Dielectric measurement of a single sub-millimeter size microcapsule

A new technique is described for measuring dielectric dispersion of a single microcapsule in suspension over a frequency range from 1 kHz to 10 MHz. It was applied to polystyrene microcapsules which showed a two-step dielectric dispersion, that is, a superposition of two Debye type dispersions. The dielectric dispersion was analyzed by an electrical model in which a spherical core covered with a shell is immersed in a continuous phase, yielding the phase parameters related to the microcapsule: the wall thickness, the permittivity and conductivity of the core phase. The advantage of this technique is that it can characterize individual microcapsules, whereas the conventional method provides average properties of many microcapsules. Hence, the technique enables us to directly determine the distributions of the phase parameters and to exactly examine the relationship between the dielectric behavior and the microcapsule structure simultaneously observed by microscopy.