Rheology of cohesive granular materials across multiple dense-flow regimes.

We investigate the dense-flow rheology of cohesive granular materials through discrete element simulations of homogeneous, simple shear flows of frictional, cohesive, spherical particles. Dense shear flows of noncohesive granular materials exhibit three regimes: quasistatic, inertial, and intermediate, which persist for cohesive materials as well. It is found that cohesion results in bifurcation of the inertial regime into two regimes: (a) a new rate-independent regime and (b) an inertial regime. Transition from rate-independent cohesive regime to inertial regime occurs when the kinetic energy supplied by shearing is sufficient to overcome the cohesive energy. Simulations reveal that inhomogeneous shear band forms in the vicinity of this transition, which is more pronounced at lower particle volume fractions. We propose a rheological model for cohesive systems that captures the simulation results across all four regimes.

Bridging the rheology of granular flows in three regimes.

We investigate the rheology of granular materials via molecular dynamics simulations of homogeneous, simple shear flows of soft, frictional, noncohesive spheres. In agreement with previous results for frictionless particles, we observe three flow regimes existing in different domains of particle volume fraction and shear rate, with all stress data collapsing upon scaling by powers of the distance to the jamming point. Though this jamming point is a function of the interparticle friction coefficient, the relation between pressure and strain rate at this point is found to be independent of friction. We also propose a rheological model that blends the asymptotic relations in each regime to obtain a general description for these flows. Finally, we show that departure from inertial number scalings is a direct result of particle softness, with a dimensionless shear rate characterizing the transition.

Solvation phenomena in dilute multicomponent solutions I. Formal results and molecular outlook.

We derive second-order thermodynamically consistent truncated composition expansions for the species residual partial molar properties--including volume, enthalpy, entropy, and Gibbs free energy--of dilute ternary systems aimed at the molecular account of solvation phenomena in compressible media. Then, we provide explicit microscopic interpretation of the expansion coefficients in terms of direct and total correlation function integrals over the microstructure of the corresponding infinite dilution reference system, as well as their pressure and temperature derivatives, allowing for the direct prediction of the species partial molar properties from the knowledge of the effective intermolecular interactions. Finally, we apply these formal results (a) to derive consistent expressions for the corresponding properties of the binary system counterparts, (b) to illustrate how the formal expressions converge, at the zero density limit, to those for multicomponent mixtures of imperfect gases obeying the virial equation of state Z = 1 + BPkT, and (c) to discuss, and highlight with examples from the literature, the thermodynamic inconsistencies encountered in the currently available first-order truncated expansions, by pinpointing the mathematical origin and physical meaning of the inconsistencies that render the first-order truncated expansions invalid.