Molecular dynamics study of epoxy/clay nanocomposites: rheology and molecular confinement

To investigate the effect of nanoparticles on molecular confinement, epoxy/clay nanocomposites in 6 % wt were prepared by low shear mixer and ultrasonication methods. According to the XRD results, high energy sonication can significantly increase the intergallery space compared to that of the low shear mixer and, therefore, provide more interfacial area for polymer-particle interaction. Rheological measurements, including dynamic mechanical moduli, continuous relaxation spectrum and zero-shear viscosity, were carried out in the linear region to reveal the solid-like characteristics induced in the pure epoxy. The longest Rouse relaxation time, which was determined from the value of zero-shear viscosity, was employed to study the segmental friction. It is clear that the chain relaxation process was slowed by the polymer-particle interactions, which created very high monomeric friction. We introduce the ratio of monomeric friction coefficients (zeta(nano)/zeta(epoxy)) as the strength of immobilization to correlate the increasing elasticity, longer relaxation time and molecular confinement quantitatively. Because more monomers can be immobilized on a clay surface due to their strong affinity, the friction ratio increased to 359.48 for the sonicated sample, whereas weak polymer-particle affinity resulted in much lower growth, with a friction ratio of 2.11 for the low shear mixing method.