Delayed sedimentation of transient gels in colloid–polymer mixtures: dark-field observation, rheology and dynamic light scattering studies

Poon, Wilson; Starrs, L; Meeker, S. P.; Moussaı̈d, A.; Evans, R. M. L.; Pusey, P. N.; Robins, Margaret M.

doi:10.1039/a900664h

Cited by 130 publications

(174 citation statements)

References 22 publications

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“…In colloid-polymer mixtures with R g /R e 0.2, the polymer induces aggregation of the colloids in the colloid-rich phase, which, at sufficiently large polymer and colloid concentrations, leads to a space-spanning particle network. 1,4,[30][31][32][33][34][35] The reversible nature of the depletion-induced particle bonds allows restructuring of the network until the gel collapses, permitting macroscopic phase separation.…”

Section: Resultsmentioning

confidence: 99%

Morphology and Kinetics of Phase Separating Transparent Xanthan−Colloid Mixtures

et al. 2003

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We present a study on the morphology and kinetics of depletion-induced phase separation in aqueous xanthan-colloid mixtures with light microscopy and small angle light scattering (SALS), using fluorinated colloids with a refractive index close to that of water to prevent complications of multiple scattering. Microscopy with the direction of observation perpendicular to gravity enabled us to observe the development of the microstructure during the entire phase separation process including the formation of a macroscopic interface. Bicontinuous structures typical of a spinodal decomposition mechanism were observed at early times. These structures coarsened in time until hydrodynamic flow resulted in lane formation. Close to the binodal, a nucleation-and-growth mechanism was observed with formation of droplets. The coarsening kinetics were studied in more detail with SALS and turbidity measurements. Above polysaccharide concentrations at which entanglements become dominant, a slower coarsening and macroscopic phase separation were found because of the high continuous phase viscosity.

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Section: Resultsmentioning

confidence: 99%

Morphology and Kinetics of Phase Separating Transparent Xanthan−Colloid Mixtures

et al. 2003

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“…[11,21,24]) is indeed the existence of a phase of large mobile aggregates, lying between the ordinary fluid phase and the gel. In fact, the phase diagrams in Fig.…”

Section: Pacs Numbersmentioning

confidence: 99%

Cluster Mode-Coupling Approach to Weak Gelation in Attractive Colloids

2004

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Mode-coupling theory (MCT) predicts arrest of colloids in terms of their volume fraction, and the range and depth of the interparticle attraction. We discuss how effective values of these parameters evolve under cluster aggregation. We argue that weak gelation in colloids can be idealized as a two-stage ergodicity breaking: first at short scales (approximated by the bare MCT) and then at larger scales (governed by MCT applied to clusters). The competition between arrest and phase separation is considered in relation to recent experiments. We predict a long-lived 'semi-ergodic' phase of mobile clusters, showing logarithmic relaxation close to the gel line. PACS numbers:Hard-sphere colloids with short-range attractions can undergo several types of arrest. At high densities they show two distinct glass transitions (repulsion-driven and attraction-driven), with a re-entrant dependence on attraction strength [1]. This scenario was first predicted by mode coupling theory (MCT) [2,3,4], and depends on both the attraction range δ (in units of particle diameter) and well-depth ε (in units of k B T ). MCT is remarkably successful, at least for large volume fractions φ 0.4.At lower volume fractions, however, there is no comparable theoretical framework. Yet 'weak gelation', in which bonding is strong but not so strong as to be irreversible, can lead to nonergodic soft solids, of nonzero static elastic modulus, at volume fractions of just a few percent [5]. It might be argued that a finite modulus requires a percolating network of bonds whose lifetime exceeds that of the experiment. However this is simplistic: as shown by the case of repulsive glasses, a finite modulus can arise with no bonding at all. We argue here that the rigidity of weak gels arises not from bond percolation but from kinetic ergodicity breaking [6], just as it does in glass formation. This suggests that an MCT-like approach to weak gelation could be fruitful.MCT takes its structural input from equilibrium liquid state theory; it cannot address states of arrest where this structure is strongly perturbed [7]. This matters relatively little at φ 0.4, where each particle interacts with many others, and not much room is left for structural development upon a quench. But more severe consequences must be expected at low volume fractions where strongly nonuniform, ramified gels arise. Here the pathway to complete nonergodicity (starting from a homogenized fluid sample, say) must involve a nontrivial episode of structure formation, akin to irreversible cluster aggregation (ICA). Such kinetics certainly dominates for irreversible ("strong") gelation (ε −1 = 0), where particles aggregate on contact into clusters, with various kinetic universality classes [8]. Relative simplicity is restored at low φ thanks to the invariance of this aggregation process under coarse graining in the (ordered) limit δ, ε −1 → 0 and φ → 0. This scaling limit is controlled by an ICA 'fixed point', where details of the short-ranged attraction are irrelevant. The resulting fractal cluster...

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“…In particular, the non-ergodicity parameters (cf. section 2.1) for several attraction ranges will be given; this is motivated by the recent measurements on colloid-polymer systems by Poon and co-workers [36]. In addition, a detailed description is given of the asymptotic model developed in I.…”

Section: Introductionmentioning

confidence: 99%

Gel transitions in colloidal suspensions

Bergenholtz

Fuchs

1999

J. Phys.: Condens. Matter

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Abstract. The idealized mode-coupling theory (MCT) is applied to colloidal systems interacting via short-range attractive interactions of Yukawa form. At low temperatures, MCT predicts a slowing down of the local dynamics and ergodicity-breaking transitions. The non-ergodicity transitions share many features with the colloidal gel transition, and are proposed to be the source of gelation in colloidal systems. Previous calculations of the phase diagram are complemented with additional data for shorter ranges of the attractive interaction, showing that the path of the nonergodicity transition line is then unimpeded by the gas-liquid critical curve at low temperatures. Particular attention is given to the critical non-ergodicity parameters; this is motivated by recent experimental measurements. An asymptotic model is developed, valid for dilute systems of spheres interacting via strong short-range attractions, and is shown to capture all aspects of the low-temperature MCT non-ergodicity transitions.

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Delayed sedimentation of transient gels in colloid–polymer mixtures: dark-field observation, rheology and dynamic light scattering studies

Cited by 130 publications

References 22 publications

Morphology and Kinetics of Phase Separating Transparent Xanthan−Colloid Mixtures

Morphology and Kinetics of Phase Separating Transparent Xanthan−Colloid Mixtures

Cluster Mode-Coupling Approach to Weak Gelation in Attractive Colloids

Gel transitions in colloidal suspensions

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