Alberto Fernández-Nieves

This paper gives an overview of our recent work on liquid crystal emulsions and their use as starting point towards making monodisperse suspensions of colloidal entities with optical and geometrical anisotropies. The procedure utilizes a monodisperse emulsion of a photopolymerizable liquid crystal that is polymerized after mechanical deformation of the drops. We have engineered solid spheres as well as oblate and prolate spheroids presenting a bipolar anisotropic character at the micrometer scale. These materials respond to optical and external electric fields by aligning their mean optic axis parallel to the field, thus constituting excellent systems for fundamental studies and applied uses.

We use electrophoretic mobility (μ) measurements of charged colloidal particles under the presence of multivalent counterions as a probe of the electrostatic correlations between them; they become important for sufficiently high surface charge densities of the colloid (σ) and result in a decreasing μ upon increasing σ. The physics of this decrease is the same as that giving rise to charge inversion. We account qualitatively for the observations by considering recent theoretical arguments that assume the counterions next to the colloid surface as a strongly correlated liquid of properties similar to that of a Wigner crystal.

We perform static light scattering experiments on a dilute suspension of microgel particles and model the resultant form factors P(q) by assuming an exponentially decaying dielectric permittivity. The result is that P(q) is a Lorentzian function of the scattering wavevector q for length scales greater than the particle size; the width approximately corresponding to twice the particle radius. This simple model reasonably accounts for scattered light from both swollen and shrunken microgel phases.