(581d) Real-Time Study of Polymer Thin Film Patterning Induced by Electric Fields Using a New SFA Technique

One of the most interesting current problems in surface and colloid science is understanding the effects of external electric fields on surface and interparticle interactions. Patterns can be induced in thin polymer films by an electric field. The formation of desired patterns has the potential to eliminate complex steps in conventional imprinting techniques, such as the photoresist and exposure stages, in the fabrication of microelectromechanical systems (MEMS). Electric field gradients also show great promise in the design of DNA separation devices. In this study, we describe a new method to measure normal and/or lateral forces between two surfaces in a surface forces apparatus (SFA) while an electric field is applied between the surfaces. Two types of experiments were performed using the new technique: (1) a dynamic study of electric field-induced pattern formation of a thin polymer film, (2) measuring the effects of an electric field on the rheology of an ~40-um-thick film of zeolite particles suspended in silicone oil and. In the dynamic study, the initially uniform film transformed into a 2-D honeycombed network of depressed cells bounded by elevated ridges that grew slowly with time in a way consistent with previously derived theories. In the second study, under an electric field of strength ~1,000,000 V/m the shear force or effective viscosity of the colloid suspension was found to be two orders of magnitude higher than in the absence of the field, when the expected bulk value was measured. The new technique should be applicable to studies of other systems and interactions, such as double-layer forces, micro- and nanoelectrorheology, electric field-induced ordering of particles, and the effects of electric fields on adhesion, friction, and lubrication. Reference: Zeng, Tian, Anderson, Tirrell, and Israelachvili, Langmuir 2008, 24, 1173-1182.