Dynamic Light Scattering and Optical Absorption in Biological Nanofluids of Gold Nanoparticles in Poly(vinyl pyrrolidone) Molecules

Nanofluids of distinctive colors are obtained of gold nanoparticles (Au-NPs) embedded in biological molecules of poly(vinyl pyrrolidone) (PVP) following in situ Au 3+ → Au reaction in 10 g/dL PVP in hot water. Varying Au-NPs by 0.05, 0.1, 0.2, 0.5, or 1.0 wt % (as per the Au-PVP) tailors a pink, bluish-pink, reddish-blue, or a light-orange color of nanofluid. In dynamic light scattering, average hydrodynamic dimension ( D h ) has increased from a few nanometers on early Au-NPs contents (≤0.2 wt %) to as big as 180 nm, i.e., larger to average size D p ≈ 100 nm for the transmission electron microscopic images of Au-NPs. Shear bands (serving as templates or beds to these Au-NPs) in counterpart PVP molecules, which are aligned in thin laminates (10−20 nm widths), can be seen in nanofluids on small Au-NPs ( D p = 5−20 nm). Enhanced viscosity, as much as four times on the presence of such Au-NPs, relaxes slowly to the base value by increasing the shear rate (10 to 50 s −1 ), characterizing a non-Newtonian rheological fluid. Shear stress describes enhanced optical absorption, which red-shifts from 535 nm average value in Au-NPs of early sizes to as large value as 571 nm in bigger sizes. Possible applications include light-sensitive drug delivery and other biological devices.