Tunable dynamic fragility and elasticity in dense suspensions of many-arm-star polymer colloids

Yang, Jian; Schweizer, Kenneth S.

doi:10.1209/0295-5075/90/66001

Cited by 32 publications

(24 citation statements)

References 38 publications

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“…Note that jamming in soft hairy materials has been also discussed in the context of activated hoping with theoretical ideas based on mode coupling, and a linear dependence of storage modulus on volume fraction was reported. 89 More generally, it seems that the linear dependence of G p on concentration is typical of jammed states 87,88,90,91 and the present soft and short cylinders conform to the emerging picture. Such a finding certainly opens a new scenario of jamming in anisotropic colloids at rest, in addition to previous experimental works addressing the jammed state induced by shear flow.…”

Section: Linear Viscoelastic Responsementioning

confidence: 62%

Short and Soft: Multidomain Organization, Tunable Dynamics, and Jamming in Suspensions of Grafted Colloidal Cylinders with a Small Aspect Ratio

et al. 2019

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The yet virtually unexplored class of soft colloidal rods with small aspect ratio is investigated and shown to exhibit a very rich phase and dynamic behavior, spanning from liquid to nearly melt state.Instead of nematic order, these short and soft nanocylinders alter their organization with increasing concentration from isotropic liquid with random orientation to one with preferred local orientation and eventually a multi-domain arrangement with local orientational order. The latter gives rise to a kinetically suppressed state akin to structural glass with detectable terminal relaxation, which, on increasing concentration reveals features of hexagonally packed order as in ordered block copolymers. The respective dynamic response comprises four regimes, all above the overlapping concentration of 0.02 g/ml: I) from 0.03 to 0.1 g/mol the system undergoes a liquid-to-solid like transition with a structural relaxation time that grows by four orders of magnitude. II) from 0.1 to 0.2 g/ml a dramatic slowing-down is observed and is accompanied by an evolution from isotropic to multi-domain structure. III) between 0.2 and 0.6 g/mol the suspensions exhibit signatures of shell interpenetration and jamming, with the colloidal plateau modulus depending linearly on concentration. IV) at 0.74 g/ml in the densely jammed state, the viscoelastic signature of hexagonally packed cylinders from microphase-separated block copolymers is detected. These 2 properties set short and soft nanocylinders apart from long colloidal rods (with large aspect ratio) and provide insights for fundamentally understanding the physics in this intermediate soft colloidal regime, as well as and for tailoring the flow properties of non-spherical soft colloids.

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Section: Linear Viscoelastic Responsementioning

confidence: 62%

Short and Soft: Multidomain Organization, Tunable Dynamics, and Jamming in Suspensions of Grafted Colloidal Cylinders with a Small Aspect Ratio

et al. 2019

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“…Limiting analytic analysis of the single-particle theory has shown that the barrier height for hard spheres (but not soft spheres 30 ) scales with the inverse of the localization length: F B ∼ σ/r loc . 22,58 We find that this scaling works very well for the r-directional barrier when r 0 = σ, but fails for the R-direction barrier at that initial separation, and for both barriers at all other initial separations.…”

Section: Model Calculationsmentioning

confidence: 99%

“…7 replots the Kramers times in a normalized format to expose the relative rate of increase with volume fraction and r 0 , a representation relevant to the question of "dynamic fragility." 1,28,30,61 The fragility is weakest for an initial interstitial configuration, and strongest when the two particles are initially in contact.…”

Section: B Mean Barrier Hopping Timementioning

confidence: 99%

“…Deep in the supercooled (or overcompressed) regime the barriers to particle motion grow significantly but without divergence below random close packing or above zero Kelvin. The relative simplicity of the NLE approach has allowed it to be generalized to many systems beyond hard spheres including polymerparticle depletion gels, 25 nonspherical particles that translate and rotate, [26][27][28][29] soft colloids, 30 binary mixtures, 31,32 supercooled polymer melts and glasses [33][34][35][36] and nonlinear rheological response. [35][36][37][38][39][40] The microscopic NLE theory is predictive in the same sense that MCT is since it relates structure, interparticle forces, and slow dynamics.…”

Section: Introductionmentioning

confidence: 99%

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Theory of correlated two-particle activated glassy dynamics: General formulation and heterogeneous structural relaxation in hard sphere fluids

Sussman

Schweizer

2011

The Journal of Chemical Physics

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We generalize the nonlinear Langevin equation theory of activated single particle dynamics to describe the correlated motion of two tagged spherical particles in a glass- or gel-forming fluid as a function of their initial separation. The theory is built on the concept of a two-dimensional dynamic free energy surface which quantifies the forces on two particles moving in a cooperative manner. For the hard sphere fluid, above a threshold volume fraction we generically find two relaxation channels corresponding largely, but not exclusively, to a center-of-mass-like displacement and a radial separation of the two tagged particles. The entropic barriers and mean first passage times are computed and found to systematically vary with volume fraction and initial particle separation; both oscillate as a function of the latter in a manner related to the equilibrium pair correlation function. A dynamic correlation length is estimated as the length scale beyond which the two-particle activated dynamics becomes uncorrelated in space and time, and is found to modestly grow with increasing mean relaxation time. The theory is also applied to a simplified model of cage escape, the elementary step of structural relaxation. Predictions for characteristic relaxation times, translation-relaxation decoupling, and stretched-exponential decay of time correlation functions are obtained. A novel mechanism for understanding why strong decoupling emerges in the activated regime, but stretched nonexponential time correlation functions do not change shape as the mean relaxation time grows, is presented and favorably compared with experiment. The theory may serve as a starting point for constructing a predictive model of multiple correlated caging and hopping (forward and backward) events of a pair of tagged particles.

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“…2,3 Softness was also shown to have a prominent influence on effective interactions, both in microgels [4][5][6][7] and star polymers. 8,9 From a dynamical perspective, the presence of an inverse correlation between softness and dynamical fragility in the supercooled regime was put forward some years ago, 10,11 and it is still a very debated issue both in experiments 12,13 and in simulations 14,15 . In addition, soft colloids can explore a variety of high density states, a) Electronic mail: nicoletta.gnan@cnr.it above the so-called jamming point [16][17][18] , here loosely defined as the limit condition in which particles can fill the available space without deforming.…”

Section: Introductionmentioning

confidence: 99%

Dynamical properties of different models of elastic polymer rings: confirming the link between deformation and fragility

Gnan,

Camerin,

Del Monte

et al. 2021

Preprint

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We report extensive numerical simulations of different models of 2D polymer rings with internal elasticity. We monitor the dynamical behavior of the rings as a function of the packing fraction, to address the effects of particle deformation on the collective response of the system. In particular, we compare three different models: (i) a recently investigated model [Gnan & Zaccarelli, Nat. Phys. 15, 683 (2019)], where an inner hertzian field providing the internal elasticity acts on the monomers of the ring, (ii) the same model where the effect of such a field on the center of mass is balanced by opposite forces and (iii) a semi-flexible model where an angular potential between adjacent monomers induces strong particle deformations. By analyzing the dynamics of the three models, we find that, in all cases, there exists a direct link between the system fragility and particle asphericity. Among the three, only the first model displays anomalous dynamics in the form of a super-diffusive behavior of the mean squared displacement and of a compressed exponential relaxation of the density auto-correlation function. We show that this is due to the combination of internal elasticity and the out-of-equilibrium force self-generated by each ring, both of which are necessary ingredients to induce such peculiar behavior often observed in experiments of colloidal gels. These findings reinforce the role of particle deformation, connected to internal elasticity, in driving the dynamical response of dense soft particles.

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Tunable dynamic fragility and elasticity in dense suspensions of many-arm-star polymer colloids

Cited by 32 publications

References 38 publications

Short and Soft: Multidomain Organization, Tunable Dynamics, and Jamming in Suspensions of Grafted Colloidal Cylinders with a Small Aspect Ratio

Short and Soft: Multidomain Organization, Tunable Dynamics, and Jamming in Suspensions of Grafted Colloidal Cylinders with a Small Aspect Ratio

Theory of correlated two-particle activated glassy dynamics: General formulation and heterogeneous structural relaxation in hard sphere fluids

Dynamical properties of different models of elastic polymer rings: confirming the link between deformation and fragility

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