Limited Coalescence in Particle-Stabilised Emulsions: Experiment and Theory
- Event time: 1:00pm
- Event date: 26th July 2004
- Speaker: Bernard P. Binks (Surfactant & Colloid Group Department of Chemistry University of Hull)
- Location: Room 2511, James Clerk Maxwell Building (JCMB) James Clerk Maxwell Building Peter Guthrie Tait Road Edinburgh EH9 3FD GB
We prepare oil-in-water (o/w) and water-in-oil (w/o) simple emulsions stabilised solely by silica nanoparticles of different hydrophobicity. If the total amount of particles is initially insufficient to cover fully the fresh oil-water interfaces so formed, the emulsion drops coalesce such that the total interfacial area is progressively reduced. Since it is likely that particles are irreversibly adsorbed, the degree of surface coverage by them increases until coalescence is halted. We follow the rate of drop coalescence from the initial fragmented state to the saturated situation using either a digital camera (large drop systems) or a video camera and optical microscope (small drop systems). Using simple theory, we find that, unlike surfactant-stabilised emulsions, the coalescence frequency depends both on time and particle concentration. The final drop size distributions are relatively narrow and we obtain a linear relation between the inverse of the average drop diameter and the total amount of solid particles; the proportionality constant depends on the intensity of mixing during emulsification. The overall features of the process are independent of the type of mixing and the drop volume fraction, allowing the fabrication of stable o/w and w/o emulsions with average drop sizes ranging from a few microns to several millimetres.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..