Charles Rosenblatt (Case Western Reserve University, Etats-Unis), présentera un séminaire le 22 mai 2014 à 14h00 dans la bibliothèque du laboratoire PHENIX (7e étage, bâtiment F, porte 754) intitulé :
Through the looking glass : Surface chirality and liquid crystals
Résumé
Chirality is the absence of mirror symmetry, i.e., the inability to superimpose an object onto its mirror image by rotation and translation. One’s hands left and right are chiral, as they are mirror images of each other ; this is the origin of the term “chiral handedness”. Chirality plays a central role in both large scale and small scale systems. On large scales, technologies such as the mechanical screw date back to antiquity. On microscopic and nanoscopic scales, chirality plays a central role in physics, chemistry, biology, and medicine, and is crucial for the existence of life (e.g., DNA is chiral). Although chirality most often is thought of as 3D, it also can exist at a surface as a quasi-two-dimensional phenomenon : For example, think of a multi-turn or multi-arm spiral. In this talk I will discuss how one can mechanically create chiral patterns on surfaces on nanoscopic length scales ; how we use liquid crystals to explore the “strength” of the chirality ; how the chirality is transmitted into the otherwise achiral molecules near the surface ; how the chirality at the surface is revealed in macroscopic physical phenomena ; and how an imposed macroscopic torsional strain can induce molecular chirality, i.e., « top-down » chirality, especially near an interface.
