Polymer Surface and Interface Properties and (Dynamic) Processes

Abstract

The application of AFM in its various modes for studies of polymers has been discussed in the previous chapters with a particular focus on imaging. It is clear that apart from “static” microscopy, AFM offers access to quantitative surface and interface properties. In addition, the family of techniques can be applied to a wide range of dynamic phenomena and processes as outlined in this chapter. The surface and interface properties addressable by AFM comprise, among others, adhesion and friction, as well as surface mechanical properties. By analyzing these properties on a more relevant length scale, it is in many cases possible for the practitioner to identify the link between microscopic and macroscopic behavior. Similarly important are the dynamic phenomena we encounter in polymers; ranging from the intrinsic thermal behavior to dynamic interactions of polymers with their environment. This is best illustrated in local thermal analysis by advanced AFM approaches and in local property mapping. As shown in Fig. 4.1a, the surface melting temperature of poly(ethylene terephthalate) was determined using a local scanned probe with an integrated heating device. Upon heating the probe that is in contact with the PET surface, the film thermally expands, which can be deduced from the increase in the deflection signal of the AFM cantilever. At the surface melting point, the AFM probe starts to penetrate into the polymer film. As shown, the local surface melting point was found to be 235°C. A second illustrative example is presented in Fig. 4.1b. The sequence of AFM images shown reveals the growth of daughter lamellae of elastomeric polypropylene nucleated on mother lamellae. This process leads eventually to the crosshatched morphology typical for iPP [2]. Open image in new window Fig. 4.1 (a) Temperature scan recorded on a PET film using a heatable AFM probe [1]. (b) TM-AFM images captured during the crystallization of an elastomeric PP film. The arrows point at homo-epitaxial nucleation events; the subsequent growth of lamellar crystals proceeds with different rates. While lamellar patches 1 and 3 grow steadily, patch 2 remains dormant for at least 500 s before growing slowly. Reprinted with permission from [2]. Copyright 2003. American Chemical Society