Novel structure and swelling dynamics of nanocomposite ultrathin films

Abstract

Structure and swelling dynamics of ultrathin films of CdS-polyacrylamide nanocomposite material were studied using gravimetric techniques and X-ray reflectivity. Ultrathin films of the polymer and the nano-composite were coated on hydrophilic Si(100) substrate using spin coating. The thickness of the composite films vary non-monotonically with spinning speed and were found to lie in discrete "bands" of thicknesses separated by "forbidden regions" unlike pure polymer films. Modified internal structure of the coils due to polymer-particle interaction was found to play a significant role in describing the novel features of the nanocomposite films. To study the mass uptake, the films were exposed to the H2O vapour and the weights of the films were recorded as functions of exposure time. The observed non-Fickian transport was explained in terms of alignment of free volume due to confinement of restricted polymer chains. To study swelling dynamics, the films were exposed to the H2O vapour and X-ray reflectivity scans were collected as functions of exposure time. The swelling dynamics of the nanocomposite films were explained in terms of a model which takes into account the polymer-particle interaction. A fraction of polymer segments that are in direct contact with the nanoparticles observed slower dynamics as compared to the free chain swelling. Larger values of excluded volume parameters corresponding to restricted segments as compared to the free segments were explained in terms of enhancement of monomermonomer interaction through particle attachment. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.