Inelastic light, neutron, and X-ray scattering related to the heterogeneous elasticity of glasses

Abstract

The effects of plasticization of poly(methyl methacrylate) glass on the boson peaks observed by Raman and neutron scattering are compared. In plasticized glass the cohesion heterogeneities are responsible for the neutron boson peak and partially for the Raman one, which is enhanced by the composition heterogeneities. Because the composition heterogeneities have a size similar to that of the cohesion ones and form quasiperiodic clusters, as observed by small angle X-ray scattering, it is inferred that the cohesion heterogeneities in a normal glass form nearly periodic arrangements too. Such structure at the nanometric scale explains the linear dispersion of the vibrational frequency versus the transfer momentum observed by inelastic X-ray scattering.

Collective Nature of the Boson Peak and Universal Transboson Dynamics of Glasses

“…Because the exponential behavior is so pronounced in the CDOS, one could also expect to trace it in the total DOS. We indeed found it in the neutron data for all glasses studied here [22,26,27,32] as well as for other molecular glasses (salol, orthoterphenyl), polymers (polybutadiene, polyisobutylene), and proteins (myoglobin) [33,29,30,34,31]. The most evident examples are shown in Figs.…”

Kovacs effect in PMMA observed by low-frequency Raman scattering (boson peak)

“…In consequence, the decrease of cohesion contrast by physical aging can be concomitant with a decrease of density contrast or of the amplitude of density fluctuations. The density contrast is not directly related to the VDOS excess, but can change C ab (x) due to its effect on the amplitude of the elasto-optic tensor fluctuations induced by the low-frequency vibrations [22]. Therefore, it is possible that a consequence of the decrease of density contrast, that is deduced from the increase of refractive index, is the decrease of C ab (x) and, therefore a decrease of the boson peak intensity.…”

Physical aging of atactic polystyrene as seen by dielectric relaxational and low-frequency vibrational Raman spectroscopies

“…This process is also called Ôphysical agingÕ, to distinguish these effects from other aging processes such as chemical reactions or degradations. The aging phenomenon in glasses is a long-standing issue, which was extensively studied due to the technological problems it causes [1][2][3][4][5][6][7][8][9]. This process occurs during long-term storage or use of polymers and may limit their applications by changing their properties.…”