Conching chocolate is a prototypical transition from frictionally jammed solid to flowable suspension with maximal solid content

Blanco, Elena; Hodgson, Daniel J. M.; Hermes, Michiel; Besseling, R.; Hunter, Gary L.; Chaikin, P. M.; Cates, Michael E.; Damme, Isabella Van; Poon, Wilson

doi:10.1073/pnas.1901858116

Cited by 58 publications

(41 citation statements)

References 33 publications

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“…Thus, σ y is reduced from some finite value to zero for all φ < φ μ , as is observed when we add PAA or ANS (Table 2). Such use of surfactants to confer a finite onset stress for nB adhesive suspensions to give essentially an infinite-fold reduction in the yield stress is perhaps the main, and certainly the most surprising, conclusion of this work, generalising a similar but less clear-cut finding in the use of surfactants to tune the rheology of molten chocolate (Blanco et al 2019). concentrations Three surfactants, PAA, ANS and PCE, were used in this work to modify the interaction between calcite particles.…”

Section: Surfactantmentioning

confidence: 56%

“…Above σ y the suspension shear thins and the viscosity decreases to a limiting plateau value. Practical examples span diverse sectors, from suspensions of mineral powders (Zhou et al 1995) and polymeric latices (Heymann et al 2002) to coal slurries (Wildemuth and Williams 1985) and molten chocolate (Blanco et al 2019), for which glass spheres with hydrophobic coating in water (Brown et al 2010) may function as a generic model system. In such applications, it is important to be able to 'tune' the yield stress, for example in unset concrete.…”

Section: Introductionmentioning

confidence: 99%

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Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction

2020

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We show that a suspension of non-Brownian calcite particles in glycerol-water mixtures can be tuned continuously from being a yield-stress suspension to a shear-thickening suspension—without a measurable yield stress—by the addition of various surfactants. We interpret our results within a recent theoretical framework that models the rheological effects of stress-dependent constraints on inter-particle motion. Bare calcite particle suspensions are found to have finite yield stresses. In these suspensions, frictional contacts that constrain inter-particle sliding form at an infinitesimal applied stress and remain thereafter, while adhesive bonds that constrain inter-particle rotation are broken as the applied stress increases. Adding surfactants reduces the yield stress of such suspensions. We show that, contrary to the case of surfactant added to colloidal suspensions, this effect in non-Brownian suspensions is attributable to the emergence of a finite onset stress for the formation of frictional contacts. Our data suggest that the magnitude of this onset stress is set by the strength of surfactant adsorption to the particle surfaces, which therefore constitutes a new design principle for using surfactants to tune the rheology of formulations consisting of suspensions of adhesive non-Brownian particles.

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Section: Surfactantmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction

2020

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“…So far, the consequences of the frictional transition and its associated S-shape rheology have been essentially investigated in rheometers, where instabilities, shear bands and spatiotemporal patterns have been documented 11,[13][14][15] . By contrast, very little is known about the behavior of shearthickening suspensions in real hydrodynamic flow configurations beyond rheometry, in spite of the numerous applications [16][17][18] .…”

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confidence: 99%

Surface-wave instability without inertia in shear-thickening suspensions

et al. 2020

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Recent simulations and experiments have shown that shear-thickening of dense particle suspensions corresponds to a frictional transition. Based on this understanding, non-monotonic rheological laws have been proposed and successfully tested in rheometers. These recent advances offer a unique opportunity for moving beyond rheometry and tackling quantitatively hydrodynamic flows of shear-thickening suspensions. Here, we investigate the flow of a shear-thickening suspension down an inclined plane and show that, at large volume fractions, surface kinematic waves can spontaneously emerge. Curiously, the instability develops at low Reynolds numbers, and therefore does not fit into the classical framework of Kapitza or ‘roll-waves’ instabilities based on inertia. We show that this instability, that we call ‘Oobleck waves’, arises from the sole coupling between the non-monotonic (S-shape) rheological laws of shear-thickening suspensions and the flow free surface.

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“…The study of chocolate is interesting for many reasons. Despite its evident importance in the food industry, this complex mixture is also a good example of some scientific curiosities [1]. For sure, some of these curiosities were found because of its technological importance and this is the case of our research: if a chocolate bar on a lab table had not become aged by chance, the observation of beautiful patterns on its surface had not inspired this ongoing study.…”

Section: Introductionmentioning

confidence: 84%

Spontaneous Pattern Growth on Chocolate Surface: Simulations and Experiments

2021

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The natural variation of temperature at ambient conditions produces spontaneous patterns on the surface of chocolate, which result from fat bloom. These metastable patterns are peculiar because of their shape and cannot be obtained by controlled temperature conditions. The formation of these spontaneous grains on the surface of chocolate is studied on experimental and theoretical grounds.Three different kinds of experiments were conducted: observation of formed patterns in time, atomic force microscopy of the initial events on the grain formation and rheology of the melted chocolate. The patterns observed in our experiments follow the trends described by the Avrami model, which considers a constant value at all spatial scales of the rate of linear growth α that governs the formation of isolated grains, starting from molecular clusters. Through NVT-ensemble computer simulations, using a Mie-segmented coarse-grained model of triacylglycerides molecules, we studied the process of nucleation that starts the pattern growth. From simulation and experiment results it is possible to derive a realistic value of α.

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Conching chocolate is a prototypical transition from frictionally jammed solid to flowable suspension with maximal solid content

Cited by 58 publications

References 33 publications

Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction

Turning a yield-stress calcite suspension into a shear-thickening one by tuning inter-particle friction

Surface-wave instability without inertia in shear-thickening suspensions

Spontaneous Pattern Growth on Chocolate Surface: Simulations and Experiments

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