title: Gravitational collapse of depletion-induced colloidal gels.
abstract: We study the ageing and ultimate gravitational collapse of colloidal gels in which the interparticle attraction is induced by non-adsorbing polymers via the depletion effect. The gels are formed through arrested spinodal decomposition, whereby the dense phase arrests into an attractive glass. We map the experimental state diagram onto a theoretical one obtained from computer simulations and theoretical calculations. Discrepancies between the experimental and simulated gel regions in the state diagram can be explained by the particle size and density dependence of the boundary below which the gel is not strong enough to resist gravitational stress. Visual observations show that gravitational collapse of the gels falls into two distinct regimes as the colloid and polymer concentrations are varied, with gels at low colloid concentrations showing the onset of rapid collapse after a delay time. Magnetic resonance imaging (MRI) was used to provide quantitative, spatio-temporally resolved measurements of the solid volume fraction in these rapidly collapsing gels. We find that during the delay time, a dense region builds up at the top of the sample. The rapid collapse is initiated when the gel structure is no longer able to support this dense layer.
authors.affiliation: SUPA and School of Physics & Astronomy, The University of Edinburgh, JCMB, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK. w.poon@ed.ac.uk.
authors.forename: R
authors.initials: R
authors.lastname: Harich
authors.affiliation: Magnetic Resonance Research Centre, Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK.
authors.forename: T W
authors.initials: TW
authors.lastname: Blythe
authors.affiliation: SUPA and School of Physics & Astronomy, The University of Edinburgh, JCMB, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK. w.poon@ed.ac.uk.
authors.forename: M
authors.initials: M
authors.lastname: Hermes
authors.affiliation: CNR-ISC Uos Sapienza and Dipartimento di Fisica, Sapienza Università di Roma, P.le A. Moro 2, I-00185, Roma, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Zaccarelli
authors.affiliation: Magnetic Resonance Research Centre, Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Sederman
authors.affiliation: Magnetic Resonance Research Centre, Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK.
authors.forename: L F
authors.initials: LF
authors.lastname: Gladden
authors.affiliation: SUPA and School of Physics & Astronomy, The University of Edinburgh, JCMB, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK. w.poon@ed.ac.uk.
authors.forename: W C K
authors.initials: WC
authors.lastname: Poon