44 research outputs found
Ultrasonic study and molecular simulation of propylene glycol at pressure up to 1.4 GPa
We report an ulsrasonic measurements of density and bulk modulus of propylene
glycol at room temperature and at the temperature of liquid nitrogen combined
with molecular dynamics simulations with two different force fields. We find
that experimental density of propylene glycol at room temperature is well
described within COMPASS force fields simulations, while the bulk modulus from
simulation deviates from the experimental one. Number of hydrogen bonds in
propylene glycol is also evaluated.Comment: 6 page
Absence of molecular mobility on nano-second time scales in amorphous ice phases
High-resolution neutron backscattering techniques are exploited to study the
elastic and quasi-elastic response of the high-density amorphous (HDA), the
low-density amorphous (LDA) and the crystalline ice Ic upon temperature
changes. Within the temperature ranges of their structural stability (HDA at T
> 80 K, LDA at T > 135 K, ice Ic at T < 200 K) the Debye-Waller factors and
mean-square displacements characterise all states as harmonic solids. During
the transformations HDA->LDA (T ~ 100 K), LDA->Ic (T ~ 150K) and the supposed
glass transition with Tg ~ 135 K no relaxation processes can be detected on a
time scale t < 4 ns. It can be concluded from coherent scattering measurements
(D_2O) that LDA starts to recrystallise into ice Ic at T ~ 135 K, i.e. at the
supposed Tg. In the framework of the Debye model of harmonic solids HDA reveals
the highest Debye temperature among the studied ice phases, which is in full
agreement with the lowest Debye level in the generalised density of states
derived from time-of-flight neutron scattering experiments. The elastic results
at low T indicate the presence of an excess of modes in HDA, which do not obey
the Bose statistics
Structural and Dielectric Relaxations in Vitreous and Liquid State of Monohydroxy Alcohol at High Pressure
2-Ethyl-1-hexanol
monoalcohol is a well-known molecular glassformer,
which for a long time attracts attention of researchers. As in all
other monohydroxy alcohols, its dielectric relaxation reveals two
distinct relaxation processes attributed to the structural relaxation
and another more intense process, which gives rise to a low-frequency
Debye-like relaxation. In this monoalcohol, the frequency separation
between these two processes reaches an extremely high value of 3 orders
of magnitude, which makes this substance a rather convenient object
for studies of mechanisms (supposedly common to all monoalcohols)
leading to vitrification of this type of liquids. In this work, we
apply two experimental techniques, dielectric spectroscopy and ultrasonic
measurements (in both longitudinal and transverse polarizations) at
high pressure, to study interference between different relaxation
mechanisms occurring in this liquid, which could shed light on both
structural and dielectric relaxation processes observed in a supercooled
liquid and a glass state. Application of high pressure in this case
leads to the simplification of the frequency spectrum of dielectric
relaxation, where only one asymmetric feature is observed. Nonetheless,
the maximum attenuation of the longitudinal wave in ultrasonic experiments
at high pressure is observed at temperatures ≈50 K above the
corresponding temperature for the transverse wave. This might indicate
different mechanisms of structural relaxation in shear and bulk elasticities
in this liquid
Phase transition in the high-order nonideal mixing model
We extend the existing second-order nonideal mixing model, which only formally allows for the second-order phase transition, into the fourth-order. The Landau theory reveals that both first-and second-order phase transitions may exist in this higher-order model. Moreover, we show that a single structural parameter determines whether the phase transition abruptly switches between first-and second-orders. We note, it provides an explanation of either appearance or absence of the liquid-liquid critical point in the liquid-liquid phase transition on debate. ?? 2020 The Author(s)