Raman spectroscopy is useful for probing conformational disorder and detecting rotator phases in n-alkanes and polyethylene. Raman spectra do not give direct information about molecular conformations or phase structure, which are inferred from spectral signatures of previously identified phases. Here, we use molecular dynamics simulations to model polymer systems and predict their Raman spectra, so spectral and structural information can be obtained at once. Central to our method is the bond polarizability model, which represents molecular polarizability as a sum of individual bond contributions. We use two approaches for generating the Raman spectrum. First is normal-mode analysis, useful for identifying Raman modes in ordered phases. More generally, we compute the time-dependent polarizability and Raman spectra directly from simulation trajectories. Our results capture the main features of experimental spectra for crystalline, rotator, and melt phases of polyethylene.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry