Study of polystyrene surface local mechanical properties by the atomic force microscopy

Composites with polymer surface layer serving as a matrix for metal nanoparticles stabilization are very promising materials for modern nano- and optoelectronics, nonlinear optics, catalysis, chemical sensors and biosensors. Successful development of such nanocomposites is impossible without intimate knowledge of polymer surface layer properties (structural, mechanical, chemical, electrical, etc.) at a nanolevel. In this study, local mechanical properties (elastic modulus, wearing qualities) of polystyrene surface layer were investigated by means of atomic force microscopy (AFM). Elastic modulus was determined from the analysis of force-distance curves within the framework of Johnson-Kendall-Roberts model. A significant decrease of elastic modulus near the polystyrene surface relative to its bulk value was observed. Strong dependence of the surface layer mechanical properties on the polymer molecular weight was found. The influence of different types of treatment (annealing, UV-irradiation) on the polystyrene surface layer mechanical properties was investigated. Strong correlations between PS surfach layer mechanical properties and its glass transition temperature variations (studied in our previous works) are discussed.