UB - University at Buffalo, The State University of New York

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As the volume fraction of hard particles is increased, the suspension develops long relaxation times associated with a glass transition. These colloidal glasses develop because particles are localized by their nearest neighbors resulting in very slow long range self diffusion. With still increasing volume factions the particles lose the ability to diffuse within cages of nearest neighbors at a volume fraction near random close packing. The increased relaxation times for suspensions with volume fractions between the glass transition and random close packing make processing suspensions in this volume fraction range difficult. There are two ways to enhance the volume fractions where suspensions can be processed. The first is to introduce weak attractions. Sufficiently weak attractions open up the cage of nearest neighbors and decrease relaxation times thus decreasing suspension viscosities. As the strength of attraction is further increased, the particles are once again localized by interparticle bonds, the suspensions gel and long relaxation times are reintroduced. By working with weak attractions, the window of volume fraction where suspensions are easily processed can be increased. The second method to increase the volume fraction where suspensions are processable is to introduce weak shape anisotropy. The volume fractions at the glass transition and at random close packing pass through maxima as the degree of anisotropy in increased. In this seminar the effects of attractions and weak shape anisotropy on the mechanical properties of amorphous suspensions will be described. Experimental results will be compared with theoretical predictions developed from naive Mode Coupling Theory. These results show that by tuning the strength of attraction and the degree of anisotropy, suspensions composed of particles of a single size will maintain short relaxation times at volume fractions in excess of 0.65.