סמינר לפיזיקה של מערכות ביולוגיות וחומרים רכים: Frustrated assemblies: from liquid crystals to twisted molecular crystals
Efi Efrati, Weitzman Institute
Unlike Lego bricks that perfectly assemble next to one another, in molecular assemblies some misfit is almost always present. The molecular constituents thus must distort in order to form an aggregate, resulting in a frustrated assembly. The generation of geometric frustration from the intrinsic geometry of the constituents of a material is not only natural and ubiquitous but also leads to a striking variety of morphologies of ground states and exotic response properties. In this talk I will review the notion of cumulative geometric frustration and discuss two distinct examples of geometrically frustrated assemblies: liquid crystals in 2D, and twisted molecular crystals that form banded spherulites. For liquid crystal we will present how to quantify the frustration and give specific examples that exhibit super-extensive elastic energy.
Motivated by the twisted crystals observed for a wide variety of organic molecular crystals studied by the Kahr group in NYU, we study a model of frustrated assembly that in particular conveys the nano-metric pitch length of the constituents to the tens of microns pitch length observed for the twisted crystalline assemblies.