Hydrogen-bonded Liquid Crystals Research Articles

Homeotropic Alignment and Selective Adsorption of Nanoporous Polymer Film Polymerized from Hydrogen-bonded Liquid Crystal

Nanoporous polymer film with a hexagonal columnar (Colh) structure was fabricated by templated hydrogen-bonding discotic liquid crystals containing methacrylate functional group. The supramolecular hydrogen-bonded complex T3Ph-L is composed of a 1,3,5-tris(1H-benzo[d]imidazol-2-yl)benzene (T3Ph) core molecule as the hydrogen-bonding acceptor and 3,4,5-tris((11-(methacryloyloxy)undecyl)oxy)benzoic acid (L) peripheral molecules as donors. And the Colh structure is always retained after self-assembly, photo-crosslinking, and removal of the template T3Ph. The nanoporous polymer film can retain the Colh phase even under the dry condition, which indicates more possibilities for practical applications. After chemical modification of the inner wall of the nanopores, the nanoporous polymer film with pores of about 1 nm selectively adsorbs ionic dyes, and the adsorption process is spontaneous and exothermic in nature. Homeotropic alignment can be obtained when the blend complex was sandwiched between two modified glasses after annealing by slow cooling, which shows that the nanoporous polymer film has potential in applications such as nanofiltration.

Nanoporous Supramolecular Liquid Crystal Polymeric Material for Specific and Selective Uptake of Melamine

Nanoporous materials derived from hydrogen-bonded supramolecular liquid crystal complexes present a promising and prevalent perspective in selective adsorption, water desalination, ion conductivity...

Computation of liquid crystal display device parameters through image analysis in supramolecule MA:nOBA

ABSTRACT In this article, the usage of the hydrogen-bonded liquid crystal complexes dicarboxylic acid (Malonic acid MA): p-n alkoxy benzoic acid (nOBA): abbreviated as MA:nOBA (where n = 10,11,12) towards the applications of liquid crystal display devices is investigated. This involves the measurement of physical parameters of displays: Luminance, Luminance uniformity, Luminance coefficient, Contrast ratio, Transmission of Display, Figure of Merit (Performance of the material) and Chromaticity. Liquid crystal texture analysis on the MATLAB platform is employed for this investigation. Display device parameters computed from the grey level intensities of the liquid crystal textures as a function of temperature and wavelength gives the information about application suitability of the material. Obtained results shows that, hydrogen-bonded liquid crystal complex MA:10OBA has high values of display parameters and make them as is a suitable material for the fabrication of display devices compared to other studied compounds.

Azobenzene-based supramolecular liquid crystals: The role of core fluorination

The impact of core fluorination on the phase behaviour of supramolecular hydrogen-bonded liquid crystals (HBLCs) is investigated in detail. Therefore, different types of HBLCs were synthesized using two benzoic acid derivatives as proton donors, namely, 4-octyloxybenzoic acid and octylbenzoic acid. The two acids were combined through intermolecular hydrogen-bonding with alkoxyazopyridine derivatives as proton acceptors. Three different types of azopyridines were used either without fluorine substitution or with one lateral fluorine substituent at different positions. The study proved the importance of using core fluorination as a significant tool to modify the liquid crystalline behaviour of HBLCs, where all azopyridines are non-mesomorphic and almost all their complexes exhibit enantiotropic mesophases. The formation of the hydrogen bond between the complementary components was confirmed using FTIR and 1H NMR spectroscopy, while the liquid crystalline self-assembly of the HBLCs was investigated in detail using polarized light microscope (PLM) and differential scanning calorimetry (DSC). Depending on the type of the terminal chain on the benzoic acid derivative and on the position of the lateral fluorine substituent different types of mesophases including nematic (N), smectic A (SmA) and smectic C (SmC) phases were observed. Finally, under UV light illumination all the prepared HBLCs show cis-trans photoisomerization resulting in tuning the liquid crystalline phases, which is of importance for industrial applications.

Observation of Induced Luminescence and Thermochromism in Achiral Hydrogen Bonded Liquid Crystal Complexes

Abstract A novel hydrogen bonded liquid crystal (HBLC) complexes are obtained from the non-mesogenic (benzylmalonic acid) and mesogenic (p-n-alkyloxybenzoic acid, where n = 6, 7 and 8) compound via intermolecular hydrogen bonds (H-bond). H-bonds are experimentally confirmed by the Fourier transform infrared spectroscopic (FT-IR) studies and the same is validated using density functional theory (DFT). Induced thermochromism is observed by the polarizing optical microscope (POM) and its possible applications are reported. Phase transition temperature and their analogous enthalpy values, stability factor and span width are determined by the differential scanning calorimetry (DSC) studies. Band gap energy is calculated using UV-visible and photoluminescence spectrum. Hyper conjugative stabilization energy and atomic charge distribution is studied by the natural bond orbital (NBO) studies. Mulliken analysis clearly reveals the intermolecular interaction and steric effect of the HBLC complexes. An interesting phenomenon is that the observation of luminescence and thermochromism in the highly fluidity nematic phase. This peculiar behavior is attributed due to the intermolecular H-bonding interaction between the BMA and nOBA compounds and the effect of rotatory motion of the molecules in nematic phase. Luminescence increases when the spacer moiety decreases in the present complexes is also reported. In nematic phase, the molecules are in different degrees of the excited state which is correlated with the hyper conjugative energy through NBO studies.

Dielectric and electro-optic properties of cybotactic nematic phase in hydrogen-bonded liquid crystals

Abstract The new compounds 4-decyloxy-2-fluorobenzoic acid and 4-dodecyloxy-2-fluorobenzoic acid display hydrogen-bonded liquid crystals (HBLC) of smectic and nematic phases. Their phase behavior established using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) consistently occurs as the sequence upon cooling: Isotropic liquid – Nematic – SmC – crystalline solid. The dielectric study in the nematic phase shows a single relaxation process at low frequency characteristic of a cybotactic nematic phase. The optical properties of the nematic phase show a decrease of birefringence as alkyl chain length increases in the high-temperature part of the nematic domain, which reveals a decrease of order parameter for longer chains.

Spectroscopic, dielectric and nonlinear current–voltage characterization of a hydrogen-bonded liquid crystalline compound influenced via graphitic nanoflakes: An equilibrium between the experimental and theoretical studies

Herein, we investigate a hydrogen-bonded liquid crystal compound, namely 4-(Heptyloxy) benzoic acid (7OBA), and its composites by dispersing Graphene and reduced graphene oxide (rGO) flakes into an optimized concentration. The pristine 7OBA and its composites are characterized by different instrumental techniques like polarized optical microscopy, differential scanning calorimetry (DSC), dielectric, UV-visible, and Fourier-transform infrared (FTIR) spectroscopy. DSC thermograms of the 7OBA composites evince the down-shift in the smectic C−nematic and nematic−isotropic phase transition temperatures. The polarized optical micrographs (POMs) of composites reveal the homogeneous distribution of graphene and rGO flakes in the 7OBA compound without any aggregation. The π-π* transitions in phenyl ring of 7OBA compound and π-π* transitions in CC bonds of graphitic materials are superimposed to each other providing an enhanced UV absorbance nearly at 255 nm for the composites. The presence of graphene and rGO enhances the tan δ and electrical conductivity of the composites, whereas dielectric anisotropy, Δϵ, reduces as a function of temperature in comparison to the pristine 7OBA compound. The sign inversion of Δϵ has been observed for the 7OBA/rGO composite which has been explained via dipole−dipole interactions. The I−V behavior of the pristine 7OBA compound yields the ohmic I−V curve with a non-zero current at 0 V attributing to the pseudocapacitance effect, whereas, after the dispersion of graphene and rGO flakes, nonlinear diode like I−V curves having a hundred times larger conduction current were obtained. Furthermore, the molecular interactions have been analyzed by the FTIR which confirms the formation of hydrogen bonding in the 7OBA/rGO composite. At last, these experimental findings are compared with the simulated results by DFT. The experimental and theoretical simulations are commensurable to each other. The studied composites have shown their vital applications in nonlinear electronics.

Analysis of linear hydrogen bonded liquid crystal binary mixtures formed between palmitic acid and p-n- alkyloxy benzoic acids

Liquid Crystalline mesogens comprising of Palmitic acid (PA) and p-n- alkyloxy benzoic acids (nBAO) are formed exhibiting rich phase polymorphism. Enhancement in the thermal range of the desired mesophase and the corresponding optical, thermal properties can be fine-tuned by preparing binary mixtures. Binary mixtures of PA + 8BAO: PA + 9BAO and PA + 8BAO: PA + 10BAO have been prepared by varying the molar ratio. Nematic and smectic G mesophases are observed. From Polarizing Optical Microscopy and Differential Scanning Calorimetry studies, the phase diagram of these binary mixtures is constructed. Specific heat, thermal stability factor, thermal equilibrium and order of phase transition are also elucidated.

IMAGE ANALYSIS STUDIES IN RE-ENTRANT SMC PHASE ON HYDROGEN BONDED LIQUID CRYSTAL SA:10OBA

Ponte Academic JournalFeb 2020, Volume 76, Issue 2 IMAGE ANALYSIS STUDIES IN RE-ENTRANT SMC PHASE ON HYDROGEN BONDED LIQUID CRYSTAL SA:10OBAAuthor(s): K. Lakshmi Sarada ,A.V.N.Ashok Kumar, K. Mallika, S. Sreehari SastryJ. Ponte - Feb 2020 - Volume 76 - Issue 2 doi: 10.21506/j.ponte.2020.2.15 Abstract:Image analysis using MATLAB software for characterization of liquid crystalline (LC) phases and phase transition temperatures in hydrogen bonded liquid crystal dimer viz., Succinic acid (SA) (for n=10) with molecular formula nOBA:SA:nOBA is described. SmC, SmX, SmCRE and SmG phase variance is observed by optical textures through Polarized Optical Microscope and which are confirmed by Differential Scanning Calorimetry experimental technique. Influence of flexible end chain length and length of spacer moiety on the LC polymorphism is studied and the results are compared with reports on other HBLC dimers with similar type of molecular structure. Statistical parameters of LC textures based on gray scale intensity as a function of temperature are computed and discussed. Download full text:Check if you have access through your login credentials or your institution Username Password

Chiral mesophases of hydrogen-bonded liquid crystals

The induction of chiral mesophase in hydrogen-bonded liquid crystals is investigated.

Photo-switching and -cyclisation of hydrogen bonded liquid crystals based on resveratrol.

A series of hydrogen-bonded liquid crystals based on resveratrol and resveratrone is reported and investigated with respect to their photo-switchability (at 405 nm) and photo-cyclisation (at 300 nm).

Thermal and Optical Characterization of Multiple Hydrogen Bonded Liquid Crystals and Its Application in Display Devices

Novel homologous series of phloroglucinol (PG) and 4-n-alkyloxybenzoic acid (nOBA, n = 4 to 12) hydrogen bonded liquid crystal (HBLC) complex have been designed and synthesized. In the self-assembly process, intermolecular interaction between the molecules produce the multiple HBLCs with various shapes and structure. Existences of multiple hydrogen bonds in the PG+nOBA HBLC complex are confirmed by FT-IR spectroscopic method. Textural changes along with that phase transition temperature are identified by polarizing optical microscope (POM). Due to the polymerization, an induced stabilized smectic phase along with re-entrant disordered phase is noticed in the present PG+nOBA HBLC complex. The thermodynamic properties such as enthalpy values, thermal stability and thermal span width are analyzed by differential scanning calorimetry (DSC). An induced re-entrant phenomenon in the present HBLC complex is due to the dipolar aggregation has been discussed. The band gap energy is calculated by UV–Visible spectrometer (UV–Vis) which gives the clear evidence for the existence of band gap energy value (Eg = 3.5 eV) in the present HBLC complex. The desirable band gap in the present HBLC and its display device application is reported in the present communication. The other liquid crystal parameters (thermal stability, tilt angle, etc.) are also discussed.

Experimental and DFT Studies on Thermochromism Induced Binary HBLC Mixture

Novel linear double hydrogen-bonded liquid crystals (HBLCs) were derived from diglycolic acid (DGA, a non-mesogenic compound) and 4-n-alkoxybenzoic acids (nOBA, n = 7 and 8 mesogenic compounds). Hydrogen bond (H bond) formation and its vibrational stretching frequencies had been calculated by experimental and theoretical IR spectroscopy. The calculated band gap energy (4.96 eV) using a UV-Vis spectrum clearly reveals the coincidence of highest occupied molecular orbital-lowest unoccupied molecular orbital band energy of the present HBLC mixture. Further, X-ray diffraction (XRD) studies at room temperature confirm the monoclinic nature of the HBLC mixture. Mesophases and their transition temperature were studied by a polarized optical microscope (POM) and differential scanning calorimetry (DSC). The order of the phase transition was evaluated by the thermal analysis. Due to the rotary motion of molecules, nematic phase (threaded texture) with thermochromic effect was observed. The induced thermochromism in the present HBLC and its possible color recording applications were discussed. Molecular descriptors (using computational density functional theory (DFT)) of the present mixture indicate the hardness and softness of the HBLC mixture. Natural bond orbital (NBO) studies revealed the O–H…O stabilization energy in the present HBLC mixture. Also, the lone pair (LP)-to-π* transition confirms the existence of intermolecular hydrogen bonding in the HBLC mixture. The calculated band gap energy of the DGA + nOBA HBLC mixture is a more useful parameter to identify suitable hydrogen-bonded liquid crystal material for photonic applications. Mulliken analysis shows clear evidence of the charge distribution in different molecules of the HBLC system.

Spontaneous polarization, tilt angle, hysteresis and low-frequency relaxations in hydrogen bonded chiral liquid crystal dimer: M*SA:9OBA

Influence of low-frequency (2-Hz-10MHz) AC field on LC phases exhibited by chiral hydrogen bonded liquid crystal dimer, viz., M*SA:9OBA is investigated. Phase transition temperatures Tc determined by capacitance C(T) and loss factor TanΔ(T) agree with the earlier report. Induced surface polarization reflected through capacitance C(E) exhibited hysteresis in behavior SmC* phase. Growth of primary order parameter in SmC* phase investigated by tilt angle θ(T) inferred critical field exponent β1. Secondary order parameter investigated as spontaneous polarization Ps in SmC* inferred Mean field exponent β2. Dipole moment (μ) is resolved as longitudinal (μl) and transverse (μt) components. Reorientation of μ to the field analyzed. Relaxation studied at different temperatures in SmC*; SmBcryst and SmG phases inferred a low-frequency (LF fR∼100Hz) and another high frequency (HF fR∼100kHz) reorientation processes. LF relaxation in SmC* phase is influenced by dc bias field to suggest polarization helix formed by coupling of field μt. Threshold field (Vth) for polarization switching estimated from the data of field variation of loss εmax″(E). LF relaxation in SmC* is identified with Goldstone mode (GM) manifested as the suppressed ε″max(E) with field. HF relaxation in SmC* is identified with Soft Mode (SM) by its decreasing trend of fR towards TIC*. Activation energies (Ea) estimated from Arrhenius behavior of fR(T) agree with reports. Field influence on GM manifests through shift of loss ε″max(E) and fR(E). Activation energy Ea is estimated from the shift of fR(E) in terms of equivalent temperature plots. Dispersion, ε″ versus ε′ in LC phases infers a non-Debye distribution of relaxation times. Cole-Cole plots inferred large shift of static permittivity εo. Data of dielectric relaxation parameters, i.e., relaxation frequency fR, relaxation time τR, activation energy Ea, loss maxima ε″max, static permittivity (εo), high frequency permittivity ε∞, dielectric strength Δε and distribution (α) parameter are presented. Dielectric strength analyzed for SM in SmC* phase confirms Ferro-Electric Curie-Weiss behavior.

Fluoro-substitution in hydrogen bonding liquid crystal benzoic acid: dielectric, electro-optic and optical proprieties and inducing polar nematic phase

ABSTRACTDielectric and electro-optic properties have been studied in order to understand the effect of the fluoro-substitution on hydrogen bonded liquid crystal proprieties. The fluoro-substitution alters the characteristics of pure LC structure and changes its physical parameters. In the present paper, variation in physical parameters like dielectric permittivity, response time, elastic constant, rotational viscosity etc. has been explained based on many factors. In addition, the fluorine substitution has lead to the appearance of the polar nematic phase.

Influence of meta-extended rigid-core, complementary hydrogen bonding and flexible chain on polymorphism in Schiff-base liquid crystals: (4)MeOBD(3)AmBA:nOBAs

ABSTRACTSchiff-base complementary hydrogen-bonded liquid crystals (HBLC), viz., (4)MeOBD(3)AmBA:nOBAs with flexible chain length for n = 3,4,5,6,7,8,9,10,11 and 12 are reported. 1H; 13C-NMR and Infra-Red spectroscopy used to confirm the formation of HBLCs. LC phases and transition temperatures (Tc) determined by polarised optical microscopy (POM) and differential scanning calorimetry (DSC). Tc and enthalpy (∆H) determined by DSC also. Odd-Even effect observed at clearing and melting transitions. Influence of Schiff base and Oxygen as bridging atom promote smectic phase abundance. HBLCs exhibit tetra- or penta-phase variance. Maximum (penta) phase variance is exhibited by n = 8 and 12 with long flexible chain. Prevalent abundance of quasi-two-dimensional (2D) LC phases of SmF and SmI is observed. Nematic phase is quenched. Lower (n = 4) and intermediate (n = 6) members exhibited SmBcryst phase. Predominant occurrence of enantiotropic LC phases is noticed. All members exhibited 3D tilted SmG phase. A-C transition exhibited by intermediate homologues (for n = 7, 8, 9 and 10) is found to be either second order or with very small enthalpy. Phase diagram reveals the abundance of multi-critical points with LC phasesinvolving exotic symmetries. Influence of meta-extended rigid core, complementary HB and flexibility is studied for the LC phase abundance with characteristic structural order. POM and DSC results are discussed in the wake of reports in other achiral calamitic LCs.

Thermal and optical characterization of multiple hydrogen bonded liquid crystals derived from mesogenic and non-mesogenic compounds: experimental and theoretical (DFT) studies

A set of new cyclic multiple hydrogen bonded liquid crystals (HBLCs) have been designed and synthesized from citric acid (CA) and 4-dodecyloxybenzoic acid (12OBA). The presence of intermolecular hydrogen bonds (H-bonds) between non-mesogenic and mesogenic compounds has been confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) studies. The hydrogen bonding interactions were explained from natural bond orbital (NBO) analysis using B3LYP/6-311G(d,p) level of theory. Additionally, the Mulliken atomic charges reveal the nature of charge distribution in the HBLC complex. The dynamics of phase transitions and the corresponding stability factor have been evaluated using polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and electrostatic potential (ESP) analysis. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of the CA+12OBA complex is theoretically calculated and experimentally verified. It is found that the variation in the mole ratio in mesogenic with non-mesogenic compound induces the stabilized nematic (N) and smectic X (Sm X) phases. Photocatalytic activity of the CA+12OBA HBLC complex reveals the usage of its optical applications.

Ionic conductivity mediated by hydrogen bonding in liquid crystalline 4-n-alkoxybenzoic acids

We describe the dielectric response of a series of liquid crystalline 4-n-alkoxybenzoic acids, nOBAs, with different alkyl chains, n = 4, 5, 7 and 8, in planarly aligned cells, as potential anhydrous electrolytes for electrochemical cells. All nOBAs display two modes of dielectric relaxations and conductivity. At moderate-high frequencies, f ∼101–104 Hz, the so-called mode 1 involves fast dipole rearrangements leading to direct current, DC, conductivities in the σdc1 ∼ 10−5 S cm−1 range, which are eventually insensitive to bias fields. At lower frequencies, f ∼10−1 to 101 Hz, the so-called mode 2 is related to slower processes with lower DC conductivities, σdc2 ∼ 10−6 S cm−1, which are further facilitated under sufficiently strong bias fields. Whilst mode 1 can be associated to the presence (and motions) of asymmetric dimers stabilised by hydrogen bonding and free acids in the nematic phase, mode 2 may involve the extension of the hydrogen-bonded network to longer ranges, probably by the formation of catemeric species, and its conductivity increases on heating in both the nematic and isotropic phases. Even though the conductivity values fall below those of benchmark electrolytes used in fuel cells (σdc ∼ 0.1 S cm−1), our results are promising, particularly for non-doped/non-hydrated electrolytes, and highlight the potential of the nOBAs and other hydrogen-bonded liquid crystals as components of electrolytes for ion conductivity.

Supramolecular hydrogen-bonded liquid crystals based on 4-n-alkylthiobenzoic acids and 4,4′-bipyridine: Their mesomorphic behavior with comparative study including alkyl and alkoxy counterparts

We designed hydrogen-bonded liquid crystals (HBLCs) between a 4-n-alkylthiobenzoic acid homologous series and a 4,4-bipyridine at each ratio of 2/1 (mol/mol), and investigated their mesomorphic behavior. They show a wide range of mesophases compared with those formed in each single component of 4-n-alkylthiobenzoic acids. With increasing alkyl chains, they represent the following gradual changing for thermally additional phase sequences; from nematic phase to smectic (Sm) A (SmA) phase, then to SmC phase and further to SmI phase. In addition, their phase transition behavior was comprehensively discussed together with those for two familiar counterparts based on 4-n-alkylbenzoic acids and 4-n-alkoxybenzoic acids. It was found that the melting points are the highest for 4-n-alkoxy complexes and the trends of those for the rest depend on the alkyl chain length, whereas the isotropic points and the resultant mesophase ranges are clearly in the order of 4-n-alkoxy >4-n-alkyl >4-n-alkylthio complexes.

Hydrogen-bonded liquid crystals with broad-range blue phases

A series of hydrogen-bonded liquid crystals with broad blue phases formed by self-assembly of low molecular weight building blocks is described.