Surface Nanomechanical Properties of Polymer Nanocomposite Layers

Abstract

The nanomechanical behavior of molecularly thick (8-10 nm) compliant polymeric layers with the nanodomain microstructure from poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS or Kraton) was probed with micromechanical surface analysis based on scanning probe microscopy. The microprobing with high lateral resolution revealed the bimodal character of the nanomechanical surface behavior with different elastic responses shown by the rubber matrix and the glassy nanodomains. High-resolution probing showed virtually constant elastic response for the compliant layer compressed to 60% of its initial thickness followed by a sharp increase of the resistance when the tip reached within 3 nm from a stiff solid substrate. Application of the double-layer model allowed the estimation of the actual elastic moduli of different nanophases within the grafted polymer monolayer: 7 ( 3 MPa for the rubber phase and 20 ( 7 MPa for the glassy domains. The relatively high elastic modulus of the rubber matrix is caused by a combination of chemical cross-linking/branching and spatial confinement within a <2Rg layer. On the other hand, the observed low modulus of the glassy nanodomains can be attributed to both the low molar weight of polystyrene segments and the presence of rubber layers in the probed volume.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…In case of very thin samples (2-20 nm) indentations should therefore be limited to 1-4 nm, and probing such depths is unstable. This important issue has been addressed especially by the researchers in the group of Tsukruk, who have exploited a semi-empirical formula of Shull et al [284] to model the deformations of thin polymeric films [285] and of polymer nanocomposite layers [286]. Such a formula gives the indentation depth as in the Hertz theory (d = a 2 /R), but the contact radius is a function of the Young's moduli of the film material (E F ) and the underlying substrate (E S ) and of the thickness of the sample t:…”

Microtribological and Nanomechanical Properties of Switchable Y-Shaped Amphiphilic Polymer Brushes

“…The samples were scanned in tapping mode before and after force measurements to ensure that no contamination, plastic deformation, or physical damage occurred during the application of force. The data processing and calculation of the elastic modulus from the surface distributions of over 1000 FDCs were carried out in accordance with the multilayered Hertzian contact mechanics model described earlier [25,36]. For quantitative results, great care was taken to analyze the AFM tip characteristics.…”

Bioinspired Material Approaches to Sensing

“…5). [46][47][48] The loading plot in coordinate of penetration 3/2 versus the applied load (Hertzian coordinate plot) was observed to be highly nonlinear (Fig. 6).…”