Determination of thermomechanical properties of a model polymer blend

Force-displacement curves have been acquired with an atomic force microscope (AFM) on a model polymer blend of polystyrene/poly(n-butyl methacrylate) (PS/PnBMA) as a function of temperature. A novel analysis technique, based on Hertz theory, permitted us to determine Young's modulus of PS and PnBMA, away from the interface (at distances larger than 1 mm) as well as close to the interface (at distances smaller than 80 mu m) with a resolution of 800 nm. The inherent difference in the glass transition temperature of the polymers resulted in their different viscoelastic behavior. For the first time, it is possible not only to measure Young's modulus of the model blend components but also to map the morphology of the PS/PnBMA model blend based on Young's modulus of the constituting polymers as a function of temperature. Furthermore, differences between the thermomechanical properties of the polymers away from and in the vicinity of the interface can be characterized. This important topic can be addressed only with a tool able to measure local quantities, and not with measurements based on averages on a large ensemble of molecules, like dynamic mechanical analysis (DMA). The modulus of PnBMA and PS calculated from AFM force-displacement curves is in excellent agreement with the DMA and AFM data from our previous measurements.