water, osmotic flow of water into the cell causes it to swell up. Eventually it may burst. 

In a detersive system containing a dilute surfactant solution and a substrate bearing a soHd polar sod, the first effect is adsorption of surfactant at the sod—bath interface. This adsorption is equivalent to the formation of a thin layer of relatively concentrated surfactant solution at the interface, which is continuously renewable and can penetrate the sod phase. Osmotic flow of water and the extmsion of myelin forms foHows the penetration, with ultimate formation of an equdibrium phase. This equdibrium phase may be microemulsion rather than Hquid crystalline, but in any event it is fluid and flushable... 

Electrostatic Repulsive Forces. As the distance between two approaching particles decreases, their electrical double layers begin to overlap. As a first approximation, the potential energy of the two overlapping double layers is additive, which is a repulsive term since the process increases total energy. Electrostatic repulsion can also be considered as an osmotic force, due to the compression of ions between particles and the tendency of water to flow in to counteract the increased ion concentration. 

You should remember that RO uses a semi-permeable membrane. As such, the membrane is permeable to only very light molecules like water. Under atmospheric condirtions the fresh water flows into the solution which is called osmotic flow. But for purification purposes, this is no use, and hence we employ the reverse of osmotic flow. For this to happen, we need to apply external pressure in excess of osmotic pressure. The osmotic pressure is given by ... 

In reverse osmosis, the osmotic pressure is increased manually to get the water to flow from a high-density area through a semipermeable membrane to the lower-density weaker solution. The water will pass through the membrane and leave the solids behind. A pressure of about 2.76 MPa will extract 90% or more of the dissolved absorbed solids further refinement may be achieved through a base exchange process. 

Total Salinity. The salinity control of oil-base mud is very important for stabilizing water-sensitive shales and clays. Depending upon the ionic concentration of the shale waters and of the mud water phase, an osmotic flow of pure water from the weaker salt concentration (in shale) to the stronger salt concentration (in mud) will occur. This may cause a dehydration of the shale and, consequently, affect its stabilization. 

Nutrient solutions used in intravenous feeding must be isotonic with blood that is, they must have the same osmotic pressure as blood. If the solution is too dilute, its osmotic pressure will be less than that of the fluids inside blood cells in that case, water will flow into the cell until it bursts. Conversely, if the nutrient solution has too high a concentration of solutes, water will flow out of the cell until it shrivels and dies. 

An alternative method of purifying water is by reverse osmosis. Under normal conditions, if an aqueous solution is separated by a semi-permeable membrane from pure water, osmosis will lead to water entering the solution to dilute it. If, however, sufficient pressure is applied to the solution, i.e. a pressure in excess of its osmotic pressure, then water will flow through the membrane from the solution the process of reverse osmosis is taking place. This principle has been... 

Using cellular automata we have an opportunity to model the flow of water from each compartment into the membrane, when a solute is present on one side of the membrane. By design, the membrane in our model is composed of 31% empty cells. At iteration zero, in our dynamics, the membrane contains no water. After several iterations, there will be flows of water from the two compartments into the membrane. If we monitor the early stages of this process, we may detect a possible preference for water to flow from one of the compartments. Such a condition would model the early stages of the osmotic effect. 

In isotonic solution, red blood cells are spherical top). At higher ion concentration center), osmotic flow removes water from the cell interior, shrinking the cell. At lower ion concentration, osmotic flow pumps water into the cell and may cause it to burst bottom). 

In these systems, osmotic pressure provides the driving force to generate controlled release of drug. Consider a semipermeable membrane that is permeable to water, but not to drug. A tablet containing a core of drug surrounded by such a membrane is shown in Fig. 9. When this device is exposed to water or any body fluid, water will flow into the tablet owing to the osmotic pressure difference. The rate of flow, dV/dt, of water into the device can be represented as... 

GM Zentner, GS Rork, KJ Himmelstein. Osmotic flow through controlled porosity films An approach to the delivery of water soluble compounds. In JM Anderson, SW Kim, eds. Advances in Drug Delivery Systems. New York Elsevier, 1986, pp 217-230. 

Reversed-phase separations currently dominate in CEC. As a result, the vast majority of the mobile phases are mixtures of water and an organic solvent, typically acetonitrile or methanol. In addition to the modulation of the retention, the mobile phase in CEC also conducts electricity and must contain mobile ions. This is achieved by using aqueous mixtures of salts instead of pure water. The discussion in Sect. 2 of this chapter indicated that the electro osmotic flow is created by ionized functionalities. The extent of ionization of these functionalities that directly affects the flow rate depends on the pH value of the mobile phase. Therefore, the mobile phase must be buffered to a pH that is desired to achieve the optimal flow velocity. Obviously there are at least three parameters of the mobile phase that have to be controlled (i) percentage of the organic solvent, (ii) the ionic strength of the aqueous component, and (iii) its pH value. 

It should be pointed out that deterioration under freeze-thaw conditions can also be caused by a mechanism other than the direct freezing of the non-evaporable water. The capillaries contain dissolved salts, such as hydroxides, sulfates and carbonates. As part of the water is frozen, the concentration of salts in the remaining water increases and water will flow by osmotic pressure from the gel pores to the capillary pores, setting up an additional disruptive pressure. 

Extractant leakage from the pores of the polymeric membrane in SLM is due to osmotic flow of massive quantities of water through the membrane. Membrane stability decreases with increasing osmotic pressure gradient and depends upon composition of the SLM system. A high tendency to solubilize water, low extractant/aqueous interfacial tension, and high wettability of polymeric membrane leads to less stable SLMs. The following measures have been proposed for improvement of stability ... 

Therefore, the volume flow of water, corresponding the volume exchange diffusional flux with polymer solute, can be regarded as osmotic flow caused by an osmotic pressure gradient29K The magnitude of this flow does however not effect the magnitude... 

It is the rate of separation rather than the efficiency of salt retention that is the primary practical issue in the development of reverse osmosis desalination. In addition to a variety of other factors, the rate of reverse osmotic flow depends on the excess pressure across the membrane. Therefore the problem of rapid flow is tied into the technology of developing membranes capable of withstanding high pressures. The osmotic pressure of sea water at 25 °C is about 25 atm. This means that no reverse osmosis will occur until the applied pressure exceeds this value. This corresponds to a water column about 840-ft high at this temperature. 

Diamond, J. M., Bossert, W. H. Stamding gradient osmotic flow. A mechanism of coupling of water and solute transport in epithelia. J. gen. Physiol. 50, 2061 (1967)... 

Central to the osmosis phenomenon is the semipermeable membrane (SPM), whose physical properties and species-selectivity directly govern the kinetics and thermodynamics of osmotic flow. Naturally occurring biomembranes of high selectivity, permeable to water but not to other solutes, are ubiquitous, for example, in macroscopic stomach linings and blood vessels, as well as in the microscopic cell membranes that encapsulate all known cell types. Some common synthetic membranes, such as Gore-Tex and cellophane, also exhibit selective permeability and osmotic activity. 

Aquaporins. Many biological membranes are not sufficiently permeable to water to allow for rapid osmotic flow. For example, the kidney membranes in... 

If P3 — P1 = osmotic pressure of the salt solution, no flow by diffusion will occur across the gap. For pressure differences less than this, AP < (P3 — Pi), normal osmotic flow would occur from the fresh water stream into the salt water. Thus, if we are to reverse this process, AP must be greater than (P3 — Pj), in order that water will distill from the salt water side to the fresh water side. 

In desalting seawater the losses can amount to 20 to 30% of the volume of the treated water. The electro-osmotic flow per unit of current is ... 

In the Nemst-Planck equations used the activity coefficients were neglected a term accounting for the electro-osmosis, however, is present. Calculated and measured concentration profiles could be made to inter-correspond by adapting the term for water transport. The values indirectly determined by electro-osmotic flow were now found to agree with those measured directly. 

Surfactants disrupt the cell wall by solubilizing the lipids in the wall. Sodium dodecylsulfate (SDS), sodium sulfonate, Triton X-100, and sodium taurocholate are examples of the surfactants often employed in the laboratory. Alkali treatment disrupts the cell walls in a number of ways including the saponification of lipids. Alkali treatment is inexpensive and effective, but it is so harsh that it may denature the protein products. Organic solvents such as toluene can also rupture the cell wall by penetrating the cell wall lipids, swelling the wall. When red blood cells or a number of other animal cells are dumped into pure water, the cells can swell and burst due to the osmotic flow of water into the cells. 

Calculate the rate of electro-osmotic flow of water at 25°C through a glass capillary tube 10 cm long and 1 mm diameter when the potential difference between the ends is 200 V. The zeta potential for the glass-water interface is -40 mV. 

Magnuson, M.L., Creed, J.T. and Brockhoffl C.A. (1997) Speciation of arsenic compounds in drinking water by capillary electrophoresis with hydrodynamically modified electro-osmotic flow detected through hydride generation inductively coupled plasma mass spectrometry with a membrane gas-liquid separator./. Anal. At. Spectrom., 12, 689-695. 

Normal urine contains no albumin or only a trace amount of it. In case of kidney failure or malfunction, the protein passes through the glomeruli and is not reabsorbed in the tubule. So, albumin and other proteins end up in the urine. The condition known as proteinuria may be symptomatic of kidney disease. The loss of albumin and other blood proteins will decrease the osmotic pressure of blood. This allows water to flow from the blood into the tissues, and creates swelling (edema). Renal malfunction is usually accompanied by swelling of the tissues. The Albustix test is based on the fact that a certain indicator at a certain pH changes its color in the presence of proteins. 

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