High-resolution Differential Scanning Calorimetry Research Articles

Калориметрия фазовых переходов «ферромагнетик ↔ парамагнетик» в железе, кобальте, никеле

There are some special features in calorimetry signal introduced by the ferromagnetic ↔ paramagnetic phase transitions in magnetic materials. The purpose of this study was to investigate, by means of high-resolution differential scanning calorimetry, the effects of heat flux change during direct and reverse second-order phase transformations of the type ferromagnetic ↔ paramagnetic in some high-purity metals possessing natural ferromagnetism: iron, cobalt, and nickel. The literature review indicates that so far there has been no research describing such phase transitions with the help of differential scanning calorimetry. Our study detected anomalies in the dependences of heat flux intensity on temperature. There was noted a shift to the region of higher temperatures during heating in the range of thermocycling rates of 5-10-20-40 K/min. A shift to the region of lower temperatures during cooling in the same range of thermocycling rates was observed in the area of registration of second-order phase transition. The possibility of using calorimetric measurements for estimating the Curie temperature at ferromagnetic ↔ paramagnetic transitions in the metals is shown. The authors highlight that, when conducting high-resolution calorimetric measurements, it is essential to take into consideration in the total heat flux balance the possible contribution from the effects associated with second-order phase transitions, including, in particular, ferromagnetic ↔ paramagnetic transitions.

Water based quad acrylic copolymer/cloisite 30B nanocomposite heat resistant adhesive: thermal and rheological properties

In this study, a quad acrylic copolymer composed of four monomers namely acrylic acid, methacrylic acid, butyl acrylate, and methyl methacrylate/cloisite30B(C30B) nanocomposites with different loading of nanoclay (0.5–3.0%) is prepared by the in-situ method for heat resistant adhesive application. Different parameters like solid content, solubility, appearance, acid value, and pH values are measured for each nanoclay filled copolymer. For dispersion and thermal characterization of nanocomposite X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) are performed. Epoxy resin along with curing agent is added to the acrylic copolymer/C30B nanocomposite to prepare adhesive. The rheological properties for amplitude sweep, frequency sweep, and temperature scan are analyzed. The nanoclay content doesn’t affect the shear-thinning component significantly but improves the complex viscosity and elastic behavior of the adhesives. The crossover point shows good dispersion of C30B up to 2.0% in nanocomposite adhesive. Peel strength is found to be increased with an increase in nanofiller content up to 2.0%. A significant improvement in peel strength is observed when exposed to 150 °C for 45 min. Temperature sweep study by rheology and peel strength results at high temperature suggest that these adhesives can be used in high-temperature resistance adhesive application areas like heat seal packaging and fabric lamination.

Structural Characterization of Al65Cu20Fe15 Melt-Spun Alloy by X-ray, Neutron Diffraction, High-Resolution Electron Microscopy and Mössbauer Spectroscopy.

The aim of the work was to characterize the structure of Al65Cu20Fe15 alloy obtained with the use of conventional casting and rapid solidification-melt-spinning technology. Based on the literature data, the possibility of an icosahedral quasicrystalline phase forming in the Al-Cu-Fe was verified. Structure analysis was performed based on the results of X-ray diffraction, neutron diffraction, 57Fe Mössbauer and transmission electron microscopy. Studies using differential scanning calorimetry were carried out to describe the crystallization mechanism. Additionally, electrochemical tests were performed in order to characterize the influence of the structure and cooling rate on the corrosion resistance. On the basis of the structural studies, the formation of a metastable icosahedral phase and partial amorphous state of ribbon structure were demonstrated. The possibility of the formation of icosahedral quasicrystalline phase I-AlCuFe together with the crystalline phases was indicated by X-ray diffraction (XRD), neutron diffraction (ND) patterns, Mössbauer spectroscopy, high-resolution transmission electron microscopy (HRTEM) observations and differential scanning calorimetry (DSC) curves. The beneficial effect of the application of rapid solidification on the corrosive properties was also confirmed.

Experimental and Molecular Dynamics Simulation Study of the Effects of Lignin Dimers on the Gel-to-Fluid Phase Transition in DPPC Bilayers.

High resolution differential scanning calorimetry (DSC) and molecular dynamics (MD) simulations were used to investigate the effect of three lignin dimers on the gel to fluid phase transition in DPPC lipid bilayers. The goal of this research is to begin to understand the partitioning of model lignin dimers into lipid bilayers and its effects on the gel to fluid transition temperature (Tm). The long-term objective is to establish structure-function relationships for well-defined lignin derivatives at biologically relevant surfaces. This work uses a newly synthesized guiacylglycerol guaiacol ester with a hydroxypropenyl (HOC3H4-) group resembling natural lignin (GG dimer), compared with a truncated GG dimer without the HOC3H4- and benzyl-modified GG dimers. The DSC results show that the dimer most like natural lignin (with a hydroxypropenyl tail) has log K = 2.72 ± 0.05, and MD simulations show that it associates with the headgroups of the lipid but does not penetrate strongly into the interior of the bilayer. Therefore, this dimer has little effect on the Tm value. In contrast, the truncated dimer, which has been used as a representative GG dimer in prior studies, partitions into the bilayer, as seen in MD simulations, and shifts Tm because of its increased lipophilicity (DSC log K = 3.45 ± 0.20). Similarly, modification of the natural GG dimer by benzylation of the phenol makes it lipophilic (DSC log K = 3.38 ± 0.28), causing it to partition into the bilayer, as seen in MD simulations and shift Tm. In MD, we capture the transition from gel to fluid phase by defining and analyzing a normalized deuterium order parameter averaged over all carbon atoms located in the middle of the lipid tails. In this way, the phase transition can be clearly observed and, importantly, MD results show the same trend of transition temperature shifts as the DSC results. Furthermore, we compare partition coefficients estimated from free energy profiles calculated in MD to those obtained from experiment and they are in qualitative agreement. The success at predicting the structural effects of lignin dimers on lipid bilayers suggests that MD simulations can be used in the future to screen the interactions of lignin oligomers and their derivatives with lipid bilayers.

Thermal Effects Due to Crystallization of Alloys with Unlimited and Limited Solubility of Components

High-resolution differential scanning calorimetry has been used to study the crystallization of binary alloys with unlimited and limited solubility of their constituents. A sharp and intense emission of crystallization heat has been invariably observed immediately below the liquidus curve. Standard techniques to describe crystallization in the intercritical temperature range cannot explain the above phenomena. It is assumed that they may be associated with a large number of local microvolumes enriched with a crystallization-controlling component (concentration fluctuations) that appear in the liquid as approaching the liquidus curve. The appearance of such microvolumes precedes the spontaneous formation of many crystallites in a large volume of the liquid phase.

Specific Features and Regularities of Melting and Crystallization Processes in Binary Metallic Alloys

The melting and crystallization processes in some binary alloys based on the Ag–Cu model system have been studied by high-resolution differential scanning calorimetry. The crystallization and melting is found to be accompanied by heat flow jumps as the liquidus line is achieved or the melting process is completed. During crystallization, these phenomena are assumed to be related to the formation in a liquid of a great number of local microvolumes (concentration fluctuations) enriched in the component leading the crystallization. Their appearance precedes the process of spontaneous formation and growth of many crystals of a new phase. It is established that our concepts on the crystallization and melting processes in binary metallic alloys should be complemented.

Особенности и закономерности процессов плавления и кристаллизации двухкомпонентных металлических сплавов

The processes of melting and crystallization in some two-component alloys based on the Ag-Cu model system have been investigated using high resolution differential scanning calorimetry. During crystallization or melting jumps in the heat flow upon reaching the liquidus line were detected. It is assumed that during crystallization, these phenomena are associated with the formation of a large number of local microvolumes (concentration fluctuations) in the liquid, enriched with the component leading to crystallization. Their appearance precedes the beginning of the processes of spontaneous formation and growth of numerous crystals of the new phase. The necessity of correcting the existing ideas about the crystallization and melting of two-component metal alloys is revialed.

Тепловые эффекты при кристаллизации и плавлении сплавов с неограниченной растворимостью компонентов

High-resolution differential scanning calorimetry (DSC) has been used to study the crystallization processes of two-component alloys with unlimited solubility of the components that form them. It is shown that in all cases, immediately below the liquidus line, a jump in the release of crystallization heat that is noticeable in magnitude and speed is recorded. It is assumed that the observed effects are associated with the formation of a significant amount of local microvolumes (concentration fluctuations) in the liquid when the liquidus line is approaching the liquidus line, enriched with the component leading to crystallization. Their appearance precedes the onset of the processes of spontaneous formation of a large number of crystals in a noticeable volume of the liquid phase.

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90° between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90° between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Poly(diallyldimethylammonium chloride)/clay nanocomposites: effect of molecular weight and concentration of polymer on the structural, thermal, and dielectric properties

Poly(diallyldimethylammonium chloride), PDADMAC, with low and high molecular weight and with concentrations 0.5, 1, and 2 times the cation exchange capacity (CEC) of the clay was used to modify sodium bentonite clay to prepare hybrid PDADMAC/clay nanocomposites using solution-intercalation method. The prepared hybrids were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Data analysis showed that PDADMAC/clay nanocomposites have intercalated structure. The results showed also that the nanocomposite prepared using high molecular weight PDADMAC with concentration one times the CEC of the clay has the most intercalated structure and the highest thermal stability between the prepared nanocomposites. The room temperature dielectric properties were studied as a function of frequency in which the values of real (e 1) and imaginary (e 2) parts of relative permittivity are calculated and discussed. Higher values of e 1 and e 2 are obtained using PDADMAC with high molecular weight. Increasing the concentration of polymer affects the values of e 1 and e 2 towards lower values.

Stepwise heat-capacity change at an orientation transition in liquid crystals.

During a phase transition in a bulk material, heat is exchanged with matter to balance the changes in the internal energy and the entropy of the system. Here we report on the thermal detection of a surface-mediated anchoring transition, a spontaneous and discontinuous orientation change between planar (P) and homeotropic (H) alignments within a single nematic phase by changing temperature. In this case a stepwise change in the heat flow, similar to a glass transition, is observed by means of high-resolution differential scanning calorimetry. We found that the jump in the specific heat does not depend on the sample volume, although the contribution of molecules in the vicinity of surfaces, which trigger the transition, becomes less with increasing the sample volume. This means that different molecular orientations, H and P, with respect to surfaces have different thermodynamic free energies. We also address why the anchoring transition occurs by means of grazing-incidence x-ray diffraction measurements, which clearly reveal the formation of quasismectic layers parallel to surfaces in the nematic phase.

General laws of the effect of hydrogen on the crystallization of amorphous alloys based on the quasi-binary TiNi-TiCu system

The crystallization processes that occur during heating of hydrogen-containing melt-quenched alloys based on the quasi-binary TiNi-TiCu system alloyed with aluminum, iron, hafnium, and zirconium are studied by high-resolution differential scanning calorimetry. The general laws of the transition of the hydrogen-containing alloys from an amorphous into a crystalline state are determined.

Influence of free volume and medium-range order on the deformation response of rapidly solidified and bulk Zr-based (Zr52Ti6Al10Cu18Ni14) metallic glass

Free volume and medium-range order (MRO) present in rapidly solidified ribbons (RSRs) and bulk metallic glasses (BMGs) of Zr52Ti6Al10Cu18Ni14 have been probed by high resolution electron microscopy, fluctuation microscopy, positron annihilation and differential scanning calorimetry. In the as-solidified condition, RSRs showed higher free volume and lower MRO in comparison to BMGs. Within BMGs, the central regions showed higher MRO and lower free volume than the peripheral regions. Uniform deformation of BMGs and RSRs modified their structures, where in, free volume increased in the former and reduced in the latter. These changes in structures led to work hardening in RSRs and work softening in BMGs. Such behaviour could be explained by invoking a concept of critical free volume in the glass phase. For samples (in as-solidified condition) having free volume higher than the critical value, free volume decreased with deformation and showed work-hardening behaviour. In contrast, the work softening behaviour was noticed in samples having free volume lower than the critical free volume.

A novel evidence for the formation of semi-permeable membrane surrounding the Portland cement particles during the induction period

This letter presents strong novel evidence for the semi-permeable membrane surrounding Portland cement during the induction period. In the cement hydration, heat curve obtained through high-resolution differential scanning calorimetry under isothermal conditions, one main and some other smaller endothermic peaks were detected. These endothermic peaks are believed to be caused by the osmotic expansion that occurs after the semi-permeable membrane forms, not the precipitation of calcium hydroxide or the imbibition of water during the induction period.

Enhancement of Thermal Conductivity with Carbon-Encapsulated Copper Nano-Particle for Nanofluids

Carbon-encapsulated copper nanoparticles were synthesized by a carbon arc discharge method. The particles were characterized in detail by transmission electron microscope, high-resolution transmission electron microscopy, thermogravimetric and differential scanning calorimetry. The result showed that the outside graphitic carbon layers effectively prevented unwanted oxidation of the copper inside. The dispersion behaviors and thermal conductivity of Carbon-encapsulated copper nanoparticles in water with different dispersants were investigated under different pH values. The results showed that the dispersion and thermal conductivity enhancements of Carbon-encapsulated copper nanoparticles nanofluids are higher than that of copper nanoparticles.

Morphology of polyethylene ski base materials

We used high-resolution Raman spectroscopy and differential scanning calorimetry for a comprehensive analysis of carbon black-filled polyethylene ski base grades at processing stages from the raw material to the structured ski base. Based on Raman mapping, we assessed the applicability of an advanced evaluation procedure for amorphous, disordered, and crystalline phase fractions of polyethylene for polyethylene extrusion and sinter grades. For sinter grades, a sufficient segregation between carbon black and polyethylene was confirmed, allowing for a comprehensive Raman spectroscopic morphological analysis. Significant morphological changes in polyethylene due to processing from the raw material to the semi-finished film and to the structured ski base were identified. Throughout the processing chain, we observed a decrease in crystallinity and an increase in the amorphous phase fraction. Although the raw material and the sintered semi-finished film exhibited a different but uniform polyethylene morphology, the morphological changes due to structuring of the ski base are limited to the top surface layer. The highest amorphous phase fractions were detected in the surface of the structured ski bases.

Mesolamellar phases containing [Fe(CN)6]3− anion

The mesostructured lamellar phases with the general formula [CnH2n+1N(CH3)3]3[Fe(CN)6] (n = 14, 16, 18) were prepared by ion-exchange/precipitation reaction of alkyltrimethylammonium surfactants and K3[Fe(CN)6] complex in aqueous medium. The phases were characterized using powder X-ray diffraction, high-resolution transmission electron microscopy, IR spectroscopy, thermogravimetric, and differential scanning calorimetry means. The results obtained all support a proposed model of crystal structure for these materials, in which the layers are constructed by monolayer of the discrete complex molecules, and the surfactants tails of opposite head groups deeply penetrate and arrange with a tilt angle of 63°.

Activation energy and thermoactivation parameters of crystallization in rapidly quenched TiNi-based alloys

The thermal effects at the transition of rapidly quenched TiNi-based alloys from the amorphous to crystalline state have been investigated by high-resolution differential scanning calorimetry. The obtained values of enthalpy, entropy, and activation energy of this phase transition suggest that the crystallization begins long before the devitrification temperature is reached.

Fractional and component analysis of crude oils by the method of dynamic microdistillation—Differential scanning calorimetry coupled with thermogravimetry

High-resolution differential scanning calorimetry was used to accurately establish the temperature intervals of oxidation/distillation of the major components of crude oils. Some theoretical aspects of the method of dynamic microdistillation, enabling consecutive distillation (oxidation) of the main components of hydrocarbon mixtures, are discussed. The experimental TG-DSC curves show that the temperature scan of the run can be divided into six regions, of which the first belongs to simple distillation of the sample's liquid constituent (the distillate) and the others to oxidative cracking distillation of the solid (heavy) residue. The latter occur in the order paraffins + light oils, middle base oils, heavy base oils, condensed aromatics (resins) and asphaltenes. The probable oxidation mechanisms of different classes of petroleum hydrocarbons operating in different temperature regions are discussed. Full quantitative fractional and group component analysis of a number of crude oils of different chemical classes and geological age was carried out by the combined TG-DSC techniques under specially chosen experimental conditions (those of dynamic microdistillation).