The glass transition of charged and hard sphere silica colloids

Abstract

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 φ=0.18 a glass transition for the charged systems and at φ=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 α and β relaxation are compared within a large Q range. Using an exponent parameter λ=0.74 for the charged particles and λ=0.76 for the hard spheres a good agreement between theory and experiment can be obtained, both for the liquidlike and the glassy state.

Tagged-particle dynamics in a hard-sphere system: Mode-coupling theory analysis

“…In the present simulations, HI are not present. Thus our study also serves to complement previous MCT analyses of colloidal hard-sphere suspensions [18][19][20][21][22], demonstrating that HI are not an important ingredient for a quantitative description of structural relaxation.…”

Theoretical predictions of structures in dispersions containing charged colloidal particles and non-adsorbing polymers

“…Various theoretical models of particle-polymer mixtures have been utilized in previous work, aiming to quantify the various interactions and to establish how they affect the macroscopic properties [5][6][7][8][9][10][11] . Several experimental methods are available to elucidate the structure of particlepolymer mixtures, which can then be compared with the model predictions [12][13][14][15][16][17][18][19][20] . Most of them are based on some form of scattering, with light or neutrons.…”

Flow curves of dense colloidal dispersions: Schematic model analysis of the shear-dependent viscosity near the colloidal glass transition

“…Hence, the marked slowing down of the mobility of concentrated suspensions can directly be traced back to the caging of a given sphere by its surrounding neighbors. The quantitative description of the dynamics of quiescent suspensions in terms of the MCT has met with gratifying success when confronted with experimental data obtained through dynamic light scattering 16,17,18,19,20,21 . Indeed, MCT was shown to explain the structural arrest of concentrated suspensions and describe quantitatively the dynamics that stretch out over many orders of magnitude.…”