The ZetaCAD determines the zeta potential of porous plugs, membranes and flat surfaces using the well-known Streaming Potential technique. This device is used in research laboratories for a broad range of applications including pharmaceuticals, cosmetics and geology.
The ZetaCAD determines the zeta potential of solid surface. The device comes with a variety of measurement cells that allow measurements of zeta for particle in a porous plug, for macroscopic flat surfaces and for filter membranes.
The zeta is determined from measurements of the streaming potential. This is the voltage difference that arises when a liquid is forced to flow through a capillary or a porous plug. This potential arises because there is an electric charge on the solid surfaces. This charge is balanced by an equal and opposite charge in the liquid that lies close to the surface.
When the liquid is forced to flow across the solid surface, it carries its charge with it. As a result there is a build up of positive charge at one end of the cell and an equal negative charge at the other end. These charges set up an electric field which tends to oppose further charge accumulation. After a short time (typically of the order of microseconds) the current due to the backfield balances that due to the flow and the voltage difference across the cell levels off. This steady voltage difference is called the streaming potential, denoted by E.
The streaming potential is recorded in the ZetaCAD along with differential pressure P across the cell, and the temperature T and electrical conductivity of the solution. The zeta potential is calculated from the slope of the streaming potential vs pressure line using the classical Helmholtz-Smoluchowski formula.