The effect of demulsifier on the stability of liquid droplets: A study of micro-force balance

Abstract

An original device was developed by our research group and used for quantitatively and qualitatively studying the stability mechanism of two liquid droplets in another liquid phase. The squeeze time can be employed to detect the stability of liquid droplets. The effect of water soluble emulsifier TX-100 and oil soluble one Span-80 on the squeeze times of both aqueous and kerosene droplets have been investigated. Moreover, the influences of three polyether demulsifiers with different structures, linear PEL, branched PEB and star-type PES, on the stability of liquid droplets have also been studied. Based on experimental results, the hydrophilic head group ethoxylation (EO) chain of TX-100 nearly flats at interface and forms compact interfacial film closed to water phase, which makes kerosene droplets stable at aqueous. On the other hand, two water droplets contain TX-100 will coalesce at once when they contact each other. For oil soluble emulsifier Span-80, the compactness of two sides of interfacial film leads to both stable water droplets and oil droplets. The molecular size of demulsifier may play the crucial role in controlling droplets coalescence: PEL with smaller size can easily destroy aqueous droplets in oil; PEB shows strong effects on both kerosene and aqueous droplets for it has a moderate molecular size; PES with larger size shows strong ability to destroy oil droplets in aqueous but little effects on aqueous droplets in oil.