Structure and Dynamics of Polymers

Two areas of research have been recently pursued:

• Supramolecular Nanophotonics
  Semiconductors and other inorganic crystals are the basis for electronics and other technologies, but aside from small changes available by doping with impurities, their chemical properties are fairly inflexible. Soft materials such as polymers, on the other hand, have almost unlimited possibilities since the chemical repeat groups can be modified to suit a particular application. We recently developed a method for the production of supramolecular nanophotonic structures (Phys. Rev. Lett 2002). These polymer-based 3-D wires (multiple spherical polymer particles) can be produced in a very simple and controlled way, making their generation and functionality intimately tunable. Light of the certain wavelengths can travel around a single particle for hundreds of round trips. Because there are multiple particles that are linked to each other, these optical resonances can pass between them and propagate through the chain structure. Such "optical wires" could be used for sensors and other light pipe devices or possibly for hybrid electro-optical devices or magnetic coatings. Determination of the range of electrical or optical energy that can be transported through such structures, optimization of the composition and size of the particles, requires detailed computational modeling and simulation.



• Vibrational Analysis of Polymer Nanocomposites
  Composite materials made up of individual polymer nanoparticles have been experimentally demonstrated to have persistence and long lifetimes. This suggests they might be used in practical applications like nanowires and structural supports. A key component in the use of these materials for specific structural applications is the vibrational behavior of the system as it is fundamentally linked to the stability of the structures, with low frequency modes corresponding to weak bonding between the particles. One of the variables which can be changed in polymer particle nanostructures is the particle size--the size of the building blocks employed. A fundamental difference that arises in the use of different particles is the amount of surface contact between them, with larger particles having larger surface contact areas. In order to characterize this behavior we will perform large-scale normal mode analysis to model the dependence of the vibrational frequencies of the particles on their size, so as to extract the surface contact force constants. From these data, a simple theoretical treatment will be formulated that can be easily applied to these systems as a tool for estimating structural stability prior to experimental design.