In this paper, the role of both non-adsorbing (depleting) and adsorbing (stabilizing) polymers is investigated in the process of sedimentation in aqueous suspension concentrates. A range of polymers with diþ erent molecular masses have been used. By measuring the rheology of these systems and also studying the sedimentation of model polystyrene latex and real agrochemical suspensions of ýuquinconazole, we have observed that the sedimentation rate is related to the nature of the particle ýocs and that the rate of sedimentation is signiücantly reduced once a continuous network of particles is formed. Rheologically this corresponds to the formation of a weak elastic gel. When the attraction between particles is sufficient, this network is formed via a diþ usion-limited aggregation mechanism, has an open structure and sediments slowly. The network, however, is able to rearrange into a more dense reaction-limited structure which sediments more rapidly. This transition from a slow to a faster sedimentation rate takes up to four days and depends on the strength of the attraction between the particles, the volume fraction of particles and molecular mass of the non-adsorbing polymer. Soft adsorbed polymer stabilizing layers lead to weaker ýocculation, require more nonadsorbing polymer for network formation and could result in more rapid sedimentation.
A range of suspensions containing diþ erent molecular mass non-adsorbing polymers and with the same sedimentation rate have diþ erent rheologies, including the zero shear viscosity. Consequently, the ýocculated network is not the only factor in sedimentation and the non-adsorbing polymer also contributes. Furthermore, there is no direct correlation between rheology and sedimentation. This diþ erence could be due to the non-adsorbing polymer molecules having to diþ use through the network of particles before the particle clusters in the network can rearrange and sedimentation occur.