41 research outputs found
Dielectric relaxation studies of acetonitrile/propylene glycol and their binary mixtures
Dielectric relaxation spectra in the frequency range 0.02 < ν/GHz < 20 have been collected for propylene glycol (PG), acetonitrile (AN) and their binary mixtures between 303 K-323 K. The average relaxation times have been calculated by the Cole-Davidson and Cole-Cole relaxation models. The experimental determined values of static dielectric permittivity (ε0), relaxation time (τ), excess permittivity (εE) and excess inverse relaxation time (1/τ)E show smooth temperature dependence. The larger relaxation time values of propylene glycol when compared to acetonitrile are due to the co-operative process of multimers with O-H-O linkage and also the steric hindrance behavior phenomena. The activation entropy (ΔS*), activation enthalpy (ΔH*), Kirkwood correlation factor (gf), Helmholtz energy (ΔFE) parameters have also been determined for propylene glycol and acetonitrile and the results have been correlated
Synthesis and mesomorphic properties of new heterocyclic liquidcrystals with Central Ester–Chalcone linkages
A series of new calamitic liquid crystals, 4-[3-(pyridin-4-yl)prop-2-enoyl]phenyl 4-alkyloxybenzoates, comprising a pyridyl core,ester–chalcone central linkage and terminal alkyloxy chain were synthesized and characterized. This series consists of four membersthat differ by the length of the alkyloxy chain (CnH2n+1O , where n = 10, 12, 14, 16). The structures of the title compounds wereelucidated using spectroscopic and spectrometric techniques, such as FT-IR, NMR (1H and13C) and EI-MS. The mesomorphicproperties were studied using differential scanning calorimetry and optical polarizing microscopy. The decyloxy-containing com-pound was found to be non-mesogenic, whilst the compounds containing n-dodecyloxy to n-hexadecyloxy chains exhibited anenantiotropic smectic A phase with a fan-shaped texture. From the structure–property relationship study, it was proposed that thenumber of carbons in the alkyloxy chain must be at least 12 (n ≥ 12) to generate the smectic phase in the corresponding substitutedArCOOArCOCH CHC5H4N compounds
Viscoelastic Properties of p-n Alkyl Benzoic Acid Mesogens
Abstract: Dynamic rheological behaviour, such as storage modulus (G') and loss modulus (G'') are measured as a function of frequency at different temperatures in nematic region and also studied linear viscoelastic behaviour of p-n alkyl benzoic acid (nBA) mesogens. Different zones are exhibited by the samples, -a plateau zone at low frequencies, a transition zone at high frequencies and a zone entire plateau showing for crossover frequencies and relaxation times. The dependence of the elastic (G′) and loss (G′′) moduli on frequency is strong. The observed crossover points of G′, G′′ in the study of frequency range is indicating that nematic phase of nBA has behaved like both viscoelastic solid and liquid for small deformations (<1% strain). A typical shear thinning behaviour of viscosity has been displayed when the samples are subjected to shearing at a constant temperature. This typical shear thinning has approached slowly moving to Newtonian viscosity at high shear rates showing progressive development of nematic molecular orientation along flow direction on increasing shear rate. Rheological behaviour of the nBA nematic phases is in general consistent like the other reported compounds except the one thermotropic liquid crystals. The higher shear force and lower viscosity ratio is observed in these compounds in which pentyl benzoic acid has high ratio indicating the high molecular orientation may be due to low chain entanglement
Dielectric Studies on Fe 3
The stability of phase transition temperatures and textural changes for thermotropic pure and nanodoped p-n-alkyloxybenzoic acid mesogens were aimed to study at considerable time periods. Frequency and temperature dependent dielectric constant and dielectric loss for the pure and nanodoped liquid crystals were carried out. Significant anomalies in dielectric studies were observed near phase transitions when dielectric constant and dielectric loss had been measured as a function of temperature and frequency. Changes in dielectric constant and loss were observed and there were no apparent changes at high frequencies instead maintaining constant values. The variations in conductivity, activation energy, and relaxation times had also been studied in the nematic and smectic phases. The temperature dependent dielectric constant stability (temperature coefficient of dielectric constant τε) had shown shift in the observed frequency range of thermotropic liquid crystals corresponding to the change in the dielectric constant values
Induced Smectic A Phase through Intermolecular Hydrogen Bonding: Part XVIII: Influence of p-n-Alkyl Benzoic Acids on Thermal and Phase Behavior οf Hydrogen-Bonded Liquid Crystals
A novel series of intermolecular hydrogen bonded liquid crystals was synthesized with the mesogens of p-n-alkyl benzoic acids (nBA where n =5 to 10) and p-(p'-octyloxy benzylidene)-cyano aniline (OBCA) moieties. The thermal and phase behaviors of these mesogens (nBA:OBCA) are studied by thermal polarizing optical microscopy and differential scanning calorimetry techniques. Induced smectic A phase with focal conic fan texture is observed in all the synthesized compounds. Moreover, the nematic phase present in all the pure p-n-alkyl benzoic acids (nBA where n =6 to 10) is quenched in all the hydrogen bonded compounds (nBA:OBCA) and smectic A phase is induced. But, in the compound 5BA:OBCA the nematic phase is also present along with the induced smectic A phase. The structural elucidation pertaining to the formation and stabilization of intermolecular hydrogen bonding is carried out by a detailed IR spectral investigation
Induced Smectic A Phase through Intermolecular Hydrogen Bonding: Part XVIII: Influence of p-n-Alkyl Benzoic Acids on Thermal and Phase Behavior οf Hydrogen-Bonded Liquid Crystals
A novel series of intermolecular hydrogen bonded liquid crystals was synthesized with the mesogens of p-n-alkyl benzoic acids (nBA where n =5 to 10) and p-(p'-octyloxy benzylidene)-cyano aniline (OBCA) moieties. The thermal and phase behaviors of these mesogens (nBA:OBCA) are studied by thermal polarizing optical microscopy and differential scanning calorimetry techniques. Induced smectic A phase with focal conic fan texture is observed in all the synthesized compounds. Moreover, the nematic phase present in all the pure p-n-alkyl benzoic acids (nBA where n =6 to 10) is quenched in all the hydrogen bonded compounds (nBA:OBCA) and smectic A phase is induced. But, in the compound 5BA:OBCA the nematic phase is also present along with the induced smectic A phase. The structural elucidation pertaining to the formation and stabilization of intermolecular hydrogen bonding is carried out by a detailed IR spectral investigation
Structural and optical properties of vanadium doped akaline earth lead zinc phosphate glasses
The structural properties of vanadium doped alkaline earth lead zinc phosphate glasses have been investigated by XRD, UV-Visible, EPR, FT-IR and Raman spectroscopy techniques. XRD analysis has confirmed that the samples are X-ray amorphous. The optical band gap energy (Eopt) is observed to decrease with the replacement of alkaline earth content, whereas reverse trend is observed in Urbach energy (ΔE) and optical basicity (th). The spin-Hamiltonian parameter, dipolar hyperfine coupling and covalency parameters have been obtained from EPR spectra. Depolymerization of the phosphate network by the replacement of alkaline earth content in glasses which are consisting of mainly PO32- and PO43- units, was detected by FT-IR spectra. The structural modification due to breakage of P=O bond and the formationof P-O-P bonds in the different compositions have been studied by Raman spectra. The physical properties have been measured and observed to increase with the replacement of alkaline earth content. The replacement of BaO has improved the strength of the cross-links between the phosphate chains of the glass
Structural and optical properties of vanadium doped akaline earth lead zinc phosphate glasses
491-498The
structural properties of vanadium doped alkaline earth lead zinc phosphate
glasses have been investigated by XRD, UV-<span style="mso-bidi-font-weight:
bold">Visible, EPR, FT-IR and Raman
spectroscopy techniques. XRD analysis has confirmed that the samples are
X-ray amorphous. The optical
band gap energy (Eopt) is observed to decrease with the
replacement of alkaline earth content, whereas reverse trend is observed in Urbach energy (ΔE) and optical basicity (th). The spin-Hamiltonian parameter, dipolar hyperfine coupling and
covalency parameters have been obtained from
EPR spectra. Depolymerization of the phosphate network by the
replacement of alkaline earth content in glasses which are consisting of mainly
PO32<span style="font-family:Symbol;
mso-ascii-font-family:" times="" new="" roman";mso-hansi-font-family:"times="" roman";="" mso-char-type:symbol;mso-symbol-font-family:symbol"="" lang="EN-GB">- and PO43- units, was detected by FT-IR spectra. The structural modification due to
breakage of P=O bond and the formationof P-O<span style="font-family:Symbol;
mso-ascii-font-family:" times="" new="" roman";mso-hansi-font-family:"times="" roman";="" mso-char-type:symbol;mso-symbol-font-family:symbol"="" lang="EN-GB">-P bonds
in the different compositions have been studied by Raman spectra. The physical properties have been measured
and observed to increase with the replacement of alkaline earth content. The replacement of BaO has improved the strength
of the cross-links between the phosphate chains of the glass.
</span
Experimental and Theoretical Studies of Ultrasonic Velocity in Binary Liquid Mixtures of Ethyl benzoate
Ultrasonic velocity is measured at 2MHz frequency in the binary mixtures of Ethyl Benzoate with 1-Propanol, 1-Butanol, 1-Pentanol and theoretical values of ultrasonic velocity have been evaluated at 303K using Nomoto's relation, Impedance relation, Ideal mixture relation, Junjie's method and free length theory. Theoretical values are compared with the experimental values and the validity of the theories is checked by applying the chi-square test for goodness of fit and by calculating the average percentage error (APE). A good agreement has been found between experimental and Nomoto’s ultrasonic velocity