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Nanorheological Analysis of Polymer Surfaces by Atomic Force Microscopy

Surfaces of polymer blends were investigated using atomic force microscopy (AFM) to study their nanomechanical properties (nanorheology). We were particularly interested in information obtained from force-distance curve methods on rubbery or melt state samples. In order to realize clear comparison, a rubbery sample, polyisobutylene (PIB), was blended with a glassy-state sample, polystyrene (PS). When PS/PIB blends were observed in contact-mode operation, PIB-rich phases appeared as depressions. However, this was an artifact caused by the very low elastic modulus of PIB. By analyzing the force-distance curve, sample deformation by the force exerted was estimated together with real height free from sample deformation. Thus, if force-distance curve measurements are performed on every point of the sample (force-volume measurements), we can reconstruct a “real height image” and a “sample deformation image.” The apparent depressions became almost flat in the “real height image” by this analysis. With further analysis using Hertz theory, an elastic modulus image of the sample was also obtained, which correlated more closely with the “real height image” than with the“apparent height image.”