TEMPERATURE DEPENDENCE OF SURFACE TENSION OF LIQUID CRYSTALS AT THE PHASE TRANSITION

1995 ◽  
Vol 09 (03n04) ◽  
pp. 237-242 ◽  
Author(s):  
R. MOLDOVAN ◽  
M. TINTARU ◽  
T. BEICA ◽  
S. FRUNZA ◽  
D. N. STOENESCU
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Surface Tension ◽  
Free Energy ◽  
Surface Layer ◽  
Order Parameter ◽  
Unit Area ◽  
Negative Slope ◽  
First Order ◽  
First Order Transition

The surface tension is calculated as the excess of the free energy per unit area, due to the presence of a surface layer, using Landau–de Gennes expansions, in the hypothesis of a first order transition in the bulk and taking into account the dependence of the surface free energy from the surface tilt angle. The surface order parameter is calculated and surface-ordered phase above the phase transition temperature has been found. A variety of calculated surface tension versus temperature curves with a jump at the phase transition, with positive or negative slope, well describing the experimental data from literature, have been attained.

Static and dynamical elastic behavior of Lu5Ir4Si10 around its first-order structural phase transition

2020 ◽  
Vol 34 (12) ◽  
pp. 2050116
Author(s):  
M. Saint-Paul ◽  
C. Opagiste ◽  
C. Guttin
Keyword(s):  
Phase Transition ◽  
Theoretical Approach ◽  
Order Parameter ◽  
Landau Theory ◽  
Structural Phase ◽  
Elastic Stiffness ◽  
Elastic Behavior ◽  
Velocity Measurements ◽  
First Order ◽  
First Order Transition

Ultrasonic velocity measurements could be performed on a good quality single crystal of [Formula: see text] around its transition around 80 K. The behavior of the stiffness components demonstrates a first-order transition. The temperature dependence of the longitudinal elastic stiffness components [Formula: see text] and [Formula: see text] can be analyzed by the classical Landau theory and assuming a stricter coupling between the strain and the order parameter. A theoretical approach and experimental results are discussed.

scholarly journals EFFECTS OF STRAIN COUPLING AND MARGINAL DIMENSIONALITY IN THE NATURE OF PHASE TRANSITION IN QUANTUM PARAELECTRICS

2013 ◽  
Vol 27 (08) ◽  
pp. 1350028 ◽  
Author(s):  
NABYENDU DAS
Keyword(s):  
Free Energy ◽  
Critical Point ◽  
Finite Temperature ◽  
Order Parameter ◽  
Quantum Critical Point ◽  
Order Transition ◽  
Zero Temperature ◽  
First Order ◽  
Quantum Paraelectrics ◽  
First Order Transition

Here a recently observed weak first order transition in doped SrTiO 3 [Taniguchi, Itoh and Yagi, Phys. Rev. Lett.99, 017602 (2007)] is argued to be a consequence of the coupling between strain and order parameter fluctuations. Starting with a semi-microscopic action, and using renormalization group equations for vertices, we write the free energy of such a system. This fluctuation renormalized free energy is then used to discuss the possibility of first order transition at zero temperature as well as at finite temperature. An asymptotic analysis predicts small but a finite discontinuity in the order parameter near a mean field quantum critical point at zero temperature. In case of finite temperature transition, near quantum critical point such a possibility is found to be extremely weak. Results are in accord with some experimental findings on quantum paraelectrics such as SrTiO 3 and KTaO 3.

SURFACE EFFECTS ON THE PHASE TRANSITIONS

1992 ◽  
Vol 06 (14) ◽  
pp. 2531-2547 ◽  
Author(s):  
G. BARBERO ◽  
T. BEICA ◽  
R. MOLDOVAN ◽  
A. STEPANESCU
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Surface Tension ◽  
Phase Transitions ◽  
Critical Temperature ◽  
Surface Energy ◽  
Order Parameter ◽  
Multilayer Model ◽  
Classical Models ◽  
New Form

The influence of the surface on the phase transitions is discussed. Classical models are reviewed and critically analyzed. Starting with a multilayer model, a new form of the surface energy is proposed. Our model predicts, contrary to previous models, a surface order parameter different from zero in a temperature range above the critical temperature characterizing the bulk phase transition. The application of the model to the evaluation of the surface tension gives results in agreement with experimental data.

ON THE SURFACE TENSION BEHAVIOUR NEAR THE CRITICAL TEMPERATURE

1991 ◽  
Vol 05 (11) ◽  
pp. 753-762 ◽  
Author(s):  
G. BARBERO ◽  
Z. GABBASOVA ◽  
E. MIRALDI
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Surface Tension ◽  
Critical Temperature ◽  
Order Phase Transition ◽  
Order Parameter ◽  
Landau Theory ◽  
Monotonic Trend

The surface tension near the critical temperature defining an order phase transition is theoretically analysed in the framework of a Landau theory. The considered medium is supposed to be characterized by a bulk order parameter different from zero below a critical temperature. It is shown that if the surface order parameter is different from the bulk one a non-monotonic trend of the surface tension versus the temperature is to be expected. This result agrees with published experimental data.

scholarly journals SUSTAINING SUPERCOOLED MIXED PHASE VIA RESONANT OSCILLATIONS OF THE ORDER PARAMETER

2004 ◽  
Vol 19 (10) ◽  
pp. 1511-1524
Author(s):  
RAJARSHI RAY ◽  
SOMA SANYAL ◽  
AJIT M. SRIVASTAVA
Keyword(s):  
Free Energy ◽  
Order Parameter ◽  
Condensed Matter ◽  
Mixed Phase ◽  
Order Transition ◽  
Stable Phase ◽  
Driving Frequency ◽  
First Order ◽  
Parameter Field ◽  
First Order Transition

We investigate the dynamics of a first order transition when the order parameter field undergoes resonant oscillations, driven by a periodically varying parameter of the free energy. This parameter could be a background oscillating field as in models of pre-heating after inflation. In the context of condensed matter systems, it could be temperature T, or pressure, external electric/magnetic field etc. We show that with suitable driving frequency and amplitude, the system remains in a type of mixed phase, without ever completing transition to the stable phase, even when the oscillating parameter of the free energy remains below the corresponding critical value (for example, with oscillating temperature, T always remains below the critical temperature Tc). This phenomenon may have important implications. In cosmology, it will imply prolonged mixed phase in a first order transition due to coupling with background oscillating fields. In condensed matter systems, it will imply that using oscillating temperature (or, more appropriately, pressure waves) one may be able to sustain liquids in a mixed phase indefinitely at low temperatures, without making transition to the frozen phase.

Molecular Ordering in Nematic MBCA and EPAPU

1990 ◽  
Vol 45 (1) ◽  
pp. 29-32
Author(s):  
S. Sreehari Sastry ◽  
V. Venkata Rao ◽  
P. Narayana Murty ◽  
G. Satyanandam ◽  
T. F. Sundar Raj
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Nematic Phase ◽  
Spin Probe ◽  
Nematic Liquid Crystals ◽  
Experimental Techniques ◽  
First Order ◽  
Molecular Ordering

AbstractBy EPR, two nematic liquid crystals (MBCA and EPAPU) were investigated using a steroidal nitroxide spin probe. In both liquid crystals the isotropic-nematic phase transition is of first order. The observed variation of the order parameter with temperature is compared with predictions from the Maier-Saupe and Humphries-James-Luckhurst models and with results obtained by several other experimental techniques.

Untersuchung des M2/M3-Phasenübergangs in V1-xFexO2 mit x = 0,024.

1976 ◽  
Vol 31 (10) ◽  
pp. 1367-1371 ◽  
Author(s):  
J. Pebler ◽  
K. Schmidt ◽  
H. Wasinski
Keyword(s):  
Phase Transition ◽  
Isomer Shift ◽  
Cell Volume ◽  
Order Phase Transition ◽  
Order Transition ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Transition ◽  
First Order Phase

The Mössbauer investigations of V1-xFexO2 with x = 0.024 indicate that Fe enters two cation positions of M2 and M3. At the phase transition the two quadrupole splittings show a discontinuous behavior whereas the isomer shift changes continuously with a crossingover at the M2, M3 transition (Tt′ = 275 K). Generally a first order phase transition is accompanied by a change of the cell volume V and a change of the isomer shift. The observed continuous behavior of the isomer shift points to a first order transition with δV ≠ 0.

scholarly journals Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

2016 ◽  
Vol 18 (6) ◽  
pp. 4394-4404 ◽  
Author(s):  
D. O. López ◽  
B. Robles-Hernández ◽  
J. Salud ◽  
M. R. de la Fuente ◽  
N. Sebastián ◽  
...  
Keyword(s):  
Field Theory ◽  
Experimental Data ◽  
Phase Transition ◽  
Liquid Crystal ◽  
Nematic Phase ◽  
Mean Field Theory ◽  
Mean Field ◽  
Landau Model ◽  
First Order ◽  
Miscibility Studies

We have developed a Landau model that predicts a first order twist-bend nematic–nematic phase transition.

CRITICAL BEHAVIOR OF THE SPECIFIC HEAT IN THE VICINITY OF THE TRANSITION TEMPERATURE FOR S-TRIAZINE

2009 ◽  
Vol 23 (09) ◽  
pp. 2253-2259 ◽  
Author(s):  
M. KURT ◽  
H. YURTSEVEN
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Transition Temperature ◽  
Critical Exponent ◽  
Specific Heat ◽  
Power Law ◽  
Order Phase Transition ◽  
Critical Behavior ◽  
First Order ◽  
Second Order Phase Transition

The critical behavior of the specific heat is studied in s-triazine ( C 3 N 3 H 3). Using the experimental data for the CP, the temperature dependence of the specific heat is analyzed according to a power-law formula and the values of the critical exponent for CP are extracted in the vicinity of the transition temperature (TC=198.07 K ). It is indicated that s-triazine undergoes a weakly first order (quasi-continuous) or second order phase transition.

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