Use of Spatially Non-Uniform Electric Fields for Contact-Free Assembly of Three-Dimensional Structures from Colloidal Particles
Wood, Jeffery Alan
AC electrokinetics , colloidal assembly , electric fields , dielectrophoresis
In this thesis, three speciﬁc research contributions to the use of non-uniform electric ﬁeld driven colloidal assembly are described. The ﬁrst relates to experimental work using dielectrophoretic and electrohydrodynamic forces (electroosmosis) to shape three-dimensional colloidal structures. Formation and stabilization of close-packed three-dimensional structures from colloidal silica was demonstrated, using gelation of pluronic F-127 to preserve medium structure against suspension evaporation. Stabilization of ordered structures was shown to be a signiﬁcant challenge, with many of the conventional techniques for immobilizing colloidal crystals being ineﬀective. Secondly, the signiﬁcance of electrohydrodynamic ﬂows resulting from electric and particle concentration (entropic) gradients during the assembly process was demonstrated using numerical simulations based on a thermodynamic framework. These simulations, as well as experimental validation of assembly and the presence of ﬂuid ﬂows, showed that assuming equilibrium behavior (stationary ﬂuid ﬂow), a common assumption for most modelling work to date in these systems, is inappropriate at all but the most dilute concentration cases. Finally, the relevance of multiparticle eﬀects on electric-ﬁeld induced phase transitions of dielectric colloids was demonstrated. The eﬀect of multiparticle/multiscattering eﬀects on the suspension permittivity were accounted for using semi-empirical continuum permittivity formulations which have been previously shown to describe a wide variety of solid packing structures, including face-centered cubic and other colloidal crystal structures. It was shown that multiparticle eﬀects have a signiﬁcant impact on both the coexistence (slow phase separation) and spinodal (fast phase separation) behavior of dielectric suspensions, which has not been demonstrated to date using a continuum framework.