Mechanical response of silver/polyvinyl alcohol thin film: From one-step and cyclic nanoindentation

Abstract

Polymer nanocomposite and its mechanical properties are the area of immense interest for material developers in academia and industry. Present study investigates mechanical behavior of novel hexagonal bipyramidal Silver-Poly (vinyl alcohol) nanocomposites (Ag/PVA NCs) thin film fabricated using aqua-mediated in-situ reduction at room temperature. Specimen was characterized through UV-Visible (λmax = 417 nm), PL (λ(em) = 482 nm), XRD (average crystallite size 29.7 nm and preferential growth of thin film along [111] plane), TEM (hexagonal bipyramidal morphology, size ∼26.25 nm), TGA (increased thermal stability), FTIR (peaks at 945, 604 cm^-1 confirms coordination of Ag and PVA matrix) and SAED. Depth sensing single-step and multi-step nanoindentation was employed to extract material’s sensitive mechanical property. Hardness (H: 0.352 to 0.192 GPa) and elastic modulus (Er: 8.718 to 6.72GPa) decreased with increasing single-step loads (from 50 μN to 10 mN), which can be attributed to indentation size effect (ISE). Cyclic nanoindentation (p∼5 mN, 23 cycles) was performed to deeply understand material sensitive degree of dislocation-structure interaction for fatigue analysis. The reduction in % elastic recovery was found at higher loads. On account of smooth surface, elastic unloading (stiffness) values linearly (y = 1.3944x + 3.8676 with R² = 0.9835) increased from cycle 1 to 23 and contact depth increases linearly (y = 0.0329x + 1.5697, R² = 0.9901) with the number of cycles. Interpretation of p-h profile indicated H and Er decreases with increasing load, along with proceeding cycles and no fracture or breakage/ weakening of NCs / progressive and localized structural damage was observed which evidenced that surface was completely uniform and defect free.