Unusual features of long-range density fluctuations in glass-forming organic liquids: A Rayleigh and Rayleigh-Brillouin light scattering study - art.no. 061503

Citation
A. Patkowski et al., Unusual features of long-range density fluctuations in glass-forming organic liquids: A Rayleigh and Rayleigh-Brillouin light scattering study - art.no. 061503, PHYS REV E, 6306(6), 2001, pp. 1503
Citations number
67
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physics
Journal title
PHYSICAL REVIEW E
ISSN journal
1063-651X → ACNP
Volume
6306
Issue
6
Year of publication
2001
Part
1
Database
ISI
SICI code
1063-651X(200106)6306:6<1503:UFOLDF>2.0.ZU;2-U
Abstract
A new feature of glass-forming liquids, i.e., long-range density fluctuatio ns of the order of 100 nm, has been extensively characterized by means of s tatic light scattering, photon correlation spectroscopy and Rayleigh-Brillo uin spectroscopy in orthoterphenyl (OTP) and 1,1-di(4'-methoxy-5' methyl-ph enyl)-cyclohexane (BMMPC). These long-range density fluctuations result in the following unusual features observed in a light scattering experiment. w hich are not described by the existing theories: (i) strong q-dependent iso tropic excess Rayleigh intensity, (ii) additional slow component in the pol arized photon correlation function, and (iii) high Landau-Placzek ratio. Th ese unusual features are equilibrium properties of the glass-forming liquid s and depend only on temperature, provided that the sample has been equilib rated long enough. The temperature-dependent equilibration times were measu red for BMMPC and are about 11 orders of magnitude longer than the a proces s. It was found that the glass-forming liquid OTP may occur in two states: with and without long-range density fluctuations (''clusters"). We have cha racterized the two states by static and dynamic light scattering in the tem perature range from T-g to T-g + 200 K. The relaxation times of the a proce ss as well as the parameters of the Brillouin line are identical in both OT P with and without clusters. The a process (density fluctuations) in OTP wa s characterized by measuring either the polarized (VV) or depolarized (VH) correlation function, which are practically identical and a-independent. Th is feature, which is commonly observed in glass-forming liquids, is not ful ly explained by the existing theories.