MONDAY, February 19, 2007
Time: 7:30 PM
OCNPS 200

Title: Modeling liquid crystal materials and processes in biological systems

Alejandro D. Rey
Department of Chemical Engineering
McGill University

Liquid crystal phases are found in DNA, proteins, lipids and polysaccharides. Frozen-in, chiral liquid crystal ordering also occurs in solid biocomposites such as insect cuticle, muscle, plant cell walls and collagen, where the helicoid structure is believed to arise by self-assembly processes. Spinning of silk fibers by spiders is another biological polymer process that relies on liquid crystal self-assembly. I will discuss the progress and challenges of modeling in three such applications: (1) Biological helicoids form by directed self-assembly. Theory and computer simulation of chiral phase ordering show that the directed self-assembly process reproduces the natural structures. The computational results shed light on the role of chiral ordering on the formation of helicoidal monodomains. (2) Spinning of spider silk involves a complex sequence of phase transitions that includes nematic phase ordering in the duct section of the spinning apparatus. Simulation of phase ordering under capillary confinement replicates the observed structures found in Nephila clavipes and other orb-weavers. The computational results shed light on the role of defect textures in the fiber spinning process. (3) Biological membranes are smectic liquid crystals that display flexoelectricity, or coupling between electric fields and curvature. Models based on smectic elasticity and polarization thermodynamics are used to derive the electroelastic shape equation, whose solution gives the membrane shape under external fields. The theoretical results shed light on the various ways electric fields affect membrane shape and functioning.