scholarly journals Model of the dynamics of an interface between a smectic phase and an isotropic phase of different density

2020 ◽  
Vol 5 (7) ◽  
Author(s):  
Eduardo Vitral ◽  
Perry H. Leo ◽  
Jorge Viñals
Keyword(s):  
Smectic Phase ◽  
Isotropic Phase

scholarly journals Statistical Physics Approach to Liquid Crystals: Dynamics of Mobile Potts Model Leading to Smectic Phase, Phase Transition by Wang–Landau Method

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1232
Author(s):  
V. Thanh Ngo ◽  
Phuong-Thuy Nguyen ◽  
Hung T. Diep
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Potts Model ◽  
High Performance ◽  
Statistical Physics ◽  
Film Surface ◽  
Smectic Phase ◽  
Isotropic Phase ◽  
Smectic Liquid Crystals ◽  
Layer By Layer

We study the nature of the smectic–isotropic phase transition using a mobile 6-state Potts model. Each Potts state represents a molecular orientation. We show that with the choice of an appropriate microscopic Hamiltonian describing the interaction between individual molecules modeled by a mobile 6-state Potts spins, we observe the smectic phase dynamically formed when we cool the molecules from the isotropic phase to low temperatures (T). In order to elucidate the order of the transition and the low-T properties, we use the high-performance Wang–Landau flat energy-histogram technique. We show that the smectic phase goes to the liquid (isotropic) phase by melting/evaporating layer by layer starting from the film surface with increasing T. At a higher T, the whole remaining layers become orientationally disordered. The melting of each layer is characterized by a peak of the specific heat. Such a succession of partial transitions cannot be seen by the Metropolis algorithm. The successive layer meltings/evaporations at low T are found to have a first-order character by examining the energy histogram. These results are in agreement with experiments performed on some smectic liquid crystals.

Dielectric Studies of trans,trans-4'-n-Pentyl-bicyclohexyl-4- carbonitrile (5CCH) under High Pressure

1996 ◽  
Vol 51 (4) ◽  
pp. 306-312 ◽  
Author(s):  
T. Brückert ◽  
A. Würflinger
Keyword(s):  
Phenyl Ring ◽  
Activation Parameters ◽  
Smectic Phase ◽  
Constant Factor ◽  
Isotropic Phase ◽  
Dielectric Relaxation Time ◽  
Dielectric Studies ◽  
Frequency Range ◽  
Static Permittivity ◽  
Temperature Dependences

Abstract Dielectric studies on the static and complex permittivity have been performed on trans,trans-4'-n-pentyl-bicyclohexyl-4-carbonitrile (5 CCH) in the pressure range 0.1-200 MPa, the frequency range 1 kHz-13MHz and the temperature range 300-390 K. Phase transitions between the isotropic, nematic, smectic B (metastable), and crystalline state have been recorded as steps in the static permittivity. Thus the phase diagram of 5 CCH was established. In particular the slow relaxation process in the nematic and smectic phase has been investigated. The dielectric relaxation time τ|| increases by a constant factor of 210 on passing the nematic-smectic B phase transition. From the pressure and temperature dependences of τ we have calculated the activation volumes (Δ≠ V/cm3 mol-1 = 88-65 (nematic), = 70-45 (smectic) and ≈ 32 for the isotropic phase) and activation enthalpies (Δ≠H/kJ mol-1 = 76-60 (nematic), ≈ 60 (smectic) and ≈ 37 for the isotropic phase), respectively, which are compared with previous results on similar homologous series. The activation parameters increase significantly, when the rigid phenyl ring is replaced by the more flexible cyclohexyl ring.

scholarly journals Nematic and Smectic Phases: Dynamics and Phase Transition

Symmetry ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1574
Author(s):  
Aurélien Bailly-Reyre ◽  
Hung T. Diep
Keyword(s):  
Phase Transition ◽  
Low Temperatures ◽  
Molecular Orientation ◽  
Nematic Phase ◽  
Smectic Phase ◽  
Spin Model ◽  
Isotropic Phase ◽  
Time Dynamics ◽  
First Order ◽  
Smectic Phases

We study in this paper the dynamics of molecules leading to the formation of nematic and smectic phases using a mobile 6-state Potts spin model with Monte Carlo simulation. Each Potts state represents a molecular orientation. We show that, with the choice of an appropriate microscopic Hamiltonian describing the interaction between individual molecules modeled by 6-state Potts spins, we obtain the structure of the smectic phase by cooling the molecules from the isotropic phase to low temperatures: molecules are ordered in independent equidistant layers. The isotropic-smectic phase transition is found to have a first-order character. The nematic phase is also obtained with the choice of another microscopic Hamiltonian. The isotropic-nematic phase transition is a second-order one. The real-time dynamics of the molecules leading to the liquid-crystal ordering in each case is shown by a video.

Freeze-fracture TEM of the helical smectic A* phase

1992 ◽  
Vol 50 (1) ◽  
pp. 278-279
Author(s):  
K.J. Ihn ◽  
R. Pindak ◽  
J. A. N. Zasadzinski
Keyword(s):  
Liquid Crystal ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Freeze Fracture ◽  
Smectic Phase ◽  
Layer Spacing ◽  
Screw Dislocations ◽  
Smectic A ◽  
Smectic Phases ◽  
Discrete Amount

A new liquid crystal (called the smectic-A* phase) that combines cholesteric twist and smectic layering was a surprise as smectic phases preclude twist distortions. However, the twist grain boundary (TGB) model of Renn and Lubensky predicted a defect-mediated smectic phase that incorporates cholesteric twist by a lattice of screw dislocations. The TGB model for the liquid crystal analog of the Abrikosov phase of superconductors consists of regularly spaced grain boundaries of screw dislocations, parallel to each other within the grain boundary, but rotated by a fixed angle with respect to adjacent grain boundaries. The dislocations divide the layers into blocks which rotate by a discrete amount, Δθ, given by the ratio of the layer spacing, d, to the distance between grain boundaries, lb; Δθ ≈ d/lb (Fig. 1).

scholarly journals Ion conformation and orientational order in a dicationic ionic liquid crystal studied by solid-state nuclear magnetic resonance spectroscopy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Debashis Majhi ◽  
Sergey V. Dvinskikh
Keyword(s):  
Ionic Liquid ◽  
Ionic Liquids ◽  
Liquid Crystals ◽  
Bond Order ◽  
Van Der Waals ◽  
Orientational Order ◽  
Smectic Phase ◽  
Side Chains ◽  
Dicationic Ionic Liquid ◽  
Ionic Liquid Crystals

AbstractIonic liquids crystals belong to a special class of ionic liquids that exhibit thermotropic liquid-crystalline behavior. Recently, dicationic ionic liquid crystals have been reported with a cation containing two single-charged ions covalently linked by a spacer. In ionic liquid crystals, electrostatic and hydrogen bonding interactions in ionic sublayer and van der Waals interaction in hydrophobic domains are the main forces contributing to the mesophase stabilization and determining the molecular orientational order and conformation. How these properties in dicationic materials are compared to those in conventional monocationic analogs? We address this question using a combination of advanced NMR methods and DFT analysis. Dicationic salt 3,3′-(1,6-hexanediyl)bis(1-dodecylimidazolium)dibromide was studied. Local bond order parameters of flexible alkyl side chains, linker chain, and alignment of rigid polar groups were analyzed. The dynamic spacer effectively “decouples” the motion of two ionic moieties. Hence, local order and alignment in dicationic mesophase were similar to those in analogous single-chain monocationic salts. Bond order parameters in the side chains in the dicationic smectic phase were found consistently lower compared to double-chain monocationic analogs, suggesting decreasing contribution of van der Waals forces. Overall dication reorientation in the smectic phase was characterized by low values of orientational order parameter S. With increased interaction energy in the polar domain the layered structure is stabilized despite less ordered dications. The results emphasized the trends in the orientational order in ionic liquid crystals and contributed to a better understanding of interparticle interactions driving smectic assembly in this and analogous ionic mesogens.

scholarly journals The interplay between spatial and heliconical orientational order in twist-bend nematic materials

2021 ◽  
Vol 23 (7) ◽  
pp. 4055-4063
Author(s):  
R. Saha ◽  
C. Feng ◽  
C. Welch ◽  
G. H. Mehl ◽  
J. Feng ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Correlation Length ◽  
Orientational Order ◽  
Smectic Phase ◽  
Sulfur Containing

In sulfur containing liquid crystal dimers we find that at the transition to the NTB phase the positional correlation length drops. The nanoscale periodicity was also observed in the upper range of a smectic phase that forms below the NTB state.

HIGH RESOLUTION CALORIMETRIC STUDIES AT PHASE TRANSITIONS OF ALKYLCYANOBIPHENYL LIQUID CRYSTALS CONFINED TO SUBMICRON SIZE CYLINDRICAL CAVITIES

1995 ◽  
Vol 09 (18n19) ◽  
pp. 2247-2283 ◽  
Author(s):  
DANIELE FINOTELLO ◽  
GERMANO S. IANNACCHIONE
Keyword(s):  
Phase Transitions ◽  
Liquid Crystals ◽  
High Resolution ◽  
Specific Heat ◽  
Pore Wall ◽  
Isotropic Phase ◽  
First Order ◽  
Smectic A ◽  
Nematic Director ◽  
Scalar Order Parameter

We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphenyl liquid crystals confined to the 0.2µm diameter cylindrical pores Anopore membranes. The nematic director alignment at the pore wall is varied from homeotropic to tangential by pore surface treatment. Several phenomena are uncovered by these studies which probed the weakly first order nematic to isotropic, the continuous smectic-A to nematic and the first order smectic-A to isotropic phase transitions. The specific heat is strongly dependent on the nematic director configuration, and confinement effects are remarkably distinct according to the order of the phase transition. The influence of elastic distortions and surface ordering and disordering effects are evident. Despite considerable departures from bulk behavior with regards to specific heat peaks size, rounding and width, and transition temperature shifts, a bulk-like critical behavior appears to be retained. The formation of smectic translational order within the pores is hindered for those liquid crystals that also possess a nematic phase. The average scalar order parameter temperature dependence is extracted from the specific heat results using a simplified Landau-de Gennes type of model, and is shown to be consistent with nuclear magnetic resonance results.

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