The possibility that the excess ’’configurational’’ specific heat ΔCp of liquids above the glass transition temperature Tg might contain contributions either from changes in vibrational frequencies with configurational state, from changes in the anharmonicity of vibrations, or from the influence of changes in configurational state on the thermodynamic contributions of molecular rearrangement processes that also give rise to secondary relaxations below Tg is investigated with the use of calorimetric data on six quenched and annealed glasses. It is concluded that at least half of ΔCp arises from these sources, the greater part of this either from anharmonicity or from the molecular rearrangement processes.

Viscous liquids and the glass transition. V. Sources of the excess specific heat of the liquid

A comprehensive study of the Rayleigh–Brillouin scattering spectra of o‐terphenyl in the liquid and supercooled liquid state has been carried out. Anomalies in the Brillouin frequency and linewidth data are observed at the glass transition temperature (Tg) and at a temperature (TK) about 36 K higher than the melting point. The anomaly at Tg is due to the absence of free volume associated with the freezing‐in of the density fluctuation. The longitudinal hypersonic frequency kink as well as the linewidth maximum and the dimunition of the transverse sound frequency at TK are interpreted as due to the relaxation of translational order which disappears above TK. The result of the depolarized Rayleigh scattering spectral study shows that cluster formation as previously proposed is unlikely. Hydrodynamic slip boundary conditions for molecular reorientation are found to be appropriate in liquid o‐terphenyl. Rotation about the short and long axes lying in the plane of the parent phenyl ring is found to be consiste...

Rayleigh–Brillouin scattering studies of liquid and supercooled liquid o‐terphenyl

Light Scattering of Glass

A comprehensive Brillouin scattering experimental study of polypropylene glycol (PPG), average molecular weight of 1025, 2025, and 4000, has been carried out. The hypersonic velocity, attenuation coefficient, the modulus of elasticity, and the Landau–Placzek ratio have been obtained as a function of temperature for each polymer. The PPG 425 data reported earlier are also included for comparison. For all the quantities measured, only the Laudau–Placzek ratio (below ambient temperature) is molecular weight dependent; the hypersonic velocity, attenuation coefficient, and elastic modulus are found to be independent of molecular weight in the present 425–4000 weight range. The differences in the Landau–Placzek ratio between the different polymers are attributed to different degree of frozen‐in density fluctuations due to the difference in the medium’s viscosity; the mechanism of structural relaxation is not sufficient to explain the increase of the Landau–Placzek ratio of each polymer below ambient temperature...

Brillouin-Rayleigh scattering studies of polypropylene glycol. III

Brillouin spectra of acoustic phonons in the orientationally disordered phase in KCN and NaCN have been studied. The phonon frequencies have been determined as a function of temperature. The frequency of the transverse acoustic phonon propagating along (110) and polarized along (001) corresponds well with mean field theory for the phase transition for the two cyanide crystals. The elastic constants C11, C12,, and C44 have been determined as a function of temperature in the cubic disordered phase. The Cauchy relation for cubic crystals is found to be invalid in KCN and NaCN. The two types of phase transitions in KCN and NaCN are discussed in terms of the vanishing shear modulii C44 and (C11−C12)/2, each of which induces lattice instability when it becomes small. The integrated intensities of the shear modes in KCN and NaCN were also measured as a function of temperature. The intensity enhancement upon approaching the phase transition temperature has been found to be due to the decrease of C44. The relative...

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Comment on ''Brillouin scattering studies of orientationally disordered sodium cyanide and potassium cyanide single crystals''

Light scattering studies of polybutadiene from 110 to 350°K reported herein include measurements of Brillouin shift, Brillouin linewidth, and Rayleigh depolarization ratios as functions of temperature. The hypersonic attenuation coefficient over one wavelength (α λs) is insensitive to temperature variation below Tg; above Tg, α λs increases rapidly with increasing temperature. The sound attenuation theory of Woodruff and Eihsenreich gives an adequate description of the measure α λs value below Tg; no quantitative theory describes the sound attenuation above Tg. The Krishnan effect, depolarization ratio ρn = Vh/Hn ≠ 1, was observed for polybutadiene below 250 °K. The frozen‐in density fluctuation mechanism proposed by Mueller fails to explain the effect; frozen‐in fluctuations of the dielectric anisotropy are a possible mechanism.

Y. Y. Huang

Papers

Brillouin and Rayleigh scattering in polybutadiene