I want to measure the DLS size of my sample, which is aqueous colloid of copper particles having size less than 100 nm. During DLS measurement in Malvern Nano ZS90 instruments it is asking for material properties (Refractive Index, Absorption). Can anyone please help me by providing these values for my sample with some references or tell me how can I measure that properties myself?
Thanks in advance.
For the intensity distribution you do not need the optical properties. See the posts by Ulf Nobbmann on ResearchGate. You can find the n and k values for Cu very easily (CRC Handbook or Luxpop.com. The density of Cu (9.3 gcm-1) is your biggest challenge. Do a Stokes' Law calculation. If your material is settling in less than 2 weeks, then it's not nano (< 100 nm)
For the intensity distribution you do not need the optical properties. See the posts by Ulf Nobbmann on ResearchGate. You can find the n and k values for Cu very easily (CRC Handbook or Luxpop.com. The density of Cu (9.3 gcm-1) is your biggest challenge. Do a Stokes' Law calculation. If your material is settling in less than 2 weeks, then it's not nano (< 100 nm)
Obviously the RI is wavelength dependent. A simple Google search will find at 632.8 nm that RI = 0.31 - 3.43k. For many small materials there is good robustness to RI change. As stated previously, this is not required for the intensity distribution. For conversion to volume, it is required. The conversion number must never be attempted.
Yes Alan sir, actually there is some ambiguity between the values of RIs, in different sources. According to the Luxpop.com, at 632.8 nm, for copper the values of n and k are 0.249 and 3.410 respectively. Where in some other source they are, 0.307 and 3.434 respectively. Actually I need the number PSD actually, so can I take the values given in Luxpop.com?
You should only use the z-average and polydispersity index from DLS as stated in the international standards (ISO13321:1996; ISO22412:2008, ASTM E2490-09). Again Ulf Nobbmann has dealt with conversions from DLS in:
http://www.materials-talks.com/blog/2014/08/05/faq-how-important-are-refractive-index-absorption-for-nanoparticles/
http://www.malvern.com/en/pdf/secure/TN101104IntensityVolumeNumber.pdf
You'll only need the RI to 2 decimal places and k to an order of magnitude. In the Rayleigh region (true nano) then there generally is good robustness to RI changes for narrow distributions. Get a number distribution from a particle counter such as the Nanosight.
Giri - can you explain how a paper on stability of MWCNT's is related to the question: "Can anyone help me in providing physical properties of the sample (copper colloid) required for DLS Measurement?" Other than the fact that DLS was used for the size determination. Having looked at the paper I have one question for you - what optical properties were used for the conversion of the intensity distribution to volume shown in the paper you mention? Also tell me why you show a linear x- (size) axis for the particle size distributions (instead of logarithmic) against the recommendations of ISO 9276-2.
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