Using DLS to determine viscosity
Can viscosity be determined by dynamic light scattering? Dynamic light scattering in essence measures the diffusion of particles and calculates the hydrodynamic radius using the Stokes-Einstein relation, D = kT/(6πηr). To find a size using dynamic light scattering, you need to input the viscosity so it can perform the calculation. If we don’t give the viscosity and use a more viscous solution than water, the particle will appear much larger since it appears to be diffusing slower. I’m not sure if it’s possible or advisable to attempt to determine solution viscosity by obtaining the apparent hydrodynamic radius, but here’s some data.
I measured the size of 10nm gold particles in 5 different glycerol concentrations. The viscosity comes from this Dow chart. This data seems fairly linear, but it may be hard to descern small changes in viscosity (this chart covers 0-50% glycerol).