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Characterization of Heterogeneous Regions in Polymer Systems Using Tapping Mode and Force Mode Atomic Force Microscopy.


pdf icon Characterization of Heterogeneous Regions in Polymer Systems Using Tapping Mode and Force Mode Atomic Force Microscopy. (720 K)
Raghavan, D.; VanLandingham, M. R.; Gu, X.; Nguyen, T.

Langmuir, Vol. 16, No. 24, 9448-9459, 2000.

Keywords:

microscopy; polymethyl methacrylate; blends; coatings; chemical properties; mechanical properties; microstructure; nanoindentation; phase contrast

Abstract:

Characterization of polymer coating surfaces is crucial to understanding and predicting the long-term performance of coatings in aggressive environments. The exposed polymer surface and near-surface regions can differ from the bulk polymer film both chemically and mechanically, which can effect the durability of the coating and its ability to protect the underlying substrate. In this study, atomic force microscopy (AFM) is used to investigate the heterogeneity of blended films of poly (methylmethacrylate) (PMMA) and polybutadiene (PB) on silicon substrates before and after annealing. The blended films with different ratios of PMMA to PB are prepared by spin casting onto silicon substrates from solution. The surface morphology and composition of these cast films are investigated using tapping mode and force mode AFM. Annealing the samples in air at 75 C + 5 deg C causes changes in the relative chemical and mechanical differences between PMMA and PB, so the phase image contrast is studied as a function of annealing time. The effect of tapping force level on phase image contrast is also explored. To identify the different components in polymer blends and to understand the influence of relative surface stiffness on the phase images, nanoscale indentation measurements. A loss in phase contrast between PB-rich and PMMA-rich regions is observed as a function of heating time. This observation correlates well with the increases in glass transition temperature, modulus, and polarity of pure PB with respect to pure PMMA.