scholarly journals Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 473 ◽  
Author(s):  
Malay Kumar Das ◽  
Barnali Barman ◽  
Banani Das ◽  
Věra Hamplová ◽  
Alexey Bubnov

The tilted ferroelectric SmC* phase of three structurally different series having three aromatic rings in the core structure connected by ester groups with different end alkyl chain lengths, all of which are derived from lactic acid, have been observed by broadband dielectric spectroscopy. Introduction of structural variations within the liquid crystalline compounds has led to the formation of chiral nematic N*, or the paraelectric orthogonal SmA* phase at higher temperatures. The dielectric spectra strongly depend both on the temperature as well as the specific molecular structure of the self-assembling compounds possessing the ferroelectric polar order. The results reveal a strong Goldstone mode in the ferroelectric SmC* phase with ~kHz relaxation frequency. In the SmC* phase, the real and imaginary parts of the complex permittivity increase up to certain temperature near the SmC*-N*/SmA* transition and then decrease with increasing temperature, perhaps due to the disruption of the molecular domains at the onset of the SmA*/N* phase transition. The dielectric strength attains a maximum value in the SmC* phase and then decreases near the SmA*/N* phase transition. The dielectric strength is also influenced by the lengths of the alkyl chain and the nature of the connecting unit of the constituent molecules. The relaxation time and the relaxation frequency are found to vary with the molecular structure of the studied ferroelectric compounds.

2017 ◽  
Vol 66 (3) ◽  
pp. 63-74
Author(s):  
Anna Drzewicz ◽  
Marzena Tykarska ◽  
Magdalena Żurowska

The infrared spectra were registered for series of three-ring liquid crystalline esters, differing in the structure of alkyl chain, in the substitution of benzene ring by fluorine atoms and in the type of helicoidal structure in the chiral smectic CA phase with antiferroelectric properties. The influence of molecular structure on the shift of signals coming from carbonyl group, located in the rigid core, was observed. Keywords: liquid crystals, helicoidal structure, chiral smectic CA phase, antiferroelectric crystalline phase, infrared spectroscopy


2017 ◽  
Vol 66 (2) ◽  
pp. 25-35
Author(s):  
Anna Drzewicz ◽  
Marzena Tykarska ◽  
Mateusz Szala ◽  
Magdalena Żurowska

Three-ring chiral liquid crystalline compounds, forming antiferroelectric phase, differing in the structure of alkyl chain and in the substitution of benzene ring by fluorine atoms were studied. The measurements of helical pitch, based on the selective light reflection phenomenon, were performed as well as 1H and 13C NMR spectra at room temperature were registered. The influence of molecular structure as well as the type of helicoidal structure on the chemical shift of signals coming from chiral center was observed. Keywords: liquid crystals, helicoidal structure, nuclear magnetic resonance, antiferroelectric phase


1980 ◽  
Vol 35 (11) ◽  
pp. 1384-1388 ◽  
Author(s):  
Gerd Heppke ◽  
Reinhard Hopf ◽  
Bernd Kohne ◽  
Klaus Praefcke

The synthesis and the phase transition temperatures of homologous liquid crystalline 4(4-alkyloxybenzoyloxy)-4'-cyanoazobenzenes with alkyl chain length n = 1-12 and n = 16 are reported. All compounds exhibit smectic A phases; the SA phase region being interrupted by a "re-entrant" nematic phase for alkyl chain lengath n ≥ 9.


2008 ◽  
Vol 55 ◽  
pp. 42-45
Author(s):  
Yoshiaki Uchida ◽  
Rui Tamura ◽  
Naohiko Ikuma ◽  
Satoshi Shimono ◽  
Hiroki Takahashi ◽  
...  

We have synthesized two types of all-organic radical liquid crystalline (LC) compounds, trans-2-alkoxyphenyl-5-[4-(4-alkoxybenzenecarbonyloxy)phenyl]-2,5-dimethylpyrrolidine-1-oxy (1) and 4-alkoxyphenyl trans-4-[5-(4-alkoxyphenyl)-2,5-dimethylpyrrolidine-1-oxy-2-yl]benzoate (2) and have fully characterized their LC properties. Although the only difference in the molecular structure between 1 and 2 is the orientation of a binding group connecting the core portion and one side-chain (-OCO- and -COO- for 1 and 2), the racemic or enantiomerically enriched 2 showed an SmA phase, or SmA* and TGBA* phases, which were not observed for 1, besides N and SmC, or N* and SmC* phases, respectively. Here we discuss the origin of these differences on the basis of their crystal structures determined by X-ray crystallographic analysis.


Author(s):  
L. T. Pawlicki ◽  
R. M. Siegoczyński ◽  
S. Ptasznik ◽  
K. Marszałek

AbstractThe main purpose of the experiment was a thermodynamic research with use of the electric methods chosen. The substance examined was olive oil. The paper presents the resistance, capacitive reactance, relative permittivity and resistivity of olive. Compression was applied with two mean velocities up to 450 MPa. The results were shown as functions of pressure and time and depicted on the impedance phase diagram. The three first order phase transitions have been detected. All the changes in material parameters were observed during phase transitions. The material parameters measured turned out to be the much more sensitive long-time phase transition factors than temperature. The values of material parameters and their dependence on pressure and time were compared with the molecular structure, arrangement of molecules and interactions between them. Knowledge about olive oil parameters change with pressure and its phase transitions is very important for olive oil production and conservation.


2013 ◽  
Vol 652-654 ◽  
pp. 459-462
Author(s):  
Ya Tong Guo ◽  
Zhu Zheng ◽  
Zhen Qi Hou ◽  
Jie Du

A series of biodegradable segmented liquid crystalline poly(ester-urethane)s were prepared by solution polymerization of poly(L-lactic acid) (PLLA), mesogenic diol prepolymer poly(butylene terephthaloyldioxy dibenzoates) (MD), and hexamethylene diisocyanate (HDI). The MD content was varied from 0 to 40 mol% so that the effects of the mesogen content on the thermal and physical properties, and hydrolytic degradation were examined respectively. It was found that introducing mesogens units could increase the thermal stability and the elastic properties, while reduced the phase transition temperatures and the hydrolytic degradation rate.


2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Harald Pleiner ◽  
Helmut R. Brand

Abstract We investigate theoretically the macroscopic dynamics of various types of ordered magnetic fluid, gel, and elastomeric phases. We take a symmetry point of view and emphasize its importance for a macroscopic description. The interactions and couplings among the relevant variables are based on their individual symmetry behavior, irrespective of the detailed nature of the microscopic interactions involved. Concerning the variables we discriminate between conserved variables related to a local conservation law, symmetry variables describing a (spontaneously) broken continuous symmetry (e.g., due to a preferred direction) and slowly relaxing ones that arise from special conditions of the system are considered. Among the relevant symmetries, we consider the behavior under spatial rotations (e.g., discriminating scalars, vectors or tensors), under spatial inversion (discriminating e.g., polar and axial vectors), and under time reversal symmetry (discriminating e.g., velocities from polarizations, or electric fields from magnetic ones). Those symmetries are crucial not only to find the possible cross-couplings correctly but also to get a description of the macroscopic dynamics that is compatible with thermodynamics. In particular, time reversal symmetry is decisive to get the second law of thermodynamics right. We discuss (conventional quadrupolar) nematic order, polar order, active polar order, as well as ferromagnetic order and tetrahedral (octupolar) order. In a second step, we show some of the consequences of the symmetry properties for the various systems that we have worked on within the SPP1681, including magnetic nematic (and cholesteric) elastomers, ferromagnetic nematics (also with tetrahedral order), ferromagnetic elastomers with tetrahedral order, gels and elastomers with polar or active polar order, and finally magnetorheological fluids and gels in a one- and two-fluid description.


2003 ◽  
Vol 07 (05) ◽  
pp. 342-350 ◽  
Author(s):  
John M. Warman ◽  
Jessica E. Kroeze ◽  
Pieter G. Schouten ◽  
Anick M. van de Craats

The pulse-radiolysis time-resolved microwave conductivity technique, “PR-TRMC”, has been used to determine the charge carrier mobility within columnar stacks of mesomorphic discotic porphyrins and phthalocyanines. The influences of temperature, morphology and variations in the primary molecular structure are demonstrated and discussed. Both the mesomorphic and conductive properties are shown to be dramatically influenced by subtle changes in the peripheral alkyl chain structure or the core-to-chain coupling element. Mobilities close to 1 cm2.V−1.s−1 are found in crystalline solids, and well in excess of 0.1 cm2.V−1.s−1 in columnar, liquid crystalline phases. These values which are even larger than those determined by PR-TRMC for conjugated polymers and similar to values found for electrons and holes in organic single crystals.


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