Temperature dependence and stability of oxygen enrichment through liquid crystalline triheptyl cellulose-containing membranes cast from three solvents

1996 ◽  
Vol 116 (2) ◽  
pp. 143-148 ◽  
Author(s):  
X Li
Keyword(s):  
Temperature Dependence ◽  
Liquid Crystalline ◽  
Oxygen Enrichment

STUDY OF MOLECULAR MOTIONS IN TWO LIQUID CRYSTAL FORMING COMPOUNDS EMPLOYING PLS

2006 ◽  
Vol 20 (14) ◽  
pp. 2019-2034 ◽  
Author(s):  
K. CHANDRAMANI SINGH ◽  
M. SHARMA ◽  
P. C. JAIN
Keyword(s):  
Liquid Crystal ◽  
Temperature Dependence ◽  
Liquid Crystalline ◽  
Positron Lifetime ◽  
Strong Temperature Dependence ◽  
Molecular Motions ◽  
Temperature Dependent ◽  
Slow Cooling ◽  
Positron Lifetime Spectroscopy ◽  
Motion Studies

Results of molecular motion studies carried out in two liquid crystal forming compounds n-p-cyano-p-hexyloxybiphenyl (M18) and n-p-ethoxybenzylidene-p-butylaniline (EBBA) using positron lifetime spectroscopy (PLS) are presented. Temperature dependent positron lifetime measurements have been performed in each compound during the heating cycle of samples prepared by either quenching or slow cooling from the respective liquid crystalline phase of the compounds. In both the compounds, behaviors of the quenched and slow cooled samples are found to be different. The material in the quenched sample, unlike the slow-cooled sample, exhibits strong temperature dependence before it undergoes a glass transition. In each case, the temperature dependence of o-Ps pick-off lifetime in the quenched sample shows broad peaks at various characteristic temperatures. These peaks have been attributed to various intra- and inter-molecular motions associated with these compounds. The characteristic frequencies of some of the modes observed in the present work agree well with the literature reported values obtained from FIR and Raman studies. The present study demonstrates the usefulness of PLS in the study of molecular motions.

scholarly journals AB Block-copolymers poly(oxyethylene)-blockpoly( dicyclohexyl itaconate): temperature dependence of the morphology

e-Polymers ◽  
2004 ◽  
Vol 4 (1) ◽  
Author(s):  
Krasimira Aleksieva ◽  
Ane Ancev ◽  
Slobodanka Koseva ◽  
Maja Cvetkovska ◽  
Emanuel Nedkov
Keyword(s):  
Block Copolymers ◽  
Temperature Dependence ◽  
Optical Microscopy ◽  
Crystalline State ◽  
Liquid Crystalline ◽  
Room Temperature ◽  
Chair Conformation ◽  
X Ray ◽  
Mesomorphic State ◽  
Determining Factor

Abstract The paper deals with AB block-copolymers poly(oxyethylene)-blockpoly( dicyclohexyl itaconate) (POE/PDCHI) containing 2000 and 5000 g/mol of the flexible POE. The study aims at revealing the thermal effect on the copolymer morphology in the 20 - 200°C range. Optical microscopy investigations were performed. The results confirm our previous X-ray studies. A liquid crystalline state is observed in the 90 - 180°C range. It is characterized by birefringence and is determined by the chair-chair conformation, a dominating structure of the cyclohexyl rings. A condis-crystal state is observed at cooling in the interval 90°C to room temperature. It is characterised by a variety of cyclohexyl conformations and, therefore, by a lack of birefringence. The PEO component in the copolymer starts crystallising into small local spherulites at about room temperature. The results obtained allow the conclusion that the presence of PDCHI is a determining factor for the mesomorphic state of the copolymers discussed.

scholarly journals Determination of the temperature dependence of the helical pitch in 1.m.7(HH) liquid crystalline compounds

2018 ◽  
Vol 67 (2) ◽  
pp. 49-61
Author(s):  
Paulina Zieja ◽  
Marzena Tykarska ◽  
Katarzyna Strójwąs
Keyword(s):  
Liquid Crystals ◽  
Temperature Dependence ◽  
Liquid Crystalline ◽  
Helical Pitch ◽  
Antiferroelectric Phase ◽  
Left Handed ◽  
Helical Twist ◽  
Phase Transition Temperatures ◽  
The Right

Homologous series 1.m.7(HH) of liquid crystalline compounds, varying in the chiral chain length m (m=4-9), were studied. These compounds are characterized by a long helical pitch in an antiferroelectric phase, which is higher than the measuring range of the available instruments. The temperature dependence of the helical pitch of these compounds was determined by the extrapolation of the results obtained for the mixtures of 1.m.7(HH) compounds with 1.4.7(HF) compound of a known helical pitch value. The helical pitch measurements were made by spectrophotometry and phase transition temperatures were measured by polarizing thermomicroscopy. Extrapolation of the results let established that the investigated liquid crystals are characterized by the helical pitch increasing and then decreasing upon heating, which is accompanied by the helical twist sense inversion from the right-handed structure to the left-handed one. Keywords: liquid crystals, antiferroelectric phase, helical pitch, miscibility study

Synthesis of New Chiral Disubstituted Binaphthol Derivatives and their use as the Chiral Dopants

1996 ◽  
Vol 425 ◽  
Author(s):  
H.-J. Deussen ◽  
P. V. Shibaev ◽  
R. A. Vinokur ◽  
K. Schaumburg ◽  
T. Bjornholm ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Temperature Dependence ◽  
Liquid Crystalline ◽  
Molecular Conformation ◽  
Molecular Model ◽  
Nematic Liquid Crystals ◽  
Spatially Extended ◽  
Chiral Dopants ◽  
Helical Twisting Power

AbstractA number of new chiral binaphthol (BN) derivatives with different substituents in the 6,6'-positions in open and bridged forms have been synthesized. Their possible liquid crystalline properties and their helical twisting power (B) of three different nematic liquid crystals (LCs) were investigated. Derivatives with spatially extended substituents in the 6,6'-positions (e.g. styryl or vinil) show unusual high helical twisting power (up to 120 μm–1). A direct correlation between the magnitude of β and the length of the substituents was found.From the different temperature dependence of β of the open and bridged BNs, a molecular model was developed relating the molecular conformation and twisting power

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