Scanning Probe Microscopy of (Complex) Polymeric Systems : Beyond Imaging their Morphology !

Scanning Probe Microscopy of (Complex) Polymeric Systems : Beyond Imaging their Morphology !

Philippe Leclère Université de Mons, Laboratory for Chemistry of Novel Materials

The development of novel materials involves a large effort to study and understand nanometerscale physical and chemical properties. Among the characterization techniques nowadays available, methods using local force probes naturally provide important contributions to these studies. In particular, dynamic force techniques, i.e., using an oscillating probe, are well adapted to soft samples such as polymer materials or biological systems. The first demonstration of their potential was the elucidation 15 years ago of the phase-separated microstructures of block copolymer thin films. Intermittent contact mode images can be of two different types : in the first, the image corresponds to the changes in the piezoactuator height that are necessary to maintain a fixed oscillation amplitude, through a feedback loop (the height image) ; in the second, the image contains the changes in the oscillator phase delay relative to the excitation signal (the phase image). The phase measurement in many cases yields images reflecting tiny variations of the local properties of the sample surface. Despite the success of the technique for microstructural characterization, important questions remain about the physical origin of the image contrast. The major factors contributing to the phase contrast are still under debate, but are thought to be a result of viscoelastic response and adhesive forces mixed with elastic surface behavior. Very recently, new scanning probe techniques based on real time data analysis have been introduced to map with much higher resolution the mechanical (stiffness, adhesion, deformation, energy dissipation,...), thermal or electrical properties of polymers by using multifrequency techniques or based on force-distance curves both aiming at providing pertinent answers to this very important issue. For some applications in the growing field of organic electronics, the measurements of the electrical properties at the nanoscale can be also addressed using these new techniques leading to a better understanding of the behaviour of organic optoelectronic devices and therefore helping in the optimization of their performances. In this talk, we will illustrate the major morphological features and the mechanical, electrical or thermal properties observed by AFM by considering a series of polymeric systems of growing complexity : homopolymers, polymer blends, block copolymers, supramolecular polymers, nanocomposites and hyperbranched polymers used for different applications (protective films, adhesives, coatings, hydrogels, field effect transistors, photovoltaic solar cells or light emitting diodes). In fine, we will discuss what the future developments of Scanning Probe Microscopy could be in the field of polymer research trying to provide more faster, more accurate, more quantitative properties with higher resolution or by combining the SPM data with other complementary techniques (Raman spectroscopy, IR spectroscopy, confocal optical microscopy, …).