Microscopic Origin of Internal Stresses in Jammed Soft Particle Suspensions

Mohan, Lavanya; Bonnecaze, Roger T.; Cloître, Michel

doi:10.1103/physrevlett.111.268301

Cited by 55 publications

(69 citation statements)

References 23 publications

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“…frequency 0.318 Hz and the hold time at each extremum was 0.5 s, during which a 0.25-s x-ray exposure was obtained, leading to a repeat time for the strain of T = 4.14 s. For comparison, g 2 (q,t) measured in the absence of shear is also shown. In this quiescent state, g 2 (q,t) has a shape common to many disordered soft solids in which it maintains a large value at short delay times t, indicating a nominally static configuration, but decays at long delay times (t 100 s) with a compressed-exponential form that can be associated with slow relaxation of heterogeneous residual stress [33][34][35][36][37]. For the measurements under in situ shear, g 2 (q,t) displays periodic peaks corresponding to echoes in the speckle pattern.…”

Section: B Xpcs With In Situ Shearmentioning

confidence: 98%

Echoes in x-ray speckles track nanometer-scale plastic events in colloidal gels under shear

et al. 2014

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We report x-ray photon correlation spectroscopy experiments on a concentrated nanocolloidal gel subject to in situ oscillatory shear strain. The strain causes periodic echoes in the speckle pattern that lead to peaks in the intensity autocorrelation function. Above a threshold strain that is near the first yield point of the gel, the peak amplitude decays exponentially with the number of shear cycles, signaling irreversible particle rearrangements. The wave-vector dependence of the decay rate reveals a power-law distribution in the size of regions undergoing shear-induced rearrangement. The gel also displays strain softening well below the threshold, indicating a range of strains at which the rheology is nonlinear but the microscopic deformations are reversible.

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Section: B Xpcs With In Situ Shearmentioning

confidence: 98%

Echoes in x-ray speckles track nanometer-scale plastic events in colloidal gels under shear

et al. 2014

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“…In that work, the aggregation number was tuned by varying the solvent composition, i.e. 13,28 Recently, using rheology as the primary technique, a dynamic phase diagram in temperature-shear rate space was reported for surfactant molecules. These authors investigated the structure-propertyrelationship (SPR) starting from the aforementioned coarsegrained model and were able to confirm quantitatively theoretical predictions concerning the equilibrium phase diagram in the plane spanned by the concentration and the aggregation number by means of small angle neutron scattering experiments (SANS).…”

Section: Flexible Polymermentioning

confidence: 99%

Dynamic phase diagram of soft nanocolloids

et al. 2015

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We present a comprehensive experimental and theoretical study covering micro-, meso- and macroscopic length and time scales, which enables us to establish a generalized view in terms of structure-property relationship and equilibrium dynamics of soft colloids. We introduce a new, tunable block copolymer model system, which allows us to vary the aggregation number, and consequently its softness, by changing the solvophobic-to-solvophilic block ratio (m : n) over two orders of magnitude. Based on a simple and general coarse-grained model of the colloidal interaction potential, we verify the significance of interaction length σint governing both structural and dynamic properties. We put forward a quantitative comparison between theory and experiment without adjustable parameters, covering a broad range of experimental polymer volume fractions (0.001 ≤ϕ≤ 0.5) and regimes from ultra-soft star-like to hard sphere-like particles, that finally results in the dynamic phase diagram of soft colloids. In particular, we find throughout the concentration domain a strong correlation between mesoscopic diffusion and macroscopic viscosity, irrespective of softness, manifested in data collapse on master curves using the interaction length σint as the only relevant parameter. A clear reentrance in the glass transition at high aggregation numbers is found, recovering the predicted hard-sphere (HS) value in the hard-sphere like limit. Finally, the excellent agreement between our new experimental systems with different but already established model systems shows the relevance of block copolymer micelles as a versatile realization of soft colloids and the general validity of a coarse-grained approach for the description of the structure and dynamics of soft colloids.

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“…Despite of that the validity of the Delaware-Rutgers rule suggests that our mixtures are not characterized by large structural heterogeneities while being amorphous and characterized by very weak ageing. Figure 13.The stress values are normalized by p, the stress corresponding to the steady-state stress (plateau) measured at the long time limit of (t) in transient tests performed at different shear rates .The probed RG(cHS=0.01 %) and APS state (cHS=5 %) relax after 100 s: the accumulated stress due to translational and rotational strain-induced motion relaxes after 100 sun like hard sphere glasses or jammed microgel suspensions which are characterized by non-negligible residual stresses [81], [82], [83]. On the other hand, the DG state is characterized by stresses not fully relaxed after 100 s. Such finding suggests that particle softness is important in determining the full relaxation of accumulated stress in colloidal glasses and also indirectly confirms that DG state is dominated by the frustrated dynamics of hard particles (HS-like stars and collapsed soft stars).Moreover, it is worth mentioning that for high shear rates, DG samples were found to be mechanically instable: for cHS> 20 % wt edge fracture systematically occurred for shear rates higher than 0.5 s -1…”

Section: Iii2 Strain Amplitude Sweeps and Yieldingmentioning

confidence: 99%

Asymmetric soft-hard colloidal mixtures: Osmotic effects, glassy states and rheology

Merola¹,

Parisi²,

Truzzolillo³

et al. 2018

Journal of Rheology

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Whereas mixtures of colloids and non-adsorbing polymers have been studied in great detail in the last two decades, binary colloidal mixtures have not received much attention. Yet, fragmental evidence from asymmetric mixtures of hard spheres indicates a wide-ranging, complex behavior from liquid to crystal to single glass and to double glass, and respective rich rheology. Recently, we addressed the question of softness by investigating a mixture of soft and virtually hard colloidal spheres. We found an unprecedented wealth of states including repulsive single glass (RG), liquid, arrested phase separation (APS) and double glass (DG). This is a consequence of the coupling of softness and osmotic forces due to the hard component. We now report on the rheology of the different states with emphasis on the nonlinear response during start-up of stress at constant rate, its relaxation upon flow cessation, and large amplitude oscillatory shearing. Distinct features are identified, whereas comparison with single-colloid (soft or hard) glasses reveals some phenomenological universalities in yielding, residual stresses and periodic intra-cycle stress response. In brief, the DG exhibits much larger yield and residual stresses as compared to the RG and APS, whereas the yield strain is the same for all states. Two-step yielding is unambiguously evidenced for the APS whereas both yield stress and strain exhibit a weak dependence on Péclet number. Large amplitude oscillatory tests reveal large value of the intrinsic nonlinear parameters, reflecting the role of colloidal interactions. Moreover, RG exhibits intra-cycle stress The following article has been accepted by Journal of Rheology. After it is published, it will be found at http://sor.scitation.org/journal/jor 2 overshoots, a feature that characterizes most of the soft glassy materials formed by interpenetrable particles and that vanishes as hard (nearly impenetrable) colloids are added in the mixtures. These results demonstrate the sensitivity of linear and nonlinear rheology to colloidal state transitions and, more importantly, the power of entropic mixing as a means to tailor the flow properties, hence performance and handling of soft composites.

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Microscopic Origin of Internal Stresses in Jammed Soft Particle Suspensions

Cited by 55 publications

References 23 publications

Echoes in x-ray speckles track nanometer-scale plastic events in colloidal gels under shear

Echoes in x-ray speckles track nanometer-scale plastic events in colloidal gels under shear

Dynamic phase diagram of soft nanocolloids

Asymmetric soft-hard colloidal mixtures: Osmotic effects, glassy states and rheology

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