Mesophase Development Research Articles

A temperature-programmed oxidation method for quantitative characterization of the thermal cokes morphology

A series of thermal cokes obtained by coking of vacuum residues and fractions have been studied by polarized light microscopy observation, scanning electron microscope (SEM), and temperature-programmed oxidation (TPO) technique. The anisotropic degrees of coke samples are found to be considerably different for discriminating characterization, which indicates that the coke morphology is closely dependent on the chemical nature of the coking materials. The restricted mesophase development in thermal coke might be ascribed to the increasing amount of heteroatoms contained in the parent coking materials. A proper signal analysis procedure of TPO profiles was obtained to discriminate the carbon species in the coke quantitatively, and then a good one-to-one correlation between determinations by polarized-light micrographs analysis and TPO method was observed, which shows that the TPO technique could be a suitable and more rapid method than polarized-light microscopy to quantitatively assess the morphology of coke, even in some situations in which the traditional method is inadequate.

Deviation of phase transition process in surface-tethered thermotropic liquid crystalline polymer nanocomposites with graphene oxide: a spectroscopic study

Temperature-resolved FTIR spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) was employed to elucidate the dynamic mesophase transition behavior of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) blended with PMPCS grafted graphene oxide (GO-PMPCS) nanofiller. After integration with 2.0 wt% nanofiller, the columnar nematic phase of polymer nanocomposites was retained while deviation of the mesophase transition temperature was identified, which was ascribed to the π–π stacking interactions and charge transfer effect between polymer and GO sheets revealed by Raman and X-ray photoelectron spectroscopy. Based on 2Dcos analysis, a sequential group motion from aromatic rings to carbonyl groups and main chains was discerned at the early stage of the phase transition. It was concluded that surface-tethering of the PMPCS matrix onto GO sheets may be preferred before the mesophase development. A two-step mesophase transition process defined as a physical adsorption process and a mesophase development process under physical cross-linking was illustrated.

Formation of Mesophase Spheres in a QI-Free Coal Tar Pitch

A QI-free coal tar pitch prepared by solvent extraction from a soft coal tar pitch was subjected to a series of thermal treatments at a predetermined temperature for different holding times. The development of mesophase was discussed in terms of its size and content in the heat-treated pitches. Results showed that the size and yield of the dispersed mesophase spheres in the isotropic matrix strongly depended on the holding temperatures. When the holding temperature was less than 400 °C, only a few of small spheres formed in the mesophase pitches. However, when the holding temperature was over 420 °C, the diameter and yield of mesophase spheres in the heat-treatment pitches increased progressively with increase of the holding time. Treatment at 440 °C for 4h led to 19.9 % of the yield and the average sphere radius was 4.5-100 . In the SEM photograph of mesocarbon microbeads obtained from the heat-treated pitches using soxhlet extraction. Many small flaky particles and sporadic rugby ball-shaped particles were observed as well as a large number of spherical particles.

Cholesteric mesophase in side-chain liquid crystalline polymers: influence of mesogen interdigitation and motional decoupling

In this paper, the thermal, optical and mesomorphic properties of side-chain liquid crystalline (SCLC) homopolymers (PNBCh-n), in which cholesteryl mesogens are linked to a polynorbornene backbone by different lengths of methylene spacer (n = 4, 5, 9, 10 and 15), are investigated. By doing so, the impact of flexible spacer length on the formation of different types of LC mesophase is explained. Because of comb-shaped SCLC polymer architecture, smectic mesophases are primarily found in PNBCh-n. Interestingly, cholesteric mesophases are identified only in PNBCh-9 and 10, which are proved by (1) the selective light reflection in UV-Vis analysis, (2) the characteristic oily streak texture under polarized optical microscope (POM) and (3) a long range periodicity in the cross-sectioned films from transmission electron microscope (TEM) investigation. Moreover, temperature-controlled X-ray scattering measurements are performed to examine mesomorphic structure evolution. By comparing the mesomorphic structures in this series of SCLC homopolymers, both extent of mesogen interdigitation and motional decoupling between backbone and mesogenic side-chains are found to play a critical role in the development of cholesteric mesophase. This structure–property study of PNBCh-n will help elucidate the importance of molecular structure, particularly the length of spacers, on the formation of cholesteric mesophase and its importance in the design of thermochromic devices.

Influence of Depressurization and Cooling on the Formation and Development of Mesophase

The effect of cooling and depressurization on the formation and growth of carbonaceous mesophase in petroleum vacuum residue was investigated using a novel stirred hot-stage reactor. This apparatus...

Molecular Simulation of a Nematic Liquid Crystal Cell with Asymmetric Recurrent Boundary Conditions

For several years now the physics and chemistry of condensed matter attracts a great deal of attention, while also occupying an extremely important position in the research activity worldwide. Liquid crystalline materials, in particular, present numerous applications in the fields of science and technology. Since the development of the liquid crystals display (LCD) technology, a significant concern was devoted to the development and characterization of these fascinating mesophases. In the present paper we perform several Monte Carlo simulations, by using the Lebwohl-Lasher model, for investigating the molecular director configuration in a nematic liquid crystal cell having varying boundary anchoring conditions in asymmetric circumstances. For this geometry, we analyze the molecular spatial behaviour, while mapping the local order parameter distribution for a nematic phase temperature. We also characterize the shape of the transition regions which strongly depend on the distance to the boundaries, and analyze the neighboring spins behaviour throughout the bulk. Furthermore, by using the Müeller matrix approach, we simulated the transmission of light through the nematic cell at normal incidence under crossed polarizers condition. These investigations seek to enrich our scientific knowledge about the fascinating research topics homeotropic in condensed matter physics by exploring interesting issues related to the orientational and optical properties of liquid crystals in confined geometries.

Effect of cooling rate on the crystal/mesophase polymorphism of polyamide 6

The solidification of the quiescent polyamide 6 (PA 6) melt has been analyzed as a function of the cooling rate in a wide range between 1.67 × 10−2 and close to 2 × 102 K s−1, by means of differential scanning calorimetry at a low cooling rate of up to about 1 K s−1, and by the recording of continuous cooling curves and time-resolved X-ray diffraction on cooling at a higher rate. The performed experiments allowed for the first time to establish the relationship between the cooling rate, the crystallization temperature, and the X-ray structure of PA 6. The exclusive formation of monoclinic α-crystals is only detected if the crystallization temperature is higher than about 430 K or if the cooling rate is slower than about 5 K s−1, respectively. The formation of α-crystals is increasingly replaced by the development of mesophase with increasing cooling rate, accompanied with a decrease of the temperature of crystallization/ordering. Finally, completely amorphous samples were obtained on cooling faster than about 102 K s−1. The continuous decrease of the temperature of crystallization with increasing cooling rate, regardless of the specific structure formed, precludes a primary effect of the nucleation mechanism on the α-crystal/mesophase polymorphism of PA 6. A preliminary discussion of the effect of molar mass of PA 6 on the cooling rate-dependent polymorphism is also included.

Real-Time WAXD Detection of Mesophase Development during Quenching of Propene/Ethylene Copolymers

Real-time development of the mesomorphic structure in random propene-ethylene copolymers has beenmonitored during fast cooling from the melt by coupling an effective quenching device with a state-of the-art detector at a synchrotron radiation facility. Even when the whole structuring process lasts onlyfew tenths of a second, it has been possible to precisely follow the progress of the phase transition.This has enabled us to appreciate that the kinetics of the mesophase development is affected to a lesserextent that of the monoclinic -form by randomly distributed ethylene constitutional defects.

Structural development of poly(ethylene terephthalate) during uniaxial stretching above the glass-transition temperature: Study of the statistical influence of the stretching variables

In this article, we present an investigation of the structural development of poly(ethylene terephthalate) (PET) during uniaxial stretching above the glass-transition temperature; this followed a statistical design of experiment approach to determine the influence of the stretching variables on the structural development. Amorphous PET was submitted to a stretching program with variations in the stretching temperature (Tst), stretching rate ( ), and stretching ratio (λst). Stretched samples were rapidly quenched and characterized by wide-angle X-ray scattering, optical birefringence, and differential scanning calorimetry. The relevance and influence of the stretching variables on the obtained parameters (phase fraction, phase orientation, and thermal parameters) were analyzed. The strain-induced crystallinity was controlled by Tst, λst, and the interactions between them. Mesophase development was not dependant on Tst but on the interactions between and λst. The molecular orientation was proportionally dependent on Tst, λst, and their interactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Conformational changes in novel thermotropic liquid crystalline polymer without conventional mesogens: A Raman spectroscopic investigation

Raman spectroscopy was applied to study the conformational changes of poly[di(alkyl) vinylterephthalate] (alkyl = n-butyl and sec-butyl). Spectral regions assigned to C–H, C–C and ester carbonyl stretching modes were utilized to provide information on the molecular motion, the relative content of trans and gauche conformers, and the specific interactions existed in the mesophase formation process of these novel thermotropic liquid crystalline polymers. Both the experimental results and the conformational analysis suggested that the aliphatic side groups do have a significant impact on the formation of stable liquid crystalline phase. Based on the van’t Hoff relation, the thermodynamic parameters in the phase transition of poly[di(n-butyl) vinylterephthalate] were estimated (ΔH = 5.52 kJ mol−1, ΔS = 14.02 J mol−1 K−1), which were much smaller than the typical values generally obtained in first-order phase transition. Based on generalized two-dimensional correlation Raman analysis, specific interaction among the phenyl-ring in the mesophase development process was elucidated.

Continuous Cooling Curves Diagrams of Propene/Ethylene Random Copolymers. The Role of Ethylene Counits in Mesophase Development

A simple method to investigate polymer crystallization during fast cooling, based on in situ temperature acquisition and ex-situ structural characterization, is proposed. The approach enables one to obtain the continuous cooling curve (CCC) diagrams, widely used in metallurgy but seldom adopted for semicrystalline polymers. This method is here exploited to gain new insights on polymorphic behavior of quenched polypropylene and its copolymers with ethylene. Experimental CCC diagrams, covering a wide range of crystallization temperatures in the domains of monoclinic structure and mesophase, are obtained for the first time. The role of counits in affecting the development of the mesophase upon fast cooling is assessed: the critical cooling rate above which a predominant fraction of mesomorphic form is generated significantly decreases with increasing comonomer concentration. This is due to the remarkable hindrance of ethylene counits on the crystallization kinetics of the R-form, which indirectly favors the development of the less affected mesophase. We expect that this concept can be extended to any kind of defects that disturbs the structuring of the monoclinic phase.

Porous structures controlled by segregation of ordered mesophases in poly(N,N-dimethylacrylamide) hydrogels polymerized from an isotropic AOT/water medium

N,N-dimethylacrylamide with cross-linker (N,N′-methylenebis(acrylamide)) is polymerized in the presence of various amounts (4.5–51% v/v) of the anionic surfactant AOT. All initial mixtures are isotropic homogeneous solutions, but with polymerization they become microheterogeneous due to development of an anisotropic mesophase whose structure varies from lamellar to cubic to hexagonal (on increasing the AOT concentration). The polymerization is started in two ways: with initiator (AIBN), and induced by X-rays (without initiator). The hydrogels obtained at the end of polymerization with AIBN are analysed regarding swelling capacity and porous structure. Swelling increases with AOT concentration, and the rate of this increase is larger when the mesophase formed is hexagonal than when it is lamellar. These ordered domains induce the following porogen effects: (i) more macropores with a better defined geometry are formed when the mesophase is hexagonal. (ii) The mean diameter of the pores is controlled by the type of mesophase: 25 μm (lamellar); 55 μm (hexagonal). The evolution of polymerization induced by X-rays is followed during a period of time to study the development of the mesophase that occurs by a segregation process, and a model in four steps is proposed to explain the results.

Microstructure of electrode pitch at OAO Zaporozhkoks

Analysis of literature data (including ASTM standards) shows that the only existing method that permits the identification of meso phase in pitch is optical microscopy. Even in special conditions conducive to meso-phase development, its formation in the pitch considered is found to be extremely slow.

Thermally induced mesophase development in ethanesilica filmsvia macromolecular templating approach

Mesoporous ethanesilica thin film was prepared using PEO-PLGA-PEO triblock copolymers as structure-directing agents and (1,2-bis(triethoxysilyl) ethane BTESE; bridged organosilicates) as inorganic precursors via one-step sol-gel condensation of ethanesilica precursors. The mesostructure of ethanesilica films is critically dependent on the processing experimental parameters after the hydrolyzed silica sol mixture was spin-cast. This study examined the effects of the block copolymer template/organosilica precursor ratio in the casting solution and aging period before calcination of the mesostructure. It was further demonstrated that mesoscopic ordering of organosilicate thin films is induced by the rearrangement of block copolymer template/organosilica hybrid during thermal decomposition of the PEO-PLGA-PEO triblock copolymer. The mesoporous structure and morphology were characterized by SAXS, TEM and solid-state NMR measurement.

Needle coke formation derived from co-carbonization of ethylene tar pitch and polystyrene

Ethylene tar pitch was co-carbonized with waste polystyrene to prepare needle coke. The modified properties of mesophase, which were greatly improved due to increasing naphthenic and other alkyl content, availed the formation of needle coke with high quality. The coefficient of thermal expansion value was decreased from 3.2 × 10 −6/°C to 0.3 × 10 −6/°C and the optical texture of the coke was changed from coarse mosaic texture to flow domain of high uniaxial orientation after adding waste polystyrene into ethylene tar pitch. The low viscosity of the mesophase pitches favored the development of mesophase and highly uniaxial arrangement. The increase in alkyl group content greatly improved characteristics of the needle coke.

Microindentation technique as a tool for investigating the development of order in PET under uniaxial stress

The development of microhardness during annealing was used as a tool to follow the development of the liquid crystalline transient mesophase during the crystallization of uniaxially oriented polyethylene terephthalate (PET). 2D X-ray diffraction was used to characterize the different stages of the crystallization process. We were able to separate those stages by quenching into air. Microindentation hardness experiments were done in real time where samples were heated with their ends fixed on a specially developed stage and microhardness was measured simultaneously. The oriented samples examined exhibit a clear difference in behavior from isotropic samples that mainly lack the existence of such an ordered mesophase. The mesophase clearly has a reinforcement effect on the whole polymer matrix that leads to an increase in hardness value with annealing of the oriented PET films. Microindentation hardness is shown to be a versatile tool to detect the existence of the liquid crystalline transient mesophase. It is also efficient in comparing and explaining results obtained by wide angle X-ray scattering.

Structural changes during pitch-based carbon granular composites carbonisation

This article deals with the study of carbon composites behavior during their carbonization. Composites were prepared using four granular carbons (graphite, anthracite, green petroleum coke, and foundry coke) and four pitches (a commercial impregnating coal-tar pitch, an air-blown and two thermally treated pitches). The evolution of the optical microstructure, porosity, volume, and weight of carbon composites was monitored at different intermediate carbonization temperatures (350, 500, 700, and finally 1000 °C). The porosity of composites increases with carbonization due to volume changes and weight loss of pitches. Weight loss of carbon composites during their carbonization mainly depends on the pitch characteristics and it was slightly influenced by the presence of granular carbon. On the other hand, carbon composites with the commercial coal-tar pitch and foundry coke, anthracite, or graphite deform in the initial stages of carbonization (<350 °C) probably due to the lower porosity of the green pellets and the high amount of low-molecular weight compounds of the pitch. Carbon composites with green petroleum coke underwent important dimensional changes during their carbonization, expanding initially and then shrinking at temperatures above 700 °C. The type of granular carbon strongly influenced the microstructure of the final carbon composite, as a result of its effect on the development of mesophase. Graphite, anthracite and foundry coke delays mesophase development, whereas green petroleum coke accelerates mesophase formation.

Molecular Composition of the High-Boiling Components of Needle Coke Feedstocks and Mesophase Development

Mesophase development during the carbonization of needle coke feedstocks in delayed coking affects the microstructural anisotropy (or graphitizability) of the resulting coke. Previous work has employed gas chromatography/mass spectrometry (GC/MS) to study the relationships between the molecular composition of the fluid catalytic cracking decant oil (FCC DO) and mesophase development. In this study, the principal emphasis was placed on analyzing the non-GC amenable fraction of DO samples using a combination of analytical techniques, including high pressure liquid chromatography with photodiode array (PDA) and mass spectrometer detectors in tandem (HPLC/PDA and HPLC/MS/MS), and laser desorption mass spectrometry (LD/MS). The experimental data showed that major molecular species in DO samples consist of 3–6 ring multimethyl-substituted polyaromatic hydrocarbons (PAHs), including phenanthrenes, pyrenes, chrysenes, benzopyrenes, perylenes, and benzo[g,h,i]perylenes. Large differences were observed in the molec...

A Laboratory Study of a Pretreatment Approach To Accommodate High-Sulfur FCC Decant Oils as Feedstocks for Commercial Needle Coke

In the delayed coking process, the actual feed to the coking drum consists of a high-boiling fraction of the feedstock, fluid catalytic cracking decant oil (FCC-DO), and the high-boiling end of the liquid products produced by delayed coking (recycle). As distinct from the parent decant oil feed, the molecular composition and coking behavior of actual feed samples to the coking drum (CF) are reported for the first time in this paper. This study examines a commercial pretreatment approach where the feedstock to the fractionator column includes a hydrotreated fraction (HYD) and a vacuum tower bottom (VTB) fraction of a decant oil. Samples of two sets of decant oils including the corresponding HYD, VTB, and CF derivatives were analyzed and carbonized in laboratory reactors to monitor mesophase development from these materials. Decant oil samples and their derivatives, HYD, VTB, and CF, have substantially different molecular composition. The CF samples are characterized by lower degrees of methyl substitution ...

Investigating carbonization and graphitization using electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM)

Electron energy loss spectroscopy (EELS) in the transmission electron microscope (TEM) is explored as a useful characterization technique in the study of carbonization and graphitization of organic precursors. A model series of carbon materials was prepared from highly graphitizable petroleum pitch heat treated in the range 200–2730°C. Initial characterization was performed using the established techniques of X-ray diffraction (XRD), He pycnometry, TEM, electron diffraction and high-resolution lattice imaging (HREM). EELS in the TEM was then examined. Two routes are presented to quantify the change in the proportion of sp 2 type hybridization accompanying the heat treatment as the material transforms to the graphitic state. Both routes suggest an initial relative sp 2 content of ∼70%, rapidly increasing to ∼90% during mesophase development and carbonization, and then slowly increasing to 100% during graphitization. The peak position of the bulk valence plasmon (π + σ) is shown to be an excellent measure of the degree of graphitic character, and its fundamental dependence upon sample density (ρ) is confirmed. The appearance and definition of features within the core loss region representing the density of unoccupied σ* states are demonstrated to be an excellent measure of the extent of order. Finally, a method is established by which to extract the C–C bond length from core loss EELS spectra with an accuracy of ±0.1 pm. This method suggests an average bond length of 1.44 Å in samples with low heat treatment temperatures, decreasing to the theoretical length of 1.42 Å as both the heteroatom content and proportion of non-sp 2-type hybridized carbon atoms decrease.