title: Depletion, melting and reentrant solidification in mixtures of soft and hard colloids.
abstract: We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft-hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star-polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid-polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft-hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures.
authors.affiliation: Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria. christos.likos@univie.ac.at.
authors.forename: Daniela
authors.initials: D
authors.lastname: Marzi
authors.affiliation: Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria. christos.likos@univie.ac.at.
authors.forename: Barbara
authors.initials: B
authors.lastname: Capone
authors.affiliation: FORTH, Institute of Electronic Structure and Laser, Heraklion, Crete 70013, Greece and Department of Materials Science and Technology, University of Crete, Heraklion, Crete 71003, Greece.
authors.forename: John
authors.initials: J
authors.lastname: Marakis
authors.affiliation: FORTH, Institute of Electronic Structure and Laser, Heraklion, Crete 70013, Greece and Dipartimento di Ingegneria Industriale e dell' Informazione, Seconda Università di Napoli, Via Roma 21, 81031 Aversa, Caserta, Italy.
authors.forename: Maria Consiglia
authors.initials: MC
authors.lastname: Merola
authors.affiliation: FORTH, Institute of Electronic Structure and Laser, Heraklion, Crete 70013, Greece and Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier, Montpellier, France.
authors.forename: Domenico
authors.initials: D
authors.lastname: Truzzolillo
authors.affiliation: Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université de Montpellier, Montpellier, France.
authors.forename: Luca
authors.initials: L
authors.lastname: Cipelletti
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Firmin
authors.initials: F
authors.lastname: Moingeon
authors.affiliation: Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Mario
authors.initials: M
authors.lastname: Gauthier
authors.affiliation: FORTH, Institute of Electronic Structure and Laser, Heraklion, Crete 70013, Greece and Department of Materials Science and Technology, University of Crete, Heraklion, Crete 71003, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Vlassopoulos
authors.affiliation: Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria. christos.likos@univie.ac.at.
authors.forename: Christos N
authors.initials: CN
authors.lastname: Likos
authors.affiliation: Centro de Investigaciones en Ciencias Básicas y Aplicadas, Universidad Antonio Nariño - Campus Farallones, Km 18 via Cali-Jamundí, 760030 Santiago de Cali, Colombia. manuel.camargo@uan.edu.co.
authors.forename: Manuel
authors.initials: M
authors.lastname: Camargo