Viscoelastic properties of particle gels

The effect of strength of attraction and volume fraction on the mechanical properties of alumina particle networks were investigated. Alumina particle gels were formed reversibly and in situ in the rheometer by cooling alumin a particle suspensions with adsorbed poly(12-hydroxy stearic acid) suspende d in a marginal solvent, hexanol. The collapse of the polymer layer with de creasing solvency (temperature) induces flocculation when the long-range va n der Waals force overcomes the remaining steric repulsion. The gelation te mperature depends on volume fraction. At the gel temperature, T-gel, the ge l becomes predominantly elastic; at. temperatures below T-gel, the elastici ty increases with decreasing temperature. We find that the elastic modulus data, measured over a wide range of volume fraction (0.2 < phi < 0.425) and temperature (10-14 degrees C), follows: G = G(0)(phi - phi(g))(s). This sc aling suggests the prefactor and exponent to be independent of temperature. We present some arguments for why subjecting a particle gel to a preshear procedure might result in an temperature-dependent prefactor. By invoking s uch an effect, we are able to rescale and collapse previously published mod uli data on presheared suspensions according to the (phi - phi(g)) expressi on. (C) 1999 Academic Press.