Structure and physical properties of colloidal crystals made of silica particles

The relationship between the particles size distribution of colloidal crystals and the structure and physical properties of the resulting 2D colloidal crystals is presented in this work. The colloids were constituted of silica sub-micron spheres with different size distributions comprised between 150 and 520 nm, synthesized by the Stöber method and assembled in one monolayer through the Langmuir–Blodgett technique. Optical and wetting properties of the resulting crystals were studied by different techniques – UV–visible spectrometry, spectroscopic ellipsometry and contact angle measurements. They were related to the crystal structure which was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The conservation of orientational and translational orders over a large area is found for crystals with narrow particle size distribution. Optical interference bands in the transmittance spectra are linked to the crystal periodicity and the presence of optical anisotropy is attributed to distortions in the film generated by the deposition process. Moreover, large particle size distribution results in the most hydrophobic crystals. Thus the physical properties of the colloidal crystals can be tailored or tuned by controlling the particle size distribution and the deposition parameters.