Mixed colloid-surfactant systems

We study the behaviour of colloidal particles when introduced into a liquid crystal matrix. First, we probe the influence of the surface anchoring energy by using various mixtures of surfactant and then, we investigate the influence of the nematogen shape. When the surface energy dominates, a hedgehog defect is formed and, according to an electrostatic analogy, the distortions around the particles exhibit a dipolar character. By contrast, for weaker anchoring, the configuration becomes quadrupolar as evidenced by the observation of Saturn ring defects in thermotropic systems and the structure of latex clusters in lyotropic systems. Also, the shape of the nematogens is shown to control the type of defect and interaction that take place in the system, going from a dipolar symmetry in the discotic phase to a quadrupolar one in the calamitic phase. A simple scaling analysis accounts for our findings