Polymer Dynamics in Concentrated Media
|Ajey Dambal |
Undergraduate Institution: Washington University in St. Louis
In general, polymer processing involves handling and manipulating concentrated solutions. The complexity of the inter/intra molecular interactions introduces phenomenological richness and adds a high degree of analytical complexity, at the same time. In the past, theoretical developments and experimental data (that were usually limited to bulk measurements) were not synergistic enough to allow for the development of an overarching concentrated solution theory.
However, recent advances in microscopy techniques along with the increases in computing power and efficiency have allowed researchers to probe polymer dynamics at a smaller scale and gain previously inaccessible data. Concentrated solution theories can now be complemented and bettered by single molecule studies that are able to resolve the motion of individual polymer molecules.
In the Shaqfeh Research Group, we perform single molecule experiments on fluorescently tagged DNA in concentrated solutions to obtain actual data about their motion at the molecular level. Furthermore, we have the ability to visualize these molecules under extensional flow conditions, allowing us to observe the effect of flow on concentrated solutions.
In conjunction we have developed novel computer simulation algorithms to quantitatively examine the effects of topological constraints on polymer motion under various flow conditions (sample simulation is visualized in the figure shown). This model has been shown to be able to reproduce many of the features of entangled polymer media - such as the scaling for the longest relaxation time with entanglement number, plateau in the steady shear stress curve etc. Furthermore, we have obtained good agreement with single molecule experiments with respect to chain sizes and orientation and power spectral density of chain extension in a wide range of flow rates.
We believe that this combined experimental and computational approach will reveal a more robust and comprehensive understanding of polymer rheology in concentrated media.