Raman spectroscopy coupled to computational approaches towards understanding self-assembly in thermoreversible poloxamer gels

Abstract

The exploitation of vibrational spectroscopy approaches towards the understanding of molecular-level events in polymers, such as poloxamers, is highly warranted. This would facilitate the development of real-time approaches to monitor processes as well as the rational realisation of superior architectures. To date, studies on poloxamer based materials are restricted to low con centration materials and the evaluation of vibrational frequencies involving C-H stretching motions. We carry out an in-depth analysis of thermally-induced micellization processes employing technologically relevant 20% w/w P407 aqueous formulations. Our results, coupling Raman spectroscopy to computational approaches, are unequivocally consistent with such temperature-controlled events not being restricted to molecular re-arrangements involving C-H stretching motions. In fact, the synergistic approach of all key spectral regions was observed to yield optimum delineation of formulations at different temperatures. Vibrational envelopes were deconvoluted and it was observed that vibrational analysis of convoluted spectra can often be misleading. Individual contributions were assigned to either PEO or PPO building blocks by means of quantum-mechanical calculations. Temperature-induced changes to both intensity and vibrational frequencies were statistically evaluated and identified variations rationalised based on intermolecular interactions and structural order/disorder of the polymer units. Such observations were identified to be critically different depending on the nature of the vibrations.