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Time-resolved optical Kerr-effect investigation on CS2/polystyrene mixtures.
Ismael A Heisler1, Ricardo R B Correia, Tiago Buckup
1Instituto de Física, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves 9500, Caixa Postal 15051, CEP 91501-970, Porto Alegre, Rio Grande do Sul, Brazil. heisler@if.ufrgs.br
The Journal of Chemical Physics
|August 20, 2005
Summary
The study reveals how carbon disulfide molecules relax in polystyrene mixtures. Increased viscosity slows molecular reorientation, while interactions with polystyrene shift vibrational frequencies.
Area of Science:
- Physical Chemistry
- Polymer Science
- Spectroscopy
Background:
- Understanding molecular dynamics in polymer mixtures is crucial for material science.
- Carbon disulfide (CS2) is a simple molecule with interesting relaxation properties.
- Polystyrene (PS) is a widely used synthetic polymer.
Purpose of the Study:
- To investigate the relaxation dynamics of carbon disulfide (CS2) in mixtures with polystyrene (PS).
- To analyze the influence of PS concentration on CS2 dynamics using time-resolved optical heterodyne-detected optical Kerr effect (OHD-OKE).
- To correlate observed dynamics with mixture viscosity and intermolecular interactions.
Main Methods:
- Time-resolved optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy.
- Model-dependent analysis assuming four temporal responses.
- Model-independent Fourier transform analysis for spectral response.
- Comparison with depolarized Rayleigh scattering data.
Main Results:
- A slow relaxation component was observed, with time constants increasing from 1.68 ps (neat CS2) to 3.76 ps (high CS2/PS concentration).
- This slow component correlates with increasing mixture viscosity, attributed to diffusive reorientation of CS2.
- The short-time nuclear response showed a broad band peaking around 30 cm(-1) for neat CS2, shifting to higher frequencies with increased PS concentration.
Conclusions:
- The reorientation dynamics of CS2 are significantly influenced by the viscosity of the PS matrix.
- Increased PS concentration strengthens interactions between PS phenyl rings and CS2 molecules, leading to shifts in vibrational frequencies.
- OHD-OKE provides valuable insights into the complex relaxation processes in CS2/PS mixtures.