Sergey Gordeyev

Polysulfone Hollow Fiber Gas Separation Membranes Filled with Submicron Particles

Abstract: Three different fillers, carbon black (CB), vapor grown carbon fibers (VGCF), and TiO2, were incorporated into polysulfone spinning solutions with the intention of producing highly selective membranes with enhanced mechanical strength. The effect of filler presence on gas permeation characteristics, mechanical strength (bursting pressure), and morphology was investigated and compared to unfilled membranes. As well as studying filler types, the influence of CB filler concentration on membrane performance was also examined. For all filler types (at a concentration of 5%w/w), the pressure‐normalized flux of O2, N2, and CH4 was greater in the composite than in the unfilled membranes. The CO2 pressure‐normalized flux was only greater in the TiO2 composite membranes. For CB and VGCF, the CO2 pressure‐normalized flux was reduced compared with unfilled membranes. Three CB concentrations were investigated (2, 5, and 10%w/w). For O2, N2, and CH4, pressure‐normalized flux peaked at 5%w/w CB. CO2 exhibited the opposite trend, showing a minimum pressure‐normalized flux at 5%w/w. Considering O2/N2 and CO2/CH4 gas pairs and the various filled membrane categories, only the O2/N2 selectivity of the 2%w/w CB filled membranes was higher than that of the unfilled fibers—all other selectivities were lower. In terms of CB concentration, selectivity was a minimum at the intermediate concentration of 5%w/w. All the filled membrane types exhibited greater mechanical strength (bursting pressure) than unfilled fibers apart from the 5%w/w VGCF composites. The 2%w/w CB composites were the strongest. Electron microscopy showed no visible differences in general morphology between the various filled and unfilled membranes.

Fluorene functionalised sexithiophenes—utilising intramolecular charge transfer to extend the photocurrent spectrum in organic solar cells

A new series of oligothiophenes bearing electron deficient fluorene units have been prepared and characterised. The materials are functionalised by C8/C11 alkyl chains or triethylene glycol side groups, yet the higher oligomers remain poorly soluble. The absorption characteristics of a sexithiophene analogue (compound 3) have been studied by UV-vis and photoinduced absorption spectroscopy. Photovoltaic cells have been fabricated from blends of 3 and fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photocurrent spectrum of the device matches the absorption spectrum of the sexithiophene system which incorporates an intramolecular charge transfer band arising from the 1,3-dithiole-fluorene units. A modest power conversion efficiency of 0.1% was achieved.

Super-selective polysulfone hollow fiber membranes for gas separation: rheological assessment of the spinning solution

A polysulfone spinning solution used recently to produce enhanced selectivity gas separation hollow fiber membranes was rheologically assessed using a rotational rheometer and an optical shear cell. Effects of temperature and shear rate on viscosity, power law behavior and normal force provided some clues regarding phase inversion and molecular orientation. At relatively low temperatures, phase inversion may occur in the absence of a shear field. At moderately low temperatures, phase inversion may be induced by applied shear. At higher temperatures, phase inversion is not induced by shear but rather shear induces molecular orientation. The results suggest that, unless spinning at low temperature, extrusion shear does not directly induce demixing during membrane formation but, instead, is linked indirectly to phase inversion through induced molecular orientation which, in turn, affects the subsequent dry or wet precipitation stages in spinning. This work is a step towards the construction of phase diagrams and determining their distortion in shear fields. Such knowledge, coupled with deeper insights into induced polymer molecule orientation, would enable further improvements in spinning techniques and membrane performance.

Rheology assessment of cellulose acetate spinning solution and its influence on reverse osmosis hollow fiber membrane performance

Cellulose acetate spinning solution used to produce reverse osmosis (RO) hollow fiber membranes was rheologically assessed using a rotational rheometer and an optical shear cell. Rheology measurements which involved flow curves were carried out so as to obtain the values of power law coefficients, n and k. The power law behaviour, normal force and flow profiles generated provided clues regarding phase inversion and molecular orientation. These rheological results are then correlated to the performance of cellulose acetate RO hollow fibers spun at different extrusion shear rates. The results suggest that extrusion shear is linked indirectly to phase inversion through induced molecular orientation, which in turn, affects the subsequent dry/wet precipitation stages in spinning. As the extrusion shear rate increases, the level of shear experienced at the walls of the spinneret also increases, thus leading to greater molecular orientation, resulting in membranes with higher rejection and flux rates.

The Introduction of Pyrrolotetrathiafulvalene into Conjugated Architectures: Synthesis and Electronic Properties

A series of new conjugated copolymers incorporating the redox-active pyrrolo-TTF unit has been synthesised. The properties of the polymers have been investigated by cyclic voltammetry and electronic absorption spectroscopy, revealing that the pyrrolo-TTF behaves very differently to its thieno-TTF variant. In comparison to thieno analogues, the band gaps of the new polymers are wider than expected due to a decrease in the polarizability of the heteratom (nitrogen vs. sulfur) and steric interactions between repeat units. Whilst the pyrrolo-TTF units are stronger electron donors than thieno-TTFs in related structures, the two redox active elements of the new polymers (TTF and conjugated chain) function independently under oxidative conditions.

Processing and properties of polysulfone hollow fibre membranes for gas separation filled with sub-micron carbon fibres

Polysulfone hollow fibre membranes, of the type produced previously with enhanced gas separation properties, were filled with vapour grown carbon fibres (VGCF) of sub-micron diameter. The effect of filler content on mechanical and gas permeation characteristics was studied. Hollow fibre membranes filled with up to 2.8 vol. % of VGCF were produced using forced convection dry jet/wet spinning. Fibre stiffness increased with increasing VGCF filler content. The fibres with the highest concentration of filler were about 30% more stiff than unfilled membranes. The addition of VGCF lead to a rise in permeability and some decrease in selectivity.

Raman study of uniaxial deformation of single-crystal mats of ultrahigh molecular weight linear polyethylene

We present for the first time a Raman spectroscopic study of the deformation process of solution-crystallized single-crystal mats of ultrahigh molecular weight linear polyethylene (UHMW PE). We study the deformed regions of the films, drawn only until the formation of the neck, and the films of much higher draw ratios, just before rupture starts. For comparison, we have also carried out Raman investigations of films produced by compression of UHMW PE powder. We have found that the uniaxial molecular orientation in the neck region of the single-crystal mat films develops more slowly as compared to the films, prepared by compression of the UHMW PE powder.

Raman study of orientational order in polymers

In this paper, we present some analytical results in the development of the classical Bower theory of Raman scattering in the partially oriented polymers. We consider more general case of arbitrary molecular orientation instead of Bowers assumption about sample having three mutually perpendicular two-fold axes of rotational symmetry. We also present here the experimental data on the study of structure of one-way-drawn polyethylene tapes and polysulfone hollow fiber membranes.

Analysis of macromolecule orientation in hot drawn polyethylene by polarized Raman spectroscopy

A new experimental method for the investigation of structure of oriented polyethylene (PE) by Raman spectroscopy is proposed. The method is based on decomposition into two separate lines the Raman line around 1300 cm-1 assigned to CH2-twisting vibrations. The decomposed lines are associated with polymer chains of crystalline and amorphous regions in structure of PE. It is assumed that the analytical relationships between the second and forth coefficients in the expansion of the orientation distribution function in a series of Legendre polynomials and the depolarization ratios previously obtained for the vibrations with B2g + B3g symmetry are valid for each line. It implies that the orientation parameters can be calculated separately for both crystalline and amorphous regions. The integral intensities of the decomposed liens have been used to estimate crystallinity. To eliminate the effects of orientation and high numerical aperture objective correction procedures were introduced. The structure changes in ultra high molecular weight PE upon draw ratio have been studied by this method. It was shown that valuable information could be obtained concerning the efficiency of fibrillar structure formation.