Characterization of micro-ZnO/PDMS composite structured via dielectrophoresis – Toward medical application

This paper proposed a new approach to achieve full characteristic of highly non-linear current density–electric field (J-E) curve, which depends on various key factors in terms of filler concentration, temperature, input voltage level, and structuration of ZnO particles (i.e. aligned or randomly dispersed). The homogeneity of particle distribution within the polymer matrix, together with the chain-like structure of the aligned composites elaborated with various ZnO volume fraction was verified via microscopic investigations. Numerical simulation was also conducted through COMSOL Multiphysics, giving an estimation of field distribution around ZnO phase. Experimental characterization in addition to analytical models was established using varying (sinusoidal) or direct current (DC) tests. The DC test was carried out in order to identify the conduction profile as well as the percolation threshold of ZnO samples. Temperature also has considerable influence on the switching field and the dielectric permittivity of the nonlinear composites. In the sinusoidal test, current discrimination was adopted using bipolar polarization loop, allowed the detailed quantification of conductivity values, while prediction in the capacitive current density enabled to distinguish the relative permittivity. These results demonstrated that the electrical properties of ZnO compound, such as conductivity and permittivity, substantially enhanced with the increasing filler content, especially when the samples were subjected to dielectrophoretic manipulation. Further analysis was carried out on sinusoidal unipolar polarization to predict the dielectric loss factor as function applied field. Finally, by playing on different pertinent parameters, it was possible to efficiently control the electric and mechanical characteristics of ZnO composite. Such properties are highly important in application of microvaristors used as protection devices. By associating with other features of ZnO like piezoelectricity, this material is undoubtedly of high interest in medical use where multifunctional system design becomes mandatory.