Graphene is anisotropic and dimensions are different, so which dimension will be considered in DLS test?
In general, DLS measures the translational diffusion constant of the particles inside. In the most basic case, the software subsequently applies Stokes-Einstein equation (which assumes a spherical particle) to deduce the particle radius (given that the visocosity of the solution is know).
Because graphene does not have rotational symmetry, you get two translational diffusion coeffecients and also the rotational diffusion coefficent comes into play. Nevertheless, assuming you really have graphene and thus the flakes diameter is way bigger than the thickness, you may can come up with a meaningful analysis. I attached a paper on the DLS of discs for reference. The third link is a short transaction where the things mentioned in this paragraph have been applied to graphene to calculate a reasonable figure for their sheet size in the µm range.
In addition, if you have access to a DLS setup that may make use of the laser polarization you can also work out directly the major and minor axis of non-spherical particles. I attach a second link where it has been done for gold nanorods, but following this approach, it might be a prerequisite that you can consider your graphene nanosheets approximately spherical.
http://www.sciencedirect.com/science/article/pii/0301462285800594
http://pubs.acs.org/doi/abs/10.1021/jp067049x
http://books.google.de/books?id=xeBH-manBesC&lpg=PA105&ots=W9cthmHOPW&dq=K.%20Kubota%2C%20Y.%20Tominaga.%20S.%20Fujime%2C%20J.%20Otomo%20and%20A.&pg=PA100#v=onepage&q=K.%20Kubota,%20Y.%20Tominaga.%20S.%20Fujime,%20J.%20Otomo%20and%20A.&f=false
It's not accurate to measure GO size via DLS. Most of manufacturer provide the average X-Y dimension of the nanosheets plus the thickness Z dimension. these dimensions were attained by AFM, doing a statistical calculation.
DLS is useless technique for graphene. it will be suitable only for the spherical metal particles. Better tool to characterize graphene is TEM and AFM.
Measuring the lateral size of liquid-exfoliated nanosheets with dynamic light scattering
http://iopscience.iop.org/article/10.1088/0957-4484/24/26/265703
I have a query, I'm trying to use the DLS technique to calculate the size of the graphene oxide , Initially I'm trying to dissolve it in THF and then check it using the DLS, I got the Z average value of Graphene oxide to be around 7000 nm which is approximately 7 microns, I'm wondering the value is too high, so just wanted to know is it the DLS technique or am I doing something wrong with the dissolution technique!
Thank you!
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