Evidence for transient kinetics of nucleation as responsible for the isothermal transformation of supercooled liquid into the glacial state of triphenyl phosphite

Abstract

The first-order transformation of the supercooled liquid into the glacial state of triphenyl phosphite was investigated by differential scanning calorimetry (DSC) using two different thermal procedures. In the first procedure the transformation was analyzed by heating run DSC experiments. The glaciation process was interpreted as an aborted crystallization because of a high nucleation rate in a temperature range where the crystal growth is low. This relative separation between the nucleation- and growth-rate curves suggests that the glacial state can be described as a supercooled liquid–nanocrystalline mixed phase, characterized by a high-density nucleation which frustrates further crystallization. In a second procedure, DSC experiments were carried out during isothermal transformations of the supercooled liquid into the glacial state. The sigmoidal shapes of DSC isotherms are interpreted as transient kinetics of nucleation rather than nucleation and growth processes.

Micro-structural investigations in the glacial state of triphenyl phosphite

“…Detailed structural investigations do not give the evidence of a structural organization different from those detected in the amorphous states (liquid and glass) and in the crystal. Moreover the analysis [19,22,29] of the influence of the parameters which control the preparation of the glacial state on the description of this state, strongly suggest that the glacial state probably results from a high nucleation rate which is responsible for the frustration of crystallization. These different studies do not converge into the existence of a first-order polyamorphic transition in TPP.…”

“…If the description of the glacial state as a liquid-nanocrystals mixed phase is adopted, the diffraction pattern of a glacial state prepared in the low-temperature range can be obtained by the combination of the weighted structure factors of supercooled liquid and the nanocrystals. For a glacial state formed at 216 K we have used an equal weight (1/2) for both structure factors [18,19]. The result is reported in Fig.…”

“…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].…”

“…The crystallite size and the volume fraction crystallized were determined drastically dependent on the temperature at which the glacial state is isothermally formed [16,18,19], independently on the thermal path followed to reach the temperature (T a ) of the isothermal transformation [23] (direct quench from room temperature down T a , or quench below T g and rapid heating up to T a ). The selection of the temperature T a allows to form the glacial states at different micro-structure scales [16,18,23]: from a nano-structured state (for glacial states isothermally formed in a low-temperature range [210 K, 216 K]) to micro-structured state (for glacial states isothermally formed in a higher temperature range [218 K, 230 K]).…”

Low-temperature properties of glassy and crystalline states of n-butanol

“…For n-butanol, under isothermal conditions in the range 125-160 K, the supercooled liquid was found [20] to gradually transform into a white solid phase, that was identified as the same "glacial state" reported for TPP. Although several experimental works have been published on TPP [13][14][15][16][17][18][19][21][22][23] and, to a lesser extent, on n-butanol [18,20,24], the very nature of this allegedly new "glacial state" remains controversial. In our previous works, we have investigated [25,26] through calorimetric, thermal conductivity, Brillouin-scattering and X-ray diffraction experiments the phase diagram of n-butanol, studying its three different states, namely glass, crystal and so-called "glacial" states.…”