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42219-B7
Dynamics and Morphology of Polymer Blends Containing Nanoscale Filler Particles

Mohamed Laradji, The University of Memphis

Effect of spherical nanoparticles on the phase separation of binary immiscible fluids with the nanoparticles interacting symmetrically with the two fluids was investigated via large scale dissipative particle dynamics. It was found that once domains are formed, the nanoparticles migrate towards the interfaces, thereby acting as surfactants, and leading to slowin down of the dynamics of phase separation. Eventually, phase separation stops once most of the interfaces are occupied by the nanoparticles. The characetristic domain size is found to decrease with increasing nanoparticles volume fraction or decreasing nanoparticles diameter.

We also investigated the effects of nanorods on the phase separation of immiscible fluids, when the nanorods interact more attractively with one of the two fluids. It was found that the dynamics and morphology of the mixture depend strongly on the aspect ratio, nu, and volume fraction of the nanorods, psi. In particular, the ternary mixture undergoes a full phase separation or a microphase separation, depending on the dimensionless Onsager parameter psi*nu. Namely, a full phase separation occurs if the nanorods volume fraction is small enough such that they remain in the isotropic phase. However, a microphase separation occurs in the situation where the nanorods should be in the nematic phase should a full phase separation occur. The observed microphase separation is metastable, as substantiated by a subdiffusive kinetics of the rods. The sluggish dynamics of the rods is the result of the anisotropy of the rods which as the result of domain growth, the effective volume fraction of the rods in the preferred component is increased, leading to a disordered jamming of the nanorods. The final characteristic domain size of the dispersion, reduced by the nanorods length is found to depend only on Onsager's dimensionless parameter. Furthermore, just like in the case of nanospheres acting as surfactant (first paragraph), the dynamics of phase separation is shown to follow a crossover scaling form.

The two studies above show that both preferentially adsorbed nanospheres, or nanorods that preferentially interact with one of the two immiscible polymers, should be considered as viable emulsifying agents of immiscible polymer blends.

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