Surface versus Volume Properties on the Nanoscale: Elastomeric Polypropylene

Abstract

In the following, the etching step index will be omitted whenever the other indices are similar for all etching steps. The data analysis procedure applied in this study can be divided in two main operations. The first operation is the extraction of the physical property. Here, each individual force distance curve , is analyzed on the theoretical basis explained in the 'Materials and Method' section of the main manuscript. The second operation is the structural and statistical analysis of the material properties.The result of the property extraction is a set of images with the same dimensionality as , .These physical maps contain quantitative information of material properties for each pixel within the array. These physical maps are:  The elasticity map , that represents the Young's modulus, computed from the re-trace portion of F k,l on the basis of the Derjaguin-Muller-Toporov (DMT) model. 1

Micromechanical Characterization of Complex Polypropylene Morphologies by HarmoniX AFM

“…As expected, by increasing the etching time, the morphology, characterized by crystalline fibrillar structures [56,57], becomes more clear and definite. The roughness, after 3 h etching, is 14.3 ± 3.0 nm; therefore, the roughness shows a slightly higher value with respect to the roughness of the nonetched sample; the increase of roughness is due to the presence of areas in which the etching probably has shown different rates between amorphous and crystallized polymers [30]. With the increase of etching time up to 12 h, the roughness decreases down to 9.7 ± 0.1 nm, since the amorphous parts have been efficiently removed and the etching procedure is effective also on the crystalline structures.…”

“…This also allows us to study the effect of the etching time on the mechanical characteristics of the sample [30]. Figure 1 shows the topography taken on the shear layer of the injection molded sample exposed to the chemical etching solution for different times, 0 h, 3 h, and 12 h. From the first image row of Figure 1, which shows an average roughness of 12.3 ± 3.5 nm, it is evident that the morphology could not be clearly detected on the nonetched sample; this observation demonstrates the presence of an amorphous layer on the top of the crystalline region [30,55]. As expected, by increasing the etching time, the morphology, characterized by crystalline fibrillar structures [56,57], becomes more clear and definite.…”

“…Since the crystalline structures generally give higher modulus values than the amorphous ones [30], it is possible to conclude that the etching procedure is very effective in removing the amorphous part and all the resultants of the microtome procedure. This finding is also confirmed by the values of adhesion force that significantly decrease from 50 nN to 7 nN for the nonetched sample and for the sample etched with 12 h etching time, respectively; generally, high values of adhesion force are due to the viscous properties of an almost amorphous polymer in the nonglassy state [58].…”

“…In addition, these techniques are able to simultaneously provide topographic maps (from tens of nanometers up to microns) of the sample allowing a direct correlation among mechanical and morphological sample 2 International Journal of Polymer Science properties. Both AFM based methods, HarmoniX and Peak Force, are appropriate for the mechanical characterization of soft matter [29,30]. In particular, HarmoniX technique operates in tapping mode and makes use of specifically designed cantilever geometries with an out-of-axis tip [31,32].…”

“…Generally, the application of AFM based techniques is limited to the mechanical characterization of homogeneous samples, and only few papers are devoted to the characterization of samples having complex morphology distribution [30].…”