(560e) Electric Field-Driven Structuring in Suspensions | AIChE

(560e) Electric Field-Driven Structuring in Suspensions

Authors 

Khusid, B. - Presenter, New Jersey Institute of Technology
Elele, E., New Jersey Institute of Technology
Lei, Q., New Jersey Institute of Technology
Emerging routes based on electro-micro-fluidic systems enable the rapid fabrication of colloidal materials without the need for expensive tooling and offer exciting opportunities for materials assembly. Although each one of such technologies is independently unique, all of them share the common feature of utilizing dielectrophoresis and structural transformations, governed by the dipolar interactions, which vary from attraction to repulsion, depending on the relative orientation of the dipoles. The ability to manipulate particles is based on the particle-fluid polarization contrast that characterizes a difference in polarizability between particles and a host fluid and depends on the mismatch of their dielectric constants and conductivities and the field frequency. Advantages include the use of an electric field that requires no moving parts, the employment of the polarization force acting on a particle that is insensitive to its charge which is difficult to control, the provision of two independent control variables (field strength and frequency) and the ease of adaptability to electronics, so that it can be incorporated more favorably into micro-and nano-systems. The widespread use of electrically driven colloidal processes emphasizes a critical need for improving fundamental understanding of the role of spatially and time varying fields in directing and controlling non-equilibrium phenomena in a suspension of interacting colloidal particles. The challenge is due to kinetic limitations because the energy of the interparticle dipolar interactions at typical field strengths is tens to hundreds of times stronger than the Boltzmann energy. The colloid can therefore be kinetically trapped into metastable configurations for a long time due to the lower mobility of multi-particle structures formed in an applied field compared to that of individual particles. Although numerous experimental studies have been performed involving â??â??electrically tunableâ??â?? dipole-dipole interactions, the rich variety of the patterns that have been described could also have been influenced by gravity effects, such as particle sedimentation, convection and jamming, which often compete with dipolar forces during the slowly evolving structure formation.

Flight tests conducted in NASA Zero-Gravity airplane demonstrate that the presence of even weak gravity forces in a suspension of not density matched particles significantly changes dielectrophoretic processes and structure formation. A requirement for precise matching of densities between particles and a host fluid in order to avoid undesirable gravity effects severely limits the possibilities for varying a particle-fluid polarization contrast in terrestrial experiments.

Microgravity offers an opportunity to probe electrically driven phenomena over a wide range of the mismatch of dielectric constants and conductivities between particles and a host fluid by conducting experiments on not density matched suspensions in long timescales without masking effects of the gravity. We will report experimental data on field driven structure formation in neutrally-buoyant suspensions and present our approach to the development of experiments in the Advanced Colloids Experiment facility of the International Space Station (ISS). The aim of the ISS experiments is to observe electrically driven phenomena in model suspensions of not density matched particles is to understand basic mechanisms of structure formation in polarized suspensions and to suggest novel routes for creating functional materials.

The phenomena selected for ISS tests are logical candidates to take advantage of microgravity because terrestrial observations failed to provide a comprehensive physical understanding of the underlying physics. The work is supported by NASA's Physical Science Research Program, NNX13AQ53G.