Synergistic Density Functional Theory and Molecular Dynamics Approach to Elucidate PNIPAM-Water Interaction...

Area of Science:

• Computational chemistry and materials science
• Polymer science and soft matter physics

Background:

• Poly(N-isopropylacrylamide) (PNIPAM) exhibits unique temperature-dependent hydration properties.
• Understanding PNIPAM's interaction with water is crucial for its applications.

Purpose of the Study:

• To investigate the molecular-level interactions between water and PNIPAM across various chain lengths.
• To elucidate the temperature-responsive hydration mechanisms of PNIPAM.

Main Methods:

• Density Functional Theory (DFT) for electronic structure and binding energies.
• Molecular Dynamics (MD) simulations for hydration dynamics and structural changes.
• Quantum Theory of Atoms in Molecules (QTAIM) and electron localization function (ELF) for detailed interaction analysis.

Main Results:

• DFT identified preferential water binding sites and quantified binding energies.
• MD simulations revealed temperature-dependent structural transitions and hydration dynamics.
• Analysis highlighted the critical roles of hydrogen bonding and steric effects, particularly at amide hydrogen and carbonyl oxygen sites.

Conclusions:

• Combined DFT and MD simulations provide a comprehensive molecular picture of PNIPAM hydration.
• Water-PNIPAM interactions weaken above the lower critical solution temperature (LCST), increasing hydrophobicity.
• Findings offer insights into water sorption mechanisms for applications like dehumidification and water harvesting.