Quantitative nanoscale mechanical properties of a phase segregated homopolymer surface
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Quantitative nanoscale mechanical properties of a phase segregated homopolymer surface J. F. Graham, M. Kovar, and P. R. Norton Interface Science Western and Department of Chemistry, University of Western Ontario, London, Ontario, N6A 5B7, Canada
P. Pappalardo Diversey Lever, Innovation Centre, 46701 Commerce Centre Drive, Plymouth, Michigan 48170
J. Van Loona) and O. L. Warren Interface Science Western and Department of Chemistry, University of Western Ontario, London, Ontario, N6A 5B7, Canada (Received 14 January 1998; accepted 19 June 1998)
Crystallization of poly(ethylene terephthalate) (PET) is accompanied by significant changes in surface topography, easily detected by atomic force microscopy (AFM). Phase imaging by AFM qualitatively indicates contrast in mechanical properties of nanometer scale areas of an annealed PET surface, but cannot provide quantitative data. Using interfacial force microscopy (IFM), we have, for the first time, made quantitative measurements of the elastic moduli of such nm-scale areas on a homopolymer surface. Values of 2.2 GPa, 4.3 GPa, and 11.8 GPa, were found, respectively, for amorphous PET and for phase segregated regions on the surface of an annealed homopolymer PET sample. The method is applicable to any phase segregated surface with nm-sized domains of differing elastic moduli.
I. INTRODUCTION
Scanning probe microscopes have facilitated the study of the surface properties of a wide variety of materials with unprecedented spatial resolution.1 They have enabled a predictive understanding of the macroscopic behavior of materials through a detailed knowledge of the microscopic or even molecular structure. This ability to correlate molecular structure with materials performance is particularly important in the case of polymers, where easily induced nanoscale transformations in molecular structure often lead to macroscopic failure.2 However, with few exceptions to date, scanning probes have not yielded quantitative data on the nanomechanical properties associated with the images. We report here the results of a quantitative study by interfacial force microscopy (IFM) of the changes in mechanical properties of the different nm-scale surface phases resulting from crystallization of a homopolymer. We believe this is the first such quantitative study combining in situ imaging and determination of the elastic properties of homopolymer surface phases on a scale of , 100 nm. In contrast to cantilever based scanning probe microscopes, such as the atomic force microscope (AFM), the unique force-feedback design of the IFM not only prevents any discontinuous or indeterminate probe a)
Present address: Department of Chemistry, Queen’s University, Kingston, Ontatio, Canada, K7L 3N6. J. Mater. Res., Vol. 13, No. 12, Dec 1998
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motion, but is also capable of providing absolute force measurements.3–5 We have chosen to study poly(ethylene terephthalate), PET, a thermoplastic polymer found in man
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