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.

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.

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.

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.

Dynamic Ginzburg-Landau Theory for the Liquid-Solid Phase Transition

1980 ◽  
Vol 35 (1) ◽  
pp. 69-74
Author(s):  
S. Hess
Keyword(s):  
Phase Transition ◽  
Entropy Production ◽  
Order Parameter ◽  
Landau Theory ◽  
Constitutive Law ◽  
Relaxation Equation ◽  
Ginzburg Landau ◽  
Specific Internal Energy ◽  
Nonlinear Relaxation ◽  
Anisotropy Tensor

Abstract The anisotropy of the probability distribution function for the unit vector joining two nearest neighbour atoms is characterized by tensorial order parameters. For cubic symmetry, the most relevant tensor is of rank 4. Starting from an ansatz for the dependence of the (specific) internal energy, volume and entropy; the entropy production is calculated which is caused by a temporial change of the 4-th rank anisotropy tensor. A constitutive law which guarantees that the entropy production is positive leads to a nonlinear relaxation equation. It shows the features typical for a dynamic Ginzburg-Landau theory. The linearized version of the relaxation equation contains an effective relaxation time and a correlation length which exhibit a temperature dependence typical for a mean field theory. For a special case where the anisotropy tensor can be characterized by a scalar order parameter, the nonlinear relaxation equation is studied in some detail. Its stationary and spatially homogeneous solutions are zero and nonzero values for the order parameter depending on whether the temperature T is larger or smaller than the transition temperature. The unordered phase corresponds to a liquid state, the ordered phase to a simple or body centered cubic crystal. The phase transition is of 1st order. There exist also metastable states.

Thermodynamical Behaviour of Quartz Around the Transitions Between α, Incommensurate and β Phases

1983 ◽  
Vol 21 ◽  
Author(s):  
G. Dolino ◽  
J.P. Bachheimer
Keyword(s):  
Phase Transition ◽  
Heat Capacity ◽  
Order Parameter ◽  
Landau Theory ◽  
Microscopic Level ◽  
Incommensurate Phase ◽  
Small Temperature ◽  
Thermal Expansion Coefficients ◽  
Α Phase ◽  
Expansion Coefficients

ABSTRACTRecently an intermediate incommensurate phase has been found around 846 K in a small temperature range of 1.3 K between the usual α and β phases of quartz. In the neighborhood of these transitions most physical properties show drastic variations which has remained a puzzle. We shall present some measurements of the heat capacity Cp and of thermal expansion coefficients αi which present very large variations in the incommensurate phase. These divergences can be related by Pippard-Garland relations in the 3 phases. Furthermore in the low temperature α phase this result can be explained by the existence of a macroscopic order parameter η related to SiO4 tetrahedra, and varying as predicted by the Landau theory of 1st order phase transition. While in the high temperature phases (β and incommensurate) η vanishes, it takes a finite value in α phase, increasing continuously upon further cooling. However at the microscopic level, the discontinuity is reduced by the existence of the incommensurate phase, which corresponds probably to modulated tilting of SiO4 tetrahedra.

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