Browsing by Author "Janarthanan, N"

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Effect of enantiomeric excess on surface structures and phase sequences in free-standing liquid-crystal films
(2002-12-01)
Cady, A
;
Liu, ZQ
;
Han, XF
;
Wang, ST
;
Veum, M
We present differential optical reflectivity and null transmission ellipsometry data from several mixtures of MHPBC enantiomers. From this data, we have determined the chiral smectic phase sequence as a function of enantiomeric excess. The data suggest a change in the structure of the smectic-C(alpha)* phase and the surface tilt state as the enantiomeric excess is reduced. The results also show that the intermediate phases, smectic C(FI2)*, smectic C(FI1)*, and smectic C(alpha)*, disappear sequentially on reducing the net chirality.
Super high birefringence isothiocyanato biphenyl-bistolane liquid crystals
(2004-11-01)
Gauza, S
;
Wen, CH
;
Wu, ST
;
Janarthanan, N
;
Hsu, CS
We have designed, synthesized, and evaluated the physical properties of some high birefringence (An) isothiocyanato biphenyl-bistolane liquid crystals. These compounds exhibit Deltan = 0.7-0.8 at room temperature and wavelength lambda = 633 nm. Laterally substituted short alkyl chains and fluorine atom eliminate smectic phase and lower the melting temperature. The moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. A eutectic mixture based on those compounds was formulated and its physical properties evaluated. The simulated absorption spectra agree reasonably well with the measured results.
Synthesis and characterization of ferroelectric side chain liquid crystal polymers bearing banana-shaped chiral mesogens
(2000-06-01)
Wu, LH
;
Chu, CS
;
Janarthanan, N
;
Hsu, CS
;
應用化學系
A series of ferroelectric liquid crystal polymers having banana-shaped side chain mesogens were synthesized through photo-polymerization of epoxide moiety. 2,5-disubstituted-thiophene sub-unit was used in synthesizing the banana-shaped monomers. These liquid crystal compounds were characterized by NMR, differential scanning calorimetry (DSC) and optical polarized microscopy (POM). Mesomorphism was investigated as a function of spacer units. All the synthesized low molar mass banana-shaped compounds exhibit smectic blue phase, but chiral smectic C phase could be observed only on compounds having longer spacer. The clearing temperature of low molar mass compounds fluctuated a little when spacer length varies. All polymers exhibit cholesteric mesophase and an observable glass transition. These liquid crystalline compounds reveal strong photoluminescence at visible region (lambda(max) = 475 nm for M9EPX) and have potential use in polarized organic light emitting diode materials.
Synthesis and characterization of naphthalene-substituted triphenylene discotic liquid crystals
(2001-01-01)
Wu, LH
;
Janarthanan, N
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
A series of naphthalene-substituted triphenylene liquid crystals (LCs), viz. triphenylene-2,3,6,7,10,11-hexayl hexakis(6-alkenyloxy-2-naphthoate)s (HTPnN compounds) were synthesized and characterized. Alkenyloxy groups containing three to eleven carbon atoms were used as peripheral spacers in these liquid crystals. The discotic liquid crystals synthesized trap one to three water molecules depending on the length of their peripheral spacers. Differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction measurements confirm both nematic (N-d) and rectangular disordered columnar (Col(rd)) phases for most of the synthesized discotic LCs. The clearing temperatures of these discotic LCs increase with increasing peripheral spacer length. A hybrid aligned HTP9N sample was investigated to evaluate its optical performance. Retardation values of this hybrid sample decrease with increasing wavelength and increase with increasing measuring angle.
Synthesis of substituted poly (arylene vinylene) films by vapor deposition polymerization
(2000-09-01)
Li, AK
;
Janarthanan, N
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
An efficient method for the synthesis of PPV based polymers, poly (2,5-dimethyl-1,4-phenylene vinylene) (DMe-PPV) and poly (2,5-dimethoxy-1,4-phenylene vinylene) (DOMe-PPV) were developed using 2,5-dimethyl-1,4-bis (chloromethyl) benzene and 2,5-dimethoxy 1,4-bis (chloromethyl) benzene via vapor phase pyrolysis and followed by vapor deposition polymerization. The structure of polymer films were confirmed by FT-IR, solid state NMR and elemental analysis. Thermal gravimetry analysis reveals that the precursor polymer films form a conjugated polymer after thermal conversion at 250 degrees C. The optical and electrical properties of the polymer films were investigated by UV-Vis absorption and photoluminescence spectroscopies. Electroluminescent devices were fabricated using these polymers.
Unique approach to measuring temperature variation of surface tension in smectic liquid crystals
(2003-12-01)
Veum, M
;
Messman, P
;
Liu, ZQ
;
Huang, CC
;
Janarthanan, N
We have measured the temperature variation of surface tension, sigma, in freestanding films of three liquid-crystal compounds. To do so, we have constructed a curvature-pressure tensiometer that uses a feedback loop to hold constant the curvature of a film while the temperature of the system is smoothly ramped. The apparatus enables us to obtain the temperature variation of sigma in a continuous manner with resolution in sigma of similar to0.2%. We interpret reproducible features of our data in terms of phase transitions. (C) 2003 American Institute of Physics.