Topic: Molecular scale solvation of responsive macromolecular solutions
Swaminath Bharadwaj G. Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Darmstadt, Germany
Venue: Committee Room,
Date:- 27th April 2022 Time: 4:00 -5:00 PM
Abstract:-
Responsive polymers can undergo structural transitions, modulate the wettability and adsorption of dif-ferent species in the presence of external stimuli. These materials are employed in a wide range of applications such as smart materials with tunable properties such as surface friction and porosity, drug delivery, responsive coatings and sensors. Therefore, it is crucial to understand the molecular mechanisms governing the phase behavior in these systems and develop methods for their thermodynamic characterization. In this talk, I will provide an overview of our research on the effects of chemical stimuli such as cosolvents, osmolytes and ions on the conformational equilibria of thermoresponsive polymers in aqueous solutions from the viewpoint of both mechanisms1–3 and methods.4,5 Toward this, a combination of molecular simulations, free energy calculations and solvation theories have been employed.
In particular, I will discuss our recent computational work, involving atomistic molecular dynamics simula-tions and Kirkwood-Buff theory, which aims to understand the experimentally observed nonadditive ion effects on the coil-globule equilibrium of the well known thermoresponsive polymer Poly(N-isopropylacrylamide) (PNI-PAM) in aqueous solutions.3,6 Here, our interest lies in polymer solutions containing a combination of a weakly hydrated and a strongly hydrated anion. From our results, we observe that the nonadditive ion effects on the coil-globule equilibrium of PNIPAM arise from the interplay between the depletion of the strongly hydrated anion and the preferential accumulation of the weakly hydrated anion on the polymer.3
Intriguingly, these two contri-butions are coupled through the role of cations which mutually enhances both effects. This mutual enhancement correlates with the partitioning of the cations from the counterion cloud of the weakly hydrated anion to that of the strongly hydrated anion indicating a delicate balance between ion-ion, ion-water and macromolecule-ion interactions.
Additionally, through a semi-quantitative analysis, we show that the change in transition temper-atures (as a function of ion concentration) predicted from the simulations are in quantitative agreement with experimental measurements.
References
1 A. Folberth, S. Bharadwaj and N. F. A. van der Vegt, Phys. Chem. Chem. Phys., 2022, 24, 2080–2087.
2 S. Bharadwaj, B.-J. Niebuur, K. Nothdurft, W. Richtering, N. F. A. van der Vegt and C. M. Papadakis, Soft
Matter, 2022. DOI:10.1039/D2SM00146B.
3 Y. Zhao, S. Bharadwaj and N. van der Vegt, Phys. Chem. Chem. Phys., 2022. DOI:10.1039/D2SM00146B.
4 S. Bharadwaj, S. J. B. and N. F. A. van der Vegt, J. Phys. Chem. B, 2021, 125, 11026–11035.
5 M. Tripathy, S. Bharadwaj and N. van der Vegt, J. Chem. Phys., 2022. DOI: 10.1063/5.0090646.
6 E. E. Bruce, P. T. Bui, B. A. Rogers, P. S. Cremer and N. F. A. van der Vegt, J. Am. Chem. Soc., 2019, 141,
6609–6616.