Wet foams and sphere packing in cylindrical tubes - a work in progress

by Prof. Adil Mughal (ISI Foundation Torino)

Thursday 29 Oct 2009, 15:00 → 16:00 Europe/Rome

Aula Careri (Dip. di Fisica - Edificio G. Marconi)

There is considerable current interest in ordered foams due to the invention of new experimental methods capable of producing highly monodisperse, sub micron sized bubbles, which spontaneously order to form substantial microcrystals. While it is known that properties, such as the morphology and rheology, of ordered foams depend directly on the nature of the confining geometry the connection between the two remains poorly understood. Recently, in collaboration with the Foams and Complex Systems Group at Trinity College Dublin (TCD) I have begun to model the morphology of wet foams (those with a high liquid fraction) in cylindrical tubes as a sphere packing problem amenable to simulate annealing. Preliminary results have produced dozens of structures as the aspect ratio D of the tube diameter (T) to the bubble diameter (B) is varied. These structures are then catalogued using phyllotactic notation, a method originating in biology. The interest in these structures is heightened by the discovery that their chirality is highly sensitive to the value of D. This suggests that synthetic crystals based on packing spheres in cylinders, either with wet foams or nanoparticles, may have host of applications in which chirality is important. These potentially include the fabrication of optically active structures, designer chiral liquid crystal phases and chiral sieves. This work will also contribute to our understanding of the dynamics of phyllotactic lattices; a fascinating new subject characterized by novel excitations (solitons and rotons) not observed in conventional systems. The application of this work to a number of areas in biology (such as the structure of tubular viruses and mircotubule lattices) and soft matter (packing and transport of colloids and other macromolecules in channels and pores) is clear.