Abstract
We perform Brownian dynamics simulations to study the gelation of suspensions of attractive, rod-like particles. We show that in detail the rod-rod surface interactions can dramatically affect the dynamics of gelation and the structure and mechanics of the networks that form. If the attraction between the rods is perfectly smooth along their length, they will collapse into compact bundles. If the attraction is sufficiently corrugated or patchy, over time, a rigid space-spanning network will form. We study the structure and mechanical properties of the networks that form as a function of the fraction of the surface, f, that is allowed to bind. Surprisingly, the structural and mechanical properties are non-monotonic in f. At low f, there are not a sufficient number of cross-linking sites to form networks. At high f, rods bundle and form disconnected clusters. At intermediate f, robust networks form. The elastic modulus and yield stress are both non-monotonic in the surface coverage. The stiffest and strongest networks show an essentially homogeneous deformation under strain with rods re-orienting along the extensional axis. Weaker, more clumpy networks at high f re-orient relatively little with strong non-affine deformation. These results suggest design strategies for tailoring surface interactions between rods to yield rigid networks with optimal mechanical properties.
Highlights
We presented the results of a simple model for aggregation and mechanical response of rod-like particles, and showed that the networks that form depend on the details of the inter rod interactions
If the rods were uniformly attractive with no irregularity in the surface interactions, disconnected clusters form
The rods were composed of beads with a fraction, f, which were able to stick to other beads of the attractive variety on other rods
Summary
The competing driving forces for dispersion and aggregation are diverse: surface charges, depletion interactions, van der Waals forces, etc These materials are important for a vast array of technologies (optoelectronics,[1,2,3,4] structural composites[5,6,7,8,9,10,11,12,13,14] etc.), and naturally occurring materials like xanthan gum[15] and wood pulp.[16] In some cases, the rod aggregates form disconnected clusters which enhance the viscosity of the suspension, but fail to gel into a solid. At large enough f, the networks completely fall apart into disconnected bundles
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