Mesomorphic Phase Transitions Research Articles

Interaction induced phenomena in Raman spectra of mesogens

We present the results of experimental studies of light scattering in the isotropic phase of two mesogens, p-n-pentyl-p′-cyanobiphenyl (5CB) and p-n-pentyl-(p′-cyanophenyl)-cyclohexane (5PCH) and in their solutions in CCl4, a globular molecules solvent. Integral intensities of various Raman bands and Rayleigh wing polarized spectra were studied. Dilution experiments have shown that in mesogen systems, due to molecular interactions, intensity of light scattering may be substantially (about 30%) reduced. Isotropic component of the scattered light is influenced by orientation-translational molecular correlations, while for anisotropic component pure orientational molecular correlations are also important. As a result, depolarization ratio in the condensed state may be substantially different from that for the isolated molecule and may vary through the mesomorphic phase transitions.

Mesomorphic phase transition and liquid crystal properties of fluoroaikyl ether derivatives

Mesomorphic phase transition and liquid crystal properties of fluoroaikyl ether derivatives

Photoconduction of a mesogenic long-chain tetraphenylporphyrin in a symmetrical sandwich-type cell

Photoconductive properties of a mesogenic long-chain tetraphenylporphyrin (C15TPPH2) were investigated for a symmetrical sandwich-type (ITO/C15TPPH2/ITO) cell. The action spectra and illumination light intensity dependence of the steady state photocurrent indicated that both extrinsic and intrinsic processes of photocarrier generation contribute to the apparent photocurrent behavior which is variant on the mesomorphic phase transitions. In particular, it was inferred that the mesomorphic phase transition from the low- to high-temperature lamellar mesophases leading to the sudden disappearance of photocurrent rectification behavior, depress the extrinsic process of charge carrier generation. These results strongly imply that the photoconductive property of mesogenic materials could be drastically affected by a change of the molecular fluctuation and long-range order through mesomorphic phase transitions.

Liquid Crystalline Epoxy Resins Consisting of Mesogenic Diepoxide and Mesogenic Hardner

Two liquid crystalline (LC) epoxy resins consisting of LC diepoxide and LC hardner were synthesized, diglycidyloxyazoxybenzene (DGA), 4,4′-bis (ω-carboxy decanoxy) azoxybenzene (CAA10) and DGA with 4, 4′-bis (ω-hydroxy undecanoxy) azoxybenzene (HAA11), and their reaction mechanism, mesomorphic phase transition and thermal expansion were investigated by use of DSC, IR, polarized microscopy, X-ray diffractometry and capillary dilatometry. The fully gelated DGA-CAA10 formed a network structure in which one interchain crosslink was made per 5.6 repeating unit, and showed no mesophase. The DGA-HAA11 of linear typed polymer showed a smectic A phase when not fully cured, while a namatic phase when gelated. It was pointed out that the mesogenicity of epoxy resin is governed by the mesogenicity of monomers but is also correlated with the crosslinking density and degree of polymerization. In the fully gelated DGA-CAA10, thermal expansion coefficient (α) was about 2.2 × 10−4 °C−1 below Tg and 3.4 × 10−4 °C−1 above Tg, while about 2.3 × 10−4 °C−1 below Tg and above 6.5 × 10−4 °C−1 above Tg in the fully gelated DGA-HAA11. It is noted that the α value for DGA-CAA10 is low even above Tg.

Liquid crystalline phase transitions of the 2-(4-alkoxybiphenyl-4-yl)-5-(4-methylphenyl)pyridines

The mesomorphic phase transitions have been studied for a series of 2-(4-alkoxybiphenyl-4-yl)5-(4-methylphenyl)pyridines (4R-Pn; the carbon number, n, of the alkoxy group is 1-10) by use of DSC and polarizing optical microscopy. The 4R-Pn compounds showed only a nematic phase for n=1 and 2, but underwent characteristic polymesomorphic sequences when n>3; Cr CrH SmF SmC SmA N I with n=3 and 4, and Cr CrH SmF SmA N I with n=5-10. This mesomorphic phase transition behaviour was similar to that of the 2-(4-alkoxyphenyl)-5-(4-methylphenyl)pyridine (3R-Pn) series reported previously and it is proposed that the 4R-Pn and 3R-Pn compounds have a minimum terminal alkoxy length (critical alkoxy length) for the generation of LC polymorphism.

Synthesis and Mesomorphic Properties of Polymethylene-α,ω–bis [2-thio- 5-(4',4"n-alcoxybenzoyIoxy)phenyl]-1,3,4-oxadiazole

Abstract Three homologous series of polymethylene-α,ω-bis[2-thio-5(4′,4″n-alkoxybenzoyloxy)- phenyl]-1,3,4-oxadiazole (series 5 a, b, c), are reported.The compounds have identical mesogenic units at both ends of a spacer (i.e. they are twins). These twins possess a spacer of 6, 8 and 10 carbon atoms joined directly to the oxadiazole ring through sulphur atoms. The lateral alkylic chains vary between 6 and 10 carbon atoms.The presence of enantiotropic and monotropic nematic phase is related to the length of the spacer group. The influence of molecular structure on the mesomorphic properties has been studied. Mesomorphic properties and phase transitions have been determined using polarizing hot-stage microscopy and differential scanning calorimetry.

Liquid crystalline epoxy resin cured by mesogenic hardening compounds

A new type of liquid crystalline epoxy resin functionalized with mesogenic hardening agent was obtained by reacting stoichiometrically 4,4′-bis (2,3-epoxypropoxy)-3,3′5,5′-tetramethyl biphenyl (EPTB) (diepoxide monomer) with 4,4′-bis (ω-carboxy decanoxy) azoxybenzene (CDA10) (mesogenic hardening monomer) at 145°C for 10 min, using tri-n-butylamine as a catalyst. Mesomorphic phase transition behavior for EPTB-CDA10 prepolymer obtained was studied as function of curing time at 140°C by use of DSC and polarized microscopy. When the curing time is shorter than a gelling time (60 min), EPTB-CDA10 showed a liquid crystalline state reminiscent of smectic phase, while that reminiscent of nematic phase, when the curing time is longer than the gelling time. This work indicates that the new type of epoxy resin cured by mesogenic hardening compound can have a liquid crystal state.

Relation between micellar structure of model bile and activity of esterase

In a model bile solution composed of lecithin (L)-bile salt (B), the solubilization of lipid and the accessibility of enzyme to the lipid were examined by observation of EPR spectra and measurement of enzyme activity. The lifetime of the spin probe in the micellar phase was estimated to be approx. 1 μs by means of line shape analysis. Both population and lifetime increased with temperature and the molar ratio of lecithin to bile salt (L/B). The EPR data indicated that simple micelle of bile salt, mixed disk micelle of bile salt-lecithin, and multi-lamellar mixed disk micelle can exist in a model bile solution, depending on the L/B molar ratio across a range from 0 to 1.5. The maximal power of the mixed disk micelle to solubilize cholesteryl ester in the model bile at a L/B molar ratio of 1:1 was confirmed by EPR measurement of cholesteryl 12-DOXYL-stearate. Observation of the enzyme activity on a mixture of model bile and substrate at 37°C revealed selective accessibility of cholesterol esterase (bovine pancreas) to mixed disk micelle, of cholesterol oxidase ( Streptomyces cinnamomeus) to both simple and mixed disk micelle, and of pancreatic lipase (porcine pancreas) to both simple micelle and an oil droplet of substrate. The temperature-dependent activity of cholesterol oxidase to cholesterol in mixed disk micelle can be explained in terms of mesomorphic phase transition of lecithin side chains followed with fluidity of liquid crystal phase. Regarding phospholipase C from Bacillus cereus, though the selective accessibility to the micelles was not observed at 37°C, a decrease in activity for mixed disk micelle could be found at lower temperatures.

Mesomorphic phase transitions of 4,4′″-dialkyloxyquaterphenyls and dialkyl quaterphenyl-4,4′″-dicarboxylates

Abstract The mesogenicities of 4,4′″-dialkyloxyquaterphenyls (DAQP) and dialkyl quaterphenyl-4,4′″-dicarboxylates (DCQP) were studied by differential scanning calorimetry, optical microscopy and miscibility tests. The DAQP homologues, for which the number of carbon atoms in the alkyloxy group (n) is 1–9, showed a SA phase, and the higher homologues (n = 9–18) showed a Sc phase. The propyl, butyl and pentyl esters of DCQP showed a SA phase, and the octyl and dodecyl esters showed SA and Sc phases. The isopropyl, isobutyl, 2-ethylhexyl and cyclohexyl esters showed a Sc phase and the branching of the alkyl group strikingly lowered the mesophase thermal stabilities.

Mesomorphic phase transitions of a series of D-phase compounds

Abstract Mesomorphic phase transitions of 4′-n-alkoxy-3′-nitrobiphenyl-4-carboxylic acids (ANBC) with numbers of carbons (n) in the alkoxy group ranging from 11 to 22 have been studied by differential scanning calorimetry (DSC) and polarizing optical microscopy. The D phase, a mesophase of particular interest through its being optically isotropic, was observed for the n = 17, 19, 20, 21, and 22 members of the ANBCs, as well as for the n = 16 and 18 members, as reported previously. The Sc-D phase transition temperature decreased with increasing n, so that the temperature range of the D phase extended over 64° at n = 22. In the n = 15 member, the D phase was certainly observed on first heating, but was not seen on subsequent cooling and second heating processes.

Liquid-crystalline behaviour of some bis(4-alkyloxyphenyl) thiazolo [5,4-d] dithiazoles

Abstract The preparation of liquid-crystalline 2,5-bis(4-alkyloxyphenyl) thiazolo [5,4-d] dithiazoles (ATT n ), in which the alkyl group is C n H2n + 1 (where n = 1 to 10, 12), has been described. Mesomorphic properties and phase transitions as determined by polarizing hot stage microscopy and differential scanning calorimetry are discussed as a function of the number of carbon atoms in the alkyloxy chain. The exhibition of tilted smectic phases (smectic C and smectic I) by these compounds is an interesting feature since there is no significant central dipole moment transverse to these molecules.

Novel photocurrent rectification behaviour for a photoconductive cell using the mesogenic 5,10,15,20-tetrakis(4-n-pentadecylphenyl)porphyrin

A novel photocurrent rectification behaviour associated with mesomorphic phase transitions was found for a symmetrical cell in which the mesogenic 5,10,15,20-tetrakis(4-n-pentadecylphenyl)porphyrin (C15TPP) was sandwiched between two indium–tin oxide electrodes; the rectification properties shown by the crystalline C15TPP cell disappears in the mesomorphic cell (discotic lamellar phase).

Structural rearrangements during mesomorphic phase transitions in poly{10-[(cyano-4′-biphenyl)oxy]decanyl vinyl ether}

The structures displayed by poly{10-[(4-cyano-4′-biphenyl)oxy]decanyl vinyl ether} were studied by small- and wide-angle X-ray scattering. It is shown that this polymer possesses two different smectic phases: an ordered smectic E phase at low temperatures, and a smectic A phase at higher temperatures. The smectic A phase is characterized by a double-layer packing with partial overlap of the cyanobiphenyl groups, while the ordered smectic E phase displays a layer packing characterized by the presence of two incommensurate periodicities. The structural rearrangements accompanying the phase transformation from the ordered to the disordered smectic phase are discussed in detail.

Mesomorphic phase transitions of tetraphenylporphyrins with four long aliphatic chains

Abstract Studies of 5,10,15,20-tetrakis(4-n-alkylphenyl)porphyrins revealed that the homologues with longer alkyl chains than hexyl were mesomorphic, in contrast to the non-mesomorphic alkoxy derivatives. Metal complexes (Co, Ni, Cu, Zn, and Pd) of the dodecyl derivative were also shown to exhibit mesophases. These mesophases were assigned as discotic lamellar (DL) phases by X-ray diffraction studies.

LIPIDAT: A database of lipid phase transition temperatures and enthalpy changes. DMPC data subset analysis

The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately these data have until now been scattered throughout the literature in a variety of books, proceedings and journals. The data have recently been compiled in a centralized database, LIPIDAT, with a view to providing ready access to the data and to the appropriate literature. LIPIDAT consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically-derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc., on the thermodynamic values. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes comprehensive literature referencing and list of authors, but does not at the present time include article titles. As of this writing, the database is current through June, 1990 and is approaching 10 000 records in length. Each record contains 28 fields. In this paper we report the contents and present an analysis of LIPIDAT as it refers to fully hydrated 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC). This database subset represents about 7% of all LIPIDAT records. It includes data collected over a 23-year period from 1967 to 1989 and consists of 702 records obtained from 336 articles in 55 different journals. The number of records per year rises steadily beginning in 1971, reaches a maximum of 89 records/year in 1977 and remains relatively constant at 60–70 records/year in the succeeding period. Journals making the greatest contribution to the DMPC subset include Biochimica et Biophysica Acta, Biochemistry, Chemistry and Physics of Lipids and the Biophysical Journal. These four journals account for 71% of the total records in the database subset. The analysis shows that differential scanning calorimetry, electron spin resonance, fluorescence, nuclear magnetic resonance and Raman spectroscopy are the methods most commonly used for DMPC transition temperature determination. An interesting pattern emerges as to the place in time the different methods assume or loose popularity. The main, pre- and subtransition have been described, respectively, in 25, 9 and 2 distinct ways in the literature, an observation that points to the urgent need for a universally accepted lipid phase notation. The distribution of main and pre-transition temperatures and enthalpies determined in the heating and cooling direction and their dependence on aqueous phase additive, scan rate and methods used is presented.

Mesomorphic phase transitions of 4,4′-bis(ω-hydroxyalkoxy)-azoxybenzenes. Appearance of isotropic mesophase

Abstract Mesomorphic phase transitions of 4,4′-bis(ω-hydroxyalkoxy)-azoxybenzenes (number of carbons in the alkoxy group n = 2,3,6,8,11 and 12) have been studied by differential scanning calorimetry (DSC) and polarized optical microscopy. For the n = 8 compound, an optically isotropic (01) mesophase reminiscent of the smectic D phase was observed in the temperature range of 4 0 M 1 1 K between smectic C (below 400 K) and nematic (above 41 1 K) phases. On the other hand, the 0 1 mesophase was not observed in the other homologues used here; the n = 2,3 and 6 compounds had only a nematic phase and the n= 11 and 12 compounds had only a smectic C phase. This preliminary work points out that the thermal and optical properties of the 01 phase for the n = 8 compound are very similar to those of the smectic D phase.

A database of lipid-phase transition temperatures and enthalpy changes

The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately, these data have, until now, been scattered throughout the literature in a variety of books, proceedings, and journals. The data have recently been compiled in a centralized database with a view to providing ready access to the same and to the appropriate literature. The compilation facilitates review of what has thus far been accomplished and highlights what remains to be done in this active research area. As such, it represents a convenient summary of the existing data which, when evaluated, will enable us to identify where deficits exist in the data, to reveal the fundamental physicochemical principles upon which lipid phase behavior is based, and to understand more completely lipid phase relations in biological, reconstituted, and formulated systems. The compilation consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes for synthetic and biologically derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect on these thermodynamic values of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes complete literature referencing and list of authors. As of this writing, the database is current through June 1990 and contains 9500 records. Each record contains 28 fields. Here, we describe how the database originated, its scope and contents, data abstraction procedures, and issues relating to mesophase and lipid nomenclature, data analysis, and evaluation, and database maintenance and distribution.

Order and thermochromism of poly(di-n-alkyl)silane copolymers

A series of poly(di-n-alkyl)silane copolymers derived from Poly(di-n-hexyl)silane, PDHS, was prepared. Mesomorphic phase transitions of these copolymers depend on fraction as well as on the size of the comonomers. DSC and temperature dependent UV-spectroscopy were employed to study the effect of constitutional disorder on the length of all-trans σ-conjugated Si-Si catenated chromophores.

A database of lipid phase transition temperatures and enthalpy changes

The systematic study of the mesomorphic phase properties of synthetic and biologically derived lipids began some 30 years ago. In the past decade, interest in this area has grown enormously. As a result, there exists a wealth of information on lipid phase behavior, but unfortunately these data have, until now, been scattered throughout the literature in a variety of books, proceedings and journals, The data have recently been compiled in a centralized database with a view to providing ready access to same and to the appropriate literature. The compilation facilitates review of what has thus far been accomplished and highlights what remains to be done in this active research area. As such, it represents a convenient summary of the existing data which, when evaluated, will enable us to identify where deficits exist in the data, to reveal the fundamental physicochemical principles upon which lipid phase behavior is based and to understand more completely lipid phase relations in biological, reconstituted and formulated systems. The compilation consists of a tabulation of all known mesomorphic and polymorphic phase transition temperatures and enthalpy changes, for synthetic and biologically-derived lipids in the dry and in the partially and fully hydrated states. Also included is the effect on these thermodynamic values of pH, and of salt and metal ion concentration and other additives such as proteins, drugs, etc. The methods used in making the measurements and the experimental conditions are reported. Bibliographic information includes complete literature referencing and list of authors. As of this writing, the database is current through June, 1990 and contains in excess of 9500 records. Each record contains 28 fields. Here, we describe how the database originated, its scope and contents, data abstraction procedures, and issues relating to mesophase and lipid nomenclature, data analysis and evaluation, and database maintenance and distribution.

Positron Lifetimes in Smectic Liquid Crystals

The mean lifetimes of positrons in 4,4'-n-octyloxycyanobiphenyl and p-decyloxybenzylidene p'-amino 2-methyl butyl cinnamate were measured. The measurements of magnetic susceptibility and differential scanning calorimetry were also carried out to study the influence of molecular order and phase transition on the mean lifetime of positrons. The poistron lifetime spectra consist of two components. The mean lifetimes of the shortlived and the longlived components in these liquid crystals increase abruptly at the solid-smectic transition. It seems that the change in the shortlived component at the mesomorphic phase transitions depends on the magnitude of transition enthalpy. The longlived component shows a maximum in the smectic A phase. The maximum mean lifetime of the longlived component in the smectic A may be related to the size of defects in the well-defined fluid regions.