P. A. Kumar

Induced crystal G phase through intermolecular hydrogen bonding II. Influence of alkyl chain length of n-alkyl p-hydroxybenzoates on thermal and phase behaviour

A new series of intermolecular hydrogen-bonded complexes have been synthesized using p-n-alkoxybenzoic acid (alkyl chain length varies from propyl- to decyl- and dodecyl-) and methyl p-hydroxybenzoate moieties. The thermal and phase behaviour of these complexes were studied by thermal microscopy and differential scanning calorimetry. Further, the stabilization of intermolecular hydrogen bonding in solution was studied by IR spectroscopy. A detailed IR spectral investigation in the solid and dissolved states suggests that the acid and phenol groups act as proton donor and proton acceptor, respectively. The thermal studies also reveal the inducement of a crystal G phase in the complexes.

Design and fabrication of an automated technique: measurement of spontaneous polarization in two new schiff base ferroelectric liquid crystals

Abstract A technique for the measurement of spontaneous polarization (P s ) in ferroelectric liquid crystals (FLC’s) is presented. Modification in the data acquisition part to measure the loop area of transient current due to the spontaneous polarization is described. Temperature dependence of the spontaneous polarization measured for the compound ZLI-3775 was found to agree with data provided by E. Merck Industrial Chemicals. The relative advantages and ease of operation in the present technique are discussed. This setup facilitates simultaneous measurement of spontaneous polarization and response times. Using the present setup, variation of the spontaneous polarization and response times with temperature are reported for two new Schiff base compounds, 4-undecyloxy benzylidene-4′-amino-2-methylbutylcinamate (UOBAMBC) and 4-(2-chloro-propionyloxy) benzylindene-4′-amino-2-methylbutylcinamate (CPOBAMBC). The magnitude of P s for CPOBAMBC is twice that of UOBAMBC.

Induced smectic G phase through intermolecular hydrogen bonding

A new series of mesomorphic complexes formed through intermolecular hydrogen bonding between p-n-alkoxybenzoic acids (where alkoxy denotes chains from propoxy- to decyloxy- and dodecyloxy-) and non-mesogenic p-hydroxybutyl benzoate, have been synthesized and characterized by thermal microscopy, differential scanning calorimetry, infrared spectroscopy (IR) and 1H NMR studies. A detailed IR spectral investigation in the solid state and in solution suggests that the acid and phenol groups are complementary to each other, each acting as both proton donor and proton acceptor. The results of comparative thermal analyses of both free p-n-alkoxybenzoic acids and H-bonded complexes exhibited an induced crystal smectic G phase in the complexes throughout the series, its thermal range increasing with alkoxy carbon number.

Induced Smectic-G Phase Through Intermolecular H-Bonding: Part III. Influence of Alkyl Chain Length of p-n-Alkoxybenzoic Acids on Thermal and Phase Behaviour

Abstract A novel series of intermolecular hydrogen bonding complexes have been synthesized by using p-n-alkoxybenzoic acids (alkyl chain length varies from propyl- to decyl and dodecyl-) (ABA) and a non-mesogenic moiety, 2-amino-5-chloro-pyridine (ACP), The thermal and phase behaviour of these complexes are studied by thermal microscopy (TM) and differential scanning calorimetry (DSC) techniques. The stabilization of intermolecular hydrogen bonding is studied by IR spectra. A detailed IR spectral investigation in solid and solution states suggest that both acid and pyridine nitrogens are complementary to one another by acting as proton donor and acceptor respectively. The comparative thermal studies with free benzoic acids and the corresponding analogous hydrogen bonded complexes reveal the inducement of a monotropic smectic-G phase with simultaneous quenching of nematic and smectic-C phases.

Synthesis of a novel antiferroelectric liquid crystal with high Ps

An antiferroelectric liquid crystal material, (S)-4-[4-(dodecyloxycarbonylphenoxy)-2-chloropropionyl] phenyl 4-{4-[2-chloro- -(4-benzamidoacetyloxyphenyl) propionyloxy] benzoyloxy}- benzoate (DCPCPB), has been designed and synthesized by using l-tyrosine as a chiral source. Preliminary investigations of the ferroelectric properties of the present material show a high magnitude of spontaneous polarization (190 nCcmO 2 ) and response times (135ms) in the antiferroelectric SmC* A phase. The possible molecular contributions towards the appearance of the antiferroelectric phase are summarized.

Evidence of re-entrant ferroelectric ordering in an achiral AFLC: a detailed study by spontaneous polarization

A winged achiral antiferroelectric liquid crystalline compound, 1,3-phenylene bis-[phenylene1-(biphenyldicarboxylato)-3-(4-n-tetradecyloxybenzoyl)biphenyldicarboxylate] (PBPBTB), having 1,3-phenylene [4-biphenyldicarboxylate-(4-n-tetradecyloxy benzoate)] units as wings, has been synthesized. Its mesogenic properties were characterized by thermal microscopy, differential scanning calorimetry, response time and spontaneous polarization measurements, and dielectric studies, suggesting the presence of new achiral phases. An interesting enantiotropic cyclic sequence among ferro- and antiferro-electric ordering was confirmed by the polarizing current profiles. The occurrence of re-entrant ferroelectric phenomena in the present compound was confirmed by detailed spontaneous polarization and preliminary dielectric studies.

Field induced intra-smectic C*A transition in a novel AFLC compound

Abstract A novel antiferroelectric liquid crystalline compound, (S)-2-chloro-3-(4-benzamidoacetophenyl)-1-[4′-(2-chloro-3-benzoatophenyl-1-(p-dodecyloxybenzoyl)-propionato)]-benzoatopropio-nate (CBCBDPBP), is synthesised and characterised by using differential scanning calorimetry (DSC), thermal microscopy (TM), while its ferroelectric properties are studied by temperature scanning method (TSM), spontaneous polarisation (Ps), response times (τ), viscosity (η) and dielectric techniques. A detailed investigation conforming the existence of a field induced intrasmectic antiferroelectric smectic C*A transition (FiT) is achieved through dielectric studies and for the first time by spontaneous polarisation current profiles. Further, the Ps normalised to unity with the electric field suggests the existence of C*γ phase. The existence of ferri-, ferro-and antiferroelectric orderings in the present system are clearly distinguished by the individual polarising current profiles. As expected, the magnitude of Ps in t...

Synthesis of Novel Ferroelectric Liquid Crystals Derived from L-tyrosine

Abstract A new series of ferroelectric liquid crystalline Schiff base compounds with the general formula, 4-(p -butyloxy-2-chloro-tyrosinate)2-hydroxy-benzylidene-4′-alkylanilines (BCTHBA) using L-tyrosine as a chiral source have been synthesized and characterized by elemental analyses, IR and PMR spectral techniques. The liquid crystalline properties viz., textural identification, the phase transition temperatures and ferroelectricity were studied by thermal microscopy, differential scanning calorimetry and spontaneous polarization (by triangular wave method) techniques, respectively.

Crystallization kinetics study on N-(p-n-alkyloxybenzylidene)-p-n-alkylanilines (nO.m compounds)

A comparative systematic kinetic study of crystallization among various smectogens of higher homologues of the benzylidene aniline nO.m series (9O.2, 13O.2, 14O.2, 15O.2, 16O.2, 2O.16, 11O.16, 16O.16 and 18O.16) has been carried out by thermal microscopy and differential scanning calorimetry (DSC). The DSC thermograms were run from crystallization temperature to the isotropic melt for different time interval. The liquid crystalline behaviour together with rate of crystallization of smectic ordering in newly synthesized nO.m compounds (16O.2, 2O.16, 11O.16, 16O.16, 18O.16) with respect to their lower homologues are discussed in relation to the kinetophase (which occurs prior to the crystallization), end chain lengths, the odd-even effect and chain length ratio. The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time (t*) at each crystallization temperature was deduced from the individual plots of log t vs. DeltaH. Further, a qualitative approach was made to the crystallization process in smectic layers.

THERMAL, FERROELECTRIC AND DIELECTRIC STUDIES ON TWO DISTINCT STRUCTURAL ISOMERS: A FIELD INDUCED TRANSITION IN PSEUDO-NEMATIC PHASE

Abstract The thermal and ferroelectric properties of a novel series comprising of two distinct ferroelectric structural isomers, (S)-1,4 – diphenylene bis (2-chloro-3- (4 – dodecyloxyphenyl)-propionate) (DCDP-1) and (S)-1,3 – diphenylene bis (2-chloro-3- (4 – dodecyloxyphenyl)-propionate) (DCDP-2), are studied by polarizing thermal microscopy (TM), differential scanning calorimetry (DSC), spontaneous polarization (PS), response times (τ), viscosity (η) and dielectric techniques. The thermal studies imply these isomers exhibit altogether different thermal and phase behaviour. The comparative ferroelectric investigations infer an increment in the magnitude of PS(three fold) and a wide ferroelectric thermal range in DCDP-2 compound. Further, the detailed ferroelectric studies on DCDP-2 compound reveal the occurrence of spontaneous polarization, for the first time, in the threaded nematic like phase (here after this phase is referred as pseudo-nematic). A detailed investigation confirming the existence of a field-induced transition (FiT) from pseudo-nematic to nematic phase is achieved through spontaneous polarization and dielectric studies.