Crystallization Enthalpy Research Articles

Influences of surface state on thermal stability and magnetic properties of Fe-Si-B-C amorphous alloy

Influences of surface state on thermal stability and magnetic properties for Fe82Si1B12C5 completely amorphous alloys and Fe83Si1B12C4 amorphous alloys with partial crystallization at their surface have been investigated by layer polished-removal method. The crystallization enthalpy of α-Fe phase for the two amorphous alloys decreases obviously with polishing removal of surface layer with the thickness of removal, due to the alteration of internal stress state. An increase of only 1.2% in Fe content causes an increase of 8.4% in crystallization enthalpy of α-Fe phase for the alloy system with an initial casting thickness, indicating that the thermal stability is stress-sensitive for Fe-based amorphous alloys with high Fe content close to amorphous forming boundary are easier to crystallize. It was found that in the as-quenched state the coercivity for both of them increases linearly with the thickness of removal, which is caused by an increase in internal stress. And it was confirmed by experiment that adequate annealing can greatly improve the soft magnetic properties and alter thermal stability.

SELF-ASSEMBLED SYNTHESIS OF MICROENCAPSULATED PARAFFIN WAX PHASE CHANGE MATERIALS WITH EXCELLENT THERMAL PROPERTIES OF CALCIUM CARBONATE SHELL

The PW@CaCO<sub>3</sub> phase change microcapsule composites with paraffin wax (PW) as core and calcium carbonate (CaCO<sub>3</sub>) as shell were successfully prepared by the self-assembly method. During the preparation process, different core-to-wall ratios and different temperatures affected the morphology, encapsulation rate, thermal stability, and thermal conductivity of the microcapsules. Eight sets of microcapsule samples were prepared under different core-to-wall ratios and different temperatures. Of these microcapsule samples, it was found that the microcapsules performed the best thermal performance at a temperature of 65° C and a core-to-wall ratio of 1:1, with a melting enthalpy of 102.8 ± 1.7 J/g, a crystallization enthalpy of 103.9 ± 1.8 J/g, an encapsulation rate of 73.7 ± 1.5%, and a thermal conductivity of 1.251 ± 0.026 W/(m K). The results showed that the prepared microcapsules have good thermal storage properties and have good prospects for application in the field of energy storage buildings.

Encapsulation and thermal properties of composite phase change materials based on cobalt/nitrogen double-doped ZIF-67 derived carbon.

To solve the problems of easy leakage and weak thermal conductivity of single-phase change material, in this experiment, cobalt/nitrogen-doped ZIF-67 derived carbon (CoN-ZIF-Cx) was constructed as the carrier material, and paraffin was used as the phase change core material to construct thermally enhanced shaped composite phase change materials (P0.6@CoN-ZIF-Cx). The composite PCMs were characterized using scanning electron microscopy, isothermal nitrogen adsorption-desorption, X-ray diffraction, and Fourier infrared spectroscopy, and their performance was evaluated using transient planar heat source techniques, differential scanning calorimetry, and thermal cycling tests. The results indicated that the impurities of the acid-washed porous carbon material were reduced and the loading of the paraffin was 60%, and the prepared P0.6@CoN-ZIF-Cx had an excellent thermal performance. Among them, P0.6@CoN-ZIF-C3 has the melting and crystallization enthalpy of 71.03 J g-1 and 68.81 J g-1. The thermal conductivity is 0.4127 W m-1 K-1, a 46.19% thermal conductivity improvement compared with pure paraffin. It still has favourable thermal storage capacity after 50 cycles without paraffin leakage during the phase transition.

Preparation of form‐stable silica/polyethylene glycol composites using flash‐drying for large‐scale melt‐spun fibers with thermal management property

AbstractThe combination of phase change materials (PCMs) with fibers can afford smart fibers with thermal management properties. However, the issues of easy leakage and poor thermal stability of PCMs often limit their use in high‐temperature spinning. Herein, we report a form‐stable PCM of spherical SiO2/PEG composite that was prepared through flash‐drying using inorganic dendritic silica (D‐SiO2) as the core skeleton to support organic polyethylene glycol (PEG). The SiO2/PEG composite not only presents high crystallization enthalpy (101.35 J/g), but also maintains a superior phase change stability. Meanwhile, it exhibits a significant temperature hysteresis effect during heating and cooling, and the endothermic and exothermic time are 381.95 and 293.57 s, respectively. Because the degradation temperature of 300°C for SiO2/PEG is higher than the melt processing temperature of 240–270°C for the preparation of polyamide 6 (PA6) fibers, PA6/SiO2/PEG fibers were prepared using melt spinning. The prepared PA6/SiO2/PEG fibers exhibit high latent heat (17.14 J/g), outstanding thermal cycling stability and satisfactory temperature adjustment properties, and the temperature‐adjustment time of 458.97 s and temperature difference of 10.68°C under the thermal environment. Moreover, the tensile strength of PCFs‐20% reached 1.97 cN/dtex after drawing, which make PCFs meet the requirements of uses in textile industries.

N-Eicosane-Impregnated nonwoven phase change mats of electrospun Poly(ethylene oxide)/Poly(methyl methacrylate) blended fibers

The ever-increasing energy demand led scientists turn to more efficient, environmentally friendly, and renewable technologies. Phase change materials (PCMs) are gaining popularity in the field of passive thermal energy storage. In the current work, polyethylene oxide/poly (methyl methacrylate) (PEO/PMMA) electrospun fibers were employed as encapsulation matrices for n-eicosane and their physicochemical properties were tested, aiming to develop stable phase change fibers (PCFs). The effect of the n-eicosane content on the morphology and thermal properties of the form-stable PEO/PMMA/n-eicosane PCFs was extensively investigated by using X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA). The melting and crystallization enthalpy of PEO/PMMA/n-eicosane remained unchanged during the first and second cycle. After 30 heating-cooling cycles, the samples with 2 and 5 wt% n-eicosane exhibited inferior thermal reliability, while no temperature and enthalpy change were observed after the thermal cycling of PCF with 7.5 and 10 wt% n-eicosane content, thus rendering these systems suitable materials for thermal energy storage applications. The most promising system was the one containing a 10 wt% n-eicosane, due to the higher crystallization enthalpy (184 J/g) and the stabilization of the melting and crystallization peaks for all cycles. The degradation kinetics were investigated for n-eicosane, the pristine PEO/PMMA fibers and the PEO/PMMA/n-eicosane fibers with a 10 wt% n-eicosane content. Moreover, the Activation Energy (Ea) and the pre-exponential factor (A) were calculated using the Friedman and Vyazovkin methods whereas the reaction mechanisms were studied using the model fitting method.

Cooling rate guiding contradictory effect of thermal treated temperature on the crystallization of PLA racemic blends upon cooling

In this work, cooling rate guiding contradictory effect of thermal treated temperature on the crystallization of PLA racemic blends upon cooling was reported. In addition, it was found that, the higher cooling rate is more favorable for the formation of stereocomplex crystals (SCs). The separation between the enantiomeric chains in the racemic melt was proposed as the reason for the contradictory effect of the thermal treated temperature on the crystallization enthalpy of PLA racemic blends upon cooling. At last, by using Flash DSC, the crystallization kinetics of PLA racemic blends after thermal treated at different temperatures were compared, and the results verified the influence of the separation between the enantiomeric chains on the contradictory effect of the thermal treated temperature.

Effect of Pendant Sulfide and Sulfonyl Groups on the Thermal, Flow, and Antioxidative Properties of Lipid-Based Aliphatic Monoesters

Thermal, flow, and oxidative stability behavior of oleyl oleate monoesters derivatized with sulfur-containing functional groups (sulfide and sulfonyl) suggests that these compounds may be suitable candidates as sustainable alternative base oils to replace mineral oils in lubricant formulations. A robust thiol-ene addition and oxidation synthesis route was utilized to prepare the materials in high yields and high purity with no byproducts. Changes in the functional properties of oleyl oleate are attributable to the enhanced intermolecular forces and irregular conformations introduced by the bulky polar sulfur-containing groups, which introduce steric hindrances and alter phase behavior. The derivatization of oleyl oleate with sulfide and sulfonyl pendant groups resulted in a lower enthalpy of crystallization (10 kJ/mol compared to 76 kJ/mol for oleyl oleate) and an increased viscosity from 16.3 mPa·s to as high as 175.5 mPa·s at 40 °C. The sulfonyl pendant groups imparted higher viscosity to oleyl oleate due to sulfonyl–sulfonyl interactions. The presence of sulfonyl and sulfide pendant groups increased oleyl oleate oxidation onset (Tonox) by 47 and 149 °C, respectively. The sulfide pendant groups converted hydroperoxides as they are formed into non-radical derivatives and thus delayed oxidation. Overall, the sulfide- and sulfonyl-branched oleyl oleate monoesters of this work presented useful thermal transition and viscosity profiles which are competitive with those of mineral oils, making them suitable alternatives for use in lubricant formulations.

The Influence of Multiple Extrusions on the Properties of High Filled Polylactide/Multiwall Carbon Nanotube Composites.

High filled polylactide/multiwall carbon nanotube composites were subjected to multiple extrusions using single-screw and twin-screw extruders. Samples of the processed composites were characterized by SEM, XRD, Raman, and FTIR spectroscopy. Thermal and rheological properties were investigated by DSC and MFR analyses. Subsequent extrusions resulted in decreased torque and process efficiency, which is a consequence of the viscosity reduction of PLA. Thermal and rheological properties of composites changed after each extrusion as well. As revealed by DSC analyses, cold crystallization temperature showed a tendency to decrease after each process, whereas cold crystallization enthalpy ΔHcc increased significantly. Melt flow rate, which is indicative of the polymer degradation, increased after each extrusion.

Crystallization Kinetics in an Immiscible Polyolefin Blend.

Motivated by the problem of brittle mechanical behavior in recycled blends of high density polyethylene (HDPE) and isotactic polypropylene (iPP), we employ optical microscopy, rheo-Raman, and differential scanning calorimetry (DSC) to measure the composition dependence of their crystallization kinetics. Raman spectra are analyzed via multivariate curve resolution with alternating least-squares (MCR-ALS) to provide component crystallization values. We find that iPP crystallization behavior varies strongly with blend composition. Optical microscopy shows that three crystallization kinetic regimes correspond to three underlying two-phase morphologies: HDPE droplets in iPP, the inverse, and cocontinuous structures. In the HDPE droplet regime, iPP crystallization temperature decreases sharply with increasing HDPE composition. For cocontinuous morphologies, iPP crystallization is delayed, but the onset temperature changes little with the exact blend composition. In the iPP droplet regime, the two components crystallize nearly concurrently. Rheological measurements are consistent with these observations. DSC indicates that the enthalpy of crystallization of the blends is less than the weighted values of the individual components, providing a possible clue for the decreased iPP crystallization temperatures.

Preparation and characterization of structurally variable inorganic nanofibrous mats with large surface area for intelligent temperature regulation textiles

Hierarchical structure and large specific surface area are vital for the substrate materials of form-stable phase change materials (FSPCMs) incoporated within intelligent temperature reulation textiles. Microemulsion electrospinning is an efficient method to prepare hierarchically porous substrate materials. Herein, structurally variable TiO2/SiO2/C (TSC) nanofibers were fabricated via microemulsion electrospinning followed by calcination as the substrate materials of FSPCMs. The interior structure, specific surface area, thermal energy storage and thermal regulation properties of TSC nanofibrous mats were characterized in detail. Interestingly, the intrinsic structure of nanofibers could be tuned by varying the composition of precursor solution. The minimum specific surface area of TiO2/SiO2/C nanofibrous mats was as high as 685.52 m2·g−1. The melting and crystallization enthalpy of TiO2/SiO2/C nanofibrous mats-based FSPCMs were more than 126.91 and 120.36 J·g−1, respectively. Furthermore, the manufactured FSPCMs were applied as the middle layer of temperature regulation textiles with a sandwich structure, the largest temperature difference between temperature regulation textiles and conventional textiles was up to 12.6 °C, indicating the manufactured temperature regulation textiles could effectively buffer the external temperature variation. The results proved microemulsion electrospinning is indeed an efficient method to prepare desired substrate materials of FSPCMs.

Composites with a Novel Core–shell Structural Expanded Perlite/Polyethylene glycol Composite PCM as Novel Green Energy Storage Composites for Building Energy Conservation

Phase change materials (PCMs) in the thermal storage of construction can reduce energy waste by shrinking the diurnal daily temperature changes inside. The thermal energy storage (TES) wood-plastic composites (WPC) are manufactured by employing expanded perlite (EP) stabilized PEG as PCM and wood powder/high-density polyethylene (WF/HDPE) as a matrix. The novel type of shell-core PCM (E-shell PCM) was prepared through cation exchange and layer upon layer self-assembly built organic network structure, which was featured by the very thin shell and ultra-high content of active core materials. The unique protective shell gave the PCM high latent heat potential (136.40 J/g), good structural stability, and broad prospects for sustainable energy application. The TES WPC has excellent morphological stability, high phase transition heat and significant thermal stability, heat storage performance, and good mechanical strength. With the gradual increase of E-Shell PCM, the latent heat of TES WPC phase transition increases gradually, and the melting enthalpy and crystallization enthalpy reach 76.06 J/g and 74.61 J/g, respectively. Simultaneously, the introduction of EP promoted the composite heat and smoke suppression ability, suggested as a building material used for temperature control. Latent heat WPC may be utilized as biological building materials with high latent heat and strong mechanical properties to cut down on energy use and enhance interior comfort.

Insight into crosslinked chitosan/soy protein isolate /PVA plastics by revealing its structure, physicochemical properties, and biodegradability

Biodegradable plastics are attracting attention for their excellent performance and eco-friendliness. In this study, various ratios of cross-linked chitosan/soybean protein isolate (SPI)/PVA ternary hybrid plastics were prepared by casting, and their structures and physicochemical properties were characterized. Due to hydrogen bonding, FT-IR and XRD results indicated good compatibility between the hybrid plastics. The hybrid plastics surface and cross-section were smoother and evener with few cracks and small free particles at chitosan to SPI ratios of 1:3 and 1:1. AFM results further verified that the relative roughness of the hybrid plastic was lower. In addition, the light transmission and water absorption gradually decreased. Also, with increasing the ratio of chitosan and SPI, the hybrid plastic thermal properties, e.g., crystallization temperature, crystallization enthalpy, melting temperature and melting enthalpy were enhanced. Moreover, blended plastics chroma values exhibited differences under various ratios. Also, the ratio increases of chitosan and SPI improved the plastics' tensile strength and elastic modulus and reduced the elongation at break. Furthermore, the hybrid plastics after soil burial possessed more pores and cracks, implying better degradability. The results obtained in this study can help expand the application and fabrication of crop-based biomacromolecules to meet various packaging requirements such as water resistance, excellent bearing capacity, and favor biodegradability. • Adding chitosan and SPI can reduce plastic surface roughness by promoting compatibility. • Hybrid plastic exhibits superior water resistance compared to pure PVA . • The addition of chitosan and SPI enhances the mechanical properties of hybrid plastics. • After soil burial, the hybrid plastic exhibited desirable degradability.

Usage of atmosphere pressure plasma for rapid polyethylene functionalisation exhibiting only minor ageing

The inert surface of polyethylene (PE) hinders its application in composites field. Here we report a rapid functionalisation method of molten PE using atmosphere pressure plasma with dry air as gas source to enhance its polarity. Treatment distance (between 10 mm and 30 mm) and treatment time (between 5 s and 20 s) are two key factors to impact the degree of functionalisation of PE. Various oxygen-containing groups, such as ketone groups (CO), ether groups (COC) and hydroxy groups (–OH), were introduced into molecules during plasma treatment. Furthermore, based on the higher relative CO content, PE in molten state was functionalised more rapidly than that in solid state. The static water contact angle dropped from 107 ° of once-molten PE to 84.5 ° of plasma treated PE at 20 mm for 20 s, which demonstrated the improved hydrophilicity of treated PE. Cross-linking structure preferred to be formed in plasma treated PE resulting in higher complex viscosity. The drop of crystallisation enthalpy and increase of half crystallisation time of plasma treated PE were due to cross-linking structure. The relative CO content in plasma treated PE remained constant even after 7 days showing only minor ageing effect. Plasma treatment is a rapid and economic method to improve polarity of PE in molten state, which provides a promising route to improve interfacial compatibility of PE-based composite.

Tm3+ Ion Blue Emission Quenching by Pd2+ Ions in Barium Phosphate Glasses: Fundamental Analysis toward Sensing Applications.

The quenching effect of Pd2+ ions on the blue emission from Tm3+ was investigated for the first time using barium phosphate glass as model matrix. Glasses containing fixed Tm2O3 at 0.5 mol % and PdO up to 0.3 mol % (added relative to P2O5) were prepared by melting and first characterized for basic structural properties by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Thermal properties were then evaluated by differential scanning calorimetry (DSC). The focus was thereafter on evaluating the optical properties by absorption and photoluminescence (PL) spectroscopy with decay kinetics assessment. XRD confirmed the amorphous nature of the glasses synthesized. The vibrational spectroscopy assessment consistently exhibited the IR- and Raman-active bands characteristic of phosphate glasses, showing no significant variation with PdO codoping. The DSC analysis revealed all glasses possessed high thermal stability assessed by the differences (ΔT = Tg - Tx ≥ 154 °C) between glass transition temperatures (Tg) and onset of crystallization (Tx). A tendency of the Tg values to increase with PdO contents was however exhibited. In addition, specific enthalpies of crystallization showed magnitudes decreasing with increasing PdO concentration, thus suggesting crystallization suppression by Pd2+. Concerning the optical properties, it was observed that codoping the glasses with PdO (0.1-0.3 mol %) led to the development of the visible Pd2+ d-d absorption band (peak ≈415-410 nm). In addition, drastic PL quenching of the Tm3+ blue emission around 452 nm (1D2 → 3F4 transition) was induced by Pd2+. Analyzing PL decay curves obtained by exciting Tm3+ ions at 359 nm while monitoring 452 nm emission revealed decreased 1D2 state lifetimes. Thus, a potential of Tm3+ for analytical sensing of Pd2+ in various matrices was suggested. Ultimately determining quenching constants from the PL data and based on the comparison of results from emission intensity and decay rates, likely Tm3+ → Pd2+ energy transfer processes underlying the PL quenching were proposed.

Facile and safety synthesis of highly loaded phase change microcapsules with paraffin/butyl stearate core and their feasible application in polymer composite

Highly paraffin/butyl stearate-loaded phase change microcapsules were synthesized by cosolvent-free interfacial polymerization using low-toxicity dicyclohexylmethane-4, 4′-diisocyanate as the shell material. The formation of the microcapsules and their distribution in the epoxy were studied by means of optical microscope and scanning electron microscopy, respectively. The chemical composition of microcapsules was confirmed through Fourier transform infrared spectrometer. And the phase change properties, thermal stability and cyclic thermal stability of microcapsules and their thermal insulation properties and thermal response behavior in the epoxy were investigated through differential scanning calorimetry, thermogravimetric analysis, leakage prevention test, thermal conductivity test and temperature response experiment, respectively. The synthesized spherical microcapsules have distinct core-shell structure with an average diameter of 220.6 μm. The microcapsules achieve an encapsulation rate of 78.5%, with the melting enthalpy and the crystallization enthalpy being 148.5 J/g and 159.2 J/g, respectively. They not only exhibit good thermal stability and cyclic thermal stability, but also can disperse in the epoxy uniformly and combine with the epoxy tightly. In addition, compared with the pure epoxy, the epoxy containing 15 wt% microcapsules experiences a 10.1% decreases in thermal conductivity and a 55.4% increase in delayed time of temperature rise/fall, showing an excellent temperature regulation ability. • HMDI was employed as the shell material due to low toxicity. • The microcapsules with core-shell structure achieve an encapsulation rate of 78.5%. • High enthalpy microcapsules exhibit 99.2% of heat-storage efficiency. • The microcapsules have high thermal stability, reliability and applicability. • 15 wt% microcapsules increase the time delay by 55.4% for temperature rise/fall.

Enhancement in Crystallizability of Poly(L-Lactide) Using Stereocomplex-Polylactide Powder as a Nucleating Agent.

High-molecular-weight poly(L-lactide) (HMW-PLLA) is a promising candidate for use as a bioplastic because of its biodegradability and compostability. However, the applications of HMW-PLLA have been limited due to its poor crystallizability. In this work, stereocomplex polylactide (scPLA) powder was prepared by precipitation of a low-molecular-weight poly(L-lactide)/poly(D-lactide) (LMW-PLLA/LMW-PDLA) blend solution and investigated for use as a fully-biodegradable nucleating agent for HMW-PLLA compared to LMW-PLLA powder. The obtained LMW-PLLA and scPLA powders with a nearly spherical shape showed complete homo- and stereocomplex crystallites, respectively. HMW-PLLA/LMW-PLLA powder and HMW-PLLA/scPLA powder blends were prepared by melt blending. The LMW-PLLA powder was homogeneously melted in the HMW-PLLA matrices, whereas the scPLA powder had good phase compatibility and was well-dispersed in the HMW-PLLA matrices, as detected by scanning electron microscopy (SEM). It was shown that the enthalpies of crystallization (ΔHc) upon cooling scans for HMW-PLLA largely increased and the half crystallization time (t1/2) dramatically decreased as the scPLA powder content increased; however, the LMW-PLLA powder did not exhibit the same behavior, as determined by differential scanning calorimetry (DSC). The crystallinity content of the HMW-PLLA/scPLA powder blends significantly increased as the scPLA powder content increased, as determined by DSC and X-ray diffractometry (XRD). In conclusion, the fully biodegradable scPLA powder showed good potential for use as an effective nucleating agent to improve the crystallization properties of the HMW-PLLA bioplastic.

Enhanced photothermal conversion and thermal conductivity of phase change n-octadecane microcapsules shelled with nano-SiC doped crosslinked polystyrene

Microcapsules incorporating phase change material n-octadecane (ODE) shelled with crosslinked polystyrene (CLPS) were prepared via the suspension polymerization. SiC nanoparticles (nano-SiC) were employed to modify the shell to improve the heat transfer and photothermal conversion of the microcapsules. The scanning electron microscopic analysis revealed the microcapsules of a general spherical shape. The surface components and chemical composition of the microcapsule samples were evaluated by the energy-dispersive X-ray and Fourier transform infrared spectroscopy, confirming that the nano-SiC have been embedded in the CLPS shell. Results show that the microcapsule sample with 1.25 wt.% nano-SiC (denoted as MPCM3) exhibits the best heat property among the four kinds of samples prepared with various nano-SiC dosages, and all the nano-SiC doped samples have improved thermal conductivity and photothermal conversion as compared to the microcapsule sample without doping (denoted as MPCM1). Compared to the MPCM1, the thermal conductivity of the MPCM3 is increased by 65.3%, reaching 0.124 ± 0.005 W·m−1·K−1. The MPCM3 has excellent thermal stability as well. Differential scanning calorimetry examination shows that the MPCM3 has higher melting and crystallization enthalpies than the MPCM1, achieving 106.8 ± 0.3 J·g−1 and 104.9 ± 0.2 J·g−1, respectively. In the photothermal conversion experiments, the MPCM3 exhibited great photothermal conversion capability, with a 54.91% photothermal conversion efficiency, which is 145.68% higher than that of the MPCM1.

Calorimetry characterization and crystallization modelling of wax-based mixtures under isokinetic and non-isokinetic cooling

Characterization and modelling of wax crystallization must be carefully addressed to understand wax-oil organogels formation. During casting process of wax-based mixtures, wax crystallization occurs under concomitant non-constant and high cooling rates. In this study, the crystallization kinetics of two representative wax-based materials were studied by power-compensated Differential Scanning Calorimetry (DSC) with moderate-high cooling rates (from − 20 to − 200 °C min−1) in constant cooling rate (isokinetic) conditions and in simplified non-constant cooling rate (non-isokinetic) conditions. Analyses based on the evolution of the mass fraction of solid wax calculated from heat flow (DSC signal) show similar kinetics trend and enthalpy of crystallization for the different isokinetic conditions, but with a significant influence on the supercooling effects. Considering the limits of the classic Avrami kinetics modelling for high aspect ratio crystals and complex mixtures, a semi-empirical modelling approach of non-isokinetic cooling conditions in a differential form is proposed. The modelling shows a good correlation with experimental results.

Identification of various salt crystallization and water freezing patterns induced by temperature variation from Na2SO4 – H2O system confined in porous materials

Among inorganic salts, sodium sulfate is considered as one of the most dangerous to porous building materials. The pores of building materials are usually occupied by aqueous salt solution. Hence, the phase transitions of both, water and salt should be considered simultaneously during temperature decrease. In the present paper we describe an extensive experimental study devoted to the analysis of combined salt crystallization and water freezing in the Na2SO4–H2O system confined in the pores of sandstone and red clay brick induced by temperature variation. Salt and water phase transition patterns were investigated using differential scanning calorimetry. Saturated samples were subjected to 20 cooling-heating scans, where the initial temperature was changed in each cycle. Such a procedure enabled us to define three different crystallization paths of Na2SO4 hydrates and ice depending on the initial conditions. Based on the recorded heat flow, the crystallization enthalpies of hepta- and decahydrate of sodium sulfate were estimated.

Crystallization Behavior and Morphology of Biodegradable Poly(ε-caprolactone)/Reduced Graphene Oxide Scaffolds.

Morphology, thermal properties and the non-isothermal melt crystallization kinetics of biodegradable poly(ε-caprolactone) (PCL)/reduced graphene oxide (rGO) scaffolds are studied with differential scanning calorimetry (DSC) at various cooling rates (5, 10, 15 and 20 °C/min). Thermally induced phase separation was used to manufacture the scaffolds (TIPS). The micrographs show a more homogeneous and defined morphology with larger pores and thicker pore walls. The melting temperature (Tm), melting enthalpy (ΔHm), crystallization enthalpy (ΔHc) and degree of crystallinity (Xc) increased with the addition of rGO, suggesting larger and more perfect crystalline structures. The degree of crystallinity increased with the presence of rGO. The crystallization peak shifted to higher temperatures as the rGO concentration increased independently of the cooling rates. The peak shifted to lower temperatures as the cooling rate increased with the same rGO composition. The values of t1/2 (time needed to reach 50% crystallization) were lower for scaffolds with rGO. The values of the crystallization rate coefficient were higher when the porous support contained rGO, which indicates that their crystallization systems are faster. The activation energy obtained with the Kissinger method decreased with the presence of rGO. The results indicate that reduced graphene oxide acts as a nucleating agent in the non-isothermal melt crystallization process. The addition of small quantities of rGO changes their thermal properties with which they can be modified for application in the field of tissue engineering.