NanoRack™ Sample Stretching Stage for MFP-3D™ Atomic Force Microscopes
The NanoRack Sample Stretching Stage provides the first direct measurement method for observing nanoscale features and effects of materials under stress control. The NanoRack stage is available as an option for all MFP-3D Atomic Force Microscopes (AFMs).
The NanoRack stage (Figure 1) is a high-strain, high-travel manual tension and compression stage that provides two-axis stress control of samples under different loads. It integrates force measurements with AFM images or other measurements and returns both stress and strain data. The stage is compatible with a wide variety of imaging techniques including Phase and Dual AC™ for enhanced contrast of material properties, as well as our Ztherm™ option for localized thermal analysis. The height-adjustable stabilizing pillar can be removed to provide bottom access to the test sample. The NanoRack is ideal for a wide range of applications including measurements of adhesive strength in polymers and stress-induced deformations and cracking in a variety of biological and inorganic materials.
A commercial impact copolymer (ICP), a multicomponent material typically used in automotive and appliance applications where a balance of stiffness and toughness is needed, was studied with the NanoRack accessory on the MFP-3D AFM to investigate material deformation and interface adhesion as a function of tensile stress. Effects of deformation were observed within both the polypropylene (PP) and ethylene-propylene (EP) components, as well as at the interface between the two materials.
There are no other direct measurement methods available to determine interfacial adhesive strength of polymer blends, and so AFM investigations of micro-domain deformation such as the one described here could be used ultimately to provide a direct determination of interfacial adhesion in complex polymer-containing materials such as ICP. Studies of this kind improve our understanding of material structure-property relationships, ultimately enabling manufacture of better quality products.
Figure 2 shows real-time stress vs. time curves of the ICP as the sample is being pulled in the NanoRack. Note that the force spikes immediately upon pulling and is followed by a lengthy relaxation process that is strongly material dependent. As the copolymer stretches, the individual components (PP and EP rubbers) deform accordingly in response to the tensile stress. Figure 3 shows before and after images of the EP component for a 3% elongation. For additional information, see our application note “Applications of the NanoRack Sample Stretching Stage to a Commercial Impact Copolymer” by D. Yablon, et al., ExxonMobil.
Crack Propagation in Bone
Due to the hierarchical structure and complexity of bone, the uncovering of structure-function relationships, i.e. the origin of material properties such as strength, toughness, and fatigue resistance, is usually a non-trivial task. The NanoRack Sample Stretching Stage, in combination with AFM imaging, offers an approach to overcome some of these difficulties. Because AFM allows for imaging in ambient – even hydrated conditions – it is feasible to perform in situ micro-mechanical testing experiments while conducting imaging. Figure 4 shows cracking generated in a cortical bovine bone. As expected due to the underlying lamellar structure, such cracking under stress is generally deflected towards the long beam axis. For additional information, see our application note “Crack Propagation in Bone Captured with In Situ Mechanical Testing During AFM”, O. Katsamenis, et. al, University of Southampton.
Dual AC, MFP-3D, NanoRack, SmartStart, and Ztherm are trademarks of Asylum Research.
Figure 1: The MFP-3D NanoRack Sample Stretching Stage is a high-strain, high-travel manual stretching stage that provides control of tensile and compressive loaded samples up to 80N.
Figure 3: Amplitude mode 2 images of identical EP domain within ICP material at (a) neutral position on NanoRack and (b) 3% elongation on NanoRack. 5µm scans.