The glass transition of charged and hard sphere silica colloids

Dynamic and static light scattering is applied to concentrated suspensions of silica nanoparticles with surface functionalizations causing highly char ged or hard sphere interaction potentials, respectively. The index of refra ction of the dispersion medium was matched to that of the particles using a mixture of water/glycerol for the charged particles and toluene/ethanol fo r the hard spheres. The static structure factors correspond to the appropri ate theoretical models, Percus-Yevick and rescaled mean spherical approxima tion. At volume fractions Phi=0.18 a glass transition for the charged syste ms and at Phi=0.53 for the hard spheres can be observed, as evident from th e nondecaying components of the intermediate scattering functions. In the g lassy state the experimental correlation functions agree with the predictio ns of the mode-coupling theory over several orders of magnitude in time. Us ing the fitted experimental structure factors as input for the mode-couplin g theory we find good agreement between the theoretical nonergodicity param eters and the measured Debye-Waller factors. In the liquid state close to t he glass transition the experimental intermediate scattering functions and the predictions of the mode-coupling theory for the alpha and beta relaxati on are compared within a large Q range. Using an exponent parameter lambda= 0.74 for the charged particles and lambda=0.76 for the hard spheres a good agreement between theory and experiment can be obtained, both for the liqui dlike and the glassy state. (C) 1999 American Institute of Physics. [S0021- 9606(99)52141-7].