Preparation and properties of colloidal core-shell rods with adjustable aspect ratios

Colloidal boehmite (AlOOH) rods were used as cores for the preparation of rods with a silica shell. Via a three-step coating procedure silica rods with adjustable aspect ratios up to 20 were obtained by varying the amount of the added silica precursor tetraethoxysilane (TES). Silica rods are stable in various solvents such as water, ethanol, propanol, and dimethylformamide (DMF). Moreover, polymer-grafted silica rods can be dispersed in ethanol/toluene mixtures and cyclohexane. Incorporation of fluorescein isothiocyanate (FITC) in the silica shell enables the study of long-time self-diffusion processes in dispersions of rodlike particles with fluorescence recovery after photobleaching (FRAP). Fluorescent silica rods also may be used in direct imaging studies with confocal scanning laser fluorescence microscopy (CSLM).