title: Microstructure, local dynamics, and flow behavior of colloidal suspensions with weak attractive interactions.
abstract: We present a comprehensive micro- and macrorheological study of the effect of weak depletion attraction (Ψdep≈ 1-10 kBT) on dense colloidal suspensions stabilized by short-range repulsive interactions. We used aqueous polymer dispersions as model system and demonstrated the unique capabilities of multiple particle tracking (MPT) to disclose structural changes in such technically important systems exhibiting many characteristic features of hard sphere systems. Below the hard sphere freezing point ϕc, viscosity increases monotonically with increasing Ψdepdue to the transition from a fluid to a fluid/crystalline and finally to a gel state. Above ϕc, increasing attraction strength first results in a viscosity reduction corresponding to the formation of large, permeable crystals and then in a viscosity increase when a network of dense, small crystals forms. The fraction of the fluid and crystal phase, particle concentration in each phase as well as the modulus of the micro-crystals are obtained, the latter decreases with Ψdep. Above the colloidal glass transition strong heterogeneities and different local particle mobility in the repulsive and attractive arrested states are found. Particles are trapped in the cage of neighboring particles rather than in an attractive potential well. The intermediate ergodic state exhibits uniform tracer diffusivity.
authors.affiliation: Karlsruhe Institute for Technology (KIT), Institute for Mechanical Process Engineering and Mechanics, Applied Mechanics, Karlsruhe, 76131, Germany.
authors.forename: Clara
authors.initials: C
authors.lastname: Weis
authors.affiliation: Karlsruhe Institute for Technology (KIT), Institute for Mechanical Process Engineering and Mechanics, Applied Mechanics, Karlsruhe, 76131, Germany.
authors.forename: Claude
authors.initials: C
authors.lastname: Oelschlaeger
authors.affiliation: Covestro Germany, Leverkusen, 51365, Germany.
authors.forename: Dick
authors.initials: D
authors.lastname: Dijkstra
authors.affiliation: BASF SE, Ludwigshafen, 67056, Germany.
authors.forename: Meik
authors.initials: M
authors.lastname: Ranft
authors.affiliation: Karlsruhe Institute for Technology (KIT), Institute for Mechanical Process Engineering and Mechanics, Applied Mechanics, Karlsruhe, 76131, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Willenbacher