B. Pittenger, S. Osechinskiy, J. Mosley, S. Loire, T. Mueller
Keywords: AFM, polymer, composite, interphase, storage modulus, loss tangent, TTS, WLF
Summary:The relationship between the microstructure of polymer composites and the mechanical properties of microscopic domains within them is important due to its influence on macroscopic material performance and function. Mechanical properties of polymers are time dependent, so a full understanding requires measurements over a range of frequencies and temperatures. Ideally, one would like to observe the mechanical behavior of these microscopic domains while they pass through their glass transitions in order to better understand the influence of size effects and confinement on time dependent mechanical properties. Atomic Force Microscopy (AFM) has the nanometer level resolution and sensitivity needed to investigate these samples, but accurate comparisons with established rheological measurements have proven to be elusive. Resonant methods like TappingMode and contact resonance provide mechanical property maps at discrete frequencies that are many orders of magnitude higher than bulk measurements, making comparisons indirect at best. Non-resonant methods like force spectroscopy and PeakForce Tapping provide a better match in frequency, but face challenges in calculating intrinsic mechanical properties like loss tangent and storage modulus. Recently, new AFM modes, improved modeling, better calibration, and more optimal probe design have become available, expanding the possibilities for quantifying mechanical properties at the nanoscale. This presentation will demonstrate the use of this new capability in examining microscopic domains and interphase regions within a polymer composite over a wide range of frequencies and temperatures. References:  O. Sahin, C. Quate, O. Solgaard, and A. Atalar, Phys. Rev. B, 2004, 69, 1. U. Rabe, S. Amelio, E. Kester, V. Scherer, S. Hirsekorn, and W. Arnold, Ultrasonics,2000, 38, 430.  A. Yango, J. Schäpe, C. Rianna, H. Doschke, and M. Radmacher, Soft Matter, 2016, 12, 8297.  T. J. Young, M. A. Monclus, T. L. Burnett, W. R. Broughton, S. L. Ogin, and P. A. Smith, Meas. Sci. Technol., 2011, 22, 125703.  B. Pittenger and D. G. Yablon, Bruker Application Note, 2017, AN149, 1.