Panagiotis Maniadis

Feigenbaum cascade of discrete breathers in a model of DNA.

We demonstrate that period-doubled discrete breathers appear from the anticontinuum limit of the driven Peyrard-Bishop-Dauxois model of DNA. These novel breathers result from a stability overlap between subharmonic solutions of the driven Morse oscillator. Subharmonic breathers exist whenever a stability overlap is present within the Feigenbaum cascade to chaos and therefore an entire cascade of such breathers exists. This phenomenon is present in any driven lattice where the on-site potential admits subharmonic solutions. In DNA these breathers may have ramifications for cellular gene expression.

Phase segregation of diblock copolymers in nanopore geometries

The self-assembly of a diblock copolymer melt in a confined regular geometry with a given pore size is studied using self-consistent field theory. For a particle in a polymer domain, we obtain the interaction potential as a function of the distance from the polymer interface. For a given concentration of particles of a certain size and separation, we find that microphase segregation is sensitive to the characteristic length scales of the geometry. In particular, novel polymer morphologies arise when the size of the pores and the distance between them are comparable to the diblock polymer radius of gyration Rg. Confinement can result in morphologies not allowed in the bulk. However, if the pore size is much larger than Rg, the effects are then limited to the vicinity of the pore surface.

Ordering and reverse ordering mechanisms of triblock copolymers in the presence of solvent.

Self-consistent field theory is used to study the self-assembly of a triblock copolymer melt. Two different external factors (temperature and solvent) are shown to affect the self-assembly. Either one or two-step self-assembly can be found as a function of temperature in the case of a neat triblock melt, or as a function of increasing solvent content (for non-selective solvents) in the case of a triblock-solvent mixture. For selective solvents, it is shown that increasing the solvent content leads to more complicated self-assembly mechanisms, including a reversed transition where order is found to increase instead of decreasing as expected, and re-entrant behavior where order is found to increase at first, and then decrease to a previous state of disorder.