Mesoscopic description of the glacial state in triphenyl phosphite from an x-ray diffraction experiment

Abstract

We present an x-ray-diffraction study performed in the different states of the molecular glass-forming liquid triphenyl phosphite ͑TPP͒. Investigations carried out in the apparently amorphous state, the so-called ''glacial'' state, formed from isothermal aging at different temperatures in the range ͓210 K, 222 K͔, confirm previous findings about the structural description of the glacial state in terms of nanocrystallized domains. The very close relationship between the diffraction patterns of the glacial and crystalline states reveals that the glaciation corresponds to an aborted crystallization process. By fitting the whole diffraction pattern of the crystalline phase, all the Bragg peaks can be indexed in a monoclinic unit cell. From this indexation, a structural organization of glacial TPP is given and the domain size can be evaluated for different aging temperatures.

Size dependence of the Raman spectra in an amorphous–nanocrystalline mixed phase: the glacial state of triphenyl phosphite

“…The ability to perform rapid acquisition of a wide low-wavenumber range allows us to analyze the structural evolution in real time from the earliest stage of the isothermal transformation in contrast to x-ray or neutron diffraction experiments reported previously. 6,8,22 The first Raman investigations in a wide high-wavenumber spectral range of TPP reported in this paper are in good agreement with the description of the glacial state from the analysis of the low-wavenumber range reported here and in previous papers. 7,9 The Raman spectrum of glacial TPP in the 850-1650 cm 1 spectral range can be regarded as a mixing of the spectra of the crystal and the supercooled liquid.…”

“…From the width of a line which was observed as the diffraction signature of a submicroscopic crystallite organization in the glacial state, 8 the crystallite size was estimated to remain nearly constant to 30Å when the glacial state was prepared between 210 and 220 K. The crystallite size was observed to increase from 30 to 290Å between 220 and 226 K, hence it is very difficult to estimate a value of L in the 220-226 K temperature range. Normalized integrated intensities I a and I c were determined in glacial states prepared at T a D 214, 218, and 220 K, where y ³ 1, by a fitting procedure using damped oscillators.…”

Micro-structural investigations in the glacial state of triphenyl phosphite

“…The discovery of an apparently amorphous state (glacial state) by Ha et al [4,5] at ambient pressure and in a very accessible temperature range (above 200 K) has given the opportunity to analyze a supposed example of polyamorphic transformation by usual laboratory equipments. However different descriptions of the glacial state emerge from extensive investigations: a defect-ordered phase [4][5][6][7][8] inherent to the development of a locally preferred structure which is not space-tiling [8][9][10], plastic or liquid crystal [11], strong liquid [12], highly correlated liquid [13], a second glassy state corresponding to a second liquid [14], and liquid/crystallites mixed system [15][16][17][18][19][20][21][22][23].…”

Microscopic identification of the order parameter governing liquid–liquid transition in a molecular liquid

“…All of the controversies come from the fact that this transition accompanies microcrystal formation and thus the final state, which is called "glacial phase," often contains microcrystallites. This led many researchers to explain the transition by non-LLT scenarios, which include a defect-ordered phase scenario predicted by a frustration limited domain theory (29,30,33,34), a microcrystallization scenario (35)(36)(37)(38), and a liquid-crystal or plastic-crystal phase scenario (39). Each scenario captures a certain feature of the glacial phase, but fails in explaining all of the experimental results in a consistent manner.…”

“…There have been structural studies on LLT by X-ray and neutron scattering measurements, focusing on local liquid structures at an inter-and intramolecular scale (36,38,(52)(53)(54) and mesoscopic structures (34,55). However, there has been no experimental evidence for the presence of locally favored structures, which characterize the liquid state uniquely, or the order parameter has still not been identified from a microscopic viewpoint.…”