Rheology of High Internal Phase Emulsions

Abstract

The mechanical dispersion technology used in this study employs rotor-stator mixers that produce water-continuous high internal phase emulsions (HIPEs) with narrow drop size distributions and small drop sizes, even when the internal phase (oil) viscosity is quite high. Analysis of these HIPEs reveals trends that are consistent with formation by a capillary instability mechanism in which a shear deformation produces highly elongated drops that rupture to form uniform, small droplets. In the search for a predictive tool to aid in the manufacture and use of HIPEs, rheology data for these shear-thinning HIPEs have been compared to data for models in the literature. Existing models do not correctly account for the effect of a high internal phase viscosity on the rheological properties of the HIPE. Another shortcoming is failure to correctly address the shear-thinning exponent. Whereas internal phase viscosity does not seem to affect the shear-thinning exponent, the surfactant apparently plays an important role, possibly through its modification of the interfacial tension and continuous phase rheology.

Emulsification in turbulent flow

“…12 (see also the discussion in Section 5.5 of the third part of this series [8]). Similar decrease of the mean drop size and of the emulsion polydispersity upon increase of Φ were reported previously in the literature [45][46][47], without giving an explicit explanation for the observed trends. The sharp change in the emulsion characteristics upon the increase of Φ above 0.6 indicates a possible change in the regime of emulsification when concentrated emulsion is passed through the homogenizer.…”

Role of liquid crystal in the emulsification of a gel emulsion with high internal phase fraction

“…The latter expression in particular refers to those that have such a high viscosity that they behave like a gel. These emulsions exhibit interesting rheology and often good stability [3][4][5]. One reason for the interest in such emulsions is their promising potential in topical applications, particularly for the encapsulation and release of actives [6][7][8][9] and as reaction media [10].…”

Water-in-oil gel emulsions from a cholesterol derivative: Structure and unusual properties

“…Clearly, the G 0 values of the gel emulsions exhibit weak dependence on frequency, specifically, $660 Pa for 85%, $1260 Pa for 75%, and $1580 Pa for 65% at 0.0628 rad s À1 , a typical viscoelastic behavior, suggesting that the gel emulsion tested have good tolerance to external forces. Comparison of the G 0 values of the gel emulsions indicates again that the storage modulus of the gel emulsion decreases along with increasing the water content in the system, an inconsistence result with those reported in the literatures [41][42][43][44][45][46]. Fig.…”

“…It is to be noted that this is a very different result from that reported in the literatures. For conventional gel emulsion systems, both G 0 and the yield stress of a system increase rather than decrease along with increasing the dispersed solvent content in the system [41][42][43][44][45][46]. This inconsistency may be understood by considering that for the present gel emulsion system, the continuous phase (the n-nonane) is always in a gel state no matter how much dispersed phase (water) in it (cf.…”

“…The structure is thus analogous to conventional gas-liquid foams with low liquid content. These emulsions are also called ''gel-emulsions" because of their viscoelastic behavior, and highly concentrated emulsions because of their large internal volume fraction [41][42][43][44][45][46]. HIPREs have found practical applications in cosmetics, aviation fuels, emulsion explosives, materials with unusual properties, and drug release etc.…”