Abstract:
In this experiment the concept of dynamic light scattering (DLS) was investigated by autocorrelation data analysis. This was used to determine the viscosity of samples composed of glycerol-water mixtures containing nano-sized latex spheres. The autocorrelation function was used to determine the diffusion coefficient, which is related to the viscosity of solutions by the Stokes-Einstein relation. The other parameters in this equation such as the hydrodynamic radii of the spheres were known for this experiment.
In the field of physics, dynamic light scattering has been commonly used to determine the size distribution profile of submicron particles and polymers suspended within a solution of known viscosity while experiencing Brownian motion [1]. This technique focuses a laser beam into a suspension while measuring the fluctuations in the intensity of the light that is scattered by the particles within the suspension [1]. Several analysis methods exist that are capable of extracting information from the measured noise in the intensity data of scattered light. This experiment used the autocorrelation function (ACF) to compare the newly collected data to mathematical models of particle motion under the same parameters. This was accomplished via least square fitting. This is then used to calculate the diffusion coefficient for the sample. The Stokes-Einstein relation was then used to calculate the viscosity of the sample now knowing the diffusion coefficient [2,3,4]. Through preliminary testing trials it was determined that low glycerol-water concentrations were most conducive for measurements. For this reason, concentrations of 16% and 38% were chosen for the final trials with spheres of radii 90 nm and 304 nm.