他物質衝突時の乳剤安定性に及ぼす初期粒子密度の影響

Abstract

A monolayer of particles at an air/water interface was used to model a Pickering emulsion, in order to determine the effect of the size of the particles in a monolayer at an air/water interface and their packing density on the physico-chemical properties of a model Pickering emulsion (a monolayer), e.g., stiffness, adhesive ability, and change in particle packing, after a collision by a particle in the water phase. A Langmuir trough was used to obtain surface pressure-area per molecule isotherms of bare TiO2 particulate monolayers at an air/water interface and the Monolayer Particle Interaction Apparatus (MPIA) to directly study the forces between the TiO2 monolayers at an air/water interface and a micro-sized TiO2 particle in the subphase. The effect of the packing density of the particles in the monolayer on its stability was observed by optical microscopy, while the forces were being measured by bringing the micro-sized TiO2 particle in the subphase in and out of contact with the TiO2 monolayer. Langmuir monolayers of bare, hydrophilic TiO2 particles were directly formed at the air/water interface by using a subphase with a pH below the isoelectric point of TiO2. The effects of the particle size on the physical properties of the monolayer were then investigated by using particles with a diameter of 75 nm, 300 nm, 3μm and 10 μm. The packing density influence was determined by measuring the forces and by imaging the air/liquid interface in the presence of the monolayer at different surface pressures. We found that the particulate monolayer became more deformable and instable as the size of the particle decreased. Large particles (micro-sized) gave the least deformable monolayer, where monolayers of a high particle packing density gave stable monolayers even upon contact by a micro-sized particle.