streaming potential

physical chemistry

1. PHYSICAL CHEMISTRY STREAMING POTENTIAL

2. INTRODUCTION The first observation of the streaming potential is generally attributed to the German physicist George Hermann Quincke in 1859. Streaming potential is a electrokinetic phenomena studied in the areas of surface chemistry & electrochemistry. It is commonly used to study the surface charge of membranes and can be calculated from Steaming potential or steaming current values. Electric potential which originates when an electrolyte is driven by pressure gradient though Channel or porous plug. Adjacent to the channel walls the charge neutrally of the liquid is violated due to the presence Of the electrical double layer ;a thin layer of counterions attracted by charged surface. The transport of counterions along with the pressure –driven flow gives rise to a net charge Transport-steaming current.

3. STREAMING POTENTIAL When an electrolyte solution is forced to flow a stationary capillary or a porous plug , an electrical potential difference will be produced between two end of capillary. The electrical potential difference is referred to as streaming potential , which means the liquid carries away the ions with the charge opposite to surface, giving rise to a streaming current, consequently leading accumulation of a charge at the ends & an electric field. Streaming potential depends on the constants that characterize the macroscopic behavior of the solution and the surface –solution microscopic interaction. The solution viscosity ,the ionic diffusivities, the dielectric constant the surface charge density[zeta potential] and the hydrodynamic radius in units of Debye lengths. A streaming potential is generated when an electrolyte solution carrying a net charge is forced , by means hydraulic pressure , there are two forms of action that this can take; The flow is through a porous plug of material ,in this case through the membrane pores , which is known as transversal steaming potential. The flow is across the surface of the membrane through a channel formed by two plates , known as tangential streaming potential.

4. MEASUREMENT METHOD A typical setup to measure streaming currents consists of two reversible electrodes placed on either side of a fluidic geometry across which a known pressure difference is applied . When both electrodes are held at the same potential ,the streaming current is measured directly as the electric current flowing through the electrodes . Alternatively, the electrodes can be left floating, allowing a streaming potential to build up between the two ends of the channel. A streaming potential is defined as positive when the electric potential is higher on the high pressure end of the flow system than on the low pressure end. The value of streaming current observed in a capillary is usually related to the zeta potential through the relation :

5. Consider given term from equation:

6. The equation above is usually referred to as the Helmholtz- Smoluchowski equation. The above equation assume that: The double layer is not too large compared to the pores or capillaries [ i.e.,ka >>1], where k is the reciprocal of the Debye length. There is no surface conduction. There is no electrical double layer polarization . The surface is homogeneous in properties. The is no axial concentration gradient . The geometry is that of a capillary /tube.

7. APPLICATIONS Steaming currents in well defined geometries are a sensitive method to characterize the zetapotential of surfaces, which is important in the fields of colloid and interface science. In geology , measurement of related spontaneous potential are used for evaluation of formations It consider in design for flow of poorly conductive fluid [gasoline lines] because of the danger of build of high voltage. The SCM [ streaming current monitor is a fundamental tool for monitoring coagulation in waste water . The higher levels of coagulant cause the small colloidal particles to coagulate and sediment out of the stream. Since, less colloid particles are in the waste water stream, the streaming potential decreases. It is used to generate usable electrical power. This typical s.p applied mechanical to electrical efficiencies are around 1%.

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