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Orientational and translational dynamics of polyether/water solutions
Adam L Sturlaugson1, Kendall S Fruchey, Stephen R Lynch
1Department of Chemistry, Stanford University, Stanford, California 94305, USA.
The Journal of Physical Chemistry. B
|April 9, 2010
Summary
Rotational diffusion of tetraethylene glycol dimethyl ether (TEGDE) follows the Debye-Stokes-Einstein equation in water mixtures. However, translational diffusion deviates from Stokes-Einstein behavior at low water concentrations.
Area of Science:
- Physical Chemistry
- Polymer Science
- Fluid Dynamics
Background:
- Understanding molecular diffusion in liquid mixtures is crucial for various chemical processes.
- Polyethers like tetraethylene glycol dimethyl ether (TEGDE) are common in industrial applications.
- The relationship between rotational and translational motion in solutions is not fully understood.
Purpose of the Study:
- To investigate the rotational and translational diffusion of TEGDE in binary mixtures with water.
- To compare experimental diffusion data with hydrodynamic theories.
- To elucidate the factors influencing molecular motion in polyether-water mixtures.
Main Methods:
- Optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy for rotational diffusion.
- Pulsed field-gradient spin-echo nuclear magnetic resonance (PFGSE-NMR) for translational diffusion.
- Hydrodynamic calculations for rigid TEGDE conformations.
Main Results:
- Rotational relaxation times of TEGDE align with the Debye-Stokes-Einstein (DSE) equation across all water concentrations.
- Translational diffusion of TEGDE deviates from Stokes-Einstein (SE) behavior, particularly at low water content.
- The deviation in translational diffusion is not attributable to changes in molecular shape.
Conclusions:
- TEGDE's rotational dynamics remain consistent with DSE predictions, indicating no significant structural changes with varying water content.
- Translational dynamics exhibit non-hydrodynamic behavior in low water fraction solutions.
- Further investigation is needed to explain the observed discrepancies between rotational and translational diffusion behaviors.
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