I am not sure how you can change the parameters in the instrument. Perhaps OP can give you some suggestion.

Hope your work is going well.

Best,

/OV

Dear Deepanjali,

DLS measurements can be performed with arbitrary parameters as long as you're interested only in intensity size distribution. So maybe you don't need to specify these properties for your experiment. Here's a nice article on this topic:

http://www.materials-talks.com/blog/2014/08/05/faq-how-important-are-refractive-index-absorption-for-nanoparticles/

Good luck!

Dear Deepanjali,

As the other Alexander has said, material properties are used in converting intensity weighted size distribution data to number and volume weighted distributions. The difference between these distributions is a weighting to take into account the greater intensity of scattering by larger particles. 

For small particles Rayleigh scattering particles, the effect of refractive index is also relatively negligible 

Thank you everyone for your suggestions, hopefully i can get good data.