The influence of interfacial ageing and temperature on the coalescence of oil droplets in water

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2011-01, Vol.374 (1-3), p.96-101
• Main Authors: Ata, S., Pugh, R.J., Jameson, G.J.
• Format: Article
• Language: English
• Subjects: Chemistry; Coalescence; Coalescing; Colloidal state and disperse state; Droplets; Dynamical systems; Dynamics; Emulsions. Microemulsions. Foams; Exact sciences and technology; Fysikalisk kemi; General and physical chemistry; Kemi; Kerosene; Mathematical analysis; NATURAL SCIENCES; NATURVETENSKAP; Oil droplets; Physical chemistry; Quality; Rupture; Surface physical chemistry
• ISSN: 0927-7757; 1873-4359; 1873-4359
• DOI: 10.1016/j.colsurfa.2010.11.012

. Post rupture oscillations of coalescing analytical grade kerosene; percent change in the total droplet surface area relative to the initial area following coalescence for analytical grade kerosene after 1 and 5min ageing (exposure to the water phase) at 25°C. [Display omitted] ▶ Using a high speed camera a preliminary understanding of the phenomenon of coalescence of fresh and aged kerosene oil droplets where observations from first contact to final damped equilibrium are reported. ▶ A distinct differences in the coalescence between fresh and aged binary droplets of analytical and technical grade kerosene was found. ▶ On ageing, we believe the more polar aromatic ingredients of kerosene diffuse to the interface modifying the interfacial elasticity and viscosity and delaying the coalescence process. Understanding the coalescence behaviour of two single droplets of industrial kerosene oil is an important precursor for predicting the stability of a concentrated kerosene emulsion system. In taking such an approach, distinct differences in the dynamic coalescence of fresh and aged binary droplets of analytical and technical grade kerosene was observed which we believe to be important with regard to the stability of concentrated systems. It was shown from induction time measurements (the time from first contact to rupture of the thin film separating the droplets) that the analytical grade kerosene binary droplets are considerable more stable than the technical grade at higher temperature (up to 65°C) but the analytical grade shows a gradual decrease in stability up to 65°C. At 75°C, both grades of kerosene droplets remained stable to coalescence. After this initial rupture, coalescence proceeded as a series of dynamic oscillations and further insight into the fusion behaviour could be obtained by analysis of the change in the surface area of the aggregated droplets as a function of time. The longer induction times correlated with the more vigorous post rupture oscillations (less damping resulting from an increase in interfacial elasticity) which were recorded during the drop fusion. These experiments reveal preliminary steps in the coalescence of oil droplets where measurements from first contact to final damped equilibrium are quantified. This aspect of coalescence has not been well represented in the earlier literature.