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Multiwalled carbon nanotubes (MWCNTs) were synthesized by the reduction of ethyl alcohol with sodium borohydride (NaBH4) under a strong basic solvent with the high concentration of sodium hydroxide (NaOH). Nanocomposites of different concentration of MWCNT dispersed in poly(3,4-ethylene dioxythiophene) polymerized with poly(4-styrene sulfonate) (PEDOT:PSS) were prepared and deposited on a flexible polyethylene terephthalate (PET) polymer substrates by the spin coating method. The thin films were characterized for their nanostructure and subsequently evaluated for their piezoresistive response. The films were subjected to an incremental strain from 0 to 6% at speed of 0.2 mm/min. The nanocomposite thin film with 0.1 wt% of MWCNT exhibits the highest gauge factor of 22.8 at 6% strain as well as the highest conductivity of 13.5 S/m. Hence, the fabricated thin film was found to be suitable for piezoresistive flexible strain sensing applications.

The seminal work of Nix and Gao in (J Mech Phys Solids, 46:411–425, 1998), laid the foundation for quantifying indentation size effect (ISE). Several groups around the world have continued to explore the various factors that influence ISE, through extensive numerical and experimental studies. In this work, a unified approach to quantify ISE is presented, wherein the effects of materials, geometry and other coupled parameters on ISE are incorporated to derive a simple unified model. The model predictions for depth dependence of hardness are validated through experimental studies on pulsed electro-deposited (PED) nickel with varying grain sizes using a Berkovich tip with a finite tip radius. Lower grain sizes, higher statistically stored dislocation densities, blunt tips, lower constraint factors and higher plastic zone sizes are found to reduce ISE. The deviation caused by these parameters from the predictions of the original Nix & Gao model are discussed. Graphical abstract