Plasma-polymerized films (interlayers) of tetravinylsilane in mixture with oxygen gas (oxygen fraction 0-0.71) were coated on glass fibers (GF) used as reinforcements in GF/polyester composite. Oxygen atoms of increased concentration (0-18 at.%) were partly incorporated into the plasma polymer network, forming SiAOAC/CAOAC bonding species and partly forming side polar (hydroxyl, carbonyl) groups with enhanced oxygen fraction. The amount of oxygen in plasma coatings influenced the Young's modulus, interfacial adhesion, and surface free energy of the interlayer. To determine the interfacial shear strength, a microindentation test was implemented for individual glass fibers on a cross-section of GF/polyester composite. The interfacial shear strength for oxidized plasma coatings was up to 21% higher than that for the non-oxidized interlayer, indicating a direct chemical effect of oxygen atoms on interphase properties. The interphase shear failure was controlled by the shear strength at the interlayer/fiber interface as follows from experimental and model data. POLYM. COMPOS., 00:000-000,

Continuous stiffness measurement (CSM) and dynamic contact module (DCM) nanoindentation measurements were used to characterize the mechanical properties of plasma‐polymerized tetravinylsilane films deposited by PECVD at RF powers ranging from 10 to 70 W. The Young's modulus and hardness as a function of the indenter displacement (5–500 nm) were investigated for films of 1‐µm thickness. The Young's modulus (hardness) was observed to increase from 8.3 (0.9 GPa) to 58 GPa (9.5 GPa) with enhanced RF power. Nanoindentation analysis together with AFM imaging revealed a grain character of films deposited at a higher power. Finite element analysis was used to simulate nanoindentation measurements and evaluate properties of the elastic–plastic material.

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Nanoindentation techniques are today a standard tool for the characterization of mechanical properties of thin films at nanoscale. In this feature article, we introduce various techniques, together with their applications for plasma-polymerized organosilicones: starting from conventional instrumented nanoindentation, followed by continuous oscillatory loading and cyclic nanoindentation by partial unloading for assessing the depth profile of mechanical properties, to continuous mechanical mapping over the sample surface. Methods of analyzing and interpreting the measured data are presented to determine the elastic modulus and hardness of tested films. Plasma polymer films are materials of viscoelastic or elastic-plastic behavior; the correct technique must therefore be selected to give the most accurate mechanical property measurements. A number of limitations of the techniques are also discussed. A list of conditions for successful analysis of mechanical properties is included.

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