Wave-vector dependence of the initial decay rate of fluctuations in polymer solutions

We present experimental results for the initial decay rate ${\mathrm{\Gamma }}_1$ of concentration fluctuations in solutions of linear polymers, for various molecular weights, concentrations, and wave vector q, in two rather different solvents. We find that under all conditions explored the dimensionless decay rate 6π${\mathrm{\eta }}_0$ ${\mathrm{\Gamma }}_1$/(${\mathrm{k}}_{\mathrm{B}{\mathrm{Tq}}^3}$) is a function only of the scaled wave vector q${\xi }_{\mathrm{H}}$. Here ${\mathrm{\eta }}_0$ is the solvent viscosity, and ${\xi }_{\mathrm{H}}$ is the length scale defined by ${\xi }_{\mathrm{H}}^{\mathrm{-}1}$≡${\lim }_{\mathrm{q}\to 0}$6π${\mathrm{\eta }}_0$Γ 1/(${\mathrm{k}}_{\mathrm{B}}$ ${\mathrm{Tq}}^2$).