Want to measure the hydrodynamic size and zeta potential of a silver nanoparticles dispersion using Dynamic light scatter (DLS) and need to know what is the proper refractive index (n) for measurement settings. I checked for bulk silver that n = 0.2066 but not sure if its okey to use this for silver nanoparticles.
Thanks in Advance
DLS gives a intensity weighted size distribution which is not a function of the refractive index of the nano particles.
Hydrodynamic,Rh size is calculated from the diffusion coefficient, D, which is calculated from the correlation function of the scattered light.
D=kT/6*pi*eta*Rh, where eta is the sample viscosity.
Refractive index is however used in the conversion from intensity weighted data to number or volume weighted data. That said, for Rayleigh scatters
Silver nanoparticles are metallic, not dielectric the way a protein or typical polymer would be. The scattering behavior is entirely different. Milton Kerker's book treats this issue in detail. Interpretation is a significant project. (Someone may have software). Also, silver nanoparticles may well have a surface charge, in which case the Stokes-Einstein conversion from diffusion coefficient to radius is invalid.
I am working with a nanoparticles and aiming to measure their crstal size and zeta potential.
What is the the right refractive index and absorption to set the zeta potential instrument?
My particles are
gamma-Fe2O3
KMnF3
KCoF3
KFeF3
GdFeO3
please help
Salim, as indicated above, the refractive index in many cases may not matter - especially for nanoparticles. For zeta potential the properties of the solvent are important. The refractive index and absorption will not matter because the zeta potential analysis is intensity based (and there is no conversion to volume/number where optical properties of the particles would be required). You could always convince yourself of the influence by editing an existing record and re-analyzing it with a different refractive index. How to edit a record is described in the post below.
http://www.materials-talks.com/blog/2014/08/05/faq-how-important-are-refractive-index-absorption-for-nanoparticles/
The refractive index of Ag NPs is 0.135 and the absorption index (k) is 3.99.
Shahid Ali
There is a wavelength dependence of refractive index as well as a slight morphology, temperature, and size dependence. It is appropriate to provide a reference. For example:
RIAg = 0.06 - i.4.28 (@ 632.8 nm) P B Johnson and R W Christy 'Optical constants of the noble metals', Phys. Rev. B 6, 4370 - 4379 (1972)
See: https://refractiveindex.info/?shelf=main&book=Ag&page=Johnson
Again, as stated above, the RI is not relevant for an intensity distribution in DLS or the measurement of mobility (from which zeta potential may be inferred).
- Badges
- Science topic