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DTSTART;VALUE=DATE:20191004T101500
DTEND;VALUE=DATE:20191004T111500
UID:6596@agenda.unifr.ch
DESCRIPTION:Colloidal dispersions of rod-like particles are widely accepted as convenient model systems\nto study the phase behavior of liquid-crystal forming systems, commonly found in LCDs. This\nis due to the fact that colloidal rods exhibit analogous phase behavior to that of elongated\nmolecules, while they can be directly observed by optical microscopy. More recently, there\nhas also been a burst of interest in the liquid crystalline behaviour of so-called bent-core, or\nbanana-shaped, molecules, which have been predicted to form exotic biaxial nematic\nphases such as the twist-bend and splay-bent nematic phase. These may be of particular\ninterest due to their fast switching response in LCDs. While there have been claims of the\nobservation of these biaxial nematic phases in molecular bent-core systems, no colloidal\nbananas have been reported in which these the structure and dynamics of these phases\ncould be imaged at the particle level.\nHere, we have developed an entirely new family of colloidal SU-8 polymer particles, with\nshapes ranging from rods, sphero-cylinders, spheres and bananas with tuneable length,\ndiameter and curvature that are stable in both aqueous and apolar solvent mixtures. Our\ncolloidal SU-8 polymer particles are produced in bulk and by varying the composition of the\nsolvent mixture, both the difference in refractive index and mass density between the\nparticles and the solvent can be independently controlled. This, for example, enables the use\nof colloidal SU-8 rods in both 3D confocal microscopy and optical trapping experiments, and\neven in experiments combining both techniques, while the effect of gravity can be carefully\ntuned. Particularly exciting is that we can tune the curvature of the bananas, which is a key\nparameter in their phase behaviour. This is demonstrated by our observations of the exotic\nstructures formed by differently curved bananas, including isotropic, anti-ferromagnetic\nsmectic and even the elusive splay-bend nematic ordering and a completely new `colloidal\nvortex liquid'.
SUMMARY:Shaping colloidal SU-8 polymer particles: from rods to spheres to bananas - Prof. Dr. Roel Dullens - University of Oxford
CATEGORIES:Séminaire
LOCATION:PER 08\, 2.73, bâtiment de Physique\, Chemin du Musée 3\, 1700 Fribourg
URL;VALUE=URI:https://agenda.unifr.ch/e/fr/6596
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