Dependence Of Transition Temperature Research Articles

Anisotropic phase transition via high temperature thin-layer evaporation of a petroleum-based isotropic pitch

Preparation of anisotropic pitch with the moderate softening point suitable for carbon material processing from heavy oil is challenging. This is because it is very difficult to suppress excessive thermal reactions that occur during the phase transition from isotropic to anisotropic phase. Due to the thermal reaction, the softening point rises excessively and infusible particles are formed, which in turn leads to severe processibility and performance degradation of the final carbon materials. Although many efforts has been devoted to prepare 100% anisotropic pitches suitable for carbon material processing so far, not a proper method for mass production was developed. In this study, we applied high temperature thin-layer evaporation (TLE) process for the phase transition of a petroleum-derived isotropic pitch. Temperature dependence of phase transition was closely examined for the temperature between 300°C and 420°C. As a result, a noticeable number of anisotropic spheres was observed at 370°C; the spheres were grown and merged together to for a bulk phase with the 84% anisotropy at 390°C. Finally, a 100% mesophase pitch was obtained in a short time of 10min at 410°C with a high production yield of 36.0%.

A Novel Temperature‐Dependent Hydrogel Emulsion with Sol/Gel Reversible Phase Transition Behavior Based on Polystyrene‐co‐poly(N‐isopropylacrylamide)/Poly(N‐isopropylacrylamide) Core–Shell Nanoparticle

As a kind of temperature-responsive hydrogel, polystyrene-co-poly(N-isopropylacrylamide)/poly(N-isopropylacrylamide) (PS-co-PNIPAM/PNIPAM) core-shell nanoparticles prepared by two-step copolymerization are widely studied and used because of their specific structures and properties. Unlike most reports about the steady stability of PS-co-PNIPAM/PNIPAM core-shell nanoparticle hydrogel emulsion, in this work, the PS-co-PNIPAM/PNIPAM core-shell nanoparticle hydrogel emulsion (symbolized as PS/PNIPAM hydrogel emulsion), which is prepared after the second step of synthesis and without washing out a large number of PNIPAM polymer segments, shows a reversible temperature-dependent sol-gel transition characteristic during the temperature range of 34-80 °C. The PS/PNIPAM hydrogel emulsion is a normal solution at room temperature, and it changes from a sol to a gel statue when the temperature approaches up to low critical solution temperature (LCST). As the temperature continues to increase, the gel (core-shell nanoparticles as the crosslinkers and the linear PNIPAM chain as the 3D gel network) of the PS/PNIPAM hydrogel emulsion gradually shrinks and drains linearly. Compared with most crosslinked hydrogels, the hydrogel here can be arbitrarily changed in shape according to use needs, which is convenient for use, transportation, and storage. Here a new route is provided for the preparation of a PS/PNIPAM core-shell hydrogel nanoparticle system, as well as a new supramolecular crosslinking sol-gel system for application in biomedical materials, sensors, biological separation, drug release, macromolecular adsorption, and purification.

Extremely sensitive and selective flammable liquefied hydrocarbon gas sensing and inter-dependence of fluctuating operating temperature and resistance: Perspective of rare-earth doped cobalt nanoferrites

In this paper, we present a variety of cobalt-based spinel ferrites doped with 4f electron rare-earth ions to be used as flammable gas sensors. These spinel ferrites were fabricated following a glycol hydrothermal chemical-process. Due to their electronic configuration and charge dynamics, they are very sensitive and selective to integrative liquefied petroleum gases (LPG). A high response of over 730 was recorded towards 1 vol% of LPG at 225 °C. The CoSm0.1Fe1.9O4 nano-ferrite meets the criteria of a potential sensor of being highly sensitive and selective with repeatability and stability that maintained a high response of 241 over 63 days. The rare-earths doped cobalt based ferrites were classified according to two categories in terms of overall performance. The first category were the ferrites doped with the low 4f electrons and the second category belonged to the high 4f electrons. The first category composed of solid and compact nanoparticles and proved to be better in the LPG performance while giving a low photoluminescence emission intensity. This latter category had the highest combined percentages of oxygen vacancies and adsorbed oxygen. A temperature dependent tuneable carrier-type transition was observed. The ferrite has p-type characteristics at 225 °C and above, otherwise n-type below this operating temperature to room temperature.

Peculiarities of Low-Temperature Behavior of Liquids Confined in Nanostructured Silicon-Based Material.

This study is devoted to the confinement effects on freezing and melting in electrochemical systems containing nanomaterial electrodes and liquid electrolytes. The melting of nanoparticles formed upon freezing of liquids confined in pores of disordered nanostructured n-type silicon has been studied by low-temperature differential scanning calorimetry. Experimental results obtained for deionized water, an aqueous solution of potassium sulfate, and n-decane are presented. A model is proposed for predicting the melting point of nanoparticles formed during freezing of liquids inside the pores of a disordered nanostructured material. The model is based on the classical thermodynamic concept of the phase transition temperature dependence on the particle size. It takes into account the issues arising when a liquid is dispersed in a matrix of another material: the effect of mechanical stress resulted from the difference in the thermal linear expansion coefficients at a temperature gradient, the effect of the volumetric liquid content in the matrix, the presence of a nonfreezing liquid layer inside the pores, and the effect of wettability of the matrix with the liquid. Model calculations for water and n-decane confined in nanostructured silicon matrix have been carried out considering the volumetric liquid content. The results obtained have been compared with the differential scanning calorimetry data.

Relation among Oxygen Stoichiometry, Structure, and Co Valence and Spin State in Single-Layer La2-xAxCoO4±δ (A = Ca, Sr) Perovskites.

We have investigated the role of oxygen stoichiometry and structural properties in the modulation of Co valence and spin state in single-layer La2-xAxCoO4±δ (A = Sr, Ca; 0 ≤ x ≤ 1) perovskites as well as the interplay between their local structural properties and the magnetic and charge-ordering phenomena. We show the results of high angular resolution powder X-ray diffraction and Co K-edge X-ray absorption and emission spectroscopy experiments on polycrystalline and single-crystal samples. The different doping-induced changes in the Co valence and spin state by Ca (or Sr) substitution can be understood in terms of the evolving oxygen stoichiometry. For Ca doping, the interstitial oxygen excess around the La/Ca atoms in underdoped samples is rapidly lost upon increasing the Ca content. The creation of oxygen vacancies leads to the stabilization of a mixed-valence Co2.5+ independently of the Ca content. In contrast, Sr substitution leads to almost stoichiometric samples and a lower oxygen vacancy concentration, which allows higher mixed-valence states for Co up to Co2.9+. The Co mixed-valence state along the two series is fluctuating between two valence states, Co2.4+ as in La2CoO4.2 and Co2.9+ as in LaSrCoO3.91, that become periodically ordered for the charge-ordered phases around the half-doping. The X-ray emission derived spin states agree well with the Co fluctuating mixed-valence state derived from X-ray absorption spectroscopy on consideration of a distribution of high-spin Co2+ and low-spin Co3+. Furthermore, there is no quenching of the orbital contribution for the high-spin Co2+, as concluded from a comparison with macroscopic magnetization measurements. Doping holes are mainly located in the ab plane and have a strong oxygen 2p character. The major lattice distortions, which are different for Sr and Ca doping, occur along the c axis, where changes in the oxygen stoichiometry take place. Moreover, charge-order transitions are clearly shown from the anomalous increase of the c lattice parameter with an increase in the temperature above 500 K but there is no signature for a temperature-dependent spin-state transition.

All-electrical switching and electrothermo-optical response of a tristable smectic-A liquid crystal

A unique switching mechanism in the smectic-A (SmA*) phase involving textural change between any two among the planar, homeotropic and focal conic states is investigated. Exploiting the temperature-dependent textural transition characteristics of a SmA* liquid crystal (LC), we proposed a multi-stable switching scheme relying on AC voltage to induce the dielectric effect and pseudo-dielectric heating. This mechanism exhibits desirable properties for LC cells with anti-parallel planar surface treatment. Compared with the electrical operation mode of conventional SmA devices, the optical states enabled by this approach show superior qualities in both transmittance and haze value. The revealed features, including the in-phase switching, tunable operating temperature and excellent optical performance, show great potential for applications in smart glass and other energy-saving devices.

Hybrid Lead Iodide Perovskites with Mixed Cations of Thiourea and Methylamine, From One Dimension to Three Dimensions.

Hybrid halide perovskites featuring as new materials of high-performance solar cells have attracted great research interest. The temperature-dependent dimensional transition of halide perovskites is a crucial handle in the preparation of perovskite films. Only the small cations of methylammonium (MA) or formamidinium (FA) have been involved for most of the dimensional transition materials. In this work, thiourea (tu) is introduced into hybrid halide materials. A new series of 1D ribbonlike hybrid lead iodides with tu and MA cations are reported that were crystallographically characterized as MAn(Htu)n+1PbnI4n+1 (n = 1-4 denoted as 1-4, respectively; in 1, MA is replaced by tu). The width of the perovskite ribbon increases from one PbI6 octahedron to four corner-fused octahedra. Compounds 2 and 3 can be turned into a black 3D perovskite after annealing. This is an unusual mixed MA-tu hybrid halide perovskite system, in which the tu molecule plays an important role in manipulating the dimensions and their photoconductive properties. Scanning electron microscopy of the blackened sample shows that there are a lot of regular vent holes on the smooth crystal surface with sizes of hundreds of nanometers. The tunable structures and porous crystals might be advantageous in the sense of material modulation.

Temperature-dependent brittle-ductile transition of α-graphyne nanotubes under uniaxial tension

As a novel one-dimensional full-carbon allotrope, the tensile property of α-graphyne nanotubes (α-GNTs) under different temperatures was studied with the reactive molecular dynamics method. A very interesting phenomenon of temperature-dependent brittle-ductile transition for carbon nanomaterials was found no matter what the chirality of the α-GNT is. The α-GNT shows a brittle behavior with an ultimate strain of ~0.2 at relatively low temperatures. When the temperature is higher than a critical temperature, it exhibits a ductile behavior with an ultimate strain of ~0.4. The ultimate strain first decreases and then increases with the increase of temperature. The fundamental mechanism of such a brittle-ductile transition phenomenon was first revealed, which is mainly due to the thermal activation energy-controlled microstructure evolution. Beyond the critical temperature, the atomic structures around some hexagonal corners in α-GNTs would recombine through the continuous formation and annihilation of some new triangular structures. Such a mechanism is totally different from the Stone-Wales defect-induced brittle-ductile transition mechanism in carbon nanotubes (Nardelli et al, Phys. Rev. Lett, 1998, 81(21): 4656). The influence of temperature on the other physical parameters of α-GNTs, such as the Young’s modulus, yield strength, ultimate stress, was also systematically studied. The results in this paper, especially the brittle-ductile transition mechanism, would be of great help to the subsequent study and application of α-GNTs.

Temperature sensitive self-assembling hydroxybutyl chitosan nanoparticles with cationic enhancement effect for multi-functional applications

Hydroxybutyl chitosan (HBC) with different degree of substitution (DS) were prepared using a homogeneous reaction system (KOH/urea), which could achieve temperature-dependent reversible morphological transition in aqueous solution. During hydrophobic assembly, amino groups on HBC chains exposed on the surface of nanoparticles formed a poly-cationic structure. The structure of HBCs was characterized by FTIR, 13C NMR, XRD, TGA and rheology. The morphology and assembly mechanism of HBC nanoparticles were studied by TEM, AFM and DLS. Also, the results of coagulation, bacteriostatic, superoxide anion clearance and anionic contaminant removal tests suggested that HBC nanoparticles had excellent flocculation and removal effect of anionic composites. Moreover, the cytocompatibility test indicated that HBC could effectively promote proliferation and division of mouse fibroblast, mouse embryonic fibroblast and rat bone marrow mesenchymal stem cells. These cationic HBC nanoparticles exhibited great potential in multi-functional applications.

On the adsorption of a polymer chain with positive or negative bending stiffness onto a planar surface

Adsorption of a single homopolymer chain with bending stiffness on a homogeneous planar surface is studied theoretically in the framework of the lattice model and the generating functions approach. The stiffness is introduced by assigning a statistical weight to a trans-isomer (a straight segment) with respect to a gauche-isomer (a kink). This statistical weight is related to the bending energy εbend associated with a kink: k=exp(εbend∕kBT) and depends on the temperature but one can also treat k as a temperature-independent parameter. Both positive and negative values of the bending energy corresponding to stiff (εbend>0, k>1, positive stiffness) and “quasi-zigzag” (εbend<0, 0<k<1, negative stiffness) chains are considered. The dependence of the adsorption transition temperature on εbend and k is non-monotonic and has a minimum for flexible chains at εbend=0 and k=1. At the same time, at moderate and strong adsorption, the fraction of adsorbed units is a strictly increasing function of the bending energy or the stiffness parameter. Adsorption is accompanied by the straightening of the chain in the case of positive εbend and its “zigzaging” in the case of negative εbend. In contrast, when k is temperature independent, a decrease in temperature leads to the increase in the fraction trans-isomers at any positive k. The temperature dependence of the specific heat can exhibit one or two maxima in addition to the jump in at the adsorption (second order) transition point.

Evaluation of Cytotoxic Effect of Cholesterol End-Capped Poly(N-Isopropylacrylamide)s on Selected Normal and Neoplastic Cells.

PurposeEfficient intracellular delivery of a therapeutic compound is an important feature of smart drug delivery systems (SDDS). Modification of a carrier structure with a cell-penetrating ligand, ie, cholesterol moiety, is a strategy to improve cellular uptake. Cholesterol end-capped poly(N-isopropylacrylamide)s offer a promising foundation for the design of efficient thermoresponsive drug delivery systems.MethodsA series of cholesterol end-capped poly(N-isopropylacrylamide)s (PNIPAAm) with number-average molar masses ranging from 3200 to 11000 g·mol–1 were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization from original xanthate-functionalized cholesterol and self-assembled into micelles. The physicochemical characteristics and cytotoxicity of cholesterol end-capped poly(N-isopropylacrylamide)s have been thoroughly investigated.ResultsPhase transition temperature dependence on the molecular weight and hydrophilic/hydrophobic ratio in the polymers were observed in water. Biological test results showed that the obtained materials, both in disordered and micellar form, are non-hemolytic, highly compatible with fibroblasts, and toxic to glioblastoma cells. It was found that the polymer termini dictates the mode of action of the system.ConclusionThe cholesteryl moiety acts as a cell-penetrating agent, which enables disruption of the plasma membrane and in effect leads to the restriction of the tumor growth. Cholesterol end-capped PNIPAAm showing in vitro anticancer efficacy can be developed not only as drug carriers but also as components of combined/synergistic therapy.

One-Dimensional Glassy Behavior of Ultraconfined Water Strings.

Water is renowned for its anomalous behaviors, which can be linked to a distributed H-bond network in bulk water. Ultraconfinement of the water molecule can remove H-bonding, leaving only molecular water. In natural cordierite crystals, water is trapped in an orthorhombic channel with an average diameter of 5.7 Å, running through the center of the unit cell parallel to the c-axis. Calorimetric measurements reveal the existence of a one-dimensional (1D) glass linked to this water. In these channels, water molecules in truncated, sparse 1D strings interact only via dipole-dipole correlations. A physical 1D glass is formed from these strings. This unusual state can be explained by a modified Ising model. This model predicts a dependence of the glass transition temperature, Tg, on the size of these domains. This is confirmed experimentally.

Evidence that the TRPV1 S1-S4 membrane domain contributes to thermosensing

Sensing and responding to temperature is crucial in biology. The TRPV1 ion channel is a well-studied heat-sensing receptor that is also activated by vanilloid compounds, including capsaicin. Despite significant interest, the molecular underpinnings of thermosensing have remained elusive. The TRPV1 S1-S4 membrane domain couples chemical ligand binding to the pore domain during channel gating. Here we show that the S1-S4 domain also significantly contributes to thermosensing and couples to heat-activated gating. Evaluation of the isolated human TRPV1 S1-S4 domain by solution NMR, far-UV CD, and intrinsic fluorescence shows that this domain undergoes a non-denaturing temperature-dependent transition with a high thermosensitivity. Further NMR characterization of the temperature-dependent conformational changes suggests the contribution of the S1-S4 domain to thermosensing shares features with known coupling mechanisms between this domain with ligand and pH activation. Taken together, this study shows that the TRPV1 S1-S4 domain contributes to TRPV1 temperature-dependent activation.

Application of a Clapeyron-Type Equation to the Volume Phase Transition of Polymer Gels.

The applicability of the Clapeyron equation to the volume phase transition of cylindrical poly(N-isopropylacrylamide)-based gels under external force is reviewed. Firstly, the equilibrium conditions for the gels under tension are shown, and then we demonstrate that the Clapeyron equation can be applied to the volume phase transition of polymer gels to give the transition entropy or the transition enthalpy. The transition enthalpy at the volume phase transition obtained from the Clapeyron equation is compared with that from the calorimetry. A coefficient of performance, or work efficiency, for a gel actuator driven by the volume phase transition is also defined. How the work efficiency depends on applied force is shown based on a simple mechanical model. It is also shown that the force dependence of transition temperature is closely related to the efficiency curve. Experimental results are compared with the theoretical prediction.

Gelation kinetics of aqueous gelatin solutions in isothermal conditions via rheological tools

We investigate the sol-gel transition of aqueous pig-skin gelatin solutions at different concentrations and temperatures. In particular, we characterize the isothermal gelation kinetics close to the critical melting temperature, previously evaluated with dynamic temperature ramp tests. The time evolution of the moduli is analyzed at a specific fixed frequency and at various temperatures and concentrations. The isothermal study allows to evaluate the gel time and to determine its dependence on concentration and temperature.The study of the gelation kinetics over a wide range of concentrations allows to link the behavior in solution to the gelation phenomenon, confirming a different temperature dependence of the sol-gel transition according to the concentration regimeAlthough some models are available to describe this dependence, they do not simultaneously account for the effect of both parameters (i.e. temperature and concentration). Here, we propose a full empirical model that accommodates the dependence upon both temperature and concentration.

Transcriptome Analysis of Dimorphic Fungus Sporothrix schenckii Exposed to Temperature Stress

PurposeSporothrix schenckii is a thermally dimorphic fungus. In a saprotrophic environment or culturing at 25 °C, it grows as mycelia, whereas in host tissues or culturing at 37 °C, it undergoes dimorphic transition and division into pathogenic yeast cells. S. schenckii can cause serious disseminated sporotrichosis in immunocompromised hosts and presents an emerging global health problem. The mycelium-to-yeast transition was a consequence of the adaptive process to different environment. Some studies showed that the transition was significantly related to the virulence and pathogenesis of dimorphic fungi. However the genetic mechanisms of this complicated biological process are poorly understood.MethodOur study presented a comparative transcriptomic analysis perspective on temperature stress in a visceral isolates of S. schenckii, obtaining more genetic information related to dimorphic transition.ResultsThe 9.38 Gbp dataset was generated and assembled into 14,423 unigenes. Compared with gene and protein databases, 9561 unigenes were annotated. Comparative analysis identified 1259 genes expressed differentially in mycelium and yeast phase, and were categorized into a number of important biological processes, such as synthesis and metabolism, transmembrane transport, biocatalysis, oxidation reduction, and cellular signal transduction.ConclusionsThe findings suggested that temperature-dependent transition was tightly associated with stress adaptation, growth and development, signal regulation, adhesion, and colonization, which was predicted to be related with virulence and pathogenesis. Collection of these data should offer fine-scale insights into the mechanisms of dimorphism and pathogenesis of S. schenckii, and meanwhile facilitate the evolutionary and function studies of other dimorphic fungi.

Binding possibilities of calcium, zinc and copper in metaphosphate glasses - a more detailed study

To study the binding possibilities of Zn2+, Ca2+ and Cu2+ ions in the glassy phosphate network, metaphosphate glasses of xZnO-(50-x)CuO-50P2O5 and yCaO-(50-y)CuO-50P2O5 systems were prepared across the entire composition lines. Using Raman spectroscopy, 31P MAS NMR, electron paramagnetic resonance (EPR) and differential scanning calorimetry (DSC), it was found that zinc and copper are both four times coordinated and interact with donor oxygens in the same phosphate chain, calcium is six times coordinated and crosslinks phosphate chains significantly increased by this the glass transition temperature. It was further found that all copper-containing glasses are phase separated, which is also clearly reflected, in addition to the 31P MAS NMR and EPR spectra, in the compositional dependence of the glass transition temperature. The experimental results obtained by all the techniques used are discussed in detail.

Impact of ferroelectric nanoparticles on the dielectric constant of nematic liquid crystals

ABSTRACT The influence of ferroelectric BaTiO3 nanoparticles on the dielectric constant in the isotropic phase of the isotropic-nematic phase transition is studied within Landau phenomenological theory. The ferroelectric BaTiO3 nanoparticles dependence of transition temperature and dielectric constant in the isotropic phase is calculated. We compare our theoretical results with experimental data available in the literature.

Unravelling the role of a green rejuvenator agent in contrasting the aging effect on bitumen: A dynamics rheology, nuclear magnetic relaxometry and self-diffusion study

This paper evaluated the potentialities of a green and biocompatible rejuvenator agent (HR) in conferring an appreciable resistance against the effects caused by artificial aging on a given bitumen. Both neat and aged bitumens were analyzed and compared to analogous samples modified with HR. Control samples containing a vegetable oil as softening agent were also tested for comparison. The tested samples were subjected to a second aging cycle. Structural differences between the samples were carried out through an inverse Laplace transform of the NMR spin-echo decay (T2) and self-diffusion measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE-NMR) spectroscopy. In addition, dynamic rheological analyses were conducted to determine the dependence of the gel-sol transition temperature on both the type of additive and ageing process. The present study clearly highlighted the fact that artificial ageing, realized here by the rolling thin film oven test (RTFOT) and the pressure ageing vessel (PAV) test, induced important structural modifications. The analysis of relaxation times and self-diffusion coefficients indicated that ageing promoted the formation of molecular populations characterized by a shift of the distribution toward higher molecular weights compared to unaged bitumen. Diffusion data showed also an Arrhenius-like temperature dependence. A correlation between all the data was attempted to understand the role of the investigated additives. The eco-friendly biocompatible rejuvenator helped not only to restore the structure of the aged bitumen, but even slowed down the processes of a second aging (aiming at the first aged sample).

РЕГУЛИРОВАНИЕ СВОЙСТВ ЭПОКСИДНЫХ ПОЛИМЕРОВ НА ОСНОВЕ ДИФЕНИЛОЛМЕТАНА С ПОМОЩЬЮ ОЛИГОБУТАДИЕНОВОГО КАУЧУКА С КОНЦЕВЫМИ КАРБОКСИЛЬНЫМИ ГРУППАМИ

The influence of modifying additives of oligobutadiene rubber with terminal carboxyl groups of the SKD-KTR brand on the deformation-strength and adhesive properties of epoxy polymers based on the EDFM-19 product, which is a diglycidyl ether of diphenylolmethane, is studied in a wide range of concentrations. The compositions are cured with triethylentetramine methylphenol UP-583T and triethylentetramine THETA without heat supply from the outside and when heated to a temperature of 120°C. It is found that with increasing rubber concentration, the tensile strength and elastic modulus indicators monotonously decrease, especially intensively when the modifier content is up to 15 mass parts. The dependence of the glass transition temperature and adhesion strength on the amount of introduced rubber is extreme. In the range of modifier concentrations from 5 to 15 parts by weight peaks are observed, the position of which depends on the chemical nature of the hardener of the epoxy resin and the curing mode of the composition. The deformation at break increases monotonously with the increase in the elastomer content, most rapidly in the range of modifier concentrations of 5-25 mass parts. The effect is shown both for samples cured at room temperature and heat-treated compositions. Due to a significant increase in the ability of the sample to develop deformation, despite the decrease in the strength parameter, the work of destruction of modified samples increases significantly. It contributes to improving the performance of composites modified by SKD-KTR rubber under the action of shock and vibration loads.