M. L. N. Madhu Mohan

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.

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.

Spontaneous polarization, tilt angle and dielectric measurements on a ferroelectric liquid crystal

A new ferroelectric liquid crystalline compound 4-(p-butyloxy-2-chloro-tyrosinate)-2-hydroxy-benzylidene-4-nonylaniline, abbreviated as BCTHBN, was characterized by various techniques. Phase sequence and transition temperature data were obtained by thermal microscopy and DSC. The values of spontaneous polarization, tilt angle, response times and viscosity, along with the wide thermal range of the SmC* phase, make this compound a candidate for applicational studies. Dielectric studies included variation of capacitance with temperature and calculation of activation energies in the soft and Goldstone modes.

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.

Design and Synthesis of Linear and Bow Shaped Ferroelectric Liquid Crystal Isomers Derived From L-Tyrosine

Abstract A novel series comprising of two distinct ferroelectric liquid crystalline structural isomers. viz., (S)-1,4-diphenylene bis(2-chloro-3-(4-dodecyloxyphenyl)- propionate) (DCDP-1) and (S)-1,3-diphenylene bis(2-chloro-3-(4-hydroxyphenyl)- propionate) (DCDP-2), have been synthesized and characterized by thermal microscopy (TM), differential scanning calorimetry (DSC), spontaneous polarisation (PS) and response times (τ). The preliminary studies on thermal and ferroelectric properties reveal that the isomers show altogether a different trend of thermal and phase behaviour. The thermal analyses (TM and DSC) suggest the existence of different phase variants. Further, the ferroelectric studies infer a different chiral behavior among DCDP-1 and DCDP-2 compounds wherein DCDP-2 showed a wide ferroelectric thermal range with high magnitudes of PS (three fold) and response times (two fold).

The measurement of electrostriction coefficients of some XH2PO4/H3BO3 binaries by interferometric technique

A new optical interferometric technique to measure the electrostrictive coefficients of XH2PO4/H3BO3 binaries (where X=Na, K and NH4) is reported. This direct method is found to be advantageous in measuring the positive as well as the negative sign of the electrostrictive coefficients. Design of the apparatus and its merits are discussed. In XH2PO4/H3BO3 binaries the addition of boric acid is found to decrease the value of binary electrostriction coefficient in comparison to their pure samples.

Crystal structure studies of mixed system of NaH2PO4 and KH2PO4 with H3BO3

X-ray powder analysis of solid solution of NaH2PO4 and KH2PO4 with H3BO3 was carried out. Both the systems were observed to be tetragonal. The crystallographic data are reported.

X-ray data for the substitutional solid solution of the binary system ammonium dihydrogen phosphate with boric acid

X-ray powder diffraction data for the binary system ammonium dihydrogen phosphate with boric acid is studied and it is inferred that the binary belongs to tetragonal system and forms a substitutional solid phase. On the basis of the space group the binary is predicted to exhibit electrooptic property along with piezoelectric and electrostriction properties. It is proposed that the phosphorus atom of ammonium dihydrogen phosphate is substituted by the boron atom of boric acid.