We report the direct measurement of the diffusion of polystyrene in porous silica by dynamic light scattering. The effective diffusion coefficient is smaller than the diffusion coefficient in bulk solution ($D_0$), and depends on the scattering wave vector $q$. At low $q$, macroscopic diffusion coefficients ($D_{\infty }$) are obtained; the ratio $\frac{D_{\infty }}{D_0}$ depends on the size of the polymer. At higher $q$, where $q^{-1\mathrm{}}$ is comparable to pore dimensions, more complicated "transitional" behavior is seen.

• Received 18 June 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.1741