Barrier hopping, viscous flow, and kinetic gelation in particle-polymer suspensions

Abstract

The naive mode coupling-polymer reference interaction site model (MCT-PRISM) theory of gelation and elasticity of suspensions of hard sphere colloids or nanoparticles mixed with nonadsorbing polymers has been extended to treat the emergence of barriers, activated transport, and viscous flow. The barrier makes the dominant contribution to the single particle relaxation time and shear viscosity, and is a rich function of the depletion attraction strength via the polymer concentration, polymer-particle size asymmetry ratio, and particle volume fraction. The dependences of the barrier on these three system parameters can be accurately collapsed onto a single scaling variable, and the resultant master curve is well described by a power law. Nearly universal master curves are also constructed for the hopping or alpha relaxation time for system conditions not too close to the ideal MCT transition. Based on the calculated barrier hopping time, a theory for kinetic gel boundaries is proposed. The form and dependence on system parameters of the kinetic gel lines are qualitatively the same as obtained from prior ideal MCT-PRISM studies. The possible relevance of our results to the phenomenon of gravity-driven gel collapse is studied. The general approach can be extended to treat nonlinear viscoelasticity and rheology of polymer-colloid suspensions and gels.

Structure and dynamics of colloidal depletion gels: Coincidence of transitions and heterogeneity

“…However this explanation is not applicable to the gel phase because it lacks a significant population of free particles. Alternatively, activated hopping transitions are a driver of rare, large displacement dynamics in glassy systems and could hypothetically arise in the attractive system studied here [29]. In addition, Puertas et al [30] discuss the possibility of a collective structure origin to dynamical heterogeneity.…”

“…Mechanistic descriptions of the dynamic transitions that accompany these regimes include predictions of particle localization due to strong short-range interactions from direct simulation [25], idealized mode coupling theory [26], and na ïve mode coupling theory [27]. Simulation and theory have attributed the arrest that leads to dynamical heterogeneity to effective particle-particle bonds arising from short-range attractive potentials [28], to the development of entropic barrier hopping [29], or to the emergence of two distinct particle populations with long exchange times [30]. Earlier work has suggested a role for arrested spinodal decomposition and other equilibrium transitions in the development of ultimate gel structure [20].…”

“…Simulation and theory have attributed the arrest that leads to dynamical heterogeneity to effective particle-particle bonds arising from short-range attractive potentials [28], to the development of entropic barrier hopping [29], or to the emergence of two distinct particle populations with long exchange times [30]. Earlier work has suggested a role for arrested spinodal decomposition and other equilibrium transitions in the development of ultimate gel structure [20].…”

“…To further discriminate between the competing mechanisms suggested by very recent theory and simulations [30], comparison to microscopic measurements of localization length, dynamical heterogeneity, structural populations, and barrier hopping are required. Suggestion that rare dynamical processes play a role in gel response [29,33] adds another argument for measurement of single particle distributions of dynamics. It is the aim of this work to fill these gaps by direct quantification of local gel structure and dynamics through confocal microscopy.…”

The effect of nanoparticle shape on polymer‐nanocomposite rheology and tensile strength

“…Numerous computational and theoretical studies have examined the clustering and network formation of nanoparticles and their effect on both the structural and rheological properties of PNCs. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] The vast majority of these efforts have focused on nanoparticles that are either spherical, polyhedral or otherwise relatively symmetric, although there are some notable exceptions. [19][20][21]23 In contrast, experiments have tended to emphasize highly asymmetric nanoparticles, 27-38 such as layered silicates or carbon nanotubes.…”