Response of the elastic properties of colloidal crystals to phase transitions and morphological changes

Abstract

We report on the shear modulus G of colloidal crystals formed from thoroughly deionized suspensions of charged latex spheres. G is measured as a function of particle number density n. Body- and face-centered-cubic (bcc and fcc) crystal structures are observed by simultaneously performed static light scattering, and a broad coexistence region is found between (2.7±0.1)×1018 m−3⩽n⩽(4.8±0.2)×1018 m−3. Below n=1019 m−3, G closely follows theoretical predictions for both bcc and fcc, while it stays constant throughout the transition region. Above n=1019 m−3, G still observes the predicted n-dependence but with values larger than expected. While in that region, an upper bound of particles per crystallite is estimated from scattering data to be on the order of 104; the abrupt change in G cannot be solely attributed to the gradual morphological transition from polycrystalline to nanocrystalline materials.