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Rearrangement of a droplets cluster under compression : from crystal to glass
A crystal and a glass are different at a molecular level which leads to strong consequences at the macroscopic scale, [1] [2]. We have developed an ideal experimental system to model such struc- tures. The 2D clusters are made of an emulsion of lightly attractive, stabilized oil droplets (of radius R ∼ 10μm) in water which are assembled droplet by droplet (tens of droplets). We study the re- sponse of the cluster when it is compressed between two thin glass rods. One glass rod is used as a force transducer in order to measure the forces as the droplets spatially rearrange under compression. Coupling the optical microscopy images of structural rearrangements within the 2D cluster with the direct force measurements provides insight into the failure mechanisms. Perfectly ordered crystals (highly monodisperse droplets) show well defined transitions. As the number of defects (substitution of a droplet by a smaller one) is increased in the crystal, we can study the transition toward a glassy system (bidisperse cluster). We study the number of force peaks which represents the number of non simultaneous events in the system.
[1] Carl P Goodrich, Andrea J Liu, and Sidney R Nagel. Solids between the mechanical extremes of order and disorder. Nature Physics, 10(8):578–581, 2014.
[2] Peter Yunker, Zexin Zhang, and A. G. Yodh. Observation of the disorder-induced crystal-to-glass transition. Phys. Rev. Lett., 104:015701, Jan 2010.