Scaling Behavior of Delayed Demixing, Rheology, and Microstructure of Emulsions Flocculated by Depletion and Bridging

T.B.J. Blijdenstein, E. van der Linden, T. van Vliet, G.A. van Aken

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46 Citations (Scopus)

Abstract

Abstract: 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, , of the aqueous phase; and the density difference between oil and water, , as tdelay ~ B-1-1. 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.
Original languageEnglish
Pages (from-to)11321-11328
JournalLangmuir
Volume20
Issue number26
DOIs
Publication statusPublished - 2004

Keywords

  • diffusing-wave spectroscopy
  • in-water emulsions
  • colloid-polymer mixtures
  • confocal microscopy
  • beta-lactoglobulin
  • disordered solids
  • elastic networks
  • transient gels
  • particle gels
  • casein gels

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