Coalescence during Emulsification

Abstract

An oil-soluble fluorescent probe, undecyl pyrene (UDP), is used to measure the amount of coalescence that occurs during the emulsification of tri-2-ethylhexyl phosphate using a high-pressure homogenizer. From these measurements, the roles of anionic surfactant (SDS) and gelatin in stabilizing drops against coalescence and promoting drop rupture during emulsification are deduced. It is found that gelatin aids in reducing coalescence, whereas SDS aids in rupture of drops. The effect of variables such as gelatin MW, surfactant type, and pH on coalescence and final drop size is investigated.

Emulsification mechanism and storage instabilities of hydrocarbon-in-water sub-micron emulsions stabilised with Tweens (20 and 80), Brij 96v and sucrose monoesters

“…We investigated this using a technique developed by Lobo [22,24,25] in which we studied the extent of coalescence after droplet break-up in a Microjet high-shear chamber as a function of surfactant type and concentration. An oil phase volume of 0.1 was used in these experiments.…”

“…The fluorescence spectrum of the unlabeled emulsion was recorded, and its value subtracted from the values of the labeled emulsion, and the unlabeled emulsion, to remove the contribution to fluorescence of the oil phase and the surfactant in subsequent calculations. Following the procedure described by Lobo [24], the extent of mixing of the dyed and un-dyed oil phases was calculated for the emulsion spectra before and after the second microfluidization process. The ratio of the peaks before re-emulsification/peak after re-emulsification was calculated.…”

“…The fluorescent dye 1-undecylpyrene was synthesized according to a synthetic route provided by Lloyd Lobo in a personal communication and discussed in Lobo et al [22,24,25]: details are given in the thesis by Henry [35].…”

“…These investigations are in turn related to the droplet sizes produced from the device. Previous work has addressed this question a number of ways; by fluorescent dye mixing, Lobo et al [24,25]; by microscopic determination of mixing of two dyes in microscopic droplets, Danner et al [26], using computer simulation, Cristini et al, [27], by turbidity [28] and by addition of brominate to oil to change the refractive index of half of the droplets followed by observation of turbidity changes as a result of changes in refractive index as a consequence of droplet mixing during emulsification [29]. Although this technique is not particularly useful for nano-emulsions as droplets approach the wavelength of light.…”

“…Following a previous study of pyrene fluorimetry in alkane-in-water emulsions [30], Lobo et al [24,25] used an oil-soluble fluorescent probe, 1-undecylpyrene (UDP) to measure the amount of coalescence that occurred during the emulsification of tri-2-ethylhexyl phosphate in a high-pressure homogenizer. The approach we have adopted follows that of Lobo et al [24,25] and uses the same water insoluble fluorescent dye, UDP, dissolved in decane, to determine the degree of coalescence occurring during formation of a decane-in-water emulsion system. UDP allows the determination of coalescence in emulsions because when it is dissolved at a sufficiently high concentration, it will exhibit an excimer peak in its fluorescence spectrum.…”