Colloidal liquids usually appear turbid due to the strong multiple scattering of electromagnetic waves from the particles in suspension. As the concentration increases, particle interactions induce positional correlations which generally lead to a reduced optical density (higher transparency). However, the optical properties of a colloidal liquid can be manipulated by tuning the interaction potential between particles. In the presence of repulsive interactions, colloidal liquids show fascinating photonic properties despite their overall disorder. Short range structural order enhances the scattering strength at certain configurations while at the same time the total light transmission shows strong wavelength dependence, reminiscent of photonic crystals. The tunable optical properties of these photonic liquids suggest potential applications such as transparency switches or improved sunblockers. On the other hand the interplay between order and disorder and the scattering properties of these systems are strikingly similar to those discussed in the transport of electrons in liquid metals. Close to the Bragg condition the transport cross section becomes anisotropic and the transmission coefficient is reduced. In materials with high refractive index mismatch such an effect might open an alternative pathway to localization of light.
The conductance of nano-sized, surface disordered wires is theoretically analyzed all the way during an elongation process. Even though wire cross-section is kept constant during the whole process, the statistical analysis of the conductance reveals clear preference to take values close to integer multiples of the conductance quantum. We show that this is a consequence of having a very small number of channels and surface disorder only.