Brillouin Scattering Near the Glass Transition of Polymethyl Methacrylate

Abstract

Local acoustoelasticity in poly(methyl methacrylate) by Brillouin scattering J. Appl. Phys. 54, 5456 (1983); 10.1063/1.332729 Brillouin scattering near the lowtemperature glass transitions of polymethyl methacrylate Brillouin scattering of laser light has been used to measure the frequency of hypersonic sound waves in the range of 10 10 Hz in PMMA as a function of temperature through the glass-transition region. A discontinuity in the temperature coefficient of sound velocity is observed at the glass-transition temperature; this is explained as a consequence of a corresponding discontinuity in the temperature coefficient of the specific volume (thermal expansion coefficient). The ratio of the light scattered by isothermal density fluctuations to that scattered by adiabatic density fluctuations was also measured. This ratio was large and did not change appreciably near the glass-transition temperature. The value of the Landau-Placzek ratio is approximately what one would expect from previously observed ultrasonic-velocity-dispersion data as a function of temperature well above the glass-transition temperature. Both the velocity and intensity ratio data indicate that no velocity-dispersion effects are present for the hypersonic sound waves up to temperatures 35 0 above the glass-transition temperature. These results also indicate that the glass transition is not a classical secondorder phase transition.

Thermomechanical Properties and Glass Dynamics of Polymer-Tethered Colloidal Particles and Films

“…In the eigenmode spectra shown in Figure a,c, the first few strongest eigenmodes can be easily resolved by Lorentzian-shaped fitting curves; each mode is characterized by its frequency position f R and line width Γ. The variation with temperature of these two quantities, f R ( T ) and Γ­( T ), depicted in Figures b and d, is of importance to deduce the glass transition. − …”

Thermal lens scanning of the glass transition in polymers

“…Thus the features of the D as a function of temperature are essentially reflecting the corresponding changes in the sound velocity. The results of numerous experimental investigations 40 carried out at low and high frequencies have shown that the sound velocity in polymers depends linearly on temperature and that only at those points where the mode of molecular motion is changed does the temperature coefficient of the sound velocity change discontinuously. Thus the unfreezing of one or another type of molecular motion can be accessed from the kink in the temperature dependence of the sound velocity.…”

Revealing the glass transition in shape memory polymers using Brillouin spectroscopy

“…44 This allows for high temporal sampling of the Brillouin shift while sweeping the temperature of the sample in time. A sudden change in the slope of this curve is indicative of the temperature of the glass transition, 45 which can be easily calculated from temperature-dependent measurements of the Brillouin shift. Thus, while early studies have shown that such methods are technically feasible, improved instrumentation which is both robust and simple may lead to widespread adoption of Brillouin scattering as a glass transition metric.…”

“…For this reason, previous studies utilizing Brillouin light to examine polymers were limited to carefully prepared samples with extremely fine optical smoothness and near-ideal transparency. 45 In this study, we utilize a Rubidium atomic vapor notch filter with a narrow D 2 absorption line at 780.24 nm in vacuum. The source laser is then electronically locked to the D 2 transition of Rubidium so that the output wavelength and thus the elastically scattered light are strongly absorbed by the Rb vapor, with extinction exceeding À100 dB over a narrow ($500 MHz) bandwidth.…”