Research Publications People Computers

Egor Maresov


Modeling the Making and Breaking of Bonds as an Elastic Microcapsule Moves over a Compliant Substrate

By integrating the lattice Boltzmann model for hydrodynamics, the lattice spring model for micromechanics of elastic solids, and the Bell model for bond formation and rupture, we examine the fluid driven motion of elastic microcapsules on compliant surfaces. The capsules, modeled as three-dimensional fluid-filled elastic shells, represent polymeric microcapsules or biological cells. We observed three regimes of capsule motion. Namely, the capsule rolls steadily along the substrate at a sufficiently high shear rate, it is stationary at a low shear rate, and exhibits an intermittent motion (saltation) at intermediate shear rates. At a given shear rate, the regime of capsule motion was found to depend on the substrate stiffness, and on the rate of rupture of the adhesive bonds. The capsule was observed to roll steadily on a sufficiently stiff substrate, and at a high rate of bond rupture. In the opposite limit of a soft substrate and low rate of bond rupture, the system was localized in the stationary regime. The findings provide guidelines for creating smart surfaces that could regulate motion of the microcapsules. Egor A. Maresov, German V. Kolmakov, Victor V. Yashin, Krystyn J. Van Vliet and Anna C. Balazs, Modeling the Making and Breaking of Bonds as an Elastic Microcapsule Moves over a Compliant Substrate, Soft Matter, DOI:10.1039/C1SM05952A

Self-assembly of mixtures of nanorods in binary, phase-separating blends

Aligned nanorod inclusions have the potential to significantly improve both the photovoltaic and mechanical properties of polymeric materials. Establishing facile methods for driving or .corralling. the nanorods to self-assemble into such aligned morphologies could facilitate the fabrication of effective, robust devices. Using a variety of computational methods, we model the self-assembly of a mixture of A-coated and B-coated rods in an AB phase-separating blend. Using dissipative particle dynamics (DPD) simulations, we first show that the steric repulsion between ligands causes the coated rods to preferentially align end-to-end within the minority phase of the binary blend. Using this information, we then utilize a coarse-grained approach, which combines a Cahn.Hilliard (CH) model for the polymer blend with a Brownian dynamics (BD) simulation for the rods, to simulate a larger sample of a rod-filled 30:70 AB thin film. We find that just a small volume fraction of B rods in the majority B phase promotes the percolation of A-like rods within A, so that the percolation threshold for the A-rods is significantly lowered. If, however, the number of B nanorods in the B phase exceeds a particular volume fraction, the B particles inhibit the percolation of the A rods. Thus, there is an optimal volume fraction of B nanorods that provides the beneficial effects. The output from these morphological studies then serves as the input to the lattice spring model (LSM) for mechanical behavior of the composite. The results reveal that nanorods oriented along the tensile direction contribute to the enhancement of the macroscopic mechanical properties of the material. This multi-scale approach, integrating techniques that cover the microscopic, mesoscopic and macroscopic, provides a valuable means of determining relationships in nanocomposites and establishing useful guidelines for tailoring the components to yield optimal materials' properties. Li-Tang Yan, Egor Maresov, Gavin A. Buxton and Anna C. Balazs, Self-assembly of mixtures of nanorods in binary, phase-separating blends, Soft Matter, 2011, 7, 595-607 DOI:10.1039/C0SM00803F

Updated: Aug, 2011

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