Rayleigh–brillouin scattering from reacting epoxy resins: Comparison with torsional braid analysis

The rheological study for isothermal curing processes of two kinds of epoxy/amine systems made by Rayleigh–Brillouin spectroscopy was compared with torsional braid analysis. The Brillouin shift increased with the increase in the density during the process. The intensity ratio of Rayleigh line to Brillouin lines (LP ratio) increased remarkably in accordance with the onset of gelation measured by extraction. The increase of scattered light suggests that some kind of density fluctuation of the order of the light wavelength takes place prior to the gelation. The longitudinal elastic modulus and the attenuation of sound in the hypersonic region changed monotonically from the start of measurement and almost leveled off after the transition to the glassy state determined by dilatometry. While the relative shear modulus in a low-frequency region (0.1 ∼ 1 Hz) was not sensitive to the onset of gelation, it was markedly affected by the approach to the glassy state.