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 charged or hard sphere interaction potentials, respectively. The index of refraction of the dispersion medium was matched to that of the particles using a mixture of water/glycerol for the charged particles and toluene/ethanol for the hard spheres. The static structure factors correspond to the appropriate theoretical models, Percus-Yevick and rescaled mean spherical approximation. At volume fractions Phi=0.18 a glass transition for the charged systems and at Phi=0.53 for the hard spheres can be observed, as evident from the nondecaying components of the intermediate scattering functions. In the glassy state the experimental correlation functions agree with the predictions of the mode-coupling theory over several orders of magnitude in time. Using the fitted experimental structure factors as input for the mode-coupling theory we find good agreement between the theoretical nonergodicity parameters and the measured Debye-Waller factors. In the liquid state close to the glass transition the experimental intermediate scattering functions and the predictions of the mode-coupling theory for the alpha and beta relaxation 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 liquidlike and the glassy state. (C) 1999 American Institute of Physics. [S0021- 9606(99)52141-7].