Issue 5, 2012

Origin of suppressed demixing in casein/xanthan mixtures

Abstract

We explore the properties of casein/xanthan mixtures for xanthan concentrations beyond those inducing phase separation. Previous work has successfully described the onset of demixing by depletion theory in the protein limit, where the xanthan polysaccharides, the polymers, are larger than the caseins from skim milk powder, the colloids (S. Bhat et al., J. Phys.: Condens. Matter, 2006, L339). We now extend these studies to xanthan concentrations in a range of c/c* = 13–88, aiming to arrest the phase separation via a (transiently) arrested casein-rich phase. Surprisingly, we find that the casein-rich phase remains fluidic deep into the two-phase region, with an equilibrium composition that significantly differs from predictions for mixtures of hard spheres plus flexible polymer chains in a good solvent. Furthermore, we show that macroscopic phase separation is arrested for c/c* > 60. Our investigations reveal that the rheological properties of the mixtures are fully determined by the xanthan-rich phase with characteristic long relaxation times that depend remarkably strongly on the xanthan concentration.

Graphical abstract: Origin of suppressed demixing in casein/xanthan mixtures

Article information

Article type
Paper
Submitted
16 Sep 2011
Accepted
14 Nov 2011
First published
12 Dec 2011

Soft Matter, 2012,8, 1547-1555

Origin of suppressed demixing in casein/xanthan mixtures

K. van Gruijthuijsen, V. Herle, R. Tuinier, P. Schurtenberger and A. Stradner, Soft Matter, 2012, 8, 1547 DOI: 10.1039/C1SM06761C

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