40 J. G. Tramell et al. P4000 sample and denoted as beads C and D. The nanomechanical properties of a sample measured using AFM consist of the height, adhesion, and Young’s modulus. These properties can be presented in two configurations, as shown in figure 9 as 3D/2D color map images and figure 10 as a plot. For the AFM analysis herein, we define adhesion as the force needed to disengage the tip of the cantilever from the surface of the sample and the Young’s modulus as the measure of the sample’s resistance to elastic deformation under a given load, calculated using the known tip geometry of the selected cantilever and assuming Hertzian contact mechanics. The adhesion and Young’s modulus values reported are relative rather than absolute because 1) it is historically difficult to validate such analytical approach across constitutes of drastically different properties and height and 2) the main goal of AFM analysis is to measure the width of the interphase (a measure of how far, moving away from the glass bead, until the binder properties are representative of the bulk). Fig. 9 3D images of P4000-SC (∼30 µm, bead A) sample topography (left) obtained over a 10 µm×10 µm FFM scan overlaid with a color map representing the adhesion (top, Inferno color map) and Young’s modulus (bottom, Viridis color map). 2D zoomed-in images (right) of adhesion (top) and modulus (bottom) interphase, where the solid red line represents the line scan across the interphase. The HTPB binder is on the left side of each image and the glass bead is on the right side Highlighted in Collinson et al. 2021 (and references therein), changes in sample height can induce non-ideal tip-surface interactions that can in turn lead to ‘dead-zones’ where the information gathered becomes non-quantitative [14]. It is extremely difficult to detangle whether the sudden change in height causes the change in nanomechanical properties, or if the sudden change in nanomechanical properties causes artifacts in the topography resulting from different indentation depths. Acknowledging the likelihood of dead-zones that could result from non-flat surface preparation, we report tentative interphase widths as we continue to investigate best practices and mitigate undesirable artifacts of multi-component systems with starkly different properties. The 3D images (figure 9, left) visualize the topography of a given binder/bead region (bead A) of a P4000-SC sample across a 10 µm×10 µm scan area, overlaid with the adhesion (figure 9, top panel) or Young’s modulus (figure 9, bottom) information. The 2D images (figure 9, right) represent a smaller portion of the sample surface, more easily depicting the color gradient moving from the bulk HTPB (represented as orange in the adhesion and dark blue in the modulus) to the bulk uncoated glass bead (represented as purple in the adhesion and green/yellow in the modulus) for both adhesion and Young’s
RkJQdWJsaXNoZXIy MTMzNzEzMQ==