Lyotropic mesophase formation in PVA/imogolite mixture

Summary The mesophase formation was observed in the ternary system consisting of a solvent, a rigid rod solute (imogolite), and a randomly coiled polymer chain (poly(vinyl alcohol); PVA). Although the mesophase formation in this system seems to follow qualitatively the scheme presented by Flory, no marked segregation of the two solute component was confirmed. The physical properties of the composite film prepared from this ternary system were also examined.     

Simulation of mesophase formation of rodlike molecule,imogolite

Summary The process of mesophase formation of rodlike molecule, imogolite, was simulated by comparing the distance distribution function computed from models with that obtained by the Fourier-transformation of small angle X-ray scattering data. In the initial state below A-point (defined as a starting point of mesophase formation), imogolite molecules assemble into loosely packed hexagonal shape with their ends aligned in a line. The columns composed of hexagonal packing are arrnaged side by side to form raft-like sheets near the A-point and finally form mesophase above A-point.     

Comparison of thermal and cholesteric mesophase properties among the three kind of hydroxypropylcellulose (HPC) derivatives

Summary Three kind series of (2-hydroxypropyl)cellulose (HPC) derivatives, the esters (ES), the ethers (ET) and the esters containing fluorocarbon components (FES) were prepared, and the thermal and cholesteric mesophase properties were compared among them. The optical pitch of ES increased with decreasing the degree of substitution (DS). Contrary to ES, the optical pitch of ET decreased with decreasing DS. The cholesteric-isotropic transition temperature of FES exhibited the even-odd oscillation according to the number of carbons in substituent. The reverse optical pitches of ET and FES were larger than that of ES, respectively, at the same temperature and at the same number of carbons in substituent.     

Mechanical/optical behaviors of imogolite hydrogels depending on their compositions and oriented structures

A robust acrylamide (AAm) hydrogel reinforced by imogolite (IG), a perfect rigid nanotubular clay mineral, exhibited distinct tensile stress–strain characteristics and strain‐induced birefringence in accordance with the compositions of the gels. The gel showed a reversible anisotropic/isotropic structural transition in response to stretching/releasing before the breakdown strain. The strain‐induced birefringence of the IG‐reinforced gels could be fixed by the in situ interpenetrating polymerization of other AAm monomers that were impregnated into the gels in the stretched states. This resulted in gels with nonvolatile anisotropic birefringence, and therefore, the fixed anisotropic IG ordering showed specific stress–strain characteristics depending on the orientation of IG. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41691.     

Compatibility and biocompatibility study of new HPC/PU blends

BACKGROUND: Polymer blending is one of the most useful methods for the improvement or modification of the physicochemical properties of polymeric materials without altering the structure and function of individual polymers. The blends between biopolymers and synthetic polymers are of particular significance because they can combine biocompatibility with good processability and mechanical resistance and can be used as biomaterials. The aim of the blending of hydroxypropylcellulose (HPC) and polyurethane (PU) is to find applications for newly synthesized PUs and also to create new materials with possible medical applications and enhanced surface properties. RESULTS: Films containing mostly HPC or mostly PU are found to be homogeneous and transparent, while for the intermediate composition range a morphology of a fine dispersion in a continuous matrix is characteristic. The values of the blood–biomaterial interfacial tension (γ_SL) are in the range 1.96–3.27 mN m^?1, which allows us to conclude that these materials have a good haemocompatibility. CONCLUSION: The thermomechanical and morphological behaviour were explored and specific interactions were evident between the PU blocks and the HPC chains especially in the 60% HPC–20% HPC/40% PU–80% PU composition range because of the high degree of compatibility. The blends obtained are not cytotoxic and exhibit good surface properties and haemocompatibility. Therefore they could be candidates for medical and pharmaceutical applications. Copyright © 2008 Society of Chemical Industry     

Effects of air oxidation on mesophase pitch-based carbon/carbon composites

Mesophase pitch-based carbon–carbon (C/C) composites were fabricated by cycles of impregnation/carbonization using two different preforms. Air oxidation was used as a stabilization process prior to carbonization. In order to study the effects of air oxidation, composites without air oxidation were also fabricated for comparison. The results showed that the effect of air oxidation was different for different preforms. For 2-dimensional (2D) punched carbon cloth preforms, air oxidation could greatly shorten the fabrication period, and had significant effects on the matrix microstructures. Without air oxidation, the carbon matrix of the composites consisted of small domains with a mosaic texture. With air oxidation, the matrix consisted of domains mingled with flow domains. However, air oxidation had little effect on composites prepared from 2D carbon felts preforms, and the corresponding carbon matrix in the composites consisted of mainly small domains with a mosaic texture irrespective of air oxidation.     

Formation and stability of mesophase during coal hydrogenation. 1. Formation of mesophase

Vitrinite samples from Australian bituminous coals were hydrogenated in autoclaves without vehicle solvent, and the solid products were examined microscopically. When a vitrinite sample was stirred during hydrogenation, the yields of liquid and gaseous products were high. However, when the samples were not stirred, the yields were low, and the solid products contained a high proportion of mesophase. In a vertical section of a vitrinite sample which was unstirred during hydrogenation, the surface in contact with hydrogen was covered by isotropic material, underlaid by a zone of mixed isotropic and mosaic-textured material. Away from the surface, the proportion of isotropic material decreased. The authors conclude that mesophase is formed from material previously liquefied, more readily under hydrogen-deficient conditions than under conditions in which hydrogen is freely available. Application of this conclusion may increase the efficiency of hydrogenation processes by reducing the deleterious effects of mesophase formation.     

Formation and stability of mesophase during coal hydrogenation 2. Destruction of mesophase

Results from Part 1 suggest that mesophase formation during coal hydrogenation is controlled, not only by temperature and time, but also by hydrogen availability. Further work was done to test whether mesophase, once formed from asphaltene, could be re-liquefied if sufficient hydrogen were made available. Several mesophase samples were hydrogenated in an autoclave without vehicle solvent. After hydrogenation, the samples produced up to 33% of benzene-soluble material and the microscopic features of the remaining solid material changed. Mesophase formation is temperature- and time-dependent, and this process cannot be reversed by simply lowering the temperature. However, if the chemical changes occurring have been introduced by hydrogenation, mesophase can be reliquefied.     

Raman spectroscopy of mesophase pitches

Raman spectra have been measured for mesophase pitches prepared from different starting materials. The spectra exhibited the two major absorption peaks characteristic of other carbonaceous materials. The relative intensities of these peaks have been related to molecular size and to the degree of order in the mesophase. A comparison of Raman data for carbonaceous materials shows that the absorption frequency of the longer wavelength band is related to the degree of graphitization.     

Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.     

Flow of molten mesophase pitch

The rheological behavior of molten mesophase pitch has become a subject of major scientific curiosity as well as of technological importance. With the exception of a few recent studies, the early experimental techniques were not entirely adequate for precise rheological characterization of such a complex fluid as molten mesophase pitch. A reasonably extensive literature, therefore, does not seem to exist on mesophase pitch rheology. The factors which could contribute to the difficulties of accurately measuring the apparent viscosity of carbonaceous anisotropic materials are discussed herein. A Couette-flow instrument has been modified for measuring the apparent viscosity of mesophase pitch, circumventing most of the experimental difficulties. The reliability of this apparatus has been tested by cross checking the apparent viscosity measurements with the values measured from two other rheometers, Instron Capillary and Seiscor/Han, for a number of fluids. Changes in rheological properties that occur during the transformation of a commercial pitch into a totally anisotropic pitch have now been studied by an improved technique on the modified Couette apparatus. The rheology of two mesophase pitches, made from model compounds, have also been investigated for comparison.     

Lyotropic Mesophases of K-Palmitate in Protic Solvents

Comparing the phase diagrams of the three binary soap systems KC₁₆/glycerol, KC₁₆/ethylene glycol and KC₁₆/butylene glycol (KC₁₆ = K-palmitate), we found alterations in types of phase diagrams that depend on the chemical structure of the protic solvent. Variation of the polymorphic transitions were observed. In the binary system KC₁₆/ G (G = Glycerol) we observed the polymorphism: C ? G ? H ? L ? S (C = crystalline phase, G = gel phase, H = hexagonal phase, L = lamellar phase, S = isotropic solution). In the binary system KC₁₆/E (E = ethylene glycol) we found the polymorphic transitions: C ? G ? L ? S. In the binary system KC₁₆/B (B = butylene glycol) we observed the same phase sequences: C ? G ? L ? S. So we came to the conclusions that the influence, which the solution medium exerts on the formation of structures in binary systems is distinct and pronounced. Differences in number, position, extension, and in the sequence of the occurring mesophases were found as a function of the composition of mixtures and temperature.     

Rheological characteristics of mesophase pitch

Rheological characteristics of two pretreated petroleum pitches, during their transformation to mesophase, have been studied by using rotalional viscometer. Simultaneously, the formation, growth, coalescence of mesuphase spheres, and the alignment of coalesced mesophase were observed by Hot-Stage-Cinema-Microscope, discussed with the results of viscosity change and the Q.I. content. It is found that both pretreated pitches were Newtonian fluids at low temperature, but behaved pseudoplastics as increase of mesophase content above 390C. Shear thinning behaviour was also apparent in the shear rate range of 1.9–20 sec⁻¹ at temperature above 390C. The apparent viscosity-temperature curves of this pyrolysed pitches were much affected by the pretreatment conditions.     

Flow behavior of mesophase pitch

The objective of this work was to provide a comprehensive rheological and structural study of AR mesophase pitch. The shear viscosity of AR mesophase pitch was found to be qualitatively similar to results from prior investigations of mesophase pitch and followed the typical trend for liquid crystalline fluids. However, a distinct hesitation, or kink, was observed in the shear viscosity curve near the shear thinning to constant viscosity transition. This behavior has been seen previously for some low molecular weight and polymeric liquid crystals and was thought to be due to a transition between tumbling and steady alignment of the uniaxial director. Optical studies of mesophase pitch revealed an orientation change of the poly-domain structure at shear rates where the kink was observed. This orientation change results in a high viscosity to low viscosity transition. This viscosity transition, and not tumbling, is responsible for the kink phenomenon. The optical studies also reaffirmed that shear flow reduces the size of the poly domain structure and elongates the domains along the flow direction. Also under quiescent conditions, the poly-domain size increased with increasing relaxation time.     

X-rays in situ investigations on mesophase formation during carbonization of decacyclene

An in situ X-ray diffraction method has been developed, permitting one to follow all the steps preceding the formation of mesophase spherules during the decacyclene carbonization. Results have been compared with those obtained from differential thermal analysis (D.T.A.), thermogravimetric analysis (T.G.A.) and transmission electron microscopy (T.E.M.).We have established that decacyclene undergoes, near 300°C, a phase transition: ₁→ ₂. This transition is reversible and purely physical; however if temperature is maintained at 300°C the decacyclene molecule is damaged and when the weight loss reaches 5% the transition ₁→ ₂ becomes irreversible, and the ₂ high temperature phase remains stable at the room temperature.This ₂ decacyclene phase is the principal stable intermediate compound in the mesophase formation: at 300°C the ₂ phase has a well organized structure; at 410°C it begins to melt slowly into a pitch in which spherules appear at 530°C. T.E.M. investigations assign the Brooks and Taylor structure to these spheres.