Flexural and Torsional Atomic Force Microscopy for Imaging Copolymer and Elastomer Blends

Mechanical strength and adhesion are playing dominant roles in modern rubber industry. Recently, these properties have been partially studied from a nanoscopic point of view and correlated with the characterization of phase morphology of blends through atomic force microscopy (AFM). Among kinds of operating modes of AFM, tapping mode is most excellent technique for imaging blends with minimizing lateral force and vertical penetration on the surface, which secures lateral imaging resolution and least shear damage at nanometer scale.

In this study, we first proposed to combine amplitude-modulated tapping mode with higher-order harmonic motions of the AFM cantilever for imaging copolymer polybutadiene-polyethylene oxide (PBD-PEO). This method can successfully separate an adhesion contrast from the energy-loss depedent phase image obtained on tapping mode, which has been complicated by intermixing of deformation, adhesion and viscoelaticity on copolymer surface. Then, we extended our method for imaging the elastomer blends with fillers. In this case, conventional phase image can not distinguish adhesion heterogeneity of filler domains with same stiffness. Relevant results show that some filler domains have clearly adhesion contrast at the interfacial regions between filler and surrounding rubber, which can be independently determined in our study. This provides us more details on the interphase and owns promising application to determine the bonding energy between phases. As well, we applied torsionl resonance mode to image lateral viscoelastic contrasts. The results can partially interpret the adhesion contrast as obtained before. Finally, some results were compared with images from force modulation mode and force volume mode.