Differential Scanning Calorimetric Techniques Research Articles

Study on metal decorated oxidized multiwalled carbon nanotube (MWCNT) - epoxy adhesive for thermal conductivity applications

In this work, an effort has been made to develop a new type of complex conductive adhesive filled with silver decorated multi-walled carbon nanotubes (Ag-MWCNT). MWCNTs have been modified using N,N-dimethyl formamide (DMF) as a reducing agent and silver nanoparticles (Ag-NPs) has been homogeneously decorated against the surface. Fourier transform infra-red spectroscopy (FTIR) and Raman spectroscopy concluded that carboxylic groups were anchored to the surface of nanotubes. X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS) confirmed that Ag-NPs were formed and uniformly deposited onto the surface of carboxylic functionalized MWCNT. Test results indicated an improvement in the thermal conductivity up to 0.88 W/mK, which was about four-fold increase over pristine epoxy. The curing kinetics of Ag-MWCNTs reinforced epoxy adhesive system was also studied using non-isothermal differential scanning calorimetric (DSC) technique. The activation energy obtained by Kissinger’s method was reduced from 57.2 to 54 kJ/mol with an addition of 0.5 wt% of Ag-MWCNT within unmodified epoxy. Lap shear strength of the adhesive containing 0.5 wt% of Ag-MWCNT was higher than the pristine polymer thus confirming reinforcing effect of Ag-MWCNT in conductivity applications.

Interaction of vasicine with calf thymus DNA: Molecular docking, spectroscopic and differential scanning calorimetric insights

The present study brings out the interaction between vasicine, an alkaloid and Adhatoda vasica Nees with double stranded DNA. The physico-chemical interaction between small molecules and nucleic acids is a major area of focus in screening drugs against various cancers. Molecular probing in our study using Molecular Operating Environment (MOE) has revealed interaction of vasicine with DNA double helix. Here we report the interaction of vasicine with Calf thymus DNA. We present for the first time the results obtained from UV–visible, fluorescence spectroscopic and differential scanning calorimetric techniques that suggest a moderate to strong electrostatic, hydrophobic and van der Waals interactions mediating the DNA binding properties of vasicine, leading to disruption of DNA secondary structure.

Facile Preparation of AP/Cu(OH)2 Core‐Shell Nanocomposites and Its Thermal Decomposition Behavior

AbstractAmmonium perchlorate (AP)/Cu(OH)2 core‐shell nanocomposites were successfully synthesized using a facile ultrasonic assisted‐coprecipitation synthesis route. The obtained AP/Cu(OH)2 nanocomposites were characterized by means of powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Its thermal decomposition was studied under the non‐isothermal conditions with thermogravimetric analysis and differential scanning calorimeter (TG‐DSC) techniques. In this procedure, SEM and TEM observations revealed that Cu(OH)2 nanoparticles with an average size of 10–15 nm were uniformly deposited on the surface of AP particles. Detailed characterization results indicated that the existence of evidence of Cu(OH)2. As expected, it was found that the AP/Cu(OH)2 nanocomposites with mass fraction of 2 wt % Cu(OH)2 remarkably decreased the peak temperature of high temperature decomposition of AP by 80.2 °C from approximately 441.3 °C to 361.1 °C. As compared with pure AP, the AP/Cu(OH)2 nanocomposites show lower impact and friction sensitivity. These results may lead to potential applications of the AP/Cu(OH)2 nanocomposites in the composite solid propellants for accelerating the thermal decomposition of AP.

The study of RDX impurity and wax effects on the thermal decomposition kinetics of HMX explosive using DSC/TG and accelerated aging methods

The thermal decomposition kinetic behavior of three HMX explosive samples containing 5.0 mass% (A-HMX) and 0.5 mass% RDX impurity (B-HMX) and HMX desensitized with 5.0 mass% paraffin wax (W-HMX) was studied by non-isothermal differential scanning calorimetric and thermogravimetric techniques at different temperature scan rates and by isothermal accelerated aging method. Using KAS isoconversional method, the mean activation energies of 229.36, 221.05, and 267.37 kJ mol−1 were obtained for B-HMX, A-HMX, and W-HMX, respectively, showing the higher thermal stability of pure and desensitized HMX. Moreover, the reaction mechanism was found in Avrami–Erofeev A2 model for all samples. In this study, by using the calculated kinetics triplets, the chemical lifetime of explosives were predicted based on 5.0 mass% mass loss and were compared with isothermal accelerated aging results, under two constant temperatures. The experimental results in the higher temperatures demonstrated relatively better consistency with predicted values.

Degradation of Polyester Polyurethane by Aspergillus sp. Strain S45 Isolated from Soil

A polyurethane (PU)-degrading fungus designated as strain S45 was isolated from a solid waste-dumping site in Islamabad, Pakistan. Strain S45 was identified as Aspergillus sp. through microscopic, morphologic as well as 18S rRNA sequencing (99% similarity with Aspergillus fumigatus). The degradation ability of strain S45, was analyzed through measurement of weight loss and evolution of CO2 as a result of breakdown of PU film. The degradation was confirmed through scanning electron microscopy, fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Surface changes like pits, cracks and holes were observed in scanning electron micrographs upon degradation of PU film by strain S45. FTIR spectra were carefully examined, changes were observed in various peaks at different wavelength ranges that also correspond to degradation of PU film. Differential scanning calorimetric technique was used to measure the melting temperature of PU film pieces before and after incubation with strain S45. DSC curve indicated an increase in melting temperature of PU from 191 to 196 °C that might be due to increase in crystallinity of the exposed PU after degradation of amorphous soft segment. A gradual increase in specific activity of esterase was observed up to the maximum of 15th day of incubation with PU film in mineral salt medium. Enzyme activity was further confirmed by tween 20 agar plates, demonstrated by formation of calcium complex. It is concluded from the results that Aspergillus sp. strain S45 might be applied for the treatment of plastics-contaminated environments.

Calorimetric studies of crystallization for multi-component glasses of Se–Te–Sn–Ag (STSA) system using model-free and model-fitting non-isothermal methods

Silver-containing chalcogenide glasses are well-known candidates for technical applications as well as for the fundamental studies. In the present report, we have studied the kinetics of glass/crystal phase transformation in novel synthesized glasses of STSA system. For this, purpose, differential scanning calorimetric technique has been employed at four different heating rates (5, 10, 15, 20 K min−1). This paper explores the thermal analysis of calorimetric data using both advanced iso-conversional methods for the determination of effective activation energy as a function of extent of crystallization and classical non-isothermal methods for the determination of over-all crystallization activation energy. Iso-conversional methods, such as Kissinger–Akahira–Sunose method and Flynn–Wall–Ozawa method, have been used to study the variation of activation energy of crystallization and other kinetic parameters with extent of crystallization. Non-isothermal methods (Kissinger method, Augis–Bennett method, and Matusita–Sakka method) have been used to determine over-all activation energy of crystallization and other significant parameter of thermally activated crystallization. We have also explained the composition dependence of various kinetic parameters.

High temperature electrical characterization of nano-crystalline BaTiO3 synthesized using Ba(NO3)2 and TiO2

ABSTRACTThe reaction of Ba(NO3)2 with TiO2 was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO3 takes place above 600°C. BaTiO3 powder was prepared by calcination of Ba(NO3)2 and TiO2 precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO3 confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (VO••).

Ternary mixture of fatty acids as phase change materials for thermal energy storage applications

The present study deals with the development of ternary mixtures of fatty acids for low temperature thermal energy storage applications. The commercial grade fatty acids such as Capric Acid (CA), Lauric Acid (LA), Palmitic Acid (PA) and Stearic Acid (SA), have been used to prepare stable, solid–liquid phase change material (PCM) for the same. In this regard, a series of ternary mixture i.e. CA–LA–SA (CLS) and CA–PA–SA (CPS) have been developed with different weight percentages. Thermal characteristics of these developed ternary mixture i.e. melting temperature and latent heat of fusion have been measured by using Differential Scanning Calorimeter (DSC) technique. The synthesized materials are found to have melting temperature in the range of 14–21 °C (along with adequate amount of latent heat of fusion), which may be quite useful for several low temperature thermal energy storage applications.

Effect of low temperature vacuum annealing on microstructural, optical, electronic, electrical, nanomechanical properties and phase transition behavior of sputtered vanadium oxide thin films

Vanadium oxide thin films were deposited on quartz substrate by pulsed RF magnetron sputtering technique at 400–600 W and subsequently annealed at 100 °C in vacuum (1.5 × 10−5 mbar). Phase analysis, surface morphology and topology of the films e.g., both as-deposited and annealed were investigated by x-ray diffraction, field emission scanning electron microscopy and atomic force microscopy techniques. X-ray photoelectron spectroscopy (XPS) was employed to understand the elemental oxidation of the films. Transmittance of the films was evaluated by UV–vis-NIR spectrophotometer in the wavelength range of 200–1600 nm. Sheet resistance of the films was measured by two-probe method both for as-deposited and annealed conditions. XPS study showed the existence of V5+ and V4+ species. Metal to insulator transition temperature of the as-deposited film decreased from 339 °C to 326 °C after annealing as evaluated by differential scanning calorimetric technique. A significant change in transmittance was observed in particular at near infrared region due to alteration of surface roughness and grain size of the film after annealing. Sheet resistance values of the annealed films decreased as compared to the as-deposited films due to the lower in oxidation state of vanadium which led to increase in carrier density. Combined nanoindentation and finite element modeling were applied to evaluate nanohardness (H), Young’s modulus (E), von Mises stress and strain distribution. Both H and E were improved after annealing due to increase in crystallinity of the film.

Experimental investigations of thermal stability of some morpholinecarbamic acid complexes of copper(II) and zinc(II)

Some new carbamates, viz. M(MorphcbmH)2X2 (MorphcbmH = morpholinecarbamic acid, M = Cu, X = Cl, ClO4,NO3; M = Zn, X = Cl, ClO4, NO3, CH3COO and X2 = SO4), have been synthesized and investigated. Compounds were characterized by elemental analysis, molar conductance, FT infrared, fluorescence, NMR (1H and 13C) and solution electronic absorption spectral studies. Room temperature field-dependent magnetic susceptibility measurements, PXRD spectral and cyclic voltametric studies were also conducted. Chelating bidentate mode of coordination of ligand, MorphcbmH with four coordination around metal ion has been proposed. Ligand and its compounds have also been studied using non-isothermal thermogravimetric analysis and differential scanning calorimetric analytical techniques which inferred formation of metal oxide/MCO3 as final thermal decomposition products. Compounds were screened against the lipase enzyme for assaying their enzyme activity and were found to retard the lipase activity from 48.16 to 0.044 µmol mL−1 min−1.

Thermogravimetric study on preparation of NiTiO3 in different reaction times

The thermodynamic properties of the fabrication of NiTiO3 material in different reaction times are reported. The design of this material is accessible through a new efficient sol–gel methods, utilizing Ni(Ac)2·4H2O and Ti(OiPr)4 as starting materials for the formation of NiTiO3 final product through thermal decomposition. The thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques were used to analyze the reaction of Ni(Ac)2·4H2O and Ti(OiPr)4, which produces precursor materials at 0.5, 1, 2, 24, 48 and 72 h of reaction times, as well as the thermal stability of these precursors and the final product. The DSC data show an exothermic phenomenon of releasing large amount of energy of −1393 J/g at T Peak 655 K due to the first event of decomposition started at T Onset 607 K and finished at T Endset 663 K for the precursor materials obtained at 0.5 h of reaction, showing the presence of starting materials in this precursor. A similar exothermic behavior was observed in the sample of 1 h of reaction time and was vanished in the materials obtained at 2–72 h of reaction, indicating the influence of the time on the completion of reaction and formation of NiTiO3 crystalline phase as final product of thermal decomposition. In addition, using the information obtained from the TG/DSC, XRD and FTIR analyses, the optimum temperature for the thermal decomposition of the precursor materials to NiTiO3 with fairly high crystallinity was also determined and discussed.

Hierarchically structured Fe3O4/C nanosheets for effective lithium-ion storage

Carbon-coated magnetite (Fe3O4/C) nanocomposites with hierarchical structure have been subjected to extensive research due to their relatively large specific surface area, extra free voids, and thus enhanced electrochemical performance for lithium-ion batteries (LIBs). In this paper, Fe3O4/C nanosheets with hierarchical structure in the form of carbon matrix supporting Fe3O4 nanocrystals have been prepared by annealing the nanosheet-like iron alkoxide precursor in N2 atmosphere. The Fe3O4/C samples are characterized with X-ray powder diffraction, Raman, scanning electron microscopy, transmission electron microscopy, N2 sorption isotherms, and thermogravimetric–differential scanning calorimetric techniques, and further evaluated in the role of anode materials for LIBs. The specific discharge capacity of Fe3O4/C nanosheets obtained by annealing the precursor in N2 at 600 °C for 3 h retains 647 and 546 mAh g−1 after 100 cycles at 100 and 200 mA g−1, respectively, exhibiting superior electrochemical performance to many other Fe3O4/C nanocomposites in previous reports. The Fe3O4/C nanosheets presented here not only enrich the nanomaterial community but also provide a promising candidate functioning as an anode material for effective lithium-ion storage.

Effect of nanoclay on the nucleation, crystallization and melting behaviour of polypropylene

Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The nanocomposites were prepared using melt intercalation method. It is observed that the crystallization peak temperature of nanocomposite is marginally higher than virgin PP at various cooling rates. The non-isothermal crystallization melt data were analysed using Avrami, Ozawa and Mos models. The half-time for crystallization decreased with incorporation of clay nanoparticles. The values of crystallization rate constant and cooling rate at unit crystallization time showed that the crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization rate of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 196 kJ mol−1, respectively. The polarized micrographs showed that the number of effective nuclei increased in the PP-clay nanocomposite, where the clay acts as a heterogeneous nucleating agent during the crystallization of the nanocomposite.

Impedance and dielectric studies of nanocomposite polymer electrolyte systems using MMT and ferroelectric fillers

Impedance and dielectric properties of nanocomposite polymer electrolyte systems modified with nano size MMT and ferroelectric fillers have been investigated for varying lithium to oxygen ratios. The changes in the structural properties of the electrolyte samples were characterized by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) technique. The ion transport number estimated by DC polarization technique is found to be between 0.86 and 0.95. The bulk conductivities of nanocomposite polymer electrolyte films were studied using impedance spectroscopic technique. The impedance plot shows high frequency semicircle, due to the bulk effect of sample and maximum ionic conductivity of 2.15 × 10−4 Scm−1 was observed for (PEO)4LiCBSM at 323 K with lithium to oxygen ratio 1: 4. The complex impedance data was used to evaluate ionic conductivity and dielectric relaxation process, to understand the ion transport mechanism in these systems.

Effect of polyethylene glycol-intercalated organoclay on vulcanization characteristics and reinforcement of natural rubber nanocomposites

Organically modified montmorillonite (OMMT) clay was intercalated with low-molecular weight polyethylene glycol (PEG) oligomer at melt stage. The intercalation behaviour of PEG into the OMMT clay galleries and its interaction with clay platelets were characterized with X-ray diffraction (XRD) and differential scanning calorimetric techniques. A natural rubber (NR)–organoclay nanocomposite (NROCN) was prepared by melt-compounding of NR with PEG-treated organoclay (P-OMMT) and other compounding chemicals using a laboratory-scale internal mixer. XRD analysis of the nanocomposites revealed the intercalation of NR molecules into the P-OMMT clay galleries and subsequent exfoliation during the melt-compounding process. Vulcanization characteristics of the NROCN, especially processing safety and optimum curing time, have been interpreted with reference to the organic modifier of the montmorillonite clay, PEG modification and the degree of exfoliation. Solid-state mechanical properties of P-OMMT clay-filled NROCN vulcanizates have shown a significant enhancement in stiffness and strength characteristics whilst without scarifying the elasticity of the nanocomposites. Results have been explained in terms of the degree of exfoliation, dispersibility of the organoclay and strain-induced crystallization of the natural rubber.

Synthesis of comb-type amphiphilic graft copolymers derived from chlorinated poly(ɛ-caprolactone) via click reaction

This work refers to the synthesis of a series of novel chlorinated poly(ɛ-caprolactone) (PCL) for further functionalization of PCL. For this aim, chlorine gas was passed through into the chloroform solution to obtain chlorinated polycaprolactone. The chlorine contents in chlorinated PCL were between 0.9 and 1.6 mol%. The molecular weights of the polymers (M n) changed from 4853 to 9497 g/mol. As the amount of passing chlorine gas increases, the molecular weight of the chlorinated PCL was found to decrease. Pendant chloride groups of PCL were reacted with sodium azide to prepare PCL with pendant azide groups (PCL-N3). Poly-(ethylene glycol) methyl ether (mPEG) was reacted with propargyl chloride to achieve alkynyl mPEG (mPEG-alkyn). Click reaction was then carried out by the reaction between PCL-N3 and mPEG-alkyn to obtain PCL-g-PEG comb-type amphiphilic graft copolymer. Interestingly, SEM images of the PCL-g-PEG comb-type amphiphilic graft copolymers showed the highly microporous structure. The resulting products were characterized by 1H NMR, FT-IR, gel-permeation chromatography, SEM, surface tension, contact angle and water uptake measurements, differential scanning calorimeter and thermogravimetric analyses techniques.

Synthesis and Analysis of Electrospun SrTiO3 Nanofibers with NiO Nanoparticles Shells as Photocatalysts for Water Splitting

SummaryThe coaxial electrospinning process was used to produce core/shell strontium titanate/nickel oxide (SrTiO3‐NiO) nanofibers. First, poly (vinyl pyrrolidone) (PVP) was dissolved in deionized (DI) water, and then titanium (IV) isopropoxide [C12H28O4Ti] and strontium nitrate [Sr(NO3)2] were added into the solution to form the inner (core) layer. Polyacrylonitrile (PAN) polymer was dissolved in dimethylformamide (DMF) at a weight ratio of 10:90. Nickel oxide was mixed with the solution to form the outer (shell) layer. This coaxial electrospinning method generated uniform‐size, defect‐free fibers. The electrospun nanofiber samples were annealed at 600°C for two hours in air in order to remove the organic part and crystallize the amorphous SrTiO3‐NiO nanofibers. Water contact angles were determined to identify surface hydrophobicity of the nanofiber films. Ultraviolet (UV) spectrophotometry, Fourier transform infrared radiation (FTIR), and differential scanning calorimeter (DSC) techniques were used to characterize the structural properties of the SrTiO3‐NiO nanocomposite fibers. The morphology and dimensions of the nanofibers were observed by scanning electron microscopy (SEM). The images showed fluctuation in the fiber diameters because of the two different polymeric solutions electrospun at the same time. The structures of the calcined nanofibers were determined by Raman spectroscopy and X‐ray diffraction (XRD), which clearly indicated the formations of SrTiO3 and NiO nanofiber structures. The fabrication of such core/shell SrTiO3‐NiO nanofibers through coaxial electrospinning suggests the further enhancement and development of photocatalytic behaviors of the new nanomaterials. This study can provide useful information for scientists, engineers, and manufacturers working in renewable energy and related fields, such as water splitting, sensors, solar cells, and catalysts.

Third order nonlinear optical properties and crystal structures of (E)-1 (3,4-dimethoxyphenyl)-3-(4-(trifluoromethyl)phenyl)prop-2-en-1-one

A new organic material (E)-1-(3,4-dimethoxyphenyl)-3-(4-(trifluoromethyl)phenyl)prop-2-en-1-one (DPTF), belonging to chalcone family, exhibiting third-order non-linear optical properties has been synthesised and grown as single crystals, by slow evaporation technique at room temperature. The grown crystal was subjected to single-crystal X-ray diffraction analysis in order to establish their crystal structure. The DPTF crystal belongs to the triclinic crystal system (a = 8.0368 Å, b = 10.4345 Å, c = 10.4560 Å and α = 114.1645°, β = 96.5748°, γ = 101.4285°) with centrosymmetric space group . The functional groups present in DPTF molecule were identified using FTIR spectral studies. The linear optical properties, direct and indirect transition energy gaps were determined using UV–visible spectral data. The melting point and thermal stability of DPTF have been established through thermo-gravimetric and differential scanning calorimetric technique. The non-linear optical properties have been studied using single-beam Z-scan technique. The coefficient of non-linear absorption and non-linear refractive index are found to be 5.11 cm/GW and −2.48 × 10−11 esu, respectively. The DPTF molecule exhibits optical power limiting property.

Thermal characteristic of nanocomposite phase change materials during solidification process

Phase change materials are widely used in various thermal management applications. Conductive nanoparticles can be added to phase change materials to improve their thermal conductivities. The selection of suitable nanoparticles and weight percent is important from thermal performance point of view. In this study, various nanoparticles (e.g. SiO2 (11nm, 20nm), Al2O3, Fe2O3, ZnO) and their combinations at different concentrations (2, 4, 6 and 8%wt) were used as thermal conductivity promoters to produce modified paraffin samples. Thermal properties of the synthesized nanocomposites were characterized by differential scanning calorimetric technique. Experimental measurements showed that the presence of nanoparticles can improve thermal conductivity of the nanocomposite (by a maximum of 150%) but the specific heat may be degraded (by a maximum of 39% max). Experimental results have indicated that considering all parameters involved, composite samples with 8wt% ZnO offer optimum thermal properties. Therefore, it is very important to identify the type and optimum amount of the nanoparticles which are added to the phase change materials. The results of this study can be used to improve thermal performance of nanocomposites phase change materials.

Nonisothermal crystallization kinetics in isotactic polypropylene/microcrystalline cellulose (II) composites

This study investigates the polymorphous transformation of microcrystalline cellulose at different NaOH concentrations and the nonisothermal crystallization kinetics of polypropylene/microcrystalline cellulose (II) composites by differential scanning calorimetric technique (DSC) with various cooling rates. The synchrotron X‐ray diffraction reveals that the polymorphous transition from cellulose (I) to cellulose (II) begins at NaOH concentration of 10 (wt%) and the complete transformation is obtained at the NaOH concentration of 15–20 (wt%) during the mercerization process. The Avrami equation was applied to depict the nonisothermal crystallization process and to analyze the experimental data of the composites. The DSC results show that the values of t1/2 for iPP/MCC (II) composites are lower than that for pure iPP. The polarized optical microscopy images reveal that the peculiar hybrid shish–calabash structure (HSC) with MCC (II) fibers serving as shish and iPP spherulites as calabash finally be formed. POLYM. COMPOS., 39:1064–1075, 2018. © 2016 Society of Plastics Engineers