Order−Disorder Transition in Monolayers of Modified Monodisperse Silica Particles at the Octane−Water Interface

Abstract

We have studied the effect of particle wettability on the structure of planar monolayers of micron size monodisperse silica particles at the octane−water interface. The particles' wettability was adjusted by silanization of their surfaces with dichlorodimethylsilane; thus their contact angle at the octane−water interface was in the range 70−150°. The modified particles were spread at the interface, and the monolayer structure was studied by direct microscope observation. A very distinct difference in the structure of monolayers depending on the particle contact angle has been observed. Very hydrophobic particles with large contact angles gave well-ordered monolayers at interparticle distances larger than 3 particle diameters. Such well-ordered monolayers in the case of silica particles are reported for the first time. The monolayers of less hydrophobic particles (with contact angles smaller than 115°) were totally disordered and aggregated. The disorder−order transition in the monolayer structure occurred...