AVS 47th International Symposium
    Material Characterization Thursday Sessions
       Session MC-ThM

Paper MC-ThM8
Study of Semicrystalline Poly(ethylene terephthalate) by Atomic Force Microscopy

Thursday, October 5, 2000, 10:40 am, Room 207

Session: Polymer Characterization
Presenter: P.R. Norton, University of Western Ontario, Canada
Authors: M. Kovar, University of Western Ontario, Canada
U. Gorodzinsky, University of Western Ontario, Canada
P.R. Norton, University of Western Ontario, Canada
Correspondent: Click to Email
We studied the surface topography of isothermally crystallized polyethylene terephthalate (PET) films by atomic force microscopy (AFM). Annealing a flat amorphous PET film at 150 @super o@C produces a semi-crystalline film which is rough on several length scales. We found good correlation of the height (3.5 nm) of small topographical features with the lamellar thickness determined by small angle X-ray scattering in previous studies. It was shown that larger agglomerates (large peaks) are multiples of small ones. The phenomenon is known as lamellar stacking. We hypothesize that the surface corrugation originates as follows: elevated (more crystalline) areas are created at the locations of crystallization nuclei. The polymer chains fold to create lamellar structures and pull "loose" ends out of amorphous regions. Subsequently, lamellar stacks grow using a similar mechanism forming the elevated regions and leaving recessed (less crystalline) ones behind Surprisingly, the density of the small topographical features is the same in the recessed and elevated regions, apparently indicating similar crystallinity, while interfacial force microscopy (IFM) data [J. Mater. Res. 12 (1998) 3565] show the elevated regions to be more crystalline. This apparent conflict results from the sensitivity of AFM phase imaging to only the outermost surface of the film compared to IFM, even for IFM indentation depths of a few nm. Therefore, the variations in the density of crystalline domains (lamellae) that are visible in AFM phase images represent a surface phenomenon that cannot be simply correlated with the state of sub-surface regions.