Scaling Behavior of Delayed Demixing, Rheology, and Microstructure of Emulsions Flocculated by Depletion and Bridging
| Autor: | George A. van Aken, Theo B. J. Blijdenstein, Ton van Vliet, Erik van der Linden |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2004 |
| Předmět: |
Diffusing-wave spectroscopy
casein gels Materials science Physics and Physical Chemistry of Foods particle gels Analytical chemistry diffusing-wave spectroscopy in-water emulsions confocal microscopy Viscosity Rheology Electrochemistry General Materials Science elastic networks Scaling Spectroscopy VLAG beta-lactoglobulin Percolation threshold Surfaces and Interfaces Dynamic mechanical analysis Condensed Matter Physics Microstructure disordered solids transient gels Chemical physics colloid-polymer mixtures Volume fraction |
| Zdroj: | Langmuir, 20(26), 11321-11328 Langmuir 20 (2004) 26 |
| ISSN: | 0743-7463 |
| Popis: | This paper describes an experimental comparison of microstructure, rheology, and demixing of bridging- and depletion-flocculated oil-in-water emulsions. Confocal scanning laser microscopy imaging showed that bridging-flocculated emulsions were heterogeneous over larger length scales than depletion-flocculated emulsions. As a consequence, G' as determined from diffusing wave spectroscopy (DWS) corresponded well with G' as measured macroscopically for the depletion-flocculated emulsions, but this correspondence was not found for the bridging-flocculated emulsions. The heterogeneity of bridging-flocculated emulsions was confirmed by DWS-echo measurements, indicating that their structure breaks up into large fragments upon oscillatory shear deformation larger than 1%. Depletion- and bridging-flocculated emulsions showed a different scaling of the storage modulus with the volume fraction of oil and a difference in percolation threshold volume fraction. These differences will be discussed on the basis of the two types of droplet-droplet interactions studied. Gravity-induced demixing occurred in both emulsions, but the demixing processes differed. After preparation of bridging-flocculated emulsions, serum immediately starts to separate, whereas depletion-flocculated systems at polysaccharide concentrations in the overlap regime usually showed a delay time before demixing. The delay time was found to scale with the network permeability, B; the viscosity, eta, of the aqueous phase; and the density difference between oil and water, Deltarho, as tdelay approximately B(-1)etaDeltarho(-1). The results are in line with the mechanism proposed by Starrs et al. (J. Phys.: Condens. Matter 2002, 14, 2485-2505), where erosion of the droplet network leads to widening of the channels within the droplet networks, facilitating drainage of liquid. |
| Databáze: | OpenAIRE |
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