Role of space charges inside a dielectric polymer in the electrohydrodynamic structure formation on a prepatterned polymer (ESF-PP)

Abstract

Electrohydrodynamic structure formation on a prepatterned polymer (ESF-PP) can duplicate structures identical to the initial geometry, but with a higher aspect ratio, under the influence of a spatially modulated electric field. In this process, a voltage is applied between a flat template and a flat substrate, sandwiching a prepatterned polymer and an air gap so as to generate an electrohydrodynamic (EHD) force at the air–polymer interface. Subsequently, the prepatterned polymer can be non-uniformly pulled upwards, causing deformation in its micro/nano-structure. Until now, most of the research into ESF-PP has explored various dielectric polymers, which are all considered to be the perfect dielectrics because of their low electrical conductivity. However, the assumption of a perfect dielectric typically creates discrepancies between theoretical analysis and experimental results in terms of the polymer motion and the final morphology. This phenomenon can be attributed to ignoring the action of the small number of free space charges within dielectric polymer motion (although the electrical conductivity of the dielectric polymer may be even lower than that of deionized water), which emphasizes the importance of the influence of space charges inside the dielectric polymer on deformation. This paper explores the role of free space charges by making a comparison between the perfect dielectric polymer and the leaky dielectric polymer on the progressive development, the surface topography and the aspect ratio from experimental tests and numerical simulations, and a discussion of the effect of the different electrical conductivities. Results show that the free charges inside the dielectric polymer can lead to a larger EHD force because of the additional Coulomb force, even at a low conductivity of 10⁻⁷ S m⁻¹, thus demonstrating the ability to duplicate a mushroom-like structure with a high aspect ratio, which has wide applications in superhydrophobicity, dry adhesion, nanogenerators, etc.