PSI - Issue 32

Ilya A. Morozov et al. / Procedia Structural Integrity 32 (2021) 131–136 I.A. Morozov et al. / Structural Integrity Procedia 00 (2021) 000–000

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nanoindentation, the elastic modulus of the areas outside the fibrils is ~6 MPa. Thus, our polymer is an elastomeric composite with heterogeneously distributed fibrilar network percolating the softer matrix; the internal structure of the material is hidden by the soft layer. The visible length of the fibrils is 0.5...2 μm and the thickness – 4 nm.

Fig. 1. AFM images of the untreated polyurethane: structure of surface (a), subsurface (b) and the map of stiffness of the subsurface (c).

The plasma treatment did not qualitatively affect the "outer" surface (images (II) in Fig. 2). Meanwhile, the subsurface structure is changed (images (I) in Fig. 2): the fibrils are partially preserved (fibrilar fragments are indicated by arrows in Fig. 2a, b) for plasma treatment up to 60 s. These fragments of the internal structure are also visible on the stiffness maps (images (III) in Fig. 2 a, b). Comparing topography and stiffness maps, the lowlands of the relief correspond to softer areas, while the local elevations correspond to stiffer areas (agglomerates of the hard phase).

Fig. 2. AFM images of materials after treatment in argon plasma for 30 s, (a), 60 s (b), 120 s (c) and 300 s (c). The subsurface (I), surface (II) structures and stiffness maps (III) are presented. Arrows indicate fragments of the fibrilar structures.

Increase of treatment time completely destroys the fibrilar structure (Fig. 2 c, d) making the subsurface topography like the surface one; the corresponding stiffness becomes homogeneous. The roughness of the subsurface is always higher, than the outer layer; this value reaches maximum of 20 nm at 120 s of treatment and then falls to