V. G. K. M. Pisipati

Phase Transition and Structural Investigations in 50.5, 50.6 and 50.7

Abstract We report X-ray diffraction, density, ultrasonic velocity and refractive index studies in the N(p-n-pentyloxy benzylidene) p-n-alkylaniline compounds, viz. 50.5, 50.6 and 50.7. The nematic-smectic A (NA) transition is found to be weak first order in 50.6 while it is second order in 50.5 and 50.7. The salient features observed are cybotactic clusters in the nematic phase in all the compounds, molecular tilt which was inferred due to the end alkyl chains tilt causing orienta-tional disorder (smaller orientational order parameters ‘s’ than expected) in smectic A phase, smectic F phase and large tilt angle variation in smectic C phase in a small temperature range in 50.5. The observed results are discussed in the light of available data in other n0.m compounds.

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.

Synthesis, Characterization, and Dilatometric Studies on N-(p-n-Alkoxybenzylidene)-p-n-pentyloxyanilines Compounds

Synthesis, textural characterization, differential scanning calorimetry, and dilatometry studies are carried out on a new homologous series of N-(p-n-alkoxy benzylidene)-p-n-pentyloxy anilines (nO.O5) where n = 1–18. The lower homologues of this series (n = 1–5) and a higher homologue (n = 16) exhibit monotropic Liquid Crystal (LC) phase. The other members of the series show enantiotropic LC phases, while 18O.O5 is a nonliquid crystal. The dilatometric studies on 7O.O5, 10O.O5, 13O.O5 and 16O.O5 reveal the first-order nature of Isotropic to Nematic Phase (IN), Isotropic to Smectic A Phase (IA), Nematic to Smectic C Phase (NC), Smectic A to Smectic B Phase (AB), Smectic C to Smectic B Phase (CB), and Smectic A to Krystal Phase (AK) transitions. The pretransition effects are estimated from dilatometry results. The results are compared with the available data on nO.m compounds.

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.

Phase Transitions in N(p-n-Bu toxybenzylidene) p-n-Alkyl Anilines: Density and Refractive Index Studies

Abstract The density and refractive index variation with temperature in N(p-n-butoxybenzylidene)p-n-alkylanilines viz., 40.m compounds for m = 4 to 12 are presented. The density, thermal expansion coefficient and the refractive index results infer first order character for IN, AB and CB transitions and a second order character for NA and AC transitions. Pretransitional effects are discussed at IN and AB transitions. The odd-even effect is observed at both the IN and NA phase transitions. The variation of refractive index anisotropy as a function of temperature, in the nematic phase of the compounds in a homologous series has shown an interesting phenomena. The temperature dependence of nematic refractive index anisotropy yields mean field exponent v = 1 in the vicinity of NA transition. The influence of molecular chemical constitution, the nematic thermal range and the McMillan parameter values on the order of NA transition is discussed in detail.

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.

Influence of hydrogen bonding on phase abundance in ferroelectric liquid crystals

The synthesis and characterization of five hydrogen-bonded ferroelectric liquid crystal complexes (HBFLCs) prepared from mesogenic p-n-alkoxy benzoic acids and non-mesogenic propionic/butyric acids with different chiral centres are reported. Complementary intermolecular hydrogen bonding is confirmed through IR study. HBFLCs are found to exhibit chiral nematic (N*), smectic C* (SmC*) and smectic G* (monotropic) phases in their cooling profiles during polarizing thermal microscopy and differential scanning calorimetry. Phase coexistence regions are observed above the IN* transition. The chiral nematic to smectic C* transition is found to be of first order. The temperature variation of spontaneous polarization exhibited by these HBFLC complexes in their SmC* phase is presented. The effect of non-covalent interaction imparted by the soft hydrogen bonding in these LC complexes on enhanced or induced thermal stability of tilted LC phases is discussed.

Nematic order near a tricritical nematic-smectic a phase transition

Abstract A symmetric tricritical point (TCP) is demonstrated for the nematic-smectic A transition by blending two nearly identical isomers and by showing that the difference in coexistence values of the nematic order parameter S goes to zero with TCP exponent β 2 = 1 as T TCP is approached. A horizonta λ-line is associated with an observed universal behavior of S when a new scaling of T is used.