Dynamic control of the photonic smectic order of membranes.

Self-assembled soft matter is often used in photonics because its characteristic length scale can be of the order of the wavelength of light. For example, a hyperswollen lamellar phase composed of bilayer membranes reflects visible light by the Bragg diffraction and acts as a photonic smectic crystal. The softness of such a structure allows us to dynamically control its photonic characteristics using an external field, as reported here. The smectic order of membranes is destabilized by doping charged colloidal particles into intermembrane water regions. However, we found that anisotropic coherent motion of particles along membranes induced by an alternating electric field enhances the degree of the photonic smectic order significantly. This demonstrates that entropic interactions can be controlled by modulating the membrane fluctuations through their dynamic coupling to an external field.