Article

# Sedimentation and multi-phase equilibria in mixtures of platelets and ideal polymer

EPL (Europhysics Letters) (Impact Factor: 2.26). 01/2007; 66(1):125. DOI: 10.1209/epl/i2003-10140-1

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**ABSTRACT:**We investigate the effects of variable linear charge density and Debye length on the mesoscopic properties of beta-lactoglobulin fibers in water, by changing the pH and ionic strength, respectively. We determine the isotropic-nematic (I-N) transition by cross-polarized microscopy and quantify by atomic force microscopy the increasing tendency of the fibers to aggregate upon raising ionic strength. We then compare experimental I-N transitions with theoretical expected values based on Onsager theory. Unlike previous reports on lyotropic liquid crystalline behavior of protein fibers, we show that, if double layer effects and aggregation of fibers are correctly included directly in the second virial coefficient and excluded volume, Onsager theory accurately predicts the experimental I-N transition versus pH and ionic strength.Langmuir 07/2010; 26(13):10401-5. · 4.38 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The phase behaviour of colloidal dispersions is interesting for fundamental reasons and for technological applications such as photonic crystals and electronic paper. Sedimentation, which in everyday life is relevant from blood analysis to the shelf life of paint, is a means to determine phase boundaries by observing distinct layers in samples that are in sedimentation-diffusion equilibrium. However, disentangling the effects due to interparticle interactions, which generate the bulk phase diagram, from those due to gravity is a complex task. Here we show that a line in the space of chemical potentials µi, where i labels the species, represents a sedimented sample and that each crossing of this sedimentation path with a binodal generates an interface under gravity. Complex phase stacks can result, such as the sandwich of a floating nematic layer between top and bottom isotropic phases that we observed in a mixture of silica spheres and gibbsite platelets.Scientific Reports 11/2012; 2:789. · 5.08 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**The observation of stacks of distinct layers in a colloidal or liquid mixture in sedimentation-diffusion equilibrium is a striking consequence of bulk phase separation. Drawing quantitative conclusions about the phase diagram is, however, very delicate. Here we introduce the Legendre transform of the chemical potential representation of the bulk phase diagram to obtain a unique stacking diagram of all possible stacks under gravity. Simple bulk phase diagrams generically lead to complex stacking diagrams. We apply the theory to a binary hard core platelet mixture with only two-phase bulk coexistence, and find that the stacking diagram contains six types of stacks with up to four distinct layers. These results can be tested experimentally in colloidal platelet mixtures. In general, an extended Gibbs phase rule determines the maximum number of sedimented layers to be $3+2(n_b-1)+n_i$, where $n_b$ is the number of binodals and $n_i$ is the number of their inflection points.Soft Matter 05/2013; 9:8636. · 4.15 Impact Factor

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