Crystal-like structures of deionized polystyrene spheres at interfaces with quartz, air, n-hexane, polystyrene and poly(methyl methacrylate)

Abstract

Ordered lattice structures [face-centred cubic (f.c.c.) and body-centred cubic (b.c.c.) lattices] of deionized polystyrene spheres (91 and 109 nm in diameter) that are close to interfaces with air, quartz glass, n-hexane, polystyrene and poly(methyl methacrylate) are analysed by reflection-spectrum measurements. When a quartz cell, which is often used for spectrophotometric measurements, is replaced by air or n-hexane, a transformation occurs from f.c.c. to b.c.c. lattices. The lattice spacing (intersphere distance) of the crystal-like structures at the interfaces decreases by 4–18% from the mean spacing on the assumption of a uniform distribution throughout the suspension. The spacings are in the following order: quartz glass > n-hexane polystyrene ≈ poly(methyl methacrylate)≈ air. This is explained reasonably by the condensation (weak adsorption) effect of the spheres around the interfacial materials produced by hydrophobic and/or dipole–dipole interactions.