Nematic-isotropic Transition Curve Research Articles

Synthesis and Evaluation of Liquid Crystalline Properties of a Novel Homologous series: α-3-[4′-n-Alkoxy Benzoyloxy] Phenyl-β-4″-Nitro Benzoyl Ethylenes

The titled homologous series consists of 11 members. The methyl and ethyl homologues are nonmesomorphic because of very high melting points, however, the propyl to hexadecyl derivatives are enantiotropic nematic with absence of smectogenic. The texture of nematic mesophase is threaded or Schlieren. The nematic-isotropic transition curve of the phase diagram behaves in a normal manner with the exhibition of an odd–even effect. The transition temperatures of the series and liquid crystal properties are observed through optical polarizing microscopy and a hot stage. The novel materials were characterized by elemental analysis, infrared, and 1H NMR spectroscopy. Analytical data support the molecular structures. The liquid crystal properties of the novel series are compared with structurally similar homologous series. The novel series is entirely nematogenic with absence of smectic character and of a middle-ordered melting type. The nematic-isotropic thermal stability varies between around 120°C and 180°C.

The Synthesis and Mesomorphic Properties of a Novel Homologous Series: α-4-[4′-n-Alkoxy benzoyloxy] Benzoyl -β-2″-nitro Phenyl Ethylenes

The synthesis and mesomorphic properties of novel homologous series are reported. All 11 members of the series, except the methoxy and ethoxy derivatives, are enantiotropically mesogenic. The propoxy to tetradecyloxy homologues exhibits smectognic amd nematogenic behavior, while the hexadecyloxy homologue shows only nematogenic behavior. An odd-even effect is observed for the smectic–nematic and the nematic–isotropic transition curve in the phase diagram. Analytical data support the structure of molecules. The textures of the nematic mesophase are threaded or Schlieren, and that of smectic mesophase are of type-A. The transition temperatures of homologues and other mesomorphic properties are determined using optical polarizing microscopy. The smectic and nematic thermal stabilities are 138.0°C and 163.8°C respectively. The novel series is predominantly nematogenic and partly smectogenic with middle-ordered melting type. The nematic and smectic phase ranges vary between 16°C and 38°C and 6°C and 22°C respectively. The mesogenic properties of the novel series are compared with other structurally similar homologous series.

A Novel Homologous Series of Thermotropic Mesogens of Ethylene Derivatives: α-4-[4′-n-Alkoxy Benzoyloxy] Phenyl β-4″Methoxy Benzoyl Ethylenes

A novel homologous series consists of 12 compounds. The shorter chain homologues do not show liquid crystal phases, but from six carbons onwards, the nematic phase is exhibited enantiotropically, with some members also showing a smectic phase. The phase behavior of the transition curves of the series shows a usual trend. The texture of the nematic phase is the threaded or Schlieren type and that of smectic phase is a smectic A. An odd–even effect is observed for smectic–nematic and nematic–isotropic transition curves. Analytical data confirm the molecular structure. The transition temperatures were determined by an optical polarizing microscopy. The mesogenic properties of the novel series are compared with a structurally similar homologous series. The average smectic–nematic and nematic–isotropic thermal stabilities are 133.4°C and 159.8°C, respectively, with a mesogenic temperature range of 10°C to 62°C.

Synthesis and Study of Liquid Crystal Properties of Novel Homologous Series: α-4-[-4′-n-Alkoxy benzoyloxy] Phenyl β-4″-Nitro benzoyl Ethylenes

The synthesis and mesomorphic properties of a novel homologous series entitled α-4-[-4′-n-Alkoxy benzoyloxy] phenyl β-4″-nitro benzoyl ethylenes are reported. All the 11 members of the series except the methoxy and ethoxy derivatives are mesogenic. The propyloxy to pentyloxy and the hexadecyloxy homologues are only enantiotropically nematogenic and the rest of the mesogenic homologues are enantiotropically smectogenic in addition to nematogenic in character. A phase diagram shows the phase behavior through transition curves is of a normal type. An odd–even effect is observed for the nematic-isotropic transition curve. Analytical and spectral data support the molecular structure of the materials. Transition temperatures and other liquid crystal (LC) properties including average thermal stabilities for smectic and nematic were determined by optical polarizing microscopy. Average thermal stability for smectic and nematic are 125.6°C and 154.6°C, respectively. Smectogenic and nematogenic phase ranges vary between 19°C to 35°C and 14°C to 50°C, respectively. The LC properties of the novel series are compared with two other structurally similar homologous series. The textures of the nematic phase are threaded or schlieren type and those of the smectic phase is of the type A or C.

Synthesis and Liquid Crystal Properties of Novel Ethylene Derivatives: α-3-[-4′-n-Alkoxy Cinnamoyloxy] phenyl β-4′′-methoxy Benzoyl Ethylenes

Eleven members of a novel homologous series of α-3-[-4′-n-alkoxy cinnamoyloxy] phenyl β-4′′-methoxy benzoyl ethylenes were synthesized. The methyloxy, ethyloxy, butyloxy, and hexadecyloxy homologues are nonmesomorphic, while all the other homologues are mesomorphic. The mesomorphic homologues are enantiotropically smectogenic in combination with nematogenic character, except for the propyloxy homologue, which shows only nematogenic character. A phase diagram of the series shows the expected mesomorphic behavior. Transition temperatures of this series are observed through an optical polarizing microscope equipped with a heating stage. An odd–even effect is observed for nematic–isotropic transition curve. Analytical data supports the structures of the molecules. Mesomorphic temperature range varies from 23°C to 51°C. Liquid crystal properties of this series are compared with a structurally similar homologous series. The smectic and nematic thermal stability of the series are 138.8°C and 165.7°C, respectively. The nematic phase shows a threaded or schlieren texture, and the smectic phase is a smectic A phase.

Synthesis and Study of a Novel Azoester Mesogenic Homologous Series: 4-[4′-n-Alkoxy Benzoyloxy]-Naphthylazo-4″-Acetyl Benzenes

The synthesis and mesomorphic properties of a novel azoester homologous series consisting of 12 members is reported. The methyl to butyl derivatives of the series are non-mesogenic, and the others are enantiotropically smectogenic and/or nematogenic. The nematic mesophase shows a threaded or Schlieren texture and smectic mesophase shows a focal conic fan-shaped texture of the SmA or the SmC. The smectic and nematic thermal stabilities are 137.4° and 166.6° respectively. Analytical data support the molecular structures. The transition temperatures of the homologues are determined using optical polarizing microscopy. An odd–even effect is observed for the nematic-isotropic transition curve and the series is equally smectogenic and nematogenic over a wide temperature range, and the melting points are in the middle order. The mesogenic properties of the present series are compared with a structurally similar homologous series.

Synthesis and Mesomorphism of Novel Liquid Crystalline: 4-(4′-n-Alkoxy Benzoyloxy)-Naphthylazo-4″-Chlorobenzenes

A new azoester homologous series 4-(4′-n-alkoxy benzoyloxy)-naphthylazo-4″-chlorobenzenes is synthesized. Its first and second homologues are nonmesomorphic, while the rest of the homologues are mesomorphic, showing enantiotropic nematic behavior. Smectic character is totally absent. An odd–even effect is observed in the nematic–isotropic transition curve with alternation in transition temperatures. The average thermal stability and liquid crystal behavior for the nematic mesophase are compared with structurally similar homologous series. Analytical data support the structures of the molecules. The texture of the nematic mesophase is of threaded type. Transition temperatures are observed through hot-stage polarizing microscope. Analytical data support the structures.

Determination of Latent Mesogenic Behavior in Nonmesogenic Compounds by Extrapolation Method

A homologous series of 8-(4′-n-alkoxybenzoyloxy) quinolines were synthesized by established methods [5,6]. On evaluation by optical microscopy, none of the homologues were found to exhibit mesogenic behavior even in the monotropic condition. Then, each homologue (B) was mixed with a liquid crystal component (A) and binary systems were studied by optical microscopy. Solid–mesomorphic or isotropic–nematic transition temperatures of binary mixtures were determined and plotted to obtain the phase diagram for transition temperatures versus percentage composition of component (A). The nematic–isotropic transition curve was extrapolated to zero mole percentage of component (A) (100%B) to determine the latent transition temperature (LTT) of each nonmesomorphic homologue. The number of carbon atoms in the n-alkyl chain of each homologue versus LTT is plotted and a phase diagram is obtained. The isotropic–nematic transition curve behaves in a normal manner like a curve behaving for a typical nematogenic homologous series, including odd–even effects in its phase diagram. This method is useful to determine the probable temperature at which a nonmesogenic substance can show mesogenic behavior, provided a suitable condition is applied. Also, it is useful to correct the LTT of a homologue from the mesomorphic–isotropic transition curve.

Homologous Series of Azomesogens: 4-(4′-n-Alkoxy Benzoyloxy)-3-Chloro Phenylazo-2″-Chlorobenzenes

The increasing demand of liquid crystalline materials in various fields of applications has inspired the present investigation. A mesogenic homologous series, 4-(4′-n-alkoxy benzoyloxy)-3-chloro phenylazo-2″-chlorobenzenes, of twelve homologues has been synthesized. All the members of the series are either monotropically or enantiotropically mesogenic except the first member of the series. The nematic mesophase commences from the ethyl derivative and goes to the dodecyl derivative of the series. Tetradecyl and hexadecyl derivatives show a monotropic smectic phase. The nematic mesophase shows a threaded texture, while the smectic mesophase shows a focal-conic-fan-shaped texture. Polymesomorphism is not displayed by any member of the series. The solid-isotropic or solid-mesomorphic transition curve follows a zigzag path of falling and rising tendency as the series is ascended. The usual odd–even effect is observed in the nematic–isotropic transition curve with alternation of transition temperature. Transition temperatures are observed through a polarizing microscope with a heating stage. Analytical data support the structure of the molecules. The average thermal stability and mesomorphic properties of the series are compared with structurally similar other homologous series. Group efficiency order for the smectic and the nematic phases is suggested.

Synthesis and Mesomorphism of Novel Liquid Crystalline: p-(p′-n-Alkoxy Benzoyloxy) Methyl Cinnamates

A new homologous series p-(p′-n-alkoxy benzoyloxy) methyl cinnamates is synthesized with a view to understand and establish the relation between mesogenic properties and structure of molecules. Ethyl to octyl, decyl, dodecyl, tetradecyl, and hexadecyl homolgues are enantiotropically nematogenic, while the methyl homologue is nonmesogenic. None of the homologues exhibit a smectogenic mesophase. An odd–even effect is observed in the nematic–isotropic transition curve. The average thermal stability is 105.0°C and the nematogenic mesophase ranges from 11.0°C to 54.0°C. Thus, the series is of a middle ordered melting type with moderate nematogenic range. Analytical data confirm the structure of the compounds, and the mesomorphism was identified by optical microscopy. The mesogenic properties are compared with structurally similar compounds.

Study of azo ester mesogenic homologous series 2-(4'-n-alkoxy benzoyloxy)- naphthyl-1-azo-4" -methyl benzenes

Mesogenic homologous series: 2-(4'-n-alkoxy benzoyloxy)-naphthyl-1-azo-4-methyl benzenes is synthesized to understand the effects of structural variation on mesogenic characteristics. All the members of the homologous series exhibit enantiotropic nematic mesophase with threaded type of textures. Smectic mesophase does not occur in any homologue of the series even in the monotropic condition. Well-known odd-even effect is observed in the nematic isotropic transition curve. Thermal stabilities and liquid crystalline properties are compared with other structurally identical homologous series. Melting and transition temperatures are determined by hot stage polarizing microscope. Analytical data support the structures of molecules.

Synthesis and mesomorphic properties of azoester mesogens 4-( 4' -n-alkoxy benzoyloxy)-2-methyl phenylazo-4"-methoxy benzenes

A new homologous series of azomesogens, 4-(4'-n-alkoxy benzoyloxy)-2-methyl phenylazo-4-methoxy benzenes is synthesized. Mesomorphism commences from the very first homologue of the series and continues upto tetradecyl derivative. Last hexadecyl derivative is nonmesomorphic. All mesomorphic homologues are enantiotropic nematic. Thus, present homologous series is purely nematogenic. The usual odd-even effect is observed in nematic-isotropic transition curve. Transition curve behaves in a normal manner. The average thermal stability and mesomorphic characteristics are compared with structurally similar homologous series. Series is of middle ordered melting type without display of smectic character even in the last member of the series.

Synthesis and study of new mesogenic homologous series 4-(4'-n-Alkoxy benzoyloxy )-napthylazo-4" -acetyl benzenes

A new homologous series of liquid crystals viz. 4-(4'-n-alkoxy benzoyloxy)-napthylazo-4-acetylbenzenes comprising eleven mesogens have been synthesized. The first four members of the series are non-mesogenic while nematic mesophase commences from fifth member of the series. Polymesomorphism occurs in eighth, tenth and twelfth member of the series. Only smectic mesophase occurs in fourteenth and sixteenth member of the series. The usual odd-even effect is observed in nematic-isotropic transition curve. The smectic-isotropic transition curve rises and falls smoothly as the series is ascended in usual manner. The mesomorphic range is wide. The thermal stability and mesomorphic characteristic are compared with structurally similar homologous series. Analytical data support the structure of molecules. It is middle ordered melting type with threaded texture of nematic phase and focal conic fan shaped texture of smectic mesophase.

Synthesis and study of new mesogenic homologous series : 4-( 4'-n-alkoxybenzoyloxy )-3-methylphenylazo-4"-bromobenzenes

A new homologous series of liquid crystals viz. 4-(4'-n-alkoxybenzoyloxy)-3-methylphenylazo-4-bromobenzene comprising of twelve mesogens have been synthesized. It is a high melting series of mesogens. The nematic type mesophase commences from the very first member of the series. Smectic and nematic mesophases are exhibited by tenth homologue. Dodecyl, tetradecyl and hexadecyl derivatives are purely smectogenic. Nematic mesophase shows threaded texture while smectic mesophase shows focal conic fan shaped texture. The usual odd-even effect is observed in nematic-isotropic transition curve. The smectic-isotropic transition curve rises gradually and falls smoothly at the hexadecyl homologue. The mesomorphic range is wide. The thermal stability and mesomorphic characteristics are compared with structurally similar homologous series.

Synthesis of new mesogens: 4(4′-n-alkoxy benzoyloxy)-phenyl-azo-4″-methyl benzenes

A homologous series with carboxy (-COO-) and azo (-N=N-), as central groups have been synthesised by treating 4-(4′-n-alkoxy benzoyl) chloride with 4-hydroxy phenylazo-4′-methyl benzenes. All the homologues of the series are mesomorphic in nature. The first eight members of the series are nematogenic and the remaining members exhibit smectic and nematic character with high melting behaviour and wide mesomorphic range. The usual odd-even effect does not predominantly appear in nematic isotropic transition curves but it appears to some extent in the first four homologues. Thermal stabilities are comparable with structurally similar known series.