Real time monitoring of structure change of W/O type emulsion by using quartz crystal microbalance

Water in Oil type emulsion is in thermodynamic unstable state. The enlargement of the water drops and phase change or phase separation could be occurred by the duration of reservation. The aim of this study is the in situ monitoring of this phase change of emulsion by using Quartz Crystal Microbalance (QCM) method. Sodium hydroxide aqueous solution was used as the water composite, and the used oil phase was liquid paraffin. Emulsifier for W/O emulsion was sorbitan sesquioleate (monoester: diester=1 : 1). W/O emulsion (water ratio : 60%) was prepared by stirring at 1000 rpm. This type of emulsion is relatively unstable because of the hydrolysis of ester emulsifier by NaOH. The silver coated crystal was immersed in the emulsion and the resonance frequency was monitored by frequency counter. After 10(4) secs of immersion, the emulsion was suddenly destroyed. At this time, the resonance frequency showed large decrease (similar to MHz). As a reference, experiment similar to this was tried with various amounts of additional emulsifier. With small amounts of additional emulsifier, the timing of decrease of resonance frequency was recorded in the early stage. So this method could be a new monitoring method for the state of W/O type emulsion.