The University of Liverpool's Department of Chemistry has pioneered a method to better understand how polymer chains react in changing solvent flows, providing valuable insights for science and industries such as oil recovery and photovoltaics. New research is an important breakthrough in polymer science.
In a paper recently published on the cover of the journal Nature Chemistry, researchers in Liverpool used mechanochemistry to describe how polymer chains in solution respond to sudden accelerations in the flow of surrounding solvent. The new method finally provides an answer to a fundamental technical question that has puzzled polymer scientists for the past 50 years.
The fragmentation of macromolecular solutes in fast flows has very important fundamental and practical significance. The sequence of molecular events preceding chain breakage is poorly understood because such events cannot be directly observed but must be inferred from changes in the bulk composition of the flowing solution. Here, we describe how the molecular geometry of chains undergoing mechanochemical reactions in sonicated solutions can be described in detail by analyzing the co-chain competition between the scission of polystyrene chains and the isomerization of the chromophores embedded in their backbones. In the latest experiments, overstretched (mechanically loaded) segments grow and drift along the backbone on the same time scale as, and in competition with, mechanochemical reactions. Therefore, less than 30% of the backbone of the fragmented chain is overstretched, and the maximum force and maximum reaction probability are located far away from the center of the chain. Therefore, quantifying intrachain competition may be of mechanistic significance for any flow that is fast enough to cause polymer chain scission.
Historical challenges and impacts
Since the 1980s, researchers have tried to understand the unique response of dissolved polymer chains to suddenly accelerated solvent flows. However, they have been limited to highly simplified solvent flows and have limited insights into real-world system behavior.
The new discovery by Liverpool chemists Professor Roman Boulatov and Dr Robert O'Neill has important scientific implications for multiple areas of the physical sciences, as well as practical implications for polymer-based rheology control used in many multi-million dollar industrial processes such as enhanced oil and gas recovery, long-distance pipelines and photovoltaic manufacturing.
Professor Roman Boulatov said: "Our discovery solves a fundamental technical problem in polymer science and has the potential to overturn our current understanding of chain behavior in cavitating solvent streams."
Dr Robert O'Neill, co-author of the paper, added: "Our methodological demonstration reveals that our understanding of how polymer chains respond to sudden accelerations of solvent flow in cavitated solutions is too simplistic to support the systematic design of new polymer structures and compositions to achieve efficient, cost-effective rheological control in this context, nor to obtain Fundamental molecular insights into flow-induced mechanochemistry. Our paper has important implications for our ability to study nonequilibrium polymer chain dynamics at the molecular length scale, allowing us to answer fundamental questions about how energy flows between and within molecules, and how energy is converted from kinetic energy to potential energy and back to free energy."
The team plans to focus on expanding the scope and capabilities of their new method and using it to map molecular-scale physics to accurately predict flow behavior for any combination of polymer, solvent and flow conditions.