Liquid crystalline phase transition studies in N(p-n-butoxybenzylidene) p-n decylaniline, 40.10

The synthesis, characterization and the temperature dependence of density and ultrasonic velocity of N(p-n-Butoxybenzylidene) p-n-decylaniline, 40.10 are presented. The compound exhibits as trivariant liquid crystalline mesomorphism Viz., NAB the Isotropic – Nematic, and Smectic A – Smectic B phase transitions are found to be first order. However, the interesting Nematic Smectic A (NA) transition shows a second order nature. The NA transition results are discussed in the light of the available data on other nO.m compounds. The computed molecular parameters: adiabatic compressibility (β_ad) molar sound velocity (R_n) and molar compressibility (A_w) are presented.     

Phase transition studies in mesogenic dimers

Schiff base liquid crystal dimers, both symmetric and non‐symmetric, in which two anisotropic groups are linked by a flexible spacer, exhibit a rich variety of smectic mesomorphism. The interest in this class of mesogens stems not only from their ability to act as model compounds for semi‐flexible mainchain liquid crystal polymers but also from their quite different properties compared to conventional low molar mass liquid crystals (monomers). We report here the phase transition studies on two examples of these schiff base liquid crystal dimers using the Differential Scanning Calorimetry and density measurements as a function of temperature. The symmetric liquid crystal dimer, α,ω‐bis (4‐n‐dodecylaniline benzylidene‐4′‐oxy)decane (10.O12O.10) exhibits a very rare Isotropic to G transition. Where as, the non‐symmetric dimer, α‐(4‐cyano biphenyl‐4′‐yloxy)‐ω‐(4‐n‐decylanilinebenzylidene‐4′‐oxy)decane (CB.O10O.10) exhibits a rare nematic to intercalated smectic A phase transition. The transitions studied, isotropic to nematic and isotropic to G exhibit a large density jump at the transition confirming their first order nature. Nematic to intercalated smectic A transition is found to be a second order transition whose behavior is similar to nematic to smectic A transition. Calculated values of pressure dependence of transition temperature and thermal expansion coefficient are also reported.     

Density studies across smectic-smectic transitions in 70.6 and 80.10

The temperature dependence of density in N(p-n-heptyloxy benzylidene) p-n-hexylaniline (70.6) and in N(p-n-octyloxy benezylidene) p-n-decylaniline (80.10) is carried out to study the nature of the phase transitions associated density jumps, to estimate the pressure dependence of transition temperatures and pretransitional effects. The compounds 70.6 exhibits a phase variant ACFG whereas 80.10 exhibits a new phase sequence variant ABF. The isotropic-smectic A, semctic A-smectic B and semctic C-smectic F phase transitions are found to be first order. The calculated thermal expansion coefficient also supported the density results. The density jumps, associated enthalpies and estimated pressure dependence of transition temperatures at the isotropic-smectic A phase transformation in other compounds are presented.     

Density Studies in Terephthalylidene-bis-p-n-dodecylaniline

The temperature dependence of density in Terephthalylidene-bis-p-n-dodecylaniline (TBAA12) is carried out to investigate the phase transitions, associated volume jumps, order of the transitions and to estimate the pressure dependence of transition temperatures and pretransitional effects. The compound exhibits smectic C, smectic I, smectic F and smectic G phases. The isotropic-smectic C and smectic C-smectic I transitions are found to be first order from the density jumps and the calculated thermal expansion coefficient data also supported the density results. The smectic I-smectic F transition is detectable by a change of slope in density studies, which is a second order transition inferred from thermal expansion coefficient variation with temperature.     

Phase transition behavior and structure of the thermotropic liquid crystal 6‐{[(4′‐{[(undecyl)carbonyl]oxy}biphenyl‐4yl)carbonyl]oxy}‐1‐hexyne

The phase transition behaviors and corresponding structures of 6‐{[(4′‐{[(undecyl)carbonyl]oxy}biphenyl‐4yl)carbonyl]oxy}‐1‐hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X‐ray diffraction (WAXD). In comparison with the published homologues, 5‐{[(4′‐heptoxy‐biphenyl‐4‐yl)carbonyl]oxy}‐1‐pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5‐{[(4′‐heptoxy‐biphenyl‐4‐yl)oxy]carbonyl}‐ 1‐pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5‐{[(4′‐heptoxy‐biphenyl‐4‐yl)carbonyl]oxy}‐1‐undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5°C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69Å. Further lowering the temperature, it enters into a metastable monotropic smectic B (SmB) phase with a longer layer spacing d=34.22Å which has a tendency towards crystallization. The metastability of the liquid crystalline phase may associate to the linkage order of the ester bridge between the mesogenic core and the flexible spacer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

DC conductivity studies in K3Na(SeO4)2 single crystals

DC electrical conductivity studies were carried out along the three crystallographic axes for Tripotassium sodium diselenate (K₃Na(SeO₄)₂ or KNSe). Earlier studies of phase transition in this crystal show successive phase transitions at 334 K, 346 K, 730 K, and 758 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303 K – 430 K along a, b and c – axes. An anomaly in conductivity was obtained around 341 K and another one around 333 K. These can be attributed as due to phase transitions in this crystal. A strong anomaly also has been observed along the c‐axis and comparatively week one along a and b axes around 395 K for the first time. This can be due to newly observed phase transition in the crystal. DSC taken for the sample also shows endothermic peak supporting the occurrence of newly observed phase transition. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal Microscopy and DSC Studies of 4-[4-n-pentyloxybenzylideneamino] Azobenzene

Phase transition studies of the liquid crystal, 4-[4-n-pentyloxybenzylidene–amino]–azobenzene (PBAAB) have been investigated by thermal microscopy and Differential Scanning Calorimetry (DSC) studies. From these studies it is confirmed that the compound, PBAAB exhibits nematic, smectic A and smectic B phases. The textures exhibited by different phases are presented. The enthalpies and entropies at various phase transitions are also reported.     

Mesomorphism dependence on molecular rigidity and substitution of same functional group on lateral or terminal position of tailed phenyl ring

Novel liquid crystal materials (LCs) of low temperature range (53°C to 75°C) have been synthesized through a series of chalconyl derivatives consisting of two phenyl rings bonded through a –CH?CH?CO? central bridge to study the effect of molecular structure on LC properties in general and with a focus on molecular rigidity. The novel homologues series (C₁ to C₁₈) consists of thirteen homologues with general formula RO?C₆H₄?CH?CH?CO?C₆H₄?OC₁₀H₂₁(n) (meta). The C₁, C₂, C₃ homologues are nonliquid crystals (NLC) and the rest of the homologues (C₄ to C₁₈) are either monotropic or enantiotropic liquid crystals. C₄ to C₆ homologues are enantiotropicnematic and the rest of the mesomorphic homologues are (C₇ to C₁₈) monotropicsmectic in addition to monotropicnematic character. Transition and melting temperatures including textures of homologues were determined by an optical polarizing (POM) microscopy equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren, and that of the smectic phase are of the type Smectic A or C as judged directly from the heating top of the microscope. Thermal stability for smectic is very poor and of the nematic is (N-I) 69.3°C whose, total mesophase length ranges between 07.0 to 14.0°C at C₈ and C₄ homologues respectively.     

Smectic A-Nematic and Nematic-Isotropic Liquid Transitions in 8CB Liquid Crystal: Comparative Analysis

A differential heat flux calorimeter has been used to study the Smectic A-Nematic and Nematic-Isotropic Liquid transitions in 8CB liquid crystal. The Faktor and Hanks model under our working conditions enables us to distinguish first-order from second-order transitions by analysis of differential signal. The critical exponent values obtained justify the proportionality between Cp evolution and the normalized differential signal (differential signal divided by the scanning rate).     

Crystal structure,thermal analysis and IR spectrometric investigation of bis (2‐amino‐6‐methyl) pyridinium sulfate

The synthesis method, crystal structure determination, phase transitions studied by thermal analysis and IR spectrometric investigation of 2C₆H₉N₂⁺.SO₄^2– are reported. The compound crystallizes in the monoclinic space group C2/c (no. 15) with a = 10.5068(4) Å, b = 10.2225(5) Å, c = 14.0422(7) Å, and β = 104.489(3)°. The atomic arrangement can be described by layers built by all the components of the structure and centered by planes z = 1/4 and 3/4. The organic molecules form channels parallel to the c direction with dimensions of 4.163(1)Å and 5.148(4)Å. Thermal analysis shows that the anhydrous compound presents an irreversible weak phase transition. The IR study, based on theoretical analyses and on the literature data allows the interpretation of the IR spectrum. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Structure of 2‐methyl cinnamanilide and 2‐methoxy cinnamanilide

The crystal structures of two cinnamanilide derivatives 2‐methyl cinnamanilide (C₁₆ H₁₅ N O – compound I) and 2‐methoxy cinnamanilide (C₁₆ H₁₅ N O₂ – compound II) are reported. In both crystal structures, the cinnamamide group is almost planar. The inter‐planar angle between the two phenyl rings are 71.6(1)° for compound I and 7.5(1)° for compound II. The N‐H…O and C‐H…O type of hydrogen bond interactions between the amide group and the carbonyl group stabilizes the molecular packing as chains in the crystal lattice.     

Crystal structure,thermal analysis,and IR spectroscopic investigation of bis(2-amino-6-methyl) pyridinium sulfate

Synthesis, crystal structure refinement, phase transitions studied by thermal analysis, and IR spectroscopic investigation of 2C₆H₉N₂ < eqid2 > ⋅SO₄²⁻ are reported. The title compound crystallizes in the monoclinic space group C2/c (no. 15) with a = 10.5068(4) Å, b = 10.2225(5) Å, c = 14.0422(7) Å, and β = 104.489(3)^∘. A crystal packing diagram shows layers built by all the components of the structure and centered by planes z = 1/4 and 3/4. The pyridine substituents stack forming channels parallel to the c direction with dimensions of 4.163(1) Å and 5.148(4) Å. Thermal analysis shows that the anhydrous compound possesses an irreversible weak phase transition.     

Synthesis,characterization and structural phase transition studies in trismethylammonium pentachloro barium dihydrate single crystals

Single crystals of trismethylammonium pentachlorobarium dihydrate were grown by slow evaporation method at ambient temperature. The crystals were characterized through powder XRD, thermal, infrared and NMR spectral studies. While the powder XRD pattern confirms the crystallinity of the title compound, the TG indicates the removal of occluded and adsorbed water molecules from the crystal when it is heated up to 86 °C. The TG study also confirms the presence of two water molecules of crystallization which are dehydrated on heating the crystal between 107 °C and 150 °C. The anhydrous compound is found to be stable at least up to 900 °C. The DTA curve shows two endothermic dips corresponding to weight losses observed in the TG curve. The low temperature DSC study shows thermal anomalies during the heating and cooling cycles indicating both first and second order phase transitions. The high temperature DSC shows the stepwise dehydration indicating phase transitions at temperatures 103 °C and 145 °C. The characteristic vibrational frequencies due to methylammonium ion, BaCl₅ and other groups are assigned based on FTIR spectra. The NMR spectrum confirms the presence of protons of the methyl group and water of crystallization in the compound. In this paper, an attempt is also made to understand the effect of methyl group on the phase transitions of the compound in comparison with a closely related compound, trisammoniumpentachloro barium dihydrate. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diffusion couple studies of the Ti‐Bi‐Zn system

The system Ti‐Bi‐Zn has been investigated using diffusion couples consisting of solid Ti and liquid (Bi+Zn) phase. The diffusion paths at 400, 500, 700 and 800 °C have been traced by means of electron microprobe analyses. The growth constants of the diffusion layers are roughly assessed. The phase diagram data obtained in this investigation are compared with previous studies of equilibrated alloys. The existence of the ternary compound TiBiZn has been confirmed. The formation of another phase with approximate formulae Ti₄Bi₃Zn to Ti₉Bi₇Zn₄ has been observed at high temperatures. The latter compound as well as the ternary extension of the Ti_XBi_Y (X ≈ 5, Y ≈ 6) phase react easily with air. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal and molecular structure studies of tris(2-hydroxy-3-t-butyl-5-methylbenzene)-methane trihydrate and N-benzyl-N-phenyl benzamide

The structures of the title compounds, tris(2-hydroxy-3-t-butyl-5-methylbenzene)-methane)C₃₄H₄₆O₃.3H₂O, 3) and N-benzyl-N-phenylbenzamide (C₂₀H₁₇NO, 6), have been investigated by X-ray crystallography. Compound 3 crystallizes in the trigonal space group with cell parameters a = 14.090(5) Å, b = 14.090(5)Å, c = 10.485(5)Å, Z = 2. Compound 6 crystallizes in the monoclinic space group C2/c with cell parameters a = 24.533(4)Å, b = 9.176(4)Å, c = 16.711(5)Å, = 125.88(2)°, Z = 8. Compound 3 has both intra-and intermolecular hydrogen bonds. It also exhibits a helical columnar arrangement of the molecules and goes into mesophase before melting into an isotropic liquid.     

Synthesis and Mesomorphic Behavior of Calamitic Liquid Crystals with a Biphenyl Moiety

A new mesogenic homologous series having a biphenyl moiety has been synthesized by condensing 4-hydroxy-4′-nitrobiphenyl- and methoxy-substituted 4-n-alkoxy cinnamoyl chlorides, and their liquid crystalline properties have been studied. All the members of the series are enantiotropic liquid crystals. The methyl to n-pentyl derivatives exhibit both Smectic A (SmA) and Nematic (N) phases; the higher members, starting with the n-hexyl derivative show only a SmA phase. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits zig-zag pattern for Sm-N and N-Isotropic (Iso) transition temperature curves. The average thermal stability is compared with other related homologous series. The introduction of polar nitro group increases significant intermolecular force of attraction which stabilizes the molecular orientation. This results into the increase in the thermal stability of the system.     

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).     

Calorimetric Study of Crystalline and Liquid-Crystalline Polymorphism in the Homologues of Terephthal-bis-n-alkylaniline

The phase sequences of the homologues with n (the number of carbon atoms in the terminal alkyl chains) from 2 to 8 are obtained. At low temperatures, i) several crystalline modifications are found in each of the members with n = 4, 5, and 6 and ii) the monotropic transitions between crystal and smectic phase are observed in almost all the members. At intermediate temperature, iii) between the smectic H and C phases, the smectic F phase is found in the homologues with n ≥ = 5 by morphological observation or by a rheological method. The constancy of the temperature of the S_H(or S_F) – S_c transition with respect to “and broadening of the temperature range of S_H with increasing n in the expense of nematic phase are worthy of note. The even-odd effect of the end chain length n is observed very distinctively on the crystal melting and clearing point. Proton NMR measurement reveals a large mobility in the terminal alkyl chains in the crystal of the member with n = 6.     

Ferroelectric Liquid Crystals with New Chiral Building Blocks

Esterification of 4-nitrocinnamoyl chloride by new chiral alcohols((d) and (1) 2-butanol; (d) 2-heptanol), followed by reduction of the nitro group by a new reagent(SnC1₂), gives new chiral 4-aminocinnamates.Condensation of these amines with 4-alkyloxybenzaldehydes or terephthaldehyde gives Schiff bases showing in some cases chiral smectic C phases. A comparative study of the mesomorphism of both these compounds and the compounds of the DOBAMBC family is made, in order to evaluate the effect of the chiral building block structure on the liquid crystalline properties.During this study, a new compound has been prepared, which exhibits the smectic O phase: ((d) 1-methylhexyl)terephthalidene Bis 4-aminocinna-mate.     

Synthesis and characterization of dihydroxylammonium tetrachlorocuprate dihydrate crystals

A new hydroxylammonium compound, [(NH₃OH)₂CuCl₄], was synthesized and its crystals were grown at room temperature by slow evaporation of aqueous solutions. The crystals were characterized through powder XRD, thermogravimetry (TG), differential thermal analysis (DTA), low temperature differential scanning calorimetric (DSC) and FTIR spectra. The X‐ray powder diffraction confirms the crystallinity of the compound. A fitting decomposition pattern of the compound was formulated based on the TG and thereby confirming the formation of the compound in the stoichiometric ratio. The thermal anomalies occurring in the low temperature DSC indicate successive phase transitions. The low temperature phase transitions are attributed to the ordering of [NH₃OH]⁺ ions. While most of the phase transitions are of first order type, the one occurring at –126 °C is of second order. Two glass transitions occur when the compound was cooled between –157.9 and –136.9 °C. The characteristic vibration bands due to [NH₃OH]⁺ and CuClequation/tex2gif-stack-1.gif ions are observed in the IR spectra. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)