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Published on: August 13, 2019
Ultrafast dynamics in aqueous polyacrylamide solutions
1Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 610 Taylor Road, Piscataway, NJ 08854-8087, USA. cshirota@mail.ecc.u-tokyo.ac.jp
Journal of the American Chemical Society
|December 26, 2001
Summary
Ultrafast dynamics in polyacrylamide (PAAm) and propionamide (PrAm) solutions reveal that polymer reorientation is driven by the constitutional repeat unit, not just side groups. This finding holds true across various concentrations and molecular weights.
Area of Science:
- Physical Chemistry
- Polymer Science
- Spectroscopy
Background:
- Understanding polymer dynamics in solution is crucial for material properties.
- Polyacrylamide (PAAm) is a widely used polymer, but its solution dynamics are not fully understood.
- Femtosecond spectroscopy offers a window into ultrafast molecular motions.
Purpose of the Study:
- To investigate the ultrafast dynamics of aqueous polyacrylamide (PAAm) solutions.
- To determine the molecular motions responsible for PAAm reorientation in water.
- To compare PAAm dynamics with a model compound, propionamide (PrAm).
Main Methods:
- Femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES).
- Studied aqueous solutions of PAAm with different molecular weights (1500 and 10,000) and concentrations (0-40 wt%).
- Utilized propionamide (PrAm) as a model for the PAAm constitutional repeat unit (CRU).
- Performed molecular dynamics simulations of a short PAAm chain.
Main Results:
- PAAm and PrAm solution dynamics showed similar time scales (4-10 ps) and concentration dependence.
- Reorientation time constants scaled linearly with concentration, contrasting with exponential viscosity changes.
- The ratio of PAAm to PrAm reorientation times matched the ratio of their molecular volumes.
- Femtosecond dynamics exhibited oscillations attributed to amide-amide and amide-water hydrogen bonding.
Conclusions:
- The primary reorientation dynamics in aqueous PAAm solutions are attributed to the motion of the entire constitutional repeat unit.
- Side group motions alone do not explain the observed polymer dynamics.
- Hydrogen bonding plays a significant role in the ultrafast dynamics of these solutions.
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