Variation of optical properties, rheology, and microstructure in fullerene/poly(vinyl pyrrolidone) nanofluids with fullerene content in n-butanol

In this study, we report non-linear variation of optical and rheology properties in fullerene (C-60)/poly(vinyl pyrrolidone) (PVP) nanofluids (NFs) with C-60-content (C) in an alcoholic medium. From the absorption spectra, we found that the absorbance maximum ((max)) follows a non-linear path with C-value due to a donor-acceptor PVP C-60 charge transfer in a C-60/PVP complex. The (max) value reaches maximum at a specific C-60-content of 13.9 M due to percolation effect and then starts decreasing with a further increase in C-value over the subsequent region covered in this experiment. Models were proposed to show donor-acceptor interaction between C-60 and PVP. The molar extinction coefficient also drops through a peak maximum at 13.9-mu M C-60. Regardless of the C-values, shear-thinning behavior was found in all NFs. The shear viscosity () value, which decreases with shear rate value over 5 to 100 s(-1), is shown to be increasing non-linearly against the C-value. The -value varies non-linearly with C-60-content and shows a dip at a point near 13.9-mu M C-60. High-resolution transmission electron microscope images reveal that the size of C-60/PVP nano-assemblies increases with C-value as PVP is anchoring C-60 molecules in specific structures.