Emulsions have applications as wide ranging as food, pharmaceuticals, oil production, printing, agrochemicals and photography. They are incorporated into a broad range of food products, and it is estimated that over 40% of processed foods contain emulsified oils or fats. The emulsified fat is includ...

Journal of Chemical Technology & BiotechnologyVolume 54, Issue 2 p. 201-202 Book Review Colloidal dispersions. Edited by W. B. Russel, D. A. Saville & W. R. Schowalter, Cambridge University Press, Cambridge, UK, 1989, xvii + 506 pp., price: £60.00. ISBN 0 521 34188 4 Margaret Robins, Margaret RobinsSearch for more papers by this authorAnnette Fillery-Travis, Annette Fillery-TravisSearch for more papers by this author Margaret Robins, Margaret RobinsSearch for more papers by this authorAnnette Fillery-Travis, Annette Fillery-TravisSearch for more papers by this author First published: 1992 https://doi.org/10.1002/jctb.280540216Citations: 9AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume54, Issue21992Pages 201-202 RelatedInformation

We introduce a simple force and flux balance model for sedimentation and creaming in high volume fraction, polydisperse colloidal suspensions. The model is set alongside monodisperse and bidisperse sedimentation data for latex spheres, and we suggest that the broadening of the larger species sedimentation profile observed in the bidisperse case is linked to the particle pressure gradient arising from the smaller species. The model gives a satisfactory qualitative description of real emulsion creaming data, but implies either that the effective droplet radius is larger than the measured droplet radius, or that the effective background viscosity is reduced. Increasing the particle pressure gradient results in interface broadening at short times. We propose that the smallest emulsion droplets contribute to this broadening.

Quality Assurance (QA) has a bad press in research circles. Fundamental researchers tend to consider that experienced scientists do not need any controls beyond their own integrity. This article attempts to show how QA can be applied even to the most original and basic research areas, and that there are benefits to the introduction of a formal system, provided all personnel are involved in the aspects that affect them.

Salmonella typhimurium LT2 was grown in batch culture (trypticase soy broth, with 0.3%(w/v) yeast extract, 1% (w/v) glucose and 0.5% (w/v/) NaCl, 20 °C) at a range of initial pH (4.4, 4.8, 5.0 and 7.0). The consumption of oxygen and glucose was found to be independent of initial pH, and stoichiometric with growth. Mean yield coefficients of 6.9×10−15 and 15.5×10−15 mol oxygen/cell were estimated. Calculation of the instantaneous state of carbon during the cultivation showed stoichiometric conversion of glucose into biomass, carbon dioxide and organic acids. The concentration of the undissociated form of the primary acidic product (acetic acid) was shown to be the factor limiting growth.

The effect of polysaccharide content on the stability of an oil-in-water emulsion (20% oil, droplet diameter 6.5 mum, pH = 7) containing soy protein (5 mg/ml) as the emulsifying agent was studied. Flocculation occurs by addition of two depletion flocculants: xanthan (0.01 - 0.4%) and lambda-carrageenan (0.001 - 2%). We report that in both cases the onset of flocculation occurs below the overlap polymer concentration (c* = 0.15% for xanthan and c* = 0.58% for lambda-carrageenan). The strength of depletion interaction is dependent on such factors as polymer concentration, molecular weight and also the presence of other macromolecules. Profiles of the creaming behaviour of the sample emulsions were obtained by measuring the height of the boundary between the cream phase and the serum as a function of time for each emulsion. The result indicates that creaming kinetics is dependent on polymer concentration in a complex way. The turbidity of the serum gave an indication of whether the system was fully flocculated or contained flocks together with unflocculated droplets. At very low polymer concentrations the droplets cream individually or in small aggregates at the top of the container. At higher concentrations the droplets appear to cream as a single entity, with a sharp lower boundary separating the cream phase from a clear serum. In these emulsions and in some of the coexistent ones, there is a delay before creaming starts. The presence of the polymers at higher concentrations resulted in a stable emulsion with a very high apparent viscosity for the continuous phase and/or a strong emulsion gel network. The length of the delay phase increased with increasing concentration of both polymers.

Emulsions remain of key interest to major sectors of the food industry. Recent advances include the development of novel scaling approaches to modelling of rheology, and the use of new characterisation techniques such as high frequency compressive oscillation, diffusing wave spectroscopy and magnetic resonance imaging. 2002 Elsevier Science Ltd. All rights reserved.

Transient gelation in colloid-polymer mixtures is an interesting but poorly understood non-equilibrium phenomenon which has recently attracted the attention of experiment and theory. In a transient gel the particles aggregate, by the depletion interaction, to form a space-spanning network which maintains its structural integrity for a finite period before suddenly collapsing. In this paper we present a study of the collapse process which provides new information on the way in which transient gels collapse. We have studied gel collapse in three ways. Firstly, we have observed the gel throughout its lifetime using dark-field optics and time-lapsed video recording. In a second experiment we have measured the concentration of gels throughout their entire height before, during and after collapse. This was performed using a non-intrusive ultrasonic technique which measures the speed of sound in the suspension. Finally, we have studied the effect of varying sample height and width on the lifetime of a gel. Our observations provide new information on the collapse process and have important implications for the formulation of a theoretical model. In discussing the effects of height and width we refer to the following companion paper which describes this particular effect.

Emulsions remain of key interest to major sectors of the food industry. Recent advances include the development of novel scaling approaches to modelling of rheology, and the use of new characterisation techniques such as high frequency compressive oscillation, diffusing wave spectroscopy and magnetic resonance imaging.

Addition of the non-adsorbing polymer hydroxyethylcellulose (HEC) to oil-in-water emulsions induces flocculation via the depletion mechanism. In the present work, we report results on the delay time prior to creaming of hexadecane-in-water emulsions, flocculated by HEC. In addition, we report on oscillation rheology measurements of a comparable, density-matched system. We compare the two in the search for rheological signatures of delay, and for insight into the delay mechanism. Our results suggest that the commonly used low-frequency relaxation time does not map simply to delay time. We do, however, find that rheology can tell which of our compositions will exhibit delay, and which will not. In addition, those compositions having the greatest shear modulus have the longest delay. A simple model, in which the delay is attributed to a slow creaming stage over a very small distance, produces an acceptable correlation with the product of complex viscosity and the strain at the end of linearity. Thus the area under the linear portion of the complex viscosity–strain plot may provide a useful marker of delay time. The unexpected observation of a liquid-like regime at high oscillation frequency merits further investigation.

Recent years have seen advances in the monitoring of emulsion stability, particularly multiple-point techniques using optical, ultrasonic and NMR sensors. In parallel, there has been interest in the mechanisms of creaming and phase separation, leading to progress in the theoretical interpretation of the process.

The addition of nonadsorbing polymer to an alkane-in-water emulsion causes the droplets to flocculate into a space-spanning, stress-bearing network. We report rheological measurements of an emulsion of 1-bromohexadecane-in-water flocculated by hydroxy-ethylcellulose. Small-deformation oscillatory measurements allowed characterization of the structure during formation and an indication of the strength of the resulting network. Emulsions without polymer, and polymer solutions alone, showed essentially viscous behavior, with dominant viscous modulus over the whole frequency range (0.01-10 Hz). However, the emulsion containing polymer demonstrated a significant elastic modulus, dependent on the oil and polymer concentrations, attributable to interdroplet depletion interactions. Power-law relationships were observed between the elastic modulus, elastic strain limit, and oil volume fraction, but the indices were lower than those predicted by fractal models, giving unrealistic fractal dimensionalities. The modulus increased exponentially with polymer concentration, but the elastic strain limit was independent of added polymer. The rate of formation of the network was not consistent with diffusion-controlled aggregation. Copyright 2000 Academic Press.