An intensive study on the optical, rheological, and electrokinetic properties of polyvinyl alcohol-capped nanogold

Abstract

Low-temperature-assisted wet chemical synthesis of nanogold (NG) using gold hydroxide, a new precursor salt in the presence of a macroscopic ligand poly(vinyl alcohol) PVA in water in the form of nanofluid, is reported for the first time in this article. In the absorption spectra, the surface Plasmon resonance absorption band in the range of 520–545 nm signifies the formation of NG via a controlled Au3+ + 3e → Au reaction grafted in small assemblies with polymer. Absorption maximum increases nonlinearly with Au-contents up to 100 µM Au in Au-PVA charge-transfer complex. Marked enhancement in the peak intensity of some of the vibration bands of PVA polymer such as C–H stretching, C=O stretching, CH2 bending, and C–C in-plane bending in the presence of NG reveals an interfacial interaction between NG and oxidized PVA via C=O group. Execution of shear thinning behavior regardless of the Au-content strongly suggests that crosslinking exists between NG and PVA in Au-PVA rheo-optical nanofluids. Hydrodynamic diameter and polydispersity index draw a nonlinear path with the Au doping with 30.0 g/L PVA in water over a wide region of 5–100 μM Au covered in this study. Enhancement in the zetapotential of Au-PVA nanofluid over bare PVA in water is ascribed to buildup of nonbonding electrons of “–C=O” moieties from the oxidized PVA on the NG surface. Displaying of lattice fringes in the microscopic image of core–shell Au-PVA nanostructure confirms that crystalline nature of NG core with inter planar spacing 0.235 nm corresponds to Au (111) plane.