Electric Field Processing of Core–Shell Nanoparticles

In many applications nanoparticles are functionalized with a thin layer of coating, which forms a core–shell structure. When nanoparticles are dispersed in a fluid, the functional properties of the colloidal suspension can be tuned by controlling the orientation of the particles with an applied electric field. This paper proposes a dynamic model for the processing of core–shell nanoparticles in a fluid. By rigorously calculating the torque induced by an electric field, we showed that the shell of a nanoparticle has an important effect on the rotational behavior, even when the shell is thin and takes only a small portion of the total volume. For lossy dielectrics, we showed that the permittivities and conductivities of both the shell and core of a particle determine the magnitude and direction of the induced torque. The core–shell structure was found to lead to frequency dependent behavior that is quite different from that of bare nanoparticles. The study also investigated the competition between the rotational alignment due to electric field and randomization due to Brownian rotation, which revealed the evolution of the orientation distribution function of many Brownian core–shell nanoparticles suspended in a fluid.