DYNAMICS OF UNCHARGED COLLOIDAL SILICA SPHERES CONFINED IN BICONTINUOUS POROUS-GLASS MEDIA

The restricted diffusion of uncharged colloidal silica spheres in an o ptically matched, porous glass with uncharged internal surfaces is mea sured by means of heterodyne dynamic light scattering (DLS) and fluore scence recovery after photobleaching(FRAP). Glass and sphere surfaces have been chemically treated such that, in addition to hydrodynamic in teractions, only hard particles-wall interactions are present. The wav evector-dependent effective diffusion coefficient inside the porous gl asses, obtained from the initial decay of the correlation functions. i s always smaller than the bulk diffusion coefficient. In particular th e diffusion coefficient at small K, probing diffusion over several por e diameters, is strongly reduced due to increasing hydrodynamic drag a t large particle to pore size ratios, The long-time self-diffusion coe fficient D-S(L) of fluorescent silica spheres measured by FRAP is in g ood agreement with the small angle DLS results. The reduction of the d iffusion coefficient as a function of the size ratio qualitatively agr ees with various models describing the restricted motion of a particle in an infinitely long cylinder.