Waterloo Soft Matter Theory 2013
We have modelled stress concentration around small gaps in anisotropic elastic sheets, corresponding to the peptidoglycan sacculus of bacterial cells, under loading corresponding to the effects of turgor pressure in rod-shaped bacteria. We find that under normal conditions the stress concentration is insufficient to mechanically rupture bacteria, even for gaps up to a micron in length. We then explored the effects of stress-dependent smart-autolysins, as hypothesised by Arthur L Koch.
We show how to utilize soft modes in the vibrational spectrum as a universal tool for the identification of defects in solids. Perfect crystals with isolated dislocations exhibit single phonon modes that localize at the dislocation core, and their polarization pattern predicts the motion of atoms during elementary dislocation glide in two and three dimensions in great detail. A superposition of soft modes can be used to construct a population of soft spots that predict the location of local plastic rearrangements at the grain boundaries of polycrystals and in amorphous solids.
Phase field crystal models and their recent extension will be summarized. Their application to non-equilibrium kinetics and phase transformations in materials will be reviewed. In particular, we review new results from applications of this modeling paradigm to solute trapping during rapid solidification of alloys, defect-mediated solid-state precipitation, and magneto-crystalline interactions. We close with a discussion of new complex amplitude representations of PFC models and how these can be used for multi-scale simulations using adaptive mesh refinement methods.
Colloids in a liquid crystal matrix exhibit very anisotropic
interactions. Further, these interactions can be altered by both properties of
the colloid and of the liquid crystal. This gives a potential for creating
specific colloidal aggregates and crystals by manipulating the interactions
between colloids. However, modelling these interacting colloids in a liquid
crystal is very challenging. We use a hybrid particle-lattice Boltzmann scheme
that incorporates hydrodynamic forces and forces from the liquid crystal
Phase transitions are ubiquitous in nature. Understanding the kinetic pathways of phase transitions has been a challenging problem in physics and physical chemistry. From a thermodynamics point of view, the kinetics of phase transitions is dictated by the characteristics of the free energy landscape. In particular, the emergence of a stable phase from a metastable phase follows specific paths, the minimum energy paths, on the free energy landscape. I will describe the characteristics of the minimum energy paths and introduce an efficient method, the string method, to construct them.
Carlo field-theoretic simulations (MC-FTS) are performed on melts of symmetric
diblock copolymer for invariant polymerization indexes extending down to
experimentally relevant values of N=104. The simulations are
performed with a fluctuating composition field, W-(r), and a pressure
that follows the saddle-point approximation. Our study focuses on the
disordered-state structure function, S(k),