Highly Fluorinated and Crosslinkable Dendritic Polymer for Photonic Applications

Summary: A novel crosslinkable dendritic polymer has been synthesized by the thermal polymerization of peripheral aryl trifluorovinyl ether moieties of a highly fluorinated dendrimer. The resulting perfluorocyclobutane(PFCB)‐containing dendritic polymer exhibited excellent processability, low optical loss (0.36 dB · cm⁻¹ at 1 310 nm with 1% dye doping), high thermal stability, and good solvent resistance for waveguide‐based photonic applications.

Structure of the crosslinkable fluorinated dendrimer synthesized.     

Structures for monodisperse oligoamides. A novel structure for unfolded three-amide nylon 6 and relationship with a three-amide nylon 6 6

Three-amide oligomers of nylon 6 and nylon 6 6 have been investigated using electron microscopy (imaging and diffraction), X-ray diffraction, and computational modeling. A new crystal structure has been discovered for the three-amide oligomer of nylon 6. This material crystallizes from chloroform/dodecane solutions into an unfolded crystal form that has progressively sheared hydrogen bonding in two directions between polar (unidirectional) chains. This structure is quite different from the usual room temperature α-phase structure of chain-folded nylon 6 crystals, in which alternatingly sheared hydrogen bonding occurs between chains of opposite polarity in only one direction. The occurrence of this new structure illustrates the extent to which progressively sheared hydrogen bonding is preferred over alternatingly sheared hydrogen bonding. Indeed, the progressive hydrogen bonding scheme occurs in the three-amide nylon 6 material even though it requires a disruption to the lowest potential energy all-trans conformation of the chain backbone, and requires all the chains in each hydrogen-bonded layer to be aligned in the same direction. We believe the presence of chain folding, which necessarily incorporates adjacent chains of opposite polarity into the crystal structure, prevents the formation of this new crystal structure in the nylon 6 polymer. In contrast, the three-amide nylon 6 6 crystal structure is analogous to the polymeric nylon 6 6 α-phase structure, found in both fibers and chain-folded crystals, and consists of progressive hydrogen-bonded sheets which stack with a progressive shear. In both structures, the molecules (≈ 3 nm in length) form smectic C-like layers with well-orchestrated stacking of 2.2 nm to form a three-dimensional crystal. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2849–2863, 1998     

Electrohydrodynamic stability of poorly conducting parallel fluid flow in the presence of transverse electric field

In this paper we study electrohydrodynamic instability (EHDI) in a poorly conducting parallel inviscid fluid in the presence of an electric field and space variation of electrical conductivity. It is shown that EHDI causes inhomogeniety in the material science processing. This inhomogeniety can be controlled by understanding the nature of EHDI in the presence of an electric field and a shear due to horizontal basic velocity. The condition for EHDI is determined in terms of the electric number rather than the point of inflexion of the basic velocity profile using both moment and energy methods combined with Galerkin expansion technique. From this analysis, it is shown that a proper choice of electric number controls inhomogeniety by controlling instability of a parallel poorly conducting inviscid fluid. For unstable motion it is shown that the growth rate, C_i, is confined in a semi circle region

     

A CHARACTERIZATION OF THE FLUORESCENT PROPERTIES OF CIRCULATING HUMAN EOSINOPHILS

Abstract— This paper presents a characterization of the fluorescence properties of human eosinophils isolated from peripheral blood of normal donors over a wide range of excitation and emission wavelengths. Circulating eosinophils possess three fluorescence excitation emission maxima: one at 280 nm excitation, 330 nm emission, attributable to tryptophan fluorescence, and currently unassigned peaks at 360 nm excitation, 440 nm emission and 380 nm excitation, 415 nm emission. Fluorescence microscopy studies show that the Huorescence of eosinophils may be site dependent; specifically, when observed at 365 nm excitation, circulating eosinophil Huorescence appears blue-violet, while the fluorescence of tissue-dwelling eosinophils appears amber-gold. These results should be considered in developing an optical biopsy technique to identify eosinophils in human tissue.     

Bactericidal mode of titanium dioxide photocatalysis

When exposed to near-UV light, titanium dioxide (TiO₂) exhibits a strong bactericidal activity. However, the killing mechanism(s) underlying the TiO₂ photocatalytic reaction is not yet well understood. The aim of the present study is to investigate the cellular damage sites and their contribution to cell death. A sensitive approach using o-nitrophenol β- galactopyranosideside (ONPG) as the probe and Escherichia coli as model cells has been developed. This approach is used to illustrate damages to both the cell envelope and intracellular components caused by TiO₂ photocatalytic reaction. Treatment of E. coli with TiO₂ and near-UV light resulted in an immediate increase in permeability to small molecules such as ONPG, and the leakage of large molecules such as β- galactosidase after 20 min. Kinetic data showed that cell wall damage took place in less than 20 min, followed by a progressive damage of cytoplasmic membrane and intracellular components. The results from the ONPG assay correlated well with the loss of cell viability. Cell wall damage followed by cytoplasmic membrane damage leading to a direct intracellular attack has therefore been proposed as the sequence of events when microorganisms undergo TiO₂ photocatalytic attack. It has been found that smaller TiO₂ particles cause quicker intracellular damage. Evidence has been obtained that indicated that the TiO₂ photocatalytic reaction results in continued bactericidal activity after the UV illumination terminates.