title: Vibrational and structural signatures of the crossover between dense glassy and sparse gel-like attractive colloidal packings.
abstract: We investigate the vibrational modes of quasi-two-dimensional disordered colloidal packings of hard colloidal spheres with short-range attractions as a function of packing fraction. Certain properties of the vibrational density of states (vDOS) are shown to correlate with the density and structure of the samples (i.e., in sparsely versus densely packed samples). Specifically, a crossover from dense glassy to sparse gel-like states is suggested by an excess of phonon modes at low frequency and by a variation in the slope of the vDOS with frequency at low frequency. This change in phonon mode distribution is demonstrated to arise largely from localized vibrations that involve individual and/or small clusters of particles with few local bonds. Conventional order parameters and void statistics did not exhibit obvious gel-glass signatures as a function of volume fraction. These mode behaviors and accompanying structural insights offer a potentially new set of indicators for identification of glass-gel transitions and for assignment of gel-like versus glass-like character to a disordered solid material.
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Lohr
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Tim
authors.initials: T
authors.lastname: Still
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Raman
authors.initials: R
authors.lastname: Ganti
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Gratale
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Zoey S
authors.initials: ZS
authors.lastname: Davidson
authors.affiliation: Department of Physics, West Chester University, West Chester, Pennsylvania 19383, USA.
authors.forename: Kevin B
authors.initials: KB
authors.lastname: Aptowicz
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Carl P
authors.initials: CP
authors.lastname: Goodrich
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sussman
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Yodh
mesh_terms: D005782:Gels / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D008962:Models, Theoretical; D014732:Vibration
chemical_list: D005782:Gels