They prepared nanofluids by dispersing and oscillating TiO2, Al2O3, Ag, Cu, SiO2, graphite nanoparticles, and carbon nanotubes into Texatherm oil.
When the dimension of metal nanoparticles is small enough compared to the wavelength of the incident light, surface plasmon can be excited due to a collective motion of free electrons in the metal nanoparticles that resonantly couples with the oscillating electric field of the light.
Superparamagnetic nanoparticles interact with an externally applied oscillating magnetic field of the right frequency to produce heat by Néel relaxation.
This change in colour was due to the collective coherent oscillation of conduction electrons at the surface of the gold nanoparticles when these particles interact with the oscillating electric field of the incident light, a phenomenon called surface plasmon resonance (SPR).
Plasmons are coherently oscillating free electrons on the surface of noble metal nanoparticles, such as silver and gold (Willets and Van Duyne, 2007).
The conduction electrons in these nanoparticles collectively oscillate with the incident light causing an enhanced electric field that is localized around the surface of the nanoparticle [1, 2].
As any change in the shape of the metal nanoparticles affect the pattern in which the free electrons are oscillating, the resonant frequency will change [6].
These nanoparticles act as antennas for light, since under resonance conditions they accommodate oscillating electric fields at their surface with the same frequency as the incident light, but with several orders of magnitude higher intensities.
Other types of nanoscale measurement approaches include mechanical means such as oscillating microscopic cantilevers as well as electrical means such as conductivity measurements across a nanopore that permits the flow of, e.g., nanoparticles.
