Elastic modulus of crystal-like structures of deionized colloidal spheres in sedimentation equilibrium as studied by the reflection-spectrum method

Abstract

The height dependences of the lattice spacing of crystal-like structures have been studied in sedimentation equilibrium and in deionized aqueous suspensions by reflection spectrum measurements of monodisperse polystyrene spheres (85–264 nm in diameter). The lattice spacing increases linearly owing to the gravitational field as the height increases. From the magnitude of the compression, Young's elastic moduli (G) for the crystal-like structures are estimated to be between 1 and 100 Pa. G increases as the concentration and/or size of spheres increase. The results confirm that an electrostatic intersphere repulsion and an elognated Debye-screening length around the spheres are essential for the formation of crystal-like structures.