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Component dynamics in polyvinylpyrrolidone concentrated aqueous solutions.

Rémi Busselez¹, Arantxa Arbe, Silvina Cerveny

¹Donostia International Physics Center, Paseo Manuel de Lardizabal 4, E-20018 San Sebastián, Spain.

The Journal of Chemical Physics

|September 4, 2012

Summary

Nuclear magnetic resonance and neutron scattering reveal nanosegregation in polyvinylpyrrolidone (PVP) aqueous solutions. Dynamic asymmetry and structural heterogeneities explain the observed anomalies in PVP water systems.

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Area of Science:

Physical Chemistry
Materials Science
Biophysics

Background:

Polyvinylpyrrolidone (PVP) is a widely used polymer with applications in pharmaceuticals and cosmetics.
Understanding the structure and dynamics of PVP aqueous solutions is crucial for optimizing its performance.
Previous studies using dielectric spectroscopy indicated complex dynamics in these systems.

Purpose of the Study:

To investigate the structure and dynamics of polyvinylpyrrolidone (PVP) aqueous solutions.
To elucidate the relationship between nanosegregation, dynamic asymmetry, and observed relaxation behaviors.
To explore the temperature-dependent dynamics of PVP and water components.

Main Methods:

Combined (2)H-nuclear magnetic resonance (NMR) and neutron scattering (NS) on isotopically labeled PVP samples.
Neutron diffraction to analyze structural organization.
Broadband dielectric spectroscopy for comparison with previous findings.
H/D labeling for isolating and analyzing individual component dynamics.

Main Results:

Neutron diffraction confirmed nanosegregation of polymer chains and water, forming water clusters.
NMR relaxation times and spectral shapes matched slower processes observed in dielectric spectroscopy.
Temperature dependence of relaxation time showed a crossover from cooperative to Arrhenius behavior.
Neutron scattering revealed anomalously stretched, non-Gaussian dynamics and strong dynamic asymmetry between PVP and water, increasing with cooling.
Atomic displacements were coupled at short times, attributed to hydrogen bonding and sample densification.

Conclusions:

The nanosegregated structure and dynamic asymmetry are key to understanding the anomalous dynamics in PVP aqueous solutions.
Hydrogen bonding and sample densification play a significant role in short-time atomic motions.
The findings provide insights into the complex interplay between polymer structure and solvent dynamics.