A Bragg scattering spectrometer for studying crystallization of colloidal suspensions

Abstract

A light scattering spectrometer is described that is used for the study of crystallization in hard sphere colloidal suspensions. Collimated laser light is Bragg scattered from the crystals as they form, and the diffracted light is focused by a liquid filled hemispherical lens onto low cost charge coupled device array detectors that are rotated about the optical axis to average the intensities around the whole Debye–Sherrer cone of scattered light. The temperature of the sample can be controlled, and this is utilized to control the amount of scattering from the sample. The spectrometer exploits the refractive index match of the colloidal particles, the solvent, the bath liquid, and the glass used for both the sample bottle and the hemispherical lens. Parameters measured are crystallization rate, the amount of crystal formed, and the average lattice spacing, all as functions of time. Results presented show that this spectrometer gives insight into the crystallization process more than 1 order of magnitude of time earlier than previous light scattering experiments, leading to understanding of the crystallization process.