moves up and down. These charged particles are momen-The streaming current detector (SCD) is an instrument used tarily immobilized on the surfaces of the piston and the for continuous characterization of colloidal surface charge. It meacylinder. As the fluid motion forces mobile counterions in sures the alternating current generated by mobile countering when the double layer past these immobile particles, half-reactions charged material momentarily adheres to cylinder and piston walls at the electrodes generate the streaming current as an alterwhile the piston reciprocates. The utility of the SCD for coagulant nating current which is directly related to the charge on control is generally accepted, as evidenced by the estimated one the particles (3, 10). Electrical circuitry capable of phasethousand units in service in North America. However, one drawsensitive amplification and rectification of the current can back to this device has been the lack of an exact quantitative model explaining its functioning. This paper provides such a description, then provide a continuous reading that characterizes the porelating the generated current to the zeta potential of the characlarity and magnitude of colloidal charge in the sample.
terized material as a function of instrument parameters and solu-
The device differs from the classical means of measuring tion chemistry. The model, programed in Mathematica, agrees streaming potential or current in that the dead-ended chamclosely with an earlier analytical solution under many conditions. ber provides electrical isolation of the cell while still Its inclusion of an inertial term, however, allows behavior of the allowing particle exchange with fresh sample on a continu-SCD to be simulated under a more general range of conditions. ous basis. These attributes allow characterization of particle