Shear induced orientation in polymer-clay solutions and their influence on the structure in multilayered films

Abstract

The influence of shear on viscoelastic solutions of poly(ethylene oxide) (PEO) and clay (Cloisite, CNA) was investigated by rheology and small angle neutron scattering (SANS) under shear. These measurements determined the shear-induced orientation of the clay and the polymer as well as their relaxation behavior after cessation of shear. Comparison of PEO-CNA solutions (~100 nm diameter platelets) to previously studied PEO-Laponite gels (~30 nm diameter platelets) found that the orientation of CNA platelets occurs at much lower shear rates. Additionally, the relaxation times were much longer for CNA platelets than for Laponite platelets. From these solutions and gels, multilayered nanocomposite films were prepared. Shear-induced orientation of polymer-clay solutions is important to the organization of the clay platelets in the films. The structure was determined by scattering and microscopy techniques. Experimental evidence suggests that clay platelets align within multilayers with their surface normal perpendicular to the spread direction. The unusual orientation of the multilayers persists on multiple length scales from nanometer to micrometer. As part of an independent research project a series of PEO-Kaolinite (~1.5 µm diameter platelets) solutions and films were studied and compared to the results mentioned above. Initial rheological studies of the PEO-Kaolinite solutions showed shear thinning behavior and possible flow irregularities. Preliminary investigation of the films made from the solutions suggests that shear orientation is preserved within the film. Continued optimization of the PEO-Kaolinite solutions leading to improved exfoliation of the platelets will result in a novel class of materials with unique properties.