Electroosmotic pressure

Electro osmosis often accompanies electrophoresis. It is the transport of Hquid past a surface or through a porous soHd, which is electricaHy charged but immovable, toward the electrode with the same charge as that of the surface. Electrophoresis reverts to electroosmotic flow when the charged particles are made immovable if the electroosmotic flow is forcibly prevented, pressure builds up and is caHed electroosmotic pressure. 

There is an additional pressure drop across the cake, developed by electroosmosis, which leads to increased flow rates through the cake and further dewatering at the end of the filtration cycle. The filtration theory proposed for electrofiltration assumes the simple superposition of electroosmotic pressure on the hydraulic pressure drop. 

Fig. 6.4 Electroosmotic pressure. Hydrostatic pressure difference Ap compensates the osmotic pressure difference between the compartments 1 and 1 and prevents the solvent from flowing through the membrane 2...

Electroosmosis This system is one where a fluid passes next to a charged material. This is actually the complement of electrophoresis. The pressure needed to make the fluid flow is called the electroosmotic pressure. 

Electroosmosis Here, the liquid (an electrolyte solution) moves past a charged surface (e.g., the surface of a capillary tube or through a porous plug) under the influence of an electric field. Thus, electroosmosis is the complement of electrophoresis. The pressure needed to balance the electroosmotic flow is known as electroosmotic pressure. 

In electroosmosis, the stationary and mobile phases are exchanged in relation to electrophoresis. As measurement of the rate of movement of a liquid through a capillary is difficult, the force that it exerts is measured, i.e. the electroosmotic pressure, or, alternatively, the volume of liquid transported through a capillary in a given time interval. The electroosmotic velocity, veo, is... 

There exist also other kinetic factors involved in the stabilising action of surfactants. For example, a relation between the lifetime of foams stabilised with various ionic surfactants and the electroosmotic pressure pti [33] the higher pel the more stable the foam is. The... 

The maximum electroosmotic pressure of the liquid flowing through a capillary or a membrane equals... 

The first results about foam electrokinetics have been reported by Sharovamikov [62,63]. An electroosmotic liquid transport is observed in foams from solutions of ionic surfactants (NaDoS, CTAB, PO-3A, etc.) and it is larger than in systems with solid capillaries (specific transport from 1.6-1 O 6 to 210 6 m3 C 1). The maximum electroosmotic pressure depends on the initial pressure in borders and reaches 1 Pa. The addition of dedecanol to the NaDoS solution sharply decreases the electroosmotic transport but increases the electroosmotic pressure. To reduce the influence of border and film non-homogeneity that originates in a static foam under gravity, the electrokinetic studies have been performed in an advancing foam [62]. The specific electroosmotic transport depends on the capillary pressure and reaches a maximum value at pg = 0.5 kPa. The streaming potential (up to 10 mV)... 

Electroosmosis The motion of liquid through a porous medium caused by an imposed electric field. The term replaces the older terms elec-trosmosis and electroendosmosis. The liquid moves with an electroos-motic velocity that depends on the electric surface potential in the stationary solid and on the electric field gradient. The electroosmotic volume flow is the volume flow rate through the porous plug and is usually expressed per unit electric field strength. The electroosmotic pressure is the pressure difference across the porous plug that is required to just stop electroosmotic flow. 

Electroosmosis—the movement of liquid relative to a stationary charged surface (e.g., a capillary or porous plug) by an applied electric field (i.e., the complement of electrophoresis). The pressure necessary to counterbalance electroosmotic flow is termed the electroosmotic pressure. 

Movahed S, Kamali R, Eghtesad M, Khosravifard A (2013) Analytical study of mixed electroosmotic-pressure-driven flow in rectangular micro-channels. Theor Comput Fluid Dyn 27(5) 599-616... 

Li HW, Wong TN, Nguyen NT (2009) Analytical model of mixed electroosmotic/pressure driven three immiscible fluids in a rectangular microchannel. Int J Heat Mass Transf 52 4459-4469... 

In 1808, Rous, a colloid chemist, observed that imposing an electrical potential difference across a porous wet clay led not only to the expected flow of electricity but also to a flow of water. He later applied hydrostatic pressure to the clay and observed a flow of electricity. This experiment displayed the electrokinetic effect and demonstrated the existence of coupled phenomena where a flow may be induced by forces other that its own driving force. Therefore, the electric current is evidently caused by the electromotive force, but it may also be induced by the hydrostatic pressure. When two chambers containing electrolytes are separated by a porous wall, an applied potential generates a pressure difference called the electroosmotic pressure. Also, mass flow may generate an electric current called the streaming current. 

The anodes used are the sprayed cellulose or tank anode systems developed to apply chloride removal. In addition to generating hydroxyl ions, the developers claim that by using a sodium carbonate electrolyte they make the treatment more resistant to further carbonation. The patent claims that sodium carbonate will move into the concrete under electroosmotic pressure. A certain amount will then react with further incoming carbon dioxide. The equilibrium is at 12.2% of 1 m sodium carbonate under atmospheric conditions ... 

Electroosmosis If a difference of potential is deliberately set up along the axis of narrow tube or across a porous plug, liquid in the tube or plug flows until a hydrostatic head sufficient to prevent continued flow has built-up to the value of the electroosmotic pressure. In aU these phenomena, the EDL and potentials are involved as stated above. 

Fluid movement through a charged material (like earth) gives rise to electroosmotic pressure. This arises from asymmetrical charge distribution at the liquid-solid interface, which depends on the magnitude of the surface potential. 

Electrokinetic phenomena are due to the coupling between electrical current and matter flow. Consider two chambers, 1 and 2, separated by a porous wall. If a voltage V is applied between the two chambers (Fig. 16.4), a current will flow until a pressure difference Ap is established at the steady state. This pressure difference is called the electroosmotic pressure. Conversely, if a fluid flow J from one chamber to another is achieved by a piston, an electric current I, called the streaming current, flows through the electrodes. As before, the thermodynamic description of these effects begins with the expression for the entropy production under the conditions specified above. In this case we essentially have... 

Figure 16.4 Electrokinetic phenomena. Two chambers containing electrolytes are separated by a porous wall or capillary, (a) An applied potential V generates a pressure difference Ap, called the electroosmotic pressure, (b) If the fluid is made to flow from one chamber to another by a piston, it generates an electrical current I, called the streaming current...

The total measured velocity of the fluorescent tracing particles is a superposition of the electroosmotic, pressure-driven and electrophoretic and Brownian motion velocity components [8]. It can be expressed as... 

A zwitterionic additive has been tested to improve the performance of electrokinetic micropumps, which use the voltage applied across a porous matrix to generate an electroosmotic pressure and flow in microfluidic systems (9). 

---