DSC Scans Research Articles

Biocomposites Based on Polyamide 11/Diatoms with Different Sized Frustules.

Amorphous diatomite was used as a filler for a thermoplastic polymer of polyamide 11 obtained from natural sources. The diatomite particles of different sizes were previously fractionated by sedimentation to obtain powders with varying particle size distribution, including powders with or without frustule particles, crushed, uncrushed or agglomerated. Biocomposites containing 2.5, 5, 10 and 20% filler were tested for their mechanical properties, including tensile strength, flexural strength and impact strength. In addition, a particle size analysis (by Dynamic Light Scattering, DLS) was performed and the dispersion of the filler in the polymer matrix (Scanning Electron Microscopy, SEM), thermal parameters (Differential Scanning Calorimetry, DSC, and Dynamic Mechanical Analysis, DMA) were determined. Testing showed that biocomposites modified with diatomaceous earth have a higher mechanical strength than the reference system, especially with larger amounts of the filler (10 and 20%), e.g., the tensile strength of pure PA11 is about 46 MPa, while 20OB and 20OF 47.5 and 47 MPa, respectively, while an increase in max. flexural strength and flexural modulus is also observed compared to pure PA11 by a maximum of 63 and 54%, respectively Diatomaceous earth can be obtained in various ways—it is commercially available or it is possible to breed diatoms in laboratory conditions, while the use of commercially available diatomite, which contains diatoms of different sizes, eliminates the possibility of controlling mechanical parameters by filling biocomposites with a filler with the desired particle size distribution, and diatom breeding is not possible on an industrial scale. Our proposed biocomposite based on fractionated diatomaceous earth using a sedimentation process addresses the current need to produce biocomposite materials from natural sources, and moreover, the nature of the process, due to its simplicity, can be successfully used on an industrial scale.

Moisture Sorption by Polymeric Excipients Commonly Used in Amorphous Solid Dispersions and its Effect on Glass Transition Temperature: II. Cellulosic Polymers

Moisture sorption by polymeric carriers used for the development of amorphous solid dispersions (ASDs) plays a critical role in the physical stability of dispersed drugs since moisture may decrease glass transition temperature (Tg) and thereby increase molecular mobility of drugs leading to their crystallization. To assist the selection of appropriate polymers for ASDs, we conducted moisture sorption by five types of cellulosic polymers, namely, hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC), hydroxypropyl methyl cellulose acetate succinate (HPMCAS), hydroxypropyl methyl cellulose phthalate (HPMCP), and ethyl cellulose (EC), as functions of relative humidity (10 to 90% RH) and temperature (25 and 40 °C). The moisture sorption was in the order of HPC>HPMC>HPMCP>HPMCAS>EC, and there was no significant effect of the molecular weights of polymers on moisture uptake. There was also less moisture sorption at 40 °C than that at 25 °C. Glass transition temperatures (Tg) of the polymers decreased with the increase in moisture content. However, the plasticizing effect by moisture on HPC could not be determined fully since, despite being amorphous, there were very little baseline shifts in DSC scans. There was also very shallow baseline shift for HPMC at >1% moisture content. In contrast, Tg of HPMCAS and HPMCP decreased in general agreement with the Gordon-Taylor/Kelley-Bueche equation, and EC was semicrystalline having both Tg and melting endotherm, with only minor effect of moisture on Tg. The results of the present investigation would lead to a systematic selection of polymeric carriers for ASDs.

Influence of Ceria Addition on Crystallization Behavior and Properties of Mesoporous Bioactive Glasses in the SiO2-CaO-P2O5-CeO2 System.

Knowledge of the crystallization stability of bioactive glasses (BGs) is a key factor in developing porous scaffolds for hard tissue engineering. Thus, the crystallization behavior of three mesoporous bioactive glasses (MBGs) in the 70SiO2-(26-x)CaO-4P2O5-xCeO2 system (x stands for 0, 1 and 5 mol. %, namely MBG(0/1/5)Ce), prepared using the sol–gel method coupled with the evaporation-induced self-assembly method (EISA), was studied. A thermal analysis of the multiple-component crystallization exotherms from the DSC scans was performed using the Kissinger method. The main crystalline phases of Ca5(PO4)2.823(CO3)0.22O, CaSiO3 and CeO2 were confirmed to be generated by the devitrification of the MBG with 5% CeO2, MBG5Ce. Increasing the ceria content triggered a reduction in the first crystallization temperature while ceria segregation took place. The amount of segregated ceria of the annealed MBG5Ce decreased as the annealing temperature increased. The optimum processing temperature range to avoid the crystallization of the MBG(0/1/5)Ce powders was established.

Rifampicin-loaded PLGA nanoparticles for local treatment of musculoskeletal infections: Formulation and characterization

Systemic treatment of orthopedic device-related infections requires potentially toxic doses to reach local therapeutic levels. A locally applied nanosized drug delivery system can provide a high drug dose at the target site. Branched PLGA of lower molar mass was used for rifampicin-loaded nanoparticles (RIF-NPs) formulation by the nanoprecipitation method. The formulation variables influenced the NPs size ranging from 200 to 380 nm. The missing peak of crystalline rifampicin on the DSC scan of the NPs indicates that the drug was molecularly dispersed. The negative charge of the NPs in the physiological buffer was masked by a nonionic surfactant or converted to a positive one by a cationic surfactant, which promotes bioadhesion, penetration, and antimicrobial effect of locally applied RIF-NPs without being toxic to proliferation. Low values of loading capacity showed that PLGA predominates in the NPs, which, however, perform their function as a drug carrier ensuring sustained RIF release. The ex vivo dissolution study of RIF-NPs impregnated into the cancellous allogeneic bone grafts showed a low initial burst followed by sustained release of RIF for 7 days. Rifampicin-loaded PLGA nanoparticles may contribute to the prevention of resistant biofilm formation in patients with implanted devices and the local treatment of infections in open musculoskeletal injuries.

A study of nanoconfined water in halloysite

Recent years have witnessed a significant level of interest on the properties and applications of halloysite. Despite the widespread interest, little is known about the nature of nanoconfined H2O and its role in governing the dehydration of halloysite (10 Å) to halloysite (7 Å). This is because most studies have utilized halloysite that has irreversibly transformed from fully hydrated halloysite (10 Å) to halloysite (7 Å). This study examined a naturally occurring fully hydrated halloysite (10 Å) that was collected in a wet state and preserved in a sealed desiccator. Thermogravimetric (TGA/DTG) and low-temperature differential scanning calorimetry (LT-DSC) were used to quantify the amount of H2O present in halloysite (10 Å) as interlayer water (ILW), lumen water (LUW) and unconfined water external to the halloysite tubes (UCW). The LT-DSC results, in particular, identified two exothermic freezing peaks and two endothermic melting peaks that could distinguish between unconfined and lumen H2O. H2O confined in the lumen is characterized not only by a depression in the freezing temperature, but also by a significant reduction in the freezing enthalpy. Consistent with work on other phyllosilicates, interlayer H2O in halloysite (10 Å) remains unfrozen, as detected by DSC scans down to −75 °C. For fully hydrated halloysite (10 Å), the half-unit cell formula is Si2Al2O5(OH)4 (H2O)2(ILW)(H2O)3.4–5.0(UCW+LUW). LT-DSC revealed that about 2.31 ± 0.09 molesH2O/molekaol of the 5.4–7.0 molesH2O/molekaol remain unfrozen down to −75 °C, consistent with 2.0 molesH2O/molekaol assigned to the interlayer and 0.31 assigned to the δ-layer on the hydrophilic surface of the inner lumen. Dehydration experiments using LT-DSC, XRD and ATR-FTIR showed that unconfined + lumen H2O was lost rapidly, with a slower release of ILW + δ-layer. ATR-FTIR spectra of dehydrated halloysite exhibited a significant shift in the δ(H-O-H) bending band of sorbed H2O, also termed hole water, to a higher frequency with a concomitant narrowing. Compared to unconfined water, which was indistinguishable from bulk water, these isolated H2O molecules trapped in siloxane ditrigonal cavities are more hydrogen bonded and more ordered.

Fabrication and characterization of mussel-inspired layer-by-layer assembled CL-20-based energetic films via micro-jet printing

Three-dimensional (3D) micro-jet printing is a droplet deposition technique based on liquid-phase materials. To improve the deposition density and performance of energetic films with micro/nanoscale on an energetic chip, polydopamine (PDA) was utilized as a linker bridge to induce the in-situ self-assembly of CL-20-based energetic film via 3D micro-jet printing. The self-assembly was extensively characterized by confocal laser scanning microscopy (CLSM), SEM, power-XRD, XPS, and DSC. The performance of the self-assembled film was verified by the mechanical properties and detonation properties, and a possible self-assembly mechanism in the layer-by-layer micro-jet printing process was proposed. The results indicated PDA-induced self-assembly enhanced the physical entanglement between the binders and energetic crystal, reduced the porosity from 15.87% to 11.28%, and improved the elastic modulus and the detonation performance of the CL-20-based energetic film. This work proposes a novel and promising energetic film design and fabrication strategy to enhance the interaction between the energetic composite layers in the micro-jet printing process.

The role of water in the reversibility of thermal denaturation of lysozyme in solid and liquid states

Although unfolding of protein in the liquid state is relatively well studied, its mechanisms in the solid state, are much less understood. We evaluated the reversibility of thermal unfolding of lysozyme with respect to the water content using a combination of thermodynamic and structural techniques such as differential scanning calorimetry, synchrotron small and wide-angle X-ray scattering (SWAXS) and Raman spectroscopy. Analysis of the endothermic thermal transition obtained by DSC scans showed three distinct unfolding behaviors at different water contents. Using SWAXS and Raman spectroscopy, we investigated reversibility of the unfolding for each hydration regime for various structural levels including overall molecular shape, secondary structure, hydrophobic and hydrogen bonding interactions. In the substantially dehydrated state below 37 wt% of water the unfolding is an irreversible process and can be described by a kinetic approach; above 60 wt% the process is reversible, and the thermodynamic equilibrium approach is applied. In the intermediate range of water contents between 37 wt% and 60 wt%, the system is phase separated and the thermal denaturation involves two processes: melting of protein crystals and unfolding of protein molecules. A phase diagram of thermal unfolding/denaturation in lysozyme - water system was constructed based on the experimental data.

Asphaltenes as model compounds of the UIBs/AIBs detected in various astrophysical objects. Part 2 – Natural bitumens asphaltenes carbonization

A series of naturally occurring bitumen samples from Central-South Italy (Maiella and Rivello) as well as from Sicily (Ragusa and Modica area), were purified and analyzed by thermal analysis (TGA-DTG-DTA) and FT-IR spectroscopy. The asphaltene fraction of these bitumen samples was isolated and analyzed by thermal analysis and by FT-IR spectroscopy. Each asphaltene fraction was then subjected to carbonization in a sealed crucible using a DSC scan to 700 °C under N2 flow and the carbonization product was studied by FT-IR spectroscopy. The naturally occurring bitumen samples, their asphaltenes and the carbonization products were used as model compounds to match the UIBs/AIBs (Unidentified Infrared Bands or Aromatic Infrared Bands) band pattern of the interstellar medium and their evolution in different interstellar and circumstellar environments. The asphaltenes extracted from the bitumen samples represent a concrete example of model compounds for the MAONs (mixed aromatic/aliphatic organic nanoparticles) theorized as the most probable carriers of the UIBs/AIBs.

Coupling between thermal ageing/degradation and creep behavior of PEKK and C/PEKK composites above the glass transition temperature

The present work aims at investigating the coupling between thermal ageing/degradation and creep behavior of PEKK and C/PEKK composites at 200 °C, above the glass transition temperature (which is close to 160 °C).Ageing tests were carried out at 200 °C, under 5 bar of oxygen conditioned atmosphere. DSC scans and DMA tests were carried out. Tests results discussion were supported by indentation tests and image analysis of the aged specimen cross-section.Coupled oxidation-thermomechanical-creep tests were carried out on C/PEKK samples at 200 °C under a 5 bar O2 environment. The resulting strain response was compared to creep tests carried out on C/PEKK samples at 200 °C under air at similar creep stress. Such comparison allowed to investigate the presence of degradation phenomena in C/PEKK samples. The analysis of X-rays µ-tomography scans allowed investigating the possible occurrence of degradation, and to discriminate between pure thermal and thermomechanical coupling with degradation phenomena.

Repeatability and Reproducibility Study of Organic Material (Musa AAB Simmonds) in the Measurement of Enthalpy and Transition Temperature

To establish repeatability and reproducibility parameters in the enthalpy values obtained in a differential scanning calorimeter, DSC Q2000, the endothermic and exothermic phase changes of Musa AAB Simmonds (Plantain). Were used peel samples were analyzed in a temperature range between -50 °C and 500 °C; with heating rates between 2 °C/min and 10 °C/min, in an N 2 atmosphere, and mass values of 3.0 mg, 6.0 mg and 9.0 mg. For variability analysis, a completely randomized experimental design with factorial structure, to model the effect of sample mass and heating rate on the enthalpies associated with three anomalies presented by the organic material studied. In the analysis of variance, it was found that, although the factors Mass (mg) and Rate (°C/min), influence the uncertainty, there is no dependence between them when it comes to the peak temperature variables. The analysis of enthalpy with respect to mass (mg) showed that there are no differences between the masses at significance levels greater than 0.20, attributable to the fact that the enthalpy measurement is made for first order phase transitions, i.e., the enthalpies correspond to latent heats which are constant for the same material.

Novel Polyimide-block-poly(dimethyl siloxane) copolymers: Effect of time on the synthesis and thermal properties

Polyimide-block-poly(dimethyl siloxane) copolymer was synthesized by a two-step process, initiated by coupling anhydride terminated poly(amic acid), AT-PAA with amino terminated poly(dimethyl siloxane), (NH2)2-PDMS to form poly(amic acid)-block-poly(dimethyl siloxane). The resulting copolymer is then thermally treated to produce polyimide-block-poly(dimethyl siloxane), PI-PDMS. Because of the high glass transition temperature, Tg of polyimide, it is usually cured at a high temperature of about 300°C for over 2.5 h. Copolymerization of polyimide with polysiloxane, reduces the imidization temperature while maintaining high thermomechanical properties. A series of instruments were used to monitor the progress of copolymerization. The time-based analysis of the product of copolymerization enables the optimization of the structure and properties of the copolymers. The chemical structure and composition of the copolymer were studied by Fourier Transform Infrared Spectroscopy, (FT-IR). The incorporation of PDMS blocks into the copolymer and the degree of imidization of the polyimide block increased with increasing reaction time. The change in the viscosity of the copolymerizing solution was monitored by simple shear viscometry conducted with the Brookfield Viscometer. The reported increase in solution viscosity with increasing copolymerization time is associated with increasing molecular weight of the copolymer. The intrinsic viscosity of the copolymer solution was measured as a function of copolymerization time and it was found that the intrinsic viscosity of the copolymer solution increased with increasing reaction time. The glass transition temperature (Tg) and the thermal stability of the copolymer were determined by differential scanning calorimetry, DSC and thermogravimetric analysis, and TGA, respectively. Between 25°C and 420°C, the copolymers synthesized in this study show two glass transition temperatures due to the polyimide, PI block at around 380°C and another peak associated with PDMS plasticized polyimide at about 290–300°C. The two Tg peaks observed in the DSC thermogram are believed to be indicative of the structure of a block copolymer. TGA analysis shows that the thermoxidative stability of the copolymers increased with increasing reaction time, due to the incorporation of increased amount of PDMS unit into the copolymer. The combination of increasing molecular weight of copolymer, higher degree of imidization of polyimide blocks and enhanced thermoxidative stability may translate into improved flame retardancy of copolymers. This suggested enhancement in flame retardancy in air atmosphere, is believed to be due the incorporated PDMS blocks, which can be converted into silica, SiO2, a recognized thermally stable material.

Experimental Investigation of In-Plane Shear Behaviour of Thermoplastic Fibre-Reinforced Composites under Thermoforming Process Conditions

In order to meet environmental regulations and achieve resource efficiency in the series production of vehicles, recyclable polymer composites with a high strength-to-weight ratio are increasingly being used as materials for structural components. Particularly with thermoplastic fibre-reinforced polymers or organo-sheets, the advantage lies in the tailored mechanical properties of the final component by adapting the orientation of fibres based on the direction of loads. These components produced by thermoforming organo-sheets also offer a cost benefit and short cycle times. During the thermoforming process, the shear behaviour of the organo-sheet is the most dominant and determines the mechanical properties and quality of the resulting component. However, the current standard for characterising the shear behaviour of organo-sheets does not consider the strain and cooling rates inherent in the thermoforming process. This research investigates the influence of thermoforming process parameters on the shear behaviour of organo-sheets with a new methodology combining DSC and DMA experiments. During the thermoforming process, the transition of the matrix material from a molten state to a solid state is dictated by the crystallisation kinetics and their dependence on heating and cooling rates. Thus, non-isothermal DSC scans, which correspond to a temperature cycle in a thermoforming process, are used in the DSC experiments to establish the relationship between the recrystallisation temperature of the organo-sheet material and the cooling/heating rates in the thermoforming process. In order to achieve thermoforming-process-relevant cooling rates, fast scanning calorimetry (Flash DSC) is used in addition to conventional DSC measurements. DMA experiments carried out with 45° fibre orientation show that the recrystallisation temperature consequently influences the shear storage modulus of the organo-sheet. The results from DSC measurements show a shift of recrystallisation temperatures to lower temperatures as the cooling rate increases. The combined analysis of results from the DSC and DMA experiments supports the findings and shows the influence of the process temperature, cooling rate and strain rate on the recrystallisation temperature and, in turn, the shear behaviour of organo-sheets. Thus, a recommendation for establishing a new standard for characterising the shear behaviour of organo-sheets is made.

A Comprehensive Investigation on 3D Printing of Polyamide 11 and Thermoplastic Polyurethane via Multi Jet Fusion.

Multi Jet Fusion (MJF) is a recently developed polymeric powder bed fusion (PBF) additive manufacturing technique that has received considerable attention in the industrial and scientific community due to its ability to fabricate functional and complex polymeric parts efficiently. In this work, a systematic characterization of the physicochemical properties of MJF-certified polyamide 11 (PA11) and thermoplastic polyurethane (TPU) powder was conducted. The mechanical performance and print quality of the specimens printed using both powders were then evaluated. Both PA11 and TPU powders showed irregular morphology with sharp features and had broad particle size distribution, but such features did not impair their printability significantly. According to the DSC scans, the PA11 specimen exhibited two endothermic peaks, while the TPU specimen exhibited a broad endothermic peak (116–150 °C). The PA11 specimens possessed the highest tensile strength in the Z orientation, as opposed to the TPU specimens which possessed the lowest tensile strength along the same orientation. The flexural properties of the PA11 and TPU specimens displayed a similar anisotropy where the flexural strength was highest in the Z orientation and lowest in the X orientation. The porosity values of both the PA11 and the TPU specimens were observed to be the lowest in the Z orientation and highest in the X orientation, which was the opposite of the trend observed for the flexural strength of the specimens. The PA11 specimen possessed a low coefficient of friction (COF) of 0.13 and wear rate of 8.68 × 10−5 mm3/Nm as compared to the TPU specimen, which had a COF of 0.55 and wear rate of 0.012 mm3/Nm. The PA11 specimens generally had lower roughness values on their surfaces (Ra < 25 m), while the TPU specimens had much rougher surfaces (Ra > 40 m). This investigation aims to uncover and explain phenomena that are unique to the MJF process of PA11 and TPU while also serving as a benchmark against similar polymeric parts printed using other PBF processes.

Novel indole-based photosensitizers coupled with PEG-HEC quasi-solid-state electrolyte to improve energy conversion and stability of organic dyes based-dye sensitized solar cells

A series of novel Indole based organic dyes were synthesized and coupled with a Poly-ethylene glycol-Hydroxy ethyl cellulose quasi-solid-state-electrolyte (PEG-HEC QSSE) polymer blended iodine electrolyte to obtain a metal-free dye-based dye-sensitized solar cell (DSSCs) with better stability. The newly synthesized organic dyes were confirmed through 1H, 13C NMR, CHN analysis. The optical and electrochemical properties of the dyes were determined using UV-visible spectrometry and cyclic voltammetry techniques. A quasi-solid state (QSS) blended polymer PEG-HEC with iodide redox couple as electrolyte was characterized via Field emission Scanning Electron microscope (FE-SEM), UV-visible spectroscopy, XRD and DSC. A foremost comparative study was analysed on DSSC devices with the newly synthesised organic dyes (DPC, DTC, DPCY, DTCY, DPTCY and DTTCY) coupled with the QSSE. The electrochemical impedance spectrum was discussed for all the six dyes coupled with PEG-HEC QSSE, among that DTTCY sensitized device exhibits good ionic conductivity (1.13 × 10−3 S cm−1), high chemical capacitance (Cµ=17.01 µF), high recombination resistance (53.97 Ω) and lower charge transfer resistance (2.35 Ω) due to the presence of a strong electron-withdrawing group in the organic dye and also QSS behaviour of electrolyte. The longer electron lifetime (τn-58.51 ms) and better diffusion coefficient (4.25 × 10−7 cm2 s−1) of the device prove the short circuit current (Jsc= 16.39 mA cm−2) and enhancement of power conversion efficiency (PCE) of 6.24 % with better stability under AM 1.5 G illumination (100 mW cm−2). The combination of new Indole based organic dyes with PEG-HEC QSSE paved a way to improve the PCE and stability of organic dyes based DSSCs.

The molecular design of drug-ionic liquids for transdermal drug delivery: Mechanistic study of counterions structure on complex formation and skin permeation

Though ionic liquids (ILs) as novel enhancers had garnered wide attention, detailed studies elucidating molecular design of drug-ILs were missing and mechanisms of their formation and skin permeation were still lacking. Herein, we systematically investigated effects of counterions structures on formation and skin permeation of drug-ILs. Firstly, effects of counterions on formation of drug-ILs were dependent on polarizability, molecular weight (M.W.) and polar surface area of counterions. It was caused by strong charge assisted hydrogen bond and van der Waals interactions revealed through FT-IR, X-ray photoelectron spectroscopy and molecular docking, which undermined ionic interactions and reduced total interaction strength, thereby produced lower lattice energy. Then, skin permeability of drug-ILs had a good parabola relationship with M.W., polarizability and log P of counterions. The underlying mechanism was the increased drug miscibility with stratum corneum, which caused conformational disorder and phase transition of lipid bilayers characterized by ATR-FTIR, DSC and confocal laser scanning microscopy. Finally, the drug-ILs proved to be non-irritating using in vivo skin erythema analysis. In conclusion, the quantitative structure-activity relationship models based on counterions structure to predict formation and skin permeation of drug-ILs were developed, which provided basic theory for design of drug-ILs with high permeation-enhancing efficiency.

Viscoelastic behavior and toughness of the DGEBA epoxy resin with 1,2-diaminocyclohexane: effect of functionalized poly(dimethylsiloxane), diglycidyl ether, PDMS-DGE, pre-reacted with 1,2-diaminocyclohexane

There is a great number of reports with the aim to reduce the inherent brittleness of epoxy resins through their modification with different types of reacting and non-reacting additives, in order to diversify their applications. In this work, the toughening effect of polydimethylsiloxane, diglycidyl ether (PDMS-DGE) as well as this rubber functionalized with 1,2-diaminocyclohexane (PDMS-DGE-DCH) on the bisphenol-A diglycidyl ether/1,2-diaminocyclohexane epoxy resin (DGEBA/1,2-DCH) was characterized by differential scanning calorimetry, DSC, and dynamic mechanical analysis, DMA. The results were correlated with those from energy-dispersive X-ray spectroscopy, EDS X-ray, scanning electronic microscopy, SEM, thermogravimetric analysis, and tension tests. The epoxy resin added with 10 phr (parts per hundred of resin) PDMS-DGE underwent phase separation evidenced by voids of c.a. 0.7 µm left after extraction of PDMS-DGE, while Young's modulus and glass transition temperature, Tg, did not decrease significantly. In contrast, the PDMS-DGE-DCH modifier at 10 phr yielded epoxy resins with two lower partially overlapping Tg over a broader temperature range and increased on both the tensile strength and the tensile strain at the break by 2.8- and 16.8-fold, respectively. No voids were observed on the SEM images after subjected to extraction conditions with acetone, and EDS X-ray elemental mapping revealed Si atoms uniformly distributed on all the fracture-surface, proving that PDMS-DGE-DCH took part in the cure reaction into the network of epoxy resin.

Structural and low-temperature magnetic properties of as-quenched and annealed Ni–Si–B alloys produced by rapid solidification

Structural characterization (differential scanning calorimetry, DSC, and X-ray diffraction, XRD) and temperature dependence of the magnetization are reported in Ni80Si10B10 and Ni75Si15B10 alloy ribbons produced by rapid solidification. XDR and DSC measurements lead to confirm the amorphous character of Ni75Si15B10 alloy while the Ni80Si10B10 alloy presents a mixture of amorphous and crystalline (Nickel face-centered cubic) phase. Low-temperature magnetization dependencies were analyzed in terms of spin-wave excitation and fluctuations of the exchange interaction. While both mechanisms are relevant for the high Ni-content alloy, fluctuations of exchange could be ascribed as mechanism for low Ni-content alloy. The effect of annealing (523 and 623 K during 1 h) on the magnetic behavior is also presented. Thus, annealing of Ni75 sample at 623 K also results in appearance of highly magnetic Ni phase.

Multifunctional composites silicone rubber/paraffin@lead tungstate with different core/shell ratio for thermal regulation and gamma shielding

Multifunctional, high-comfort flexible radiation protection materials are highly desired for future human health-related applications but generally hindered due to the single function, poor heat dissipation performance. Herein, a new type of flexible radiation protection shielding materials with thermal regulation function was prepared with silicone rubber (SR) as matrix and paraffin(Pn)@lead tungstate(PWO) phase change microcapsules as fillers. The effect of different core/shell ratio of microcapsules on the properties of flexible radiation protection shielding materials was discussed. The obtained flexible radiation protection material not only shows high latent heat storage capacity, but also includes excellent phase change reversibility and long-term durability. Through the programmed DSC scanning, the thermal charging and discharging behavior of the composites in the thermal management process was optimized. The thermal regulation experiment of the composites show a good temperature regulation ability. Compared with SR, the mechanical properties and gamma ray shielding ability of SR/(Pn@PWO) composites are greatly improved, and the enhancement effect is more obvious with core/shell ratio of the microcapsules decreases. The gamma ray shielding ability of SR/(Pn@PWO) composites is 144.05% higher than that of SR. This work provides a new perspective for the design and development of high comfort radiation protection products, and broadens the application prospects of radiation protection materials.

The heat capacities and fusion thermochemistry of sugar alcohols between 298.15 K and Tm: The study of D-sorbitol, D-mannitol and myo-inositol

Fusion enthalpy and its temperature dependence are important characteristics of phase change materials efficiency. These parameters of three sugar alcohols: D-sorbitol, d-mannitol and myo-inositol – were investigated in the temperature range between 298.15 K and Tm by combination DSC, fast scanning calorimetry and solution calorimetry. Fast scanning calorimetry and DSC were applied to determine the heat capacities of crystal and supercooled liquid states. Using Kirchhoff's law of Thermochemistry, the fusion enthalpies at 298.15 K were derived from the data at Tm and the heat capacities. On the other hand, a quick and reliable way to estimate the fusion enthalpies of sugar alcohols at 298.15 K using solution calorimetry data was proposed. Results of implementation of the two independent approaches agreed within the limits of experimental error.

Model-free cure kinetics of tetra-functional epoxy reinforced with GO and p-Phenylenediamine modified GO

Tetra-functional epoxy was reinforced with graphene oxide (GO) and p-Phenylenediamine functionalized graphene oxide (fGO). FTIR and XPS analysis of fGO confirmed the attachment of amine groups on its surface. Data obtained from nonisothermal DSC scans of neat epoxy and epoxy modified with 0.1 and 0.5 wt.% GO and fGO was studied to evaluate the effect of filler content and chemistry on the curing behavior of epoxy. Cure analysis was performed quantitatively using the integral isoconversional method to identify the dependence of activation energy (Eα) on conversion. Eα for neat epoxy increased with increase in conversion, possibly because at higher conversions, reactions such as etherification and homo-polymerization controlled the reaction kinetics. The addition of GO and fGO both displayed a lower activation energy in the conversion range α = 0.5−0.9 as compared to neat epoxy. The activation energy of fGO reinforced epoxy remained almost constant with change in conversion. This behavior was attributable to the amine groups attached to the surface of the filler, which acted as a secondary hardener and triggered the epoxide ring opening reaction. This fact was supported by the comparative XPS analysis of fGO and curing agent which clearly indicated the compositional similarities between the two. Further the autocatalytic model was used to determine reaction parameters. The overall order of the curing reaction was more than unity throughout, indicative of a complex reaction mechanism.