(316e) Optically Induced Assembly of Colloidal Crystals | AIChE

(316e) Optically Induced Assembly of Colloidal Crystals


Shah, A. A., University of Michigan
Solomon, M. J., University of Michigan

We report and analyze a simple, directed assembly method that uses light to yield three-dimensional colloidal crystals that are simultaneously reconfigurable in space and time.  The method uses simple illumination at a glass substrate coated with an unpatterned layer of indium tin oxide (ITO) to induce accumulation and assembly of colloids at the illuminated region. The colloids used are commonly available, sterically stabilized, charged latex colloids dispersed in low dielectric constant solvents that are refractive index matched with the colloids.  The three-dimensional crystals generated by this method are about 5 layers thick, extending 10 microns into the bulk. We quantify the effect of initial volume fraction and light intensity on the kinetics of the photoinduced assembly, and by analysis of these experiments conclude that the assembly mechanism is electrophoretic in origin.  Specifically, the data support a mechanism in which light catalyzes reactions at the surface that drive ion flows.  These ion flows establish an electric field that drives electrophoretic motion of the colloids. We apply this mechanistic understanding to induce colloidal crystal assembly in regions of complex shape through simple optical manipulations.  Because we can rapidly create colloidal crystals that can be reconfigured in time and space, this technology represents a new kind of template free, photolithography technique for the production of colloidal crystals.  Potential applications of the method are in areas such as adaptive colloidal crystal optics and reconfigurable colloidal electrodes.