Mesomorphism dependence of a terminal or lateral alkoxy group

A novel homologous series of thermotropic mesomorphs has been synthesized and studied with a view to understanding and establishing the effect of molecular structure on mesomorphic properties with reference to rigidity and flexibility of the homologues series: RO-C₆H₄-CH?CH-CO-C₆H₄-OC₁₈H₃₇(n). The novel homologous series comprises 13 novel homologues (C₁ to C₁₈), from which 11 homologues are enantiotropically mesogenic (C₃ to C₁₈). Smectogenic mesophase commences from C₇ homologue, and nematogenic mesophase is exhibited by C₃ to C₁₈ homologues in enantiotropic manner. Thus, C₇ to C₁₈ homologues are enantiotropically smectogenic plus nematogenic. Textures of smectic phase are of the type A or C, and that of nematic phase are threaded or Schlieren as confirmed through an optical polarizing microscope equipped with a heating stage. Transition curve of a phase diagram behaved in a normal manner except N-I transition curve, which shows minor deviating trend (C₁₂ to C₁₈) from expected normal behavior. An odd-even effect is exhibited by N-I and Sm-N transition curves. Analytical, spectral, and thermal data confirm the molecular structures of novel homologues. Thermal stabilities for smectic and nematic are 52.7°C and 66.6°C, respectively, whose total mesophase lengths range from 12.0°C to 28.0°C. Thus, novel series of chalcones is a low melting series whose mesogenic transition temperatures vary between 38.0 and 86.0°C.     

Topology of a Surface of the Phase Diagram of the Cholesteric Lyotropic Mesophase: Potassium Laurate/1-Decanol/Water/I-N-Lauroyl Potassium Alaninate

A surface of the phase diagram of the lyotropic cholesteric mesophase of potassium laurate/1-decanol/H₂O/l-N-lauroyl potassium alaninate (l-LAK) is studied by optical microscopy and X-ray diffraction as a function of the relative molar concentration of l-LAK and temperature. Cholesteric discotic and calamitic phases are observed and also a large domain of biaxial cholesteric phase. The inverse pitch as a function of the l-LAK relative molar concentration presents a linear behavior in the doping range studied. The l-LAK doping and its influence in favoring cholesteric calamitic phase formation are discussed in terms of the packing of the l-LAK amphiphile in the bilayer and the orientational fluctuations of the intrinsically biaxial correlation volumes.     

Two phase diagrams of Pb(Ti0.485Zr0.515)0.98(Nb0.5Bi0.5)0.02O3 solid solution in the temperature range 20 ≤ t ≤ 600°C

A high-temperature analysis of Pb(Ti_0.485Zr_0.515)_0.98(Nb_0.5Bi_0.5)_0.02O₃ solid solution has been carried out in the temperature range 20 ≤ t ≤ 600°C by X-ray powder diffraction. Two different phase diagrams are plotted: one is based on the change in the diffraction pattern of main reflections, while the other is based on the diffraction pattern of real (defect) structure. A transition to the cubic phase can be observed at t ≥ 360°C (in the former diagram) and t ≥ 450°C (in the latter diagram). The nonmonotonic (with inflection points) behavior of the temperature dependence of the cell volume in the cubic phase is explained.     

X-ray diffraction study of mesophase bitemplate-containing silicas

The effect of the composition of a bitemplate (solubilization) mixture on the formation of a spatially organized structure of mesophase siliceous systems has been investigated by X-ray diffraction. Alkylpyridinium halides (C _n PyHal with n = 8?16 (counterion Cl) and 18 (counterion Br)) were used a solubilizator, and monoethanolamides (EAC _m ) of saturated n-aliphatic acids (m = 10?16) and trialkylphosphine oxides (H_{2e + 1}C _e )₃PO, where e = 8, 10, or 12, were used as solubilizates. Differences in the mesophase structure of template-containing silicas synthesized in aqueous and aqueous salt (NaCl) solutions have been revealed. It is shown that the type and degree of ordering of the silica mesophase structure depends on the nature, spatial organization, and the solubilizator and solubilizate concentrations.     

Effect of Nitro Terminal Substituent on the Liquid Crystalline Characteristics of Ester Mesogens: p-Nitrophenyl-p'-n-Alkoxycinnamates

The homologous series p-nitrophenyl-p'-n-alkoxycinnamates is a medium melting homologous series; the first two members are non-mesogens and do not exhibit even monotropy. The nematic phase begins from the third derivative in monotropic condition; from the fourth member enantiotropic mesomorphism commences. Polymesomorphism begins from the sixth member with the appearance of smectic mesophase and ends at the seventh member. The rest of the homologues up to the octadecyl are purely smectogens. Thus the homologous series is predominantly smectogenic even though -NO₂ group is reported to be enhancing nematic character.^' Within the polymesomorphic region the nematic mesophase is homeotropic; however, it shows a clear threaded texture where it is the only mesophase shown. The N-I transitions do not exhibit the usual alternation in transitions which is a rare phenomenon. The N-I transition curve is unusually neither rising nor falling though a slight curve is seen; it merges with the S-I curve which shows a slight rising tendency as the alkyl chain length is increased. The S-N transition curve steeply rises and seems to be merging with the S-I curve. The mesomorphic range is good; the nature of the curve can predict the latent N-S or I-N transitions. All smectic orientations are of focal conic smectic A texture except in the case of sixth and seventh homologues where homeotropic nature prevails.     

Synthesis and characterization of mesogenic triphenylene-perylene dyads with phenoxy-alkoxy linkers

Three novel triphenylene-perylene dyads with phenoxy-alkoxy linkers (PDI-OPhO-C_n-O- TP₆, n = 6, 8, 10) have been synthesized and characterized by FT-IR, MS, ¹³C, and ¹H NMR. The mesomorphic properties of these compounds were investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). It was found that the dyads (PDI-OPhO-C_n-O-TP₆, n = 6, 8) only showed thermotropic columnar mesophase in the heating process, while the dyad (PDI-OPhO-C₁₀-O-TP₆) showed enantiotropic columnar mesophase in both heating and cooling processes.     

Synthesis of novel azoester homologous series of liquid crystalline behavior and the study of mesomorphism dependence on lateral substitution of middle phenyl ring

The titled azoester liquid crystalline homologous series consists of eleven homologues. The pentyl to tetradecyl derivatives of the series are nematogenic without exhibition of smectogenic character. Rest of the members of the series are nonliquid crystalline in nature. Textures of the nematic mesophase are schlieren or threaded type. Transition curves in the phase diagram showed normal phase behavior. Transition temperatures and liquid crystal behavior observed under an optical polarizing microscope equipped with a heating stage. An odd even effect is observed for nematic-isotropic transition curve. Analytical and spectral data confirms the structures of the molecules. Present homologous series is predominant nematogenic and partly nonmesogenic. Average thermal stability for nematic is 125.33°C and nematogenic mesophase length varies between 12°C to 48°C at tetradecyl (C₁₄) and octyl (C₈) derivatives, respectively.     

New chalcone based liquid crystals with allylidene amino linking unit: Synthesis and characterization

In this study, the synthesis, structural characterization and mesomorphic properties of newly thirteen calamitic shaped compounds derived from allylidene amino chalcone and 4-n-alkoxy benzoyloxy benzoic acid. Comp.H₁ to H₃ exhibited nonliquid crystalline nature, while comp.H₄ to comp.H₁₈ displayed enantiotropical smectic C phase. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC) and powder X-ray diffraction (PXRD) techniques. Thermal stabilities of smectic to isotropic phase are 150.0 °C and temperature range of mesophase is in decreasing order from comp.H₃ to comp.H₁₈ respectively. The presences of SmC phase are the type of broken fan and needle type in present synthesized series. It is also shown that presence of chalcone amino allylidene central linking group favors a calamitic liquid crystalline behaviour in molecules with lower member to higher member aliphatic side chain in alkoxy group (-OR).     

Phase Transitions of Urea Adducts with n-Paraffins under High Pressure

The temperatures of the phase transition between orthorhombic and hexagonal structures of the urea adducts with n-paraffins, n-C_nH_2n+2 (n = 14–44), have been measured by differential thermal analysis for the pressure range up to 250MPa. The transition temperatures increase both with pressure and with the number of carbon atoms of the guest paraffins. The increasing rate of the transition temperatures with pressure is about half of that of pure paraffin crystals. The pressure dependences of the lattice constants have also been measured by X-ray diffraction. The specific volume changes discontinuously at the transition pressure; the result suggests that the phase transition of the urea adducts with n-paraffins is a first-order one. Furthermore, the specific volume change at the transition pressure decreases with the number of carbon atoms of the guest paraffins; 3.4 × 10-⁶ m³/Kg for n = 16 and 2.1 × 10-⁶ m³/Kg for n = 44.     

Mesomorphic and DFT studies of terminal ester containing salicylaldimines and their copper (II) complexes

In this article, we report synthesis and characterization of a novel homologous series of butyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino)benzoates, C_nLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and powder X-ray diffraction (XRD) studies. The ligands and their copper(II) complexes exhibit wide range of enantiotropic smectic A mesophase as confirmed by their typical optical texture under polarizing microscope. Thermal stability of the compounds is determined by thermo gravimetric analyses. DFT calculations have been performed using GAUSSIAN-09 program at B3LYP level to obtain the stable electronic structure of the ligand and its copper(II) complex.     

New Mesogenic Compounds Exhibiting a Thermotropic Optically Isotropic Phase

Abstract

The only two series of carboxylic acids, 3-nitro- or 3-cyano-4-alkoxybiphenyl-4′-carboxylic acid, are known to exhibit the optically isotropic phase (S_D). Now we synthesised 4-(branched alkoxy)-anilinebenzylidene-4′-carboxylic acid series, all being racemic, and investigated their mesophase properties by means of DSC, optical microscopy and X-ray measurement. As a result, some branched azomethine derivatives were found to form a S_D phase. We also synthesised cinnamic acid derivatives with branched alkoxy tail that were turned out to exhibit either S_D phase or hexagonal columnar phase. We tried biphenyl or azobenzene core analogues which were found to produce a highly ordered smectic phase or no mesophase, respectively. At this stage, we suppose it plays an important role that the branch is introduced into the terminal chain and a certain dipole moment is located within the mesogenic core. These factors may allow the peculiar molecular packing that causes an optically isotropic property.     

Behavior of ammonium ion in β-LiRb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(NH<Subscript>4</Subscript>)<Subscript>x</Subscript>SO<Subscript>4</Subscript> mixed crystals (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1.0)

The influence of replacement of an ammonium ion by rubidium on the x-T phase diagram in the concentration range 0.50 ≤ x ≤ 1.0 has been studied by X-ray and neutron powder diffraction over a wide temperature range. It is shown that a decrease in the ammonium concentration is accompanied by an increase in the temperature of the II ? I phase transition and stabilization of phase II up to low temperatures (20 K). The changes occurring in the dynamics of mixed crystals are studied by inelastic incoherent neutron scattering. The spectra of the generalized vibrational density of states obtained allowed one to establish the difference in the phonon modes corresponding to phase III of β-LiNH₄SO₄ and phase II of β-LiRb_1?x(NH₄)_xSO₄ mixed crystal with x = 0.91 and x = 0.77 at 20 K. It is shown that a mixed crystal with x = 0.77 at 20 K is in the orientational glass state.     

Molecular and crystal structure of liquid crystalline p-octyloxyphenyl p′-pentyloxybenzoate

The crystal and molecular structure of p-octyloxyphenyl p′-pentyloxybenzoate C₅H₁₁-O-C₆H₄-C(O)-O-C₆H₄-O-C₈H₁₇, which forms a nematic mesophase upon melting, was determined by X-ray diffraction. There is one system of weak directional intermolecular C-H…π interactions responsible for the formation of the nematic phase in these crystals.     

Dependence of mesomorphism on geometrical shapes of isomeric and nonisomeric series of chalconyl esters

A meta substituted chalconyl ester homologous series: RO?C₆H₄?COO?C₆H₄(meta)?CO?CH?CH?C₆H₄?OC₁₂H_25(n)(para) is synthesized and studied with a view to understanding the effect of molecular substitution at meta position in a molecular structure on thermotropic liquid crystal properties. The novel homologous series consists of thirteen homologues (C₁ to C₁₈). All the homologues except the nonliquid crystal homologues C₁, C₂, C₃ are enantiotropic nematic with the absence of smectic properties. The transition and melting temperatures were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren. Transition curves (Cr-N/I and N-I) behave in normal manner except homologues between C₁₀ and C₁₄ of N-I curve, which show negligible deviation from normal and a smooth descending tendency. The N-I transition curve exhibits an odd-even effect up to C₁₀ homologue and then the odd-even effect disappears for higher homologues. Analytical and the spectral data support the molecular structures. Thermal stability for nematic is 107.3°C and the mesophase lengths range between 13.0°C and 35.0°C at the C₁₈ and C₁₂ homologues respectively. Group efficiency order for nematic is derived on the basis of thermal stability as ?OC₁₂H_25(n) (linear) > ?OC₁₂H_25(n) (nonlinear) > ?OC₁₆H₃₃ (nonlinear).     

Synthesis and Mesomorphic Characteristics of Fluoroaniline Derivatives with Different Lateral Groups

Two new homologous series of liquid crystals viz. 4-(4'-n-alkoxybenzoyloxy)-2-chlorophenylazo-4”-fluorobenzenes(I) and 4-(4'-n-alkoxybenzoyloxy)-2-methylphenyl azo-4”-fluorobenzenes(II) with terminal fluoro, lateral chloro(I) and methyl(II) group and central ester and azo linkages are synthesized and their mesomorphic properties are studied. Both the series are similar in molecular structure with the difference in their lateral substitutions; series I has chloro group and series II has methyl group as laterally substituted groups. All the twelve homologues of each of the series are mesogenic in nature. Series I shows nematic mesophase from the first C₁ to the last C₁₆ derivative synthesized; smectic mesophase is exhibited by last two viz. C₁₄ and C₁₆ derivative, where as all the members from C₁ to C₁₆ of series II only show nematic mesophase. The nematic mesophase shows marble texture and the smectic mesophase shows Schlirene texture of the Smectic C variety. Both the series are compared with structurally related series.     

Synthesis and Liquid Crystal Behavior of a Novel Ester Homologous Series

A novel ester homologous series of 4-[4’-n-alkoxy cinnamoyloxy] benzyl benzoates has been synthesized. The series consists of 12 homologues. Liquid crystal properties commence from the sixth member to the last member of the series with the exhibition of an enantiotropic nematic phase without the exhibition of any smectogenic mesophase. The remaining homologues do not exhibit liquid crystal behavior. The texture of the nematic phase is of the threaded or Schlieren type. The solid-nematic or isotropic transition curve adopts a zigzag path and the nematic-isotropic transition curve steeply rises and then falls in the phase diagram and behaves in normal manner. An odd–even effect is absent in the nematic-isotropic transition curve with an alteration of transition temperatures. The average thermal stability for the nematic mesophase is 153.1°C, and the nematogenic temperature ranges vary from 12°C to 50°C. Analytical data confirm the molecular structures of the homologues. The Liquid Crystal properties and transition temperatures were observed through an optical polarizing microscope, equipped with a heating stage. The mesomorphic characteristics of the novel ester series are compared with other, known and structurally similar series. The novel series is predominantly nematogenic with the absence of any smectogenic character, with relatively short mesophase temperature ranges and of the middle ordered melting type.     

Growth and study of single crystals of Pb1 − x BaxSc0.5Nb0.5O3 solid solutions

Crystals of Pb_{1 ? x} Ba_xSc_0.5Nb_0.5O₃ solid solutions with 0 ≤ x ≤ 0.58 have been grown by the method of mass crystallization from flux. It is established that, unlike the concentration dependence of the corresponding ceramic, the concentration dependence of the temperature T _m (the maximum dielectric constant ε in crystals) does not attain saturation. Cooling of crystals with x ≤ 0.04 resulted in a spontaneous transition from the relaxor to the macrodomain ferroelectric state. In crystals with a higher barium content, the relaxor state is “locked in.”     

Molecular and crystal structure of 4-hexylbenzoic acid: Design of the mesophase

The crystal structure of 4-hexylbenzoic acid C₆H₁₃-C₆H₄-COOH, which forms a nematic mesophase upon melting, is determined. The crystal contains three crystallographically independent molecules. Their molecular skeletons are made up of two almost planar fragments: a benzene ring, π-conjugated with the carboxyl group and a planar zigzag aliphatic fragment. One of the independent molecules forms centrosymmetric dimers via pairs of hydrogen bonds between carboxyl groups, whereas the two others are linked via hydrogen bonds. The dimers in the crystal are packed into pseudostacks with a pronounced nonparallel arrangement of conjugated fragments. There is no good mutual projecting of benzene rings in the stacks, which corresponds to efficient π-stacking interaction. The graph describing the mesophase of this compound contains only one structure-forming element (a hydrogen bond) and corresponds to the nematic mesophase.     

X-ray diffraction investigation of two mesomorphic copper(II) complexes of tetra-4-[(4-alkoxycarbonyl)phenyleneoxy]phthalocyanine

The mesomorphism and supramolecular structure of two homologues of copper tetra-4-[(4-alkoxycarbonyl)phenyleneoxyl]phthalocyanines are investigated using optical polarizing microscopy, differential scanning calorimetry (DSC), and X-ray diffraction. It is revealed that both homologues, which contain four and nine carbon atoms in aliphatic fragments of the lateral substituents, exhibit thermotropic columnar mesomorphism with a hexagonal arrangement of ordered columns (Col _ho). A change in the length of the aliphatic fragment has no noticeable effect on the mesophase type and leads only to variations in the parameters of the hexagonal lattice formed by the columns. The glass transition temperature of the homologue with n = 4 (T _g = 88°C) is considerably lower than that of the homologue with n = 9 (T _g = 88°C). It is established that the introduction of the cyclic fragment into the lateral substituent substantially affects the type of column packing as compared to the copper tetra-4-[(n-alkoxy)carbonyl]phthalocyanines studied in our earlier works. The assumption is made that this difference is associated, in particular, with the specific features of the penetration of the lateral substituents of the adjacent columns either in the presence or in the absence of the cyclic fragment in the lateral substituent.