B. Pittenger, S. Osechinskiy, J. Thornton, S. Loire, T. Mueller
Keywords: polymer, composite, AFM, viscoelastic, modulus, PeakForce QNM, AFM-nDMA, mechanical properties
Summary:The macroscale performance of polymer composites is controlled by both the microstructure of the material and the mechanical properties of microscopic components. As confinement effects and interphase formation can alter the mechanical properties of the microphases, only high-resolution measurements performed directly on the composite can provide the local property distribution needed to understand the relationship between microstructure and bulk. With its proven ability to map mechanical properties at the nanometer level, Atomic Force Microscopy (AFM) has the resolution and sensitivity needed to investigate these microscopic domains. With careful calibration, nanomechanical results from AFM on homogeneous materials agree with those obtained from established rheological techniques like Dynamic Mechanical Analysis (DMA) and Nanoindentation. When AFM based mechanical property mapping techniques are applied to heterogeneous samples like polymer composites, new possibilities emerge for understanding macroscopic behavior. PeakForce QNM and AFM-nDMA are highly capable AFM based mechanical property mapping modes. Both provide consistent maps of sample modulus, but PeakForce QNM is typically faster while AFM-nDMA is more suited to viscoelastic measurements across a wide range of frequencies and temperatures. AFM-nDMA is therefore preferred when the bulk mechanical properties of interest are viscoelastic, or are influenced by the viscoelastic properties of the microphases within the material. This presentation will discuss efforts to correlate bulk mechanical properties to nanomechanical maps and examine recent results showing how viscoelastic dynamics at the filler-matrix interface can influence toughness in polymer composites.