Global analysis of correlation functions: Dynamic light scattering from polymers and block copolymers

摘要

Dynamic light scattering has become a standard technique for investigating colloidal suspensions, polymer solutions, melts, blends, gels and other more complex systems. The experimental field autocorrelation function (g) over cap (1)(t) can often be well modeled by a Laplace transform relating (g) over cap (1)(t) to a distribution of decay times A(tau). In simple systems, A(tau) can usually be directly related to a distribution of molecular weights, particle sizes, diffusion coefficients, relaxation times or other physically relevant quantities. With constrained regularization methods, the parameter-free estimation of A(tau) has become straightforward In complex systems, the resulting A(tau) may contain several components the identification of which is not always obvious. The problem often originates in a superposition of components that have different Variations of the decay time with the scattering vector. We present a method based on a simultaneous fit of several autocorrelation functions (ACF) measured at several different scattering angles, which, using simple and reasonable assumptions, yields a robust analysis of the spectra of decay times. The application of the method is illustrated on simulated autocorrelation functions as well as on real experimental data obtained on a variety of polymer systems. [References: 14]