Thermal and dielectric studies of self-assembly systems formed by hydroquinone and alkyloxy benzoic acids

Self-assembly systems formed by hydroquinone and alkyloxy benzoic acids are isolated and characterized. Hydroquinone formed double hydrogen bonds with p-n-alkyloxy benzoic acids. Various hydrogen bonded complexes have been synthesized with hydroquinone and pentyloxy to dodecyloxy benzoic acid, respectively. FTIR studies confirm the hydrogen bond formation in the complex. Polarizing Optical Microscopic (POM) studies revealed the textural information while the transition and enthalpy values are experimentally deduced from Differential Scanning Calorimetry (DSC) studies. Phase diagram has been constructed from the POM and DSC data. The members of the present homologous complexes are characterized by POM, DSC, optical tilt angle and dielectric studies. Odd-even effect has been evinced in enthalpy values and transition temperatures corresponding to the isotropic to nematic phase transition. Optical tilt angle in Smectic C phase data has been fitted to a power law and it has been observed that the temperature variation of the tilt angle follows Mean Field theory prediction. Results of Fourier Transform Infrared Spectra (FTIR), POM, DSC, tilt angle and dielectric studies are discussed.     

Design, synthesis and characterization of a linear hydrogen bonded homologous series

A linear hydrogen bonded liquid crystalline homologous series has been synthesized and characterized. Hydrogen bond is formed between p-n-dodecyloxy benzoic acid and various p-n-alkyl benzoic acids whose alkyl chain vary from octyl to ethyl. Synthesized complexes are characterized by FTIR, ¹H NMR and ¹³C NMR studies for inferring the formation of hydrogen bonds. Polarizing Optical Microscopy (POM) and DSC studies reveal various mesophases and their corresponding transition temperatures along with respective enthalpy values. All the seven synthesized complexes exhibit rich liquid crystalline mesomorphism. A new phase namely smectic X has been observed in five of the complexes with a narrow thermal range. This phase has been characterized by optical textural, DSC, tilt angle and helicoidal pitch studies. Smectic X is sandwiched between traditional smectic C and re-entrant smectic C (designated as C_R) phases. Homeotropic transition in nematic phase is observed in all the mesogens and thus these materials can be used as thermally controlled optical shutters. Tilt angle in smectic C, smectic X and smectic C_R phases have been experimentally elucidated for all the mesogens.     

Systematic studies on eight homologous series of supramolecular hydrogen bonded liquid crystals

Design, synthesis and characterization of hydrogen bonded liquid crystals (HBLC) formed by alkyloxy benzoic acids (referred as nOBA?:?ABOm) are discussed. Eight such homologous series of HBLC are synthesized with varying the carbon chain length from 5 to 12 referred as nOBA?:?ABOm. These complexes are characterized by polarizing optical microscope (POM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) studies. Phase diagrams of the individual series have been constructed from the data of POM and DSC respectively. The effect of the chain length on the phase formation is discussed. Thermodynamic evaluation of nOBA?:?ABOm homologues series has been carried out. It is observed that the entire eight homologous series possess thermodynamically equilibrium energy states. The results of phase variance influence of chain length, phase transitions and corresponding enthalpy values are discussed.     

A study on polymorphism of hydrogen-bonded thermotropic liquid crystals

A novel mesogenic homologous series comprising of eight hydrogen-bonded liquid crystalline complexes are isolated and analyzed by forming a hydrogen bond between p-n alkyloxy benzoic acids (where n represent alkyloxy carbon number which varies from 5 to 12) and mesaconic acid, respectively. Eight synthesized complexes are subjected to Fourier transform infra-red spectroscopy, polarizing optical microscopy and differential scanning calorimetry studies to meet the basic characterization. The variation of optical tilt angle with respect to temperature in various conventional and smectic X phases are investigated and analyzed. A phase diagram is constructed to elucidate the mesogenic behavior of novel liquid crystalline series. The Cox ratio that reveals the order of various mesophases and the stability factor, to invoke the thermal stability of mesophases, is studied under the results of DSC thermogram.     

Optical modulation in nematic phase of halogen substituted hydrogen bonded liquid crystals

A series of halogen-substituted hydrogen-bonded liquid crystalline complexes have been designed and synthesised. A successful attempt has been made to form complementary hydrogen bonding between the dodecyloxy benzoic acid (12BAO) and halogen-substituted benzoic acids and the physical properties exhibited by the individual complexes are studied. The complexes obtained are analysed by polarising optical microscope (POM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and dielectric studies. The formation of complementary hydrogen bond is confirmed through FTIR spectra. An interesting feature of this series is the observation of a field-induced transition (FiT) in nematic phase. Another interesting phenomenon is the observation of a new smectic X phase (worm-like texture) in all the synthesised complexes. Dielectric relaxation studies in the smectic C phase of these hydrogen bonded complexes along with the Arrhenius and the Cole–Cole plots are discussed. Optical tilt angle in smectic C phase and the corresponding fitted data analysis concur with the Mean field theory prediction.     

Optical shuttering action in nematic phase of SMHBLC: observation of a ribbon-like texture

In this study, complexes belonging to supramolecular hydrogen-bonded liquid crystal homologous series are synthesized and characterized. Hydrogen bond is formed between p-n-alkyloxy benzoic acids (nBAO, where n?=?5–11) and chlorobenzoic acid (ClBAO), respectively. The isolated homologues are characterized by various techniques such as polarizing optical microscopic (POM) studies, differential scanning calorimetry (DSC), and Fourier transform–infrared spectroscopy. Based on the POM and DSC studies, the phase diagram has been constructed and discussed. A new smectic ordering, labeled as smectic R, has been characterized, which exhibits a ribbon-like texture. This phase is observed in the complexes pertaining to the higher homologous series. Tilt angle in this phase has been experimentally deduced and the results are fitted to the power law which concurs with the mean-field theory predicted value. Optical shuttering action in the homologue has been detected in the nematic phase and the results are also discussed.     

Design,synthesis and characterization of a linear hydrogen bonded homologous series exhibiting reentrant smectic C ordering

Design, synthesis and characterization of seven linear hydrogen bonded liquid crystal complexes derived from mesogenic p–n-decyloxy benzoic acid and p–n-alkyl benzoic acids designated as 10OØn (where n varied from ethyl to octyl) are reported. FTIR studies confirm the hydrogen bond formation in all these complexes. The phase transition temperatures and their corresponding enthalpy values are experimentally deduced from Differential Scanning Calorimetry (DSC) studies. POM and DSC data are further utilized for the construction of 10OØn phase diagram. Two Odd–even effects have been evinced, one in enthalpy values and the other in corresponding transition temperatures across the isotropic to nematic phase transition. An interesting result is the observation of re-entrant smectic ordering, designated as smectic C_R in three higher ordered mesogens. A new smectic ordering, smectic X, has been observed which is sandwiched between traditional smectic C and re-entrant smectic C_R. Magnitudes of optical tilt angle in smectic C, smectic X and smectic C_R are experimentally found to attain saturation with decrement of temperature in the corresponding phase. The occurrence of smectic X and smectic C_R are discussed with relation to the molecular chemical structure. The optical filtering action in smectic C and re-entrant smectic C_R phases have been analyzed.     

Thermal and optical characterization of a novel series of supramolecular liquid crystals

Supramolecular hydrogen bonded liquid crystal (SMHBLC) homologous series is synthesized and characterized. Hydrogen bond is formed between p-n-alkyloxy benzoic acids (nOBA, where n=7 to 12) and Iodo substituted benzoic acid (I_mBA) respectively. The isolated homologs are characterized by various techniques like Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC), ¹H Nuclear Magnetic Resonance Spectroscopy (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). From the POM and DSC studies phase diagram has been constructed and discussed. A new smectic ordering, labeled as smectic R, has been characterized which exhibits a ribbon like texture. This phase is observed in a complex pertaining to the undecyloxy carbon number. Tilt angle in smectic R phase and in traditional smectic C of all the complexes have been experimentally deduced and the results are fitted and so obtained β value concurrences with the Mean field theory predicted value.     

Study and characterization of the smectic X* phase in binary mixtures of thermotropic double hydrogen bonded ferroelectric liquid crystals

Thermotropic double hydrogen bonded ferroelectric liquid crystals (DHBFLCs) composed of N-carbamyl-L-glutamic acid (CGA) and p-n-alkyloxy benzoic acids (BAO) have been investigated. Variation in the molar proportion of X and Y (where X = CGA + 5BAO and Y = CGA + 6BAO, CGA + 7BAO, and CGA + 8BAO) composed of three series yielded 27 binary mixtures. Optical and thermal properties of these mixtures are meticulously studied in the present article. A novel smectic ordering, namely smectic X*, is observed in all the three series. The aim of the investigation is to obtain an abundance occurrence of smectic X* and hence the proportions of the binary mixtures are so chosen that the preamble task is accomplished. Phase diagrams of three series are constructed from the data obtained from polarizing optical microscope (POM) and differential scanning calorimetry (DSC) studies. Odd–even effect, order of the phase transition, thermal stability factor, thermal equilibrium, and optical tilt angle are also premeditated.     

Thermally controlled optical shutter in an inter-molecular hydrogen bonded liquid crystal

Novel homologs series of supra-molecular liquid crystals have been isolated. Hydrogen bond is formed between mandelic acid (MD) and various homologs of p-n-alkyloxy benzoic acids (nOBA) and has been confirmed by FTIR studies. Optical polarizing microscopic observations show that all these materials exhibit rich liquid crystallinity with various mesophases. Phase transition temperatures and enthalpy values are experimentally evaluated by DSC studies and the phase diagram of homologous series has been constructed. An interesting feature is the observation of thermally controlled reversible optical shuttering action in one of the homolog, wherein with the increment of temperature the homeotropic texture changes to homogenous texture of smectic F. Thus, this optical shuttering phenomenon is reversible. Optical tilt angle data of two homologs have been fitted to power law equation and it is found that the mean field theory prediction is valid. The light intensity profile in homeotropic region of smectic F in one complex has been experimentally analyzed and a steep sudden decrement of the intensity of light manifesting the distortion of the molecular alignment is experimentally found.     

Thermal and Optical Properties of Some Hydrogen-Bonded Liquid Crystal Mixtures

Phase transition properties of the mixtures of hydrogen-bonded nematic liquid crystals (HBLC) 4-hexylbenzoic acid (6BA), 4-(octyloxy)benzoic acid (8OBA), and 4-(decyloxy)benzoic acid (10OBA) have been investigated by means of differential scanning calorimetry (DSC) and polarize optic microscope (POM). The DSC and POM results clearly indicate the existence of smectic and nematic phase transitions in binary mixtures. The phase transition temperature values of 6BA/10OBA mixtures have clearly increased with increasing heating rate. The activation energies were calculated for the phase transitions of 6BA/10OBA liquid crystal (LC) mixture. The optical transmittance of these mixed hydrogen-bonded nematic liquid crystals was investigated in terms of temperature variations through electrooptic methods. The electrooptic experiments indicate that, while low in the nematic phase, the optical transmittance is very high at the nematic-isotropic phase transition. The transmitted light intensity values of 6BA/8OBA mixture are somewhat higher than those of other binary mixtures, 6BA/10OBA and 8OBA/10OBA, a result associated with the different alkyloxy chain lengths.     

Induced Smectic X Phase Through Intermolecular Hydrogen-Bonded Liquid Crystals Formed Between Citric Acid and <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis>-(Octyloxy)Benzoic Acid

Hydrogen-bonded liquid crystal (HBLC) is synthesized from citric acid (CA) and 4-(octyloxy)benzoic acid (8OBA) with different mole ratios. Fourier transform infrared spectroscopy (FT-IR) confirms the presence of hydrogen bond between CA and 8OBA. Nuclear magnetic resonance (NMR) spectroscopic studies validate the intermolecular complementary, cyclic type of hydrogen bond, and molecular environment in the designed HBLC complex. Powder X-ray diffraction analysis reveals the monoclinic nature of liquid crystal complex in solid phase. Liquid crystal parameters such as phase transition temperature and enthalpy values for the corresponding mesogenic phases are investigated using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). It is observed that the change in chain length and steric hindrance while increasing the mole ratio in HBLC complex induces a new smectic X (Sm X) along with higher-order smectic G (Sm G) phases by quenching of smectic C (Sm C). From the experimental observations, induced Sm X phase has been identified as a finger print texture. Also, Sm G is a multi-colored mosaic texture in 1:1, 1:2, and 1:3 mol ratios. The optical tilt angle, thermal stability factor, and enhanced thermal span width of CA + 8OBA complex are discussed.     

Study of optical shuttering action in supramolecular hydrogen bonded nematogens

Supramolecular hydrogen bonded mesogens are formed between p-n-undecyloxy benzoic acid (11BAO) and p-n-alkyl benzoic acids (nBA, where n?=?2–8). The isolated mesogens are characterized by distinct techniques in order to appreciate the optical, thermal, electrical, and dielectric properties. The optical tilt angle measurement is studied for all the members of this homologous series and is found to concur with the mean field theory predicted value. An interesting factor to notice is the observation of optical shuttering action in nematic phase of the entire series which privilege these materials to be used as light modulators. Dielectric measurements were carried out and the dispersion curves were discussed in terms of relaxation frequency and activation energies.     

Design and characterization of hydrogen bonded ferroelectric liquid crystals: A study of light modulation in nematic and smectic orderings

A novel series of hydrogen bonded ferroelectric liquid crystals (HBFLC) have been isolated. Phase transition temperatures obtained by differential scanning calorimetry (DSC) and textural observations elicited by polarizing optical microscope (POM) studies are discussed. Phase diagram is constructed from the above data. Salient feature of the present work is observation of a light modulation due to field induced transitions (FiT) in nematic and smectic C* phases. Tilt angle measurements in various FiT of smectic C* phase are discussed. One of the mesogens in nematic phase behaves like an optical modulator; helical pitch measurements support the above observation.     

Double hydrogen bonded ferroelectric liquid crystals: A study of field induced transition (FiT)

A novel series of chiral hydrogen bonded liquid crystals have been isolated. Hydrogen bond was formed between chiral nonmesogen ingredient levo tartaric acid and mesogenic p-n-alkoxybenzoic acids. Phase diagram was constructed from the transition temperatures obtained by DSC and polarizing optical microscopic (POM) studies. Thermal and electrical properties exhibited by three complexes namely LTA+8BA, LTA+7BA and LTA+5BA were discussed. Salient feature of the present work was the observation of a reentrant smectic ordering in LTA+8BA complex designated as C_r¹ phase. This reentrant phenomenon was confirmed by DSC thermograms, optical textures of POM and temperature variation of capacitance and dielectric loss studies. Tilt angle was measured in smectic C¹ and reentrant smectic C_r¹ phases. Another interesting feature of the present investigation was the observation of a field induced transition (FiT) in the LTA+nBA homologous series. Three threshold field values were noticed which give rise to two new phases (E₁ and E₂) induced by electric field and on further enhancement of the applied field the mesogen behaves like an optical shutter. FiT is reversible in the sense that when applied field is removed the original texture was restored.     

氢键诱导液晶的DSC和变温红外光谱研究

制备了两个分别基于4,4’-联吡啶(BPy)和丙基反式环己基苯甲酸(PCBA)以及BPy和丙基反式双环己基甲酸(PCCA)的氢键液晶复合物(PCBA-BPy和PCCA-BPy),结合使用偏光显微镜(POM),用差示扫描量热(DSC)和变温傅里叶变换红外光谱对它们的中间相性能和分子间氢键的热稳定性进行了表征。结果表明,这两个氢键复合物都具有由于分子间氢键作用而导致的近晶相,但它们中存在的氢键作用却不相同,在PCBA-BPy中,温度变化时,发生氢键结合的羰基的吸收峰的位置仅在发生晶型转变时有突变,而在PCCA-BPy中,温度变化时,其羰基的吸收峰的位置则基本不发生突变。另外,当温度高于它们的清亮点时,这两个氢键液晶复合物的分子间氢键都发生部分分解。     

Experimental and computational studies on induced thermochromic effect and re-entrant smectic phase in linear double hydrogen-bonded binary liquid crystal mixtures

Design and synthesis of the hydrogen-bonded liquid crystalline (HBLC) mixtures are accomplished from diglycolic acid and 4-n-alkoxybenzoic acid (n?=?9–12). Spectroscopic characterization such as UV–Vis, FT-IR, and DSC has supported the presence of molecular geometry of HBLC mixtures. Thermochromic effect is analyzed for the polarizing filter applications. Induced new phases (Smectic X and Smectic Cr) and their first-order transitions are confirmed through DSC along with its corresponding textures using polarizing optical microscope. Furthermore, the induced re-entrant smectic ordering due to the lone pair to π* transition is reported using density functional theory (DFT) studies. Dipole moment studies (DFT) clearly give a strong evidence of the existence of nematic and smectic phases due to the monopole–dipole interaction in the present HBLC mixtures. Band gap of the present HBLCs is 5.175?eV, which is calculated by the HOMO–LUMO analysis and is validated using experimental observations. Liquid crystal parameters such as transition temperature, enthalpy values, stability factor and tilt angles are reported.     

Experimental indication of macroscopic polarization parallel to the tilt plane in free-standing films of ferroelectric liquid crystals 8SI* and DOBAMBC

Optical reflectivity and x-ray studies have been conducted on free-standing films and bulk samples of ferroelectric liquid crystals near the smectic-A-smectic-C ^* transition. A tilt plane rotation with respect to the direction of an applied electric field is found in the ferroelectric films above the bulk transition temperature. Whereas the macroscopic polarization is perpendicular to the tilt plane at low temperature, it is parallel to the tilt plane at elevated temperature. The temperature dependence of the average tilt angle is measured. Zh. éksp. Teor. Fiz. 116, 1329–1334 (October 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Synthesis/structural and mesomorphic properties of substituted hydrazide based calamitic molecules

A set of rod-shaped molecules with central hydrazide moiety has been synthesized and characterized using standard spectroscopic techniques. The thermal behaviors of the final compounds were established by the combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and high-temperature powder X-ray method (XRD). The structure and conformation of the molecules were achieved by FTIR, ¹H NMR, ¹³C NMR spectroscopy and DFT calculations. It is found that two compounds are non-liquid crystalline and two compounds are liquid crystalline (LC). The structure property correlations with alkyl chain, connecting position, hydrogen bonding and without hydrogen bonding were established. The studies envisaged that LC properties are induced due to hydrogen bonding and elongation of the molecular length.