Dissociation of functional surface groups and/or adsorption of ions are the most important processes. Figure 2 shows a number of possibilities. Surface charges on suspended particles can be caused by a variety of phenomena. 1 Model examples of pH Vs zeta functions showing dissociation of acid or alkaline surface groups and adsorption These curves are found for example in the protolysis of acid or alkaline surface groups and in pH-dependent adsorption processes.įig. Figure 1 shows schematic examples of zeta potential Vs pH functions that are characteristic of certain surface conditions. However stability assessment using the zeta potential as the measurable variable may only be useful if the system is sufficiently well understood.Įlectrokinetic measurements can be used to investigate the effect of each of the excipients in a formulation on the dispersed materials surface characteristics. In many cases, the zeta potential can be used directly as the criterion for assessing product quality. The basis of DLVO is to use the sum of the repulsive force (V R – electrostatic BORN forces) and attractive (VA – van der WAALS forces) to calculate the particle interaction potential. Using DLVO theory, it is possible to assess the stability of suspensions and emulsions by means of the zeta potential. The zeta potential is a consequence of the existence of surface charge, and can give information on electrical interaction forces between the dispersed particles. The zeta potential ( x ), or electrophoretic mobility (µ E), is increasingly being used to investigate fine particle systems. This potential is usually more of interest because particles interact according to the magnitude of this value, rather than the potential at the surface of the particle.
Instead the charge at a distance from the particle, called the zeta potential is measured. The surface charge cannot be measured directly. This is an important factor in determining the interactions between particles, and hence dispersion characteristics such as dispersion stability, flocculation, viscosity, film forming characteristics etc. One of the significant surface properties is the surface charge. Particle size is often considered one of the most important parameters, however, as particle size reduces, the surface area increases significantly in comparison with the volume, so surface properties increasingly determine the dispersions characteristics. There are many aspects of a particle dispersion that need to be investigated to fully characterize a system. Temperature control range: 0☌ – 90☌ +/-0.Methods for determining the zeta potentialĪpplications – possibilities for automation.