Characterization of surface viscoelasticity and energy dissipation in a polymer film by atomic force microscopy

The characterization of surface viscoelasticity and energy dissipation in a polymer film by atomic force microscopy was investigated. The SEBS consisting of hard PS and soft PEB components was selected. The number-average molecular weight, M_n, is 74 000, and the molecular weight distribution, M_w/M_n, was about 1.1. The weight fraction of PS for this triblock copolymer was 42%. The as-prepared films were first dried in a fume hood for 3 days and then in vacuum at room temperature for another 7 days to remove residual solvent. The quality factor Q was calculated by dividing the resonant frequency by the width of the resonant peak at half the maximum power. The samples were scanned at constant force using a triangular Si₃N₄ cantilevers with nominal spring constant of 0.32 N/m. The regions exhibiting larger E_dis could be identified as the soft PEB blocks, while the regions showing smaller E_dis correspond to the hard PS blocks.