B. Pittenger, S. Osechinskiy, J. Thornton, S. Loire, T. Mueller
Keywords: polymer composites, time-temperature
Summary:The performance of polymer composites is influenced by the microstructure of the material as well as the properties of the individual components. As confinement effects and interphase formation can alter the properties of any microphases that are present, only measurements performed directly on the composite can provide the needed local property distribution. Mechanical properties of polymers are generally 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 to appreciate the full influence of size effects and confinement on time dependent mechanical properties. With its proven ability to map mechanical properties at the nanometer level , Atomic Force Microscopy (AFM) has the resolution and mechanical sensitivity needed to investigate these domains. Unfortunately, established AFM measurement modes do not yield results that allow direct comparison to established rheological techniques like Dynamic Mechanical Analysis (DMA). Contact resonance  provides mechanical property maps at well-defined frequencies, but cantilever resonances are many orders of magnitude higher than DMA, making comparisons indirect at best. Intermittent contact methods like TappingMode , force volume, and PeakForce Tapping  face challenges in calculating intrinsic mechanical properties like storage and loss modulus (or tan delta) due to the non-linear process of making and breaking contact . AFM based nano-DMA (AFM-nDMA) provides viscoelastic results that can be directly compared with bulk DMA . Like bulk DMA, it provides spectra of storage and loss modulus across frequency and temperature allowing construction of master curves through Time Temperature Superposition (TTS) . In addition, it allows high resolution measurements localized to the microscopic structures within heterogeneous samples. This presentation will examine the capabilities of this new mode with examples in a wide range of polymers and composites.  F. Rico, C. Su, and S. Scheuring, Nano Lett., 2011, 11, 3983.  U. Rabe, S. Amelio, E. Kester, V. Scherer, S. Hirsekorn, and W. Arnold, Ultrasonics, 2000, 38, 430.  O. Sahin, C. Quate, O. Solgaard, and A. Atalar, Phys. Rev. B, 2004, 69, 1.  B. Pittenger and D. G. Yablon, Bruker Application Note, 2017, AN149, doi: 10.13140/RG.2.2.15272.67844.  M. Chyasnavichyus, S. L. Young, and V. V Tsukruk, Langmuir, 2014, 30, 10566.  B. Pittenger, S. Osechinskiy, D. Yablon, and T. Mueller, JOM, 2019, 71, 3390.  M. L. Williams, R. F. Landel, and J. D. Ferry, J. Am. Chem. Soc.,1955, 77, 3701.