Measurement of the Newly Defined "Constrained Polymer Region" in Polymer Clay Nanocomposites
Measurements on two exfoliated polymer-clay nanocomposites systems, Nylon 6 and Nylon-MXD6, were conducted to determine the size of the constrained polymer regions. Analysis performed through Atomic Force Microscopy established that the range fell in agreement with speculated values proposed by Beall, which extend 50-100 nm away from the surface of the clay. With an increase in clay loading, topographical hills and valleys became more frequent for a given area. In higher clay loaded samples the clay plates were closer to each other and as a result the frequency of hills and valleys were higher than on those of the lower clay loaded PCNs. Experimentally measured distances between clay plates were in reasonable agreement with the expected values. In systems with lower clay loading, the distances between clay plates were higher. Lower distances between clay plates were seen in systems with higher clay contents. The swelling behavior of the studied PCNs is attributed to their crystalline makeup along with H-bonding. The addition of clay turns the amorphous Nylon-MXD6 polymer into one with a pseudo-crystalline character. This crystalline behavior is observed in areas which are in close proximity to the surface of the clay, the constrained polymer region. When comparing the unconstrained to the constrained polymer region of Nylon-MXD6, a decrease in free volume is observed in the areas which act crystalline. As a result the swelling effect caused by the solvent is amplified in the areas in which clay is absent, the unconstrained polymer region. The distinct amplitude of hills and valleys of NylonMXD6 was a result of a transition from a crystalline domain to an amorphous one. The swelling imparted by the solvent on Nylon 6, already in a crystalline state, was more uniform. The topographical relief on the surface was significantly lower than those on Nylon-MXD6. In Nylon 6 the transition was between two crystalline forms and therefore the swelling amplitude for both areas acted quite similarly.
Clay, Nanostructured materials, Polymeric composites
Adame, D. (2006). <i>Measurement of the newly defined "constrained polymer region" in polymer clay nanocomposites</i> (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.