David Adolf Ph.D.
University of Leeds Department of Physics and AstronomyCurrent Research Interests
Segmental Polymer Dynamics:
Local polymer dynamics on the length scale of a few repeat units are a composite of processes including bond length oscillations, valence angle flexing in addition to the activity of dihedral angles and are therefore highly influenced by the chemical representation of the repeat unit. Illustrations attesting to the importance of information on the segmental level within polymer viscoelasticity can be found in several well-known theories and observations of macromolecular rheology. The importance of these motions is felt to become more pronounced as a polymer is quenched through its glass transition temperature. The drastic reduction of free volume accompanying this transition freezes out longer length scale relaxations leaving those occurring on "short" length scales in the spotlight and hence an important ingredient in the mechanical properties of the glass.
Our ongoing work monitors local polymer dynamics within dilute and concentrated solutions in addition to miscible blends. Current computational efforts are focussing on NVE, NVT, and NPT molecular dynamics simulations of local polymer dynamics with current experimental efforts monitoring segmental dynamics under pressures of up to 3000 atmospheres using time-resolved optical spectroscopy
Members of group performing this work. Dr. Andrey Kirpach
Dendrimers and Hyperbranched Molecules:
Macromolecular architecture has received considerable interest as the search for polymeric materials with new properties intensifies. One such class of materials are dendrimers. A specific example of these tree-like structures are built from AB2 monomers where each B-group may be connected to an A-group of another monomer with monomers of inner generations being fully branched. One of the interesting properties of dendrimers is that log-log plots of a dendrimer's intrinsic viscosity, IV, versus molecular weight increases until, at a critical generation, a maximum is observed followed by a steady fall in IV. In contrast to dendrimers, linear polymers obey the Mark-Houwink equation indicating a steady increase of IV with increasing molecular weight. The strategy for synthesizing dendrimers includes several protection and deprotection steps making the synthesis both expensive and time consuming. A hyperbranched polymer (HP) is synthesized in a much more economical one-pot reaction and the question arises as to the extent to which these materials illustrate dendrimer-like properties.
Current computational efforts are using Molecular and Brownian dynamics techniques to simulate the conformational and rheological properties of these materials under shear and elongational flows.
Members of group performing this work. Dr. Igor Neelov and Mr. Phil Drew
By this Researcher