B. M. Fung

Orientational Ordering of 4-n-Alkyl-oxy-4′-Cyanobiphenyls Studied by 2D Carbon-13 NMR

Abstract The orientational ordering of four 4-n-alkyloxy-4′-cyanobiphenyls (50CB, 60CB, 70CB and 80CB) in their nematic phase at TNI - T= 10K was studied by carbon-13 NMR. The technique used is a combination of separated local field spectroscopy (SLF) and variable angle spinning (VAS). Rapid sample spinning of these compounds causes the nematic director to align along the spinning axis, resulting in narrow peaks in the C-13 NMR spectra. The 2D method of SLF produces a first order splitting pattern for each carbon signal, from which C-H dipolar coupling constants can be determined. The order parameters for each phenyl ring and each aliphatic C-H segment can then be calculated. Results for the kOCB series are presented.

Nematic and Smectic Ordering of 4-n-Octyl-4′-cyanobiphenyl Studied by Carbon- 13 NMR

Abstract A new NMR method called RHODIUM (Removal of HOmonuclear DIpolar-couplings and the Use of off-Magic-angle-spinning) has been applied to study the molecular ordering of 4-n-octyl-4′-cyanobiphenyl (8CB) as a function of temperature. C-H dipolar coupling constants of various carbon atoms in 8CB were obtained from natural abundance carbon-13 NMR. Order parameters of the benzene rings and those of the C-H bonds in the octyl chain were calculated from the dipolar coupling constants. The order parameter of the -CN axis can also be calculated from the chemical shift of the -CN group. The results are consistent with the second order nature of the smectic A-nematic phase transition in 8CB.

Thrombolysis Using Liposomal-Encapsulated Streptokinase: An In Vitro Study

Abstract The clot-lysing ability of streptokinase (SK) was examined using membrane-bound thrombi. Encapsulation of SK in large unilamellar phospholipid vesicles (liposomes) resulted in entrapping approximately 30% of its original activity. Measurements of streptokinase activity for liposomal-encapsulated streptokinase (LESK) indicated little loss of activity or leakage in Tris-buffered saline over a 24-hr period at temperatures of 4 and 23°C. However, incubation of free SK and LESK in platelet-poor plasma (PPP) at 37°C resulted in a decrease of SK activity. The retention of SK activity in LESK was considerably higher than that of unentrapped SK. Clot-dissolving time (CDT) was measured by monitoring the pressure drop during slow filtration in plasma through membrane-bound thrombi. The results indicated that both LESK and free SK were able to activate the fibrinolytic system. Without prior incubation in PPP at 37°C, the CDT of a SK and PPP mixture (SK/PPP) was 10.7 ± 1.9 min (n = 12), while that of a LESK and PPP mixture (LESK/PPP) was 12.4 ± 1.7 min (n = 12). The CDT-detected clot-lysing abilities of both SK and LESK were diminished by incubation in PPP, but to different extents. After 15- and 30-min incubations, the CDT of SK/PPP increased significantly to 15.5 ± 1.5 and 24.1 ± 2.4 min (n = 5, P < 0.05), respectively. In contrast, the CDT of LESK/PPP increased to 13.3 ± 0.8 min (n = 5) after 15 min of incubation and to 16.0 ± 1.1 min (n = 5, P < 0.05) after a 30-min incubation. These results suggest that entrapment of SK in liposomes preserves the thrombolytic potential of the plasminogen activator by limiting its exposure to the components of the plasma.

Syntheses of perfluoroalkyl N-polyethoxylated amides

Abstract Monodisperse perfluoroalkyl N-polyethoxylated amides, CnF2n+1CONH(CH2CH2O)mH, with n = 6, 7, 8 and 9 and m = 2, 3, and 4, are potential nonionic fluorinated surfactants. The syntheses: of these compounds are described.

Liquid Crystals With a Chiral Core: Cyclohexene Carboxylates

Abstract A series of new liquid crystals containing a cyclohexene ring have been synthesized and characterized. The cyclohexene ring is formed by the Diels-Alder reaction between myrcene and methyl acrylate, and has a chiral center. Hydrolysis of the resulting methyl ester into the corresponding acid and esterification of the latter with 4-hydroxy-4′-n-alkoxybiphenyl yields a homologous series of liquid crystals with the structure: The compounds thus prepared are racemic mixtures. The lower members of this series (n = 1 and 2) have a large nematic range, and the higher members (n = 3–10) have multiple smectic phases in addition to the nematic phase. When (1R,2S,5R)-(-)-menthyl acrylate was used instead of methyl acrylate in the Diels-Alder synthesis, optically active compounds with 40% enantiomeric excess were obtained.

Effect of polymer mixtures on the performance of PDLC films

Generally one type of polymer is used in the construction of polymer dispersed liquid crystal (PDLC) films. The authors tested the effect of incorporating an additional fluoropolymer in varying percentages on the electro-optic performance of PDLC films based on poly(methyl methacrylate). Compared to samples made from a single polymer, several correlations are noted, including a decrease in liquid crystal fall-time, an increase in rise-time, and an increase in the threshold voltage (Vt).

Improvement in the electro-optic response of PDLC films (Invited Paper)

We have investigated two approaches to improving the electro-optic performance of polymer dispersed liquid crystal (PDLC) films. One involves using a partially fluorinated epoxy based thermoset to serve as the PDLC binding matrix. Results indicate that this causes an enhanced phase separation of the liquid crystal which leads to significant changes in the contrast ratio and fall time of a PDLC film. The other approach involves using duel frequencies to enhance the electro-optic performance of another type of PDLC film. Studies suggest that the hysteresis effect can be minimized and the overall control of the electro-optic response can be greatly increased by adding a second high frequency component to the PDLC driving voltage.

The effect of partial fluorination on the performance of epoxy based PDLC films

Abstract Changes in the electro-optic performance of polymer dispersed liquid crystal (PDLC) films caused by partial fluorination of the epoxy polymer binder have been investigated. The switching performance of the PDLC films was characterized by threshold voltage, rise time, fall time and contrast ratio. The results indicate that fluorine substitution in the polymer can cause a better phase separation, resulting in significant increases in the contrast ratio as well as large decreases in the fall time.

The effect of dual-frequency addressing on the electro-optic response of a PDLC film

Abstract The effect of using dual-frequency addressing in the reduction of the response time in polymer dispersed liquid crystal (PDLC) displays has been investigated. The utilization of a second high frequency component of the driving voltage enables an added control of the waveform not possible in a single frequency addressed system. The use of dual-frequency addressing, combined with some special driving techniques, opens up the possibility of controlling the response of PDLC displays in sweeping-mode operations.

Modifications of nonionic surfactants with perfluorinated terminal groups

Abstract Two industrial nonionic surfactants, Pluronic F68 and Butronic R1, were modified by diesterification with perfluorobenzoic or linear perfluorinated carboxylic acids. The modified surfactants form more stable emulsions with perfluorodecalin and perfluorodecalin/perfluorotripropylamine mixtures compared to the parent compounds. Stabilities of the different emulsions are compared quantitatively. The sizes of the emulsified particles do not show significant variations with the modification of the surfactants.