LOCAL MECHANICAL SPECTROSCOPY WITH NANOMETER-SCALE LATERAL RESOLUTION

A new technique has been developed to probe the viscoelastic and anela stic properties of submicron phases of inhomogeneous materials. The me asurement gives information related to the internal friction and to th e variations of the dynamic modulus of nanometer-sized volumes. It is then the nanoscale equivalent to mechanical spectroscopy, a well-known macroscopic technique for materials studies, also sometimes called dy namic mechanical (thermal) analysis. The technique is based on a scann ing force microscope, using the principle of scanning local-accelerati on microscopy (SLAM), and allows the sample temperature to be changed. It is called variable-temperature SLAM, abbreviated T-SLAM. According to a recent proposition to systematize names of scanning probe micros cope based methods, this technique should be included in the family of ''mechanothermal analysis with scanning microscopy.'' It is suited fo r studying defect dynamics in nanomaterials and composites by locating the dissipative mechanisms in submicron phases. The primary and secon dary relaxations, as well as the viscoplasticity, were observed in bul k PVC. The wide range of phenomena demonstrate the versatility of the technique. A still unexplained increase of the stiffness with increasi ng temperature was observed just below the glass transition. All of th ese observations, although their interpretation in terms of physical e vents is still tentative, are in agreement with global studies. This t echnique also permits one to image the variations of the local elastic ity or of the local damping at a fixed temperature. This enables the s tudy of, for instance, the homogeneity of phase transitions in multiph ased materials, or of the interface morphologies and properties. As an illustration, the homogeneity of the glass transition temperature of PVC in a 50/50 wt % PVC/PB polymer blend has been demonstrated. Due to the small size of the probed volume, T-SLAM gives information on the mechanical properties of the near-surface, which may differ from bulk properties. (C) 1998 American Institute of Physics.