Percolation in a Model Transient Network:  Rheology and Dynamic Light Scattering

Michel, Eric; Filali, M.; Aznar, R.; Porte, and Grégoire; Appell, J.

doi:10.1021/la000317c

Cited by 82 publications

(140 citation statements)

References 39 publications

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“…Our model system is a coarse-grained representation [17] of a transient gel which has been studied in experiments [18]. In this system, an equilibrium lowdensity gel is obtained by adding telechelic polymers to an oil-in-water microemulsion.…”

Section: Model and Details Of Simulationmentioning

confidence: 99%

“…The space of control parameters is quite large. Therefore we set ℓ = 3.5 σ as measured in experiments [18], T = 1, and ǫ 0 = 1 and ǫ 2 = 50, and vary the remaining parameters {φ, R, τ link }. These choices for the parameter values leads to a phase diagram which is similar to the one obtained in experiments.…”

Section: Model and Details Of Simulationmentioning

confidence: 99%

“…In general, these paths lead to spatially heterogeneous structures. However, in recent times, considerable effort has been made to devise ways by which spatially homogeneous physical gels can be formed [10,[17][18][19][20][21][22][23][24][25][26]. For such gel-forming systems, a wide variety of relaxation functions have been reported: logarithmic [27][28][29][30], stretched [16] or compressed exponentials [21,31].…”

Section: Introductionmentioning

confidence: 99%

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Relaxation dynamics in a transient network fluid with competing gel and glass phases

Chaudhuri

Hurtado

Berthier

et al. 2015

The Journal of Chemical Physics

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We use computer simulations to study the relaxation dynamics of a model for oil-in-water microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, three-step decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the four-point dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics.

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Section: Model and Details Of Simulationmentioning

confidence: 99%

Section: Model and Details Of Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Relaxation dynamics in a transient network fluid with competing gel and glass phases

Chaudhuri

Hurtado

Berthier

et al. 2015

The Journal of Chemical Physics

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“…Associating polymers constitute another well-studied example of reversible gels [1]. In that case, gels can be obtained far from phase separation, producing viscoelastic materials with highly non-linear rheological properties that are not well understood [10,11]. In many cases, a close similarity between gelation and glass formation is reported [1].…”

mentioning

confidence: 99%

“…[11]. It is a microemulsion of stable and monodisperse oil droplets in water mixed with telechelic polymers, i.e.…”

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confidence: 99%

Heterogeneous Diffusion in a Reversible Gel

2007

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We introduce a microscopically realistic model of a physical gel and use computer simulations to study its static and dynamic properties at thermal equilibrium. The phase diagram comprises a sol phase, a coexistence region ending at a critical point, a gelation line determined by geometric percolation, and an equilibrium gel phase unrelated to phase separation. The global structure of the gel is homogeneous, but the stress is only supported by a fractal network. The gel dynamics is highly heterogeneous and we propose a theoretical model to quantitatively describe dynamic heterogeneity in gels. We elucidate several differences between the dynamics of gels and that of glass-formers.PACS numbers: 61.43. Bn, 82.70.Gg, 61.20.Lc Although gels are commonly used in everyday life they continue to offer fundamental challenges to research. Their physics is determined by a wide window of lengthscales, from the molecular size of particles in the solvent to macroscopic structures, and by a similarly broad range of timescales: Gels are "complex" fluids [1]. Of particular interest are physical gels which are typically made of molecules forming a stress-sustaining network, with links that have a finite lifetime, as opposed to chemical gels where junctions are permanent and properties follow directly from geometry. The transient character of the network in physical gels results in a complex interplay between structure and dynamics, leading to non-trivial flow properties. Here we propose a model of a reversible physical gel which is microscopically realistic (we are in fact inspired by one particular material), and specifically design a hybrid Monte Carlo / molecular dynamics numerical approach to successfully bridge the gap between microscopic details and macroscopic observations, while offering deep insight on the nature of physical gels.Inspired by recent experimental work on gelation, a variety of "minimal" models have recently been studied to elucidate the connection between gelation and seemingly related phenomena: Geometric percolation [2, 3], glass transition [4,5,6], phase separation [7,8]. Detailed experiments performed with colloidal particles with tunable interactions [9] revealed that a non-trivial interplay between phase separation and kinetic arrest may produce gel-like structures. Associating polymers constitute another well-studied example of reversible gels [1]. In that case, gels can be obtained far from phase separation, producing viscoelastic materials with highly non-linear rheological properties that are not well understood [10,11]. In many cases, a close similarity between gelation and glass formation is reported [1]. We explain below this similarity but discuss also important differences.Our model is inspired by a material described in Ref. [11]. It is a microemulsion of stable and monodisperse oil droplets in water mixed with telechelic polymers, i.e. long hydrophilic chains with hydrophobic end caps. A polymer can form a loop around a single droplet, or, more interestingly, a bridge between two drople...

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