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Identifier

000342686

Title

Shear induced crystallization of a colloidal glass

Alternative Title

Κρυστάλλωση υπό διάτμηση ενός κολλοειδούς υάλου

Author

Κουμάκης, Νικόλαος Ν.

Thesis advisor

Πετεκίδης, Γεώργιος

Abstract

The phase behavior of a suspension of monodisperse colloidal hard spheres is determined solely by its volume fraction. At low concentrations it is in a liquid state and at higher concentrations it forms an ordered crystal as a way to maximize entropy. At a transition volume fraction of 0.58 the system becomes mechanically trapped in a metastable glassy state. When put under oscillatory strain, hard spheres suspensions generally tend to order. When a high volume fraction hard sphere glass is under oscillatory shear it is given enough energy to order into the entropically favorable crystal structure. This study focuses on the rheological properties of the glassy state and the differences to its shear induced crystal. We have rheologically studied the crystallization process of the glass with increasing strain and probed the linear frequency dependence of both glass and shear induced crystal. The concentration dependence of the linear viscoelastic properties of the glass and crystal was compared. It shows a lower G’ and G’’ for the shear induced crystal. Additionally the comparison of the yield strains and Lissajous plots provided information on the shearing mechanisms of the crystal and the glass. The rheological aging was also probed, surprisingly revealing an increase of viscoelasticity not only for the glass, but also for the shear induced crystal. Light Scattering Echo experiments and Brownian Dynamics Simulations were also carried out in order to complement the rheology experiments by showing the microscopic rearrangements of the hard spheres under shear. Light scattering-Echo from a crystal at rest showed larger de-correlation compared to the glass, verified by the increased in cage Mean Squared Displacements (MSD) found by the BD simulations. The MSD of both the glass and the crystal under shear were extracted from the simulations giving more insight to the crystallization process. Additionally the simulations allowed the visualization of the crystal slipping layers under oscillatory strain.

Language

English

Subject

aging

colloids

crystal

glass

hard spheres

rheology

shear

simulation

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