A study of the surface anchoring at a polymer/liquid crystal interface in the neighbourhood of the glass transition

Abstract

Recently, we have observed dramatic changes in the electro-optic properties of PDLC films composed of droplets of the liquid crystal E7 in a matrix of polyvinylformal (PVFM) in the vicinity of the glass transition temperature of the matrix. One plausible explanation for these changes is a decrease in the surface anchoring strength on passing through the glass transition. For this reason, we undertook a study of the surface anchoring strength between E7 and a thin film of PVFM using the technique of Yokoyama and van Sprang. To mimic the properties of the matrix more closely, we dissolved 20 per cent E7 liquid crystal into the PVFM film. The surface anchoring for this film was compared with that of a pure PVFM film. From these data, we observed no obvious changes in the surface anchoring on passing through the glass transition of the matrix. However, the incorporation of liquid crystal into the matrix did cause a decrease in the surface anchoring strength. We discuss the impact of these results on the interpretation of the PDLC electro-optic properties.     

Groups in which every automorphism centralizes a subgroup of prime index

A complete classification is given of all groups G with the property that every automorphism centralizes a subgroup with prime index in G.     

Smectic liquid crystals. VIII. Some new laterally substituted smectic C compounds

Abstract

The synthesis and liquid crystal transition temperatures of a new class of compounds incorporating a trans-1,4-disubstituted cyclohexane ring have recently been reported. Many of these novel materials exhibit an enantiotropic smectic C mesophase over a wide temperature range and are suitable for commercial display device applications. The influence of several lateral substituents in various positions on the liquid crystal transition temperatures of these compounds has now been investigated systematically. A linear relationship between the size of the lateral substituent and the magnitude of the transition temperatures of various liquid crystal mesophases has been established for several of the series synthesized. A number of series incorporating a lateral substituent and an optically active centre have also been prepared and similar effects have been found.     

Crosslinker Copolymerization for Property Control in Inverse Vulcanization

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.     

[18F]Ethenesulfonyl Fluoride as a Practical Radiofluoride Relay Reagent

Fluorine-18 is the most utilized radioisotope in positron emission tomography (PET), but the wide application of fluorine-18 radiopharmaceuticals is hindered by its challenging labelling conditions. As such, many potentially important radiotracers remain underutilized. Herein, we describe the use of [¹⁸F]ethenesulfonyl fluoride (ESF) as a novel radiofluoride relay reagent that allows radiofluorination reactions to be performed in minimally equipped satellite nuclear medicine centres. [¹⁸F]ESF has a simple and reliable production route and can be stored on inert cartridges. The cartridges can then be shipped remotely and the trapped [¹⁸F]ESF can be liberated by simple solvent elution. We have tested 18 radiolabelling precursors, inclusive of model and clinically used structures, and most precursors have demonstrated comparable radiofluorination efficiencies to those obtained using a conventionally dried [¹⁸F]fluoride source.     

Unusual Structures of the Parent Molecules Diarsene,Distibene, and Dibismuthene: Toward Their Observation

There is considerable interest, from both experimental and theoretical perspectives, in molecules incorporating multiple bonds between main group elements. Herein, we not only consider the parent molecules HE=EH (E=As, Sb, Bi), but also a number of their isomers. For each E₂H₂ molecule, a number of different structures were optimized with four different DFT methods. Final structures were determined with the coupled cluster method CCSD(T) using large basis sets, namely cc-pVQZ-PP, incorporating relativistic psuedopotentials. All feasible dissociation pathways are examined. For all three E₂H₂ molecules the trans isomer lies lowest in energy, with the cis isomer higher by 2.7 (As), 2.1 (Sb), and 1.8 (Bi) kcal mol⁻¹, respectively. However, both cis and trans structures should be observable, as large barriers (27.7, 20.5, and 17.7 kcal mol⁻¹) separate them. For both the cis and trans structures, in the infrared the strong E-H stretching frequencies should also be observable. Only the cis structures have dipole moments (0.62, 0.01, and 0.83 debye, respectively), and their observation by microwave spectroscopy would be stunning. Also considered were the higher energy vinylidene-like, pyramidal, monobridged, and linear structures. We conclude that molecules such as HSb=SbH-Fe(CO)₄, HBi=BiH-Fe(CO)₄, and related systems, should be feasible synthetic targets.     

Laser-Induced Infrared Fluorescence of Ozone. Application to Remote Sensing

Over the past several years studies of laser induced infrared fluorescence have been reported.^1-5 These studies were carried out on about fifty compounds. Many of the compounds absorbed the laser radiation and fluoresced strongly. Some of these compounds; such as methane, nitromethane, chloroform, carbon disulfide, nitrous oxide, and sulfur dioxide; did not appreciably absorb at the laser wavelength (10.6 microns). Nevertheless it was found that they fluoresced, although, at a relatively low intensity.