Structural relaxation, viscosity, and network connectivity in a hydrogen bonding liquid.

Area of Science:

• Physical Chemistry
• Molecular Dynamics
• Biophysics

Background:

• Viscosity in liquids describes flow, influenced by molecular interactions.
• Hydrogen bonds (H-bonds) create transient networks, complicating viscosity.
• Understanding these networks is key to diverse phenomena.

Purpose of the Study:

• To determine the dominant dynamical timescale governing viscosity in H-bonding liquids.
• To investigate the role of H-bond network reorganization in viscosity.
• To analyze the dynamics of n-methylacetamide (NMA) as a model system.

Main Methods:

• Experimental techniques to observe molecular behavior.
• Computational simulations to model liquid dynamics.
• Analysis of H-bond lifetimes and network reorganization timescales.

Main Results:

• Identified H-bond network reorganization as the dominant timescale for viscosity in NMA.
• Observed individual H-bond fluctuations on a 1.5 ps timescale.
• Measured collective motions and longest H-bond lifetimes around 20 ps, matching the Maxwell relaxation time.

Conclusions:

• The timescale of H-bond network reorganization is critical for liquid viscosity.
• This finding provides insight into phenomena like protein dynamics and the glass transition.
• Explains the unique properties of H-bonding liquids through transient molecular structures.