PSI - Issue 40

I.A. Morozov et al. / Procedia Structural Integrity 40 (2022) 314–320

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I.A. Morozov et al. / Structural Integrity Procedia 00 (2022) 000 – 000

The upper soft layer vanishes (Fig. 2a) after the etching in argon plasma. Shallow elevations and depressions appear, repeating the agglomerates of the hard phase of the subsurface of untreated polymer; the fibrillar structure is partially destroyed. The elastic modulus of such modified surface is not uniform (Fig. 2, bottom row), which is related to the mechanical heterogeneities of the initial substrate.

Fig. 2. AFM images of surfaces (top row) and elastic modulus maps (bottom row): polyurethane activated in argon plasma (a) and treated in Ar/C 2 H 2 plasma for 30 (b), 60 (c) and 120 (d) seconds. The insets show elastic modulus maps in higher detail.

Structure of the surface after Ar/C 2 H 2 plasma with the shortest time (Fig. 2b) does not qualitatively differ from the initial one (Fig. 2a); the RMS roughness increases from 1.8 to 2.1 nm. Further, a wrinkled relief is formed (Fig. 2c, d): a result of the stability loss of the hard coating on the soft substrate. The contrast of the elastic modulus of acetylene-treated surfaces is related both to inhomogeneities of the activated substrate and to the fact that at the initial stage of treatment with Ar/C 2 H 2 plasma, an inhomogeneous (discontinuous) carbon-containing coating is formed (Carvalho et al. (2015)). High topography gradient gives the contrast of mechanical properties of the wrinkled structures; the measurement of the elastic modulus in these areas is not reliable. Nevertheless, areas of different stiffness also occur outside the immediate vicinity of the folds. The analysis of the topography and local mechanical properties showed that the elevations have a higher elastic modulus than the surrounding lowlands. Note that, due to the complex structural-mechanical properties of the initial polymer, it is not possible to determine the local boundaries of the growing islet nanocoating.