Transient scattering changes induced by pulsed sinusoidal electric fields

Surface-charge determination of crocidolite particles in suspension

“…(Shaw, 1969). Schiller et al (1980) measured various crocidolite samples and produced a graph of u for samples of variable axial ratio.…”

“…It is also assumed that the average orientation of the rods within an applied electric field will be parallel to the field direction. Under such conditions the electrophoretic mobility is given by Smoluchowski's equation (Shaw, 1969) …”

“…From the equation (Shaw, 1969), also for small ~ca, u = QDt/kT (6) with k and T the Boltzmann constant and the absolute temperature, respectively, the effective charge Q at the shear plane of the electric double layer can be evaluated. This may itself be equated to the product Q = nez…”

“…From equations 9a and 9b it may be noted that: (i) An is proportional to E 2 at low E but reaches a saturation value with increasing E; (ii) from the high-field data, (gl -gz) can be evaluated (equation 9a); (iii) at low fields, the factor in the brackets of equation 9b can be enumerated, 09 being the angular frequency of any applied electric field; (iv) this frequency dependence affords a means of isolating the permanent and induced contributions, since if pulses of alternating voltage are used with a sufficiently high ~o, then only the (a~ a 2) factor contributes (Schweitzer & Jennings, 1972). With low frequency (or d.c.) pulses, both p and Aa contribute and can thus be evaluated.…”

“…In this case the electrophoretic mobility (u) is also determined. This is a parameter which has long been used to estimate the net surface-charge density of suspended particles, from which may be derived information on the sol stability (Shaw, 1969;Mysels, 1959;Kruyt, 1969). Whereas conventional electrophoretic methods are laborious and also difficult for particles which are sub-microscopic, the electrophoretic light-scattering method is fast and should be particularly suited to the study of such small particles.…”