Elastic and Yield Behavior of Strongly Flocculated Colloids

We have investigated theorectically the elastic and yield behaviors of strongly flocculated colloids by first examining the yield forces between two particles within the framework of Derjaguin‐Landau‐Verwey‐Overbeck (DLVO) interactions. Under highly attractive conditions, i.e., in the absence of the secondary minimum in the DLVO potential, the radial (tensile) motion between particles is nonelastic because of the lack of an inflection point in the DLVO potential. However, the lateral (shear) motion is shown to be elastic up to a distance y max , providing a mechanism for the observed elasticity in colloidal gels. If r 0 and s 0 are, respectively, the closest center‐to‐center and surface‐to‐surface distances between two particles, image where zeta is the zeta potential of the particles and alpha a defined constant. Moreover, the yield force between two particles is much smaller in the lateral direction than in the radial direction. These results suggest that yielding of a particulate network is likely to occur through the lateral movements between particles. The yield strain can be approximated as that at which all the bonds in a certain direction have a perpendicular displacement > y max , resulting in image The shear modulus of the network, G ′, can be deduced by combining the elastic constant of the lateral movement with the existing elastic theory of a particulate network. The yield stress can be approximated as sigma image where A is the Hamaker constant and R the particle radius. These predictions are shown to compare favorably with existing experiments.