Conventional DSC Research Articles

Hysteresis in the β–α phase transition in silver iodide

The nature of the β to α phase transition in silver iodide was investigated by conventional and modulated temperature DSC and dielectric property measurements. On cooling, the high temperature phase remained stable 2.5°C below its normal transition temperature even at a very slow cooling rate 0.2°C h–1. Dielectric property measurements under conventional and microwave heating suggested an anomalous effect of the latter on the β to α phase transition in this material.

Applications of Thermal Mechanical Compression Tests in Food Powder Analysis

A new Thermal Mechanical Compression Test (TMCT) was applied for glass-rubber transition and melting analyses of food powders and crystals. The TMCT technique measures the phase change of a material based on mechanical changes during the transition. Whey, honey, and apple juice powders were analyzed for their glass-rubber transition temperatures. Sucrose and glucose monohydrate crystals were analyzed for their melting temperatures. The results were compared to the values obtained by conventional DSC and TMA techniques. The new TMCT technique provided the results that were very close to the conventional techniques. This technique can be an alternative to analyze glass-rubber transition of food, pharmaceutical, and chemical dry products.

Oxidative Stability of Biodiesel by Dynamic Mode Pressurized-Differential Scanning Calorimetry (P-DSC)

Biodiesel, an alternative diesel fuel made from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain fatty acid alkyl esters. During long-term storage, oxidation caused by contact with ambient air presents legitimate concerns for monitoring fuel quality. Extended oxidative degradation can affect kinematic viscosity, cetane number, and acid value of the fuel. This work investigates the suitability of dynamic mode (positive air purge) pressurized-differential scanning calorimetry (P-DSC) as a means for evaluating the oxidation reaction during non-isothermal heating scans. Methyl oleate, methyl linoleate, and soybean oil fatty acid methyl esters (FAME) were analyzed by P-DSC and the results compared with those from thermogravimetric analyses (TGA), conventional DSC, and static mode (zero purge gas flow) P-DSC scans. Results from TGA showed that ambient air pressure was too low to allow measurable oxidation during analyses. Although some degree of oxidation was detected for DSC and static mode P-DSC heating scans, results demonstrated that the highest degree of oxidation occurred during dynamic mode P-DSC scans. For DSC and P-DSC analyses, oxidation onset temperature (OT) increased with relative oxidative stability, with the highest values being observed for methyl oleate. Treating soybean oil FAME with antioxidants increased their relative oxidative stability, resulting in an increase in OT. Statistical comparison of response factors (RF) relative to methyl oleate obtained from non-isothermal heating scans with those obtained from OSI analyses showed the highest degree of correlation (P = 0.79) with respect to dynamic mode P-DSC.

Determination of the enthalpy of solid phase transition for isotactic polypropylene using a modified DSC technique

This paper investigates the enthalpy of solid phase transition of isotactic polypropylene from the mesomorphic phase to the monoclinic crystal form using DSC. iPP fibres with either monoclinic crystal form or mesomorphic phase were obtained by varying the conditions of melt spinning. XRD and mechanical tests were used to confirm the crystal forms. It is found that conventional DSC techniques fail to detect the transition enthalpy; a technique using silicon oil as the thermal medium was then employed to determine the transition enthalpy, which is of 3% the melting enthalpy for crystallites with monoclinic form, or 6.1 J/g on 100% crystallinity basis.

Multiple melting behaviour of poly(3-hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5V), 8 wt.% (PHB8V) and 12 wt.% (PHB12V)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC), wide angle X-ray diffraction (WAXRD) and hot stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by isothermal crystallisation kinetics. Thermal properties were investigated after isothermal crystallisation treatment. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting–recrystallisation–remelting during heating, as evidenced by exothermic peaks in the IsoK baseline ( C p,IsoK , non-reversing signal). An increase in degree of crystallinity due to significant melt–recrystallisation was observed for isothermally crystallised polymers. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat ( C p,ATD , reversing signal). PHB and PHBV showed different crystal morphologies for similar crystallisation condition. HSPOM results showed that the crystallisation rates reduced and sizes of spherulites were significantly increased as HV content increased.

Thermal behaviour of two room-temperature ionic liquids containing the methylimidazolium cation

We have investigated the glass transition relaxation of two room-temperature ionic liquids using Modulated Temperature Differential Scanning Calorimetry (MTDSC). Furthermore, conventional DSC was used to clarify their crystallisation behaviour. One of the liquids avoids crystallisation, while the other shows cold crystallisation. A step-by-step temperature scanning experimental procedure was used to analyse in detail the thermal behaviour of the latter in the crystallisation and melting temperature regions. The existence of polymorphism is discussed.

A High Voltage Dye-sensitized Solar Cell using a Nanoporous NiO Photocathode

Abstract An np tandem dye-sensitized solar cell (np-DSC) comprising a titanium dioxide (TiO2) anode and a nickel oxide (NiO) cathode prepared as porous nanostructured films by a sol–gel method using a triblock copolymer template (P123, HO(OCH2CH2)20(OCH(CH3)CH2)70(OCH2CH2)20OH))CH2 exhibited a high open circuit voltage (Voc) of 0.92 V that surpassed the long time champion data, ≈0.8 V for conventional DSC.

Melting and thermal history of poly(hydroxybutyrate-co-hydroxyvalerate) using step-scan DSC

Melting behaviour and crystal morphology of poly(3-hydroxybutyrate) (PHB) and its copolymer of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with various hydroxyvalerate (HV) contents [5 wt.% (PHB5HV), 8 wt.% (PHB8HV) and 12 wt.% (PHB12HV)] have been investigated by conventional DSC, step-scan differential scanning calorimetry (SDSC) and hot-stage polarised optical microscopy (HSPOM). Crystallisation behaviour of PHB and its copolymers were investigated by SDSC. Thermal properties were investigated after different crystallisation treatments, fast, medium and slow cooling. Multiple melting peak behaviour was observed for all polymers. SDSC data revealed that PHB and its copolymers undergo melting–recrystallisation–remelting during heating, as evidenced by exothermic peaks in the IsoK baseline (non-reversing signal). An increase in degree of crystallinity due to significant melt–recrystallisation was observed for slow-cooled copolymers. PHB5HV showed different crystal morphologies for various crystallisation conditions. SDSC proved a convenient and precise method for measurement of the apparent thermodynamic specific heat (reversing signal) HSPOM results showed that the crystallisation rates and sizes of spherulites were significantly reduced as crystallisation rate increased.

Study of Crystallization Processes in Ethylene−Styrene Copolymers by Conventional DSC and Temperature-Modulated Calorimetry: Linear Polyethylene and Low Styrene Content Copolymers

Using a combination of differential scanning calorimetry and quasi-isothermal temperature-modulated calorimetry, we investigated the temporal evolutions of the melting temperature, degree of crystallinity, and excess heat capacity during crystallization of linear polyethylene and low styrene content ethylene−styrene copolymers. Describing isothermal crystallization as the succession of three stages (primary, mixed and secondary crystallization stages), we established the following correlations: (1) the evolution of the melting temperature with time parallels that of the degree of crystallinity, (2) the excess heat capacity increases linearly with degree of crystallinity during the primary stage, reaches a maximum during the mixed stage, and decays during the secondary stage, (3) the rate of decay of the excess heat capacity parallels the rate of secondary crystallization, and (4) the rates of shift of the melting temperature and decay of the excess heat capacity lead to apparent activation energies that are very similar to these reported for the crystal αc relaxation by solid-state NMR, dynamic mechanical, and dielectric spectroscopies. Strong correlations in the time domain for secondary crystallization by lamellar thickening and evolution of the excess heat capacity suggest that the reversible crystallization/melting phenomenon is associated with molecular events in the melt−crystal fold interfacial region. Specifically, we conclude that the excess heat capacity observed during the high-temperature crystallization of linear polyethylene and low styrene content copolymers is most likely to originate from the segmental processes in the crystal/melt fold region that have been discussed by Fischer, Mansfield, and Strobl. These studies also provide preliminary indications that the excess heat capacity observed during crystallization at lower temperatures in the case of ethylene copolymers of high comonomer content is consistent with the lateral surface model proposed by Wunderlich.

Thermal, Structural and Ferroelectric Properties of Amorphous Phases in Quenched Nylon 6 Film

Three types of amorphous phases (ferroelectric metastable phase A with large remanent polarization, ferroelectric metastable phase B with small remanent polarization and paraelectric stable phase C) are identified in as-quenched and/or annealed nylon 6 films on the basis of the thermal data obtained by light-modulated differential scanning calorimetry (LMDSC) as well as X-ray data, which show different glass transition temperatures and d -spacings. The irreversible exothermic anomaly at 328 K observed through heating process in the conventional DSC is attributed to transition from phases A and/or B to nematic phase. The transition from phase A to phase B is considered to complete after 15 min annealing at 320 K on the basis of the LMDSC data, which corresponds to abrupt diminution of the remanent polarization by the correspondent annealing condition. Such results suggest that ferroelectricity of nylon 6 film is mainly attributed to phase A (frozen state of the melt) formed in the quenched nylon 6 thin film.

The potential of high speed DSC (Hyper-DSC) for the detection and quantification of small amounts of amorphous content in predominantly crystalline samples

The purpose of this study was to explore whether it is possible to use hyper differential scanning calorimetry (HDSC) to detect and quantify low levels of amorphous content in samples that are mostly crystalline. HDSC uses scan rates that are much faster than conventional DSC, and consequently results in greater sensitivity. It was found that with every increase in scan rate it became easier to detect the glass transition ( T g) response. Scanning at 500 °C/min was possible and this gave such great sensitivity that very low sample mass (ca. 1 mg) could be used without any loss in detection of T g. Mixtures of crystalline and amorphous (spray dried) lactose were prepared and scanned at 500 °C/min. It was observed that the T g response was easily detected even for samples that contained 1.5% amorphous content when using very low samples mass. The view held at present is that DSC is not well suited to studies of amorphous content if the sample contains 10% or less of the amorphous material. The data generated here show that much better detection sensitivity is possible when using the rapid scan rates. As well as being able to detect the presence of very low amorphous contents it was also possible to obtain a quantification, as a linear response was obtained for the step height change in heat flow as a function of amorphous content. It was concluded that HDSC provides a method of obtaining a very fast assessment of the presence of amorphous form, the possibility to quantify this and the need to use a very low sample mass. The combination of speed, low sample mass and sensitivity makes this a very valuable technique for studies on partially amorphous samples.

Modeling the interactions between light and crystallizing polymer during fast cooling

In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the experimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evolution is proposed and applied to some fast cooling runs. The method was applied to quenching runs of an iPP carried out under cooling conditions more than one order of magnitude faster than those allowed for the DSC technique. The crystallization temperature dependence upon cooling rate was obtained from these runs in a cooling rate range never before explored.

Comparison of simulated and actual DSC measurements for first-order transitions

A system of differential equations modeling a heat flux DSC is solved and the results are compared with those obtained using a TA Instruments Q1000™ DSC. 1 US Patent 6,431,747 additional patents applied for. 1 It incorporates a new heat flow rate measurement technique that determines the heat flow rate between the sample and its pan. Two types of first-order transitions are investigated: melting of a pure substance and solidification of a pure substance including super-cooling. In both transitions, the peak shape obtained using the new heat flow rate measurement and predicted by the model is quite different from that measured using conventional DSC. It is shown that the differences are the result of simplifications implicit in the conventional heat flow rate measurement that is based solely on the difference between sample and reference calorimeter temperatures. Heat flow rates measured using the improved measurement agree very well with the model predictions for heat exchange between the sample and its pan.

Melting and crystallization behavior of poly(trimethylene 2,6-naphthalate)

The melting and crystallization behavior of poly(trimethylene 2,6-naphthalate) (PTN) are investigated by using the conventional DSC, the temperature-modulated DSC (TMDSC), wide angle X-ray diffraction (WAXD) and polarized light microscopy. It is observed that PTN has two polymorphs (α- and β-form) depending upon the crystallization temperature. The α-form crystals develop at the crystallization temperature below 140 °C while β-form crystals develop above 160 °C. Both α- and β-form crystals coexist in the samples crystallized isothermally at the temperature between 140 and 160 °C. When complex multiple melting peaks of PTN are analyzed using the conventional DSC, TMDSC and WAXD, it is found that those arise from the combined mechanism of the existence of different crystal structures, the dual lamellar population, and melting–recrystallization–remelting. The equilibrium melting temperatures of PTN α- and β-form crystals determined by the Hoffman–Weeks method are 197 and 223 °C, respectively. When the spherulitic growth kinetics is analyzed using the Lauritzen–Hoffmann theory of secondary crystallization, the transition temperature of melt crystallization between regime II and III for the β-form crystals is observed at 178 °C. Another transition is observed at 154 °C, where the crystal transformation from α- to β-form occurs.

Decomposition of FeSn intermetallic induced by mechanical milling

Under mechanical milling (MM) in a planetary ball mill the FeSn intermetallic decomposes with formation of the Fe 5Sn 3 and FeSn 2 phases, which have the highest density among the phases of the Fe–Sn system. This process was investigated using conventional X-ray diffraction, DSC, magnetization and alternative current susceptibility measurements. If the amount of decomposition of FeSn is relatively small (<60%), the milled powder shows superparamagnetic behavior at room temperature. In this case, magnetization curves can be fitted by superposition of two Langevin functions. The particle sizes for the ferromagnetic Fe 5Sn 3 phase determined from the fitting parameters are in good agreement with the crystallite sizes determined from XRD data and remain approximately constant during MM. The decomposition of FeSn is attributed to the effects of local temperature and local pressure produced by ball collisions.

Interrelation between side chain crystallization and dynamic glass transitions in higher poly( n-alkyl methacrylates)

Calorimetric and dielectric results for crystallizable poly( n-alkyl methacrylates) (PnAMA) with C=12, 16 and 18 alkyl carbons per side chain are presented. Degree of crystallization D cal and melting peak temperature T M are estimated from conventional DSC measurements. For poly( n-hexadecyl methacrylate) ( C=16) the influence of isothermal crystallization is studied by DSC as well as TMDSC. Changes in dielectric relaxation strength Δ ε and α peak shape during crystallization are investigated. Effects of side chain crystallization on the complex dynamics of PnAMA are discussed. The results are related to the relaxation behavior of lower nanophase-separated PnAMA with two co-existing glass transitions, the conventional glass transition ( a or α) and the polyethylene-like glass transition ( α PE) within alkyl nanodomains formed by aggregated alkyl rests. It is shown that amorphous as well as semicrystalline PnAMA can be understood as nanophase-separated polymers with alkyl nanodomains having a typical dimension of 1–2 nm. The results are compared with the predictions of simple morphological pictures for side chain polymers. X-ray scattering data for the amorphous and semicrystalline PnAMA are included in the discussion. Common aspects of nanophase-separated systems in both states as well as differences caused by crystallization are discussed. Indications for the existence of rigid amorphous regions are compiled. Different approaches to explain a similar increase of T g( α PE)—the glass temperature of the amorphous alkyl nanodomains—and T M—the melting temperature of crystalline alkyl nanodomains—with side chain length are considered. Pros and cons of both approaches, based on increasing order within the alkyl nanodomains and confinement effects in nanophase-separated systems, are discussed. Main trends concerning crystallization and cooperative dynamics are compared with those in other systems with self-assembled nanometer confinements like microphase-separated blockcopolymers or semicrystalline main chain polymers.

Aging Behavior of a Novel kind of Poly(ether ether ketone)

In this paper, aging behaviors of a novel kind of poly(ether ether ketone) were studied by alternating differential scanning calorimetry(ADSC). Samples were annealed at 129°C, about 20°C below its glass transition temperature, for different periods, then scanned in the ADSC. The effect of aging time on these parameters is illustrated. We found that the total heat flow closely corresponded to conventional DSC in respect of peak endotherm temperature. The phase angle became sharper on aging and the peak moved towards higher temperatures.

Relation of glass transition temperature to the hydrogen bonding degree and energy in poly( N-vinyl pyrrolidone) blends with hydroxyl-containing plasticizers: 3. Analysis of two glass transition temperatures featured for PVP solutions in liquid poly(ethylene glycol)

The phase behaviour of poly( N-vinyl pyrrolidone)–poly(ethylene glycol) (PVP–PEG) blends has been examined in the entire composition range using Temperature Modulated Differential Scanning Calorimetry (TM-DSC) and conventional DSC techniques. Despite the unlimited solubility of PVP in oligomers of ethylene glycol, the PVP–PEG system under consideration demonstrates two distinct and mutually consistent glass transition temperatures ( T g) within a certain concentration region. The dissolution of PVP in oligomeric PEG has been shown earlier (by FTIR spectroscopy) to be due to hydrogen bonding between carbonyl groups in PVP repeat units and complementary hydroxyl end-groups of PEG chains. Forming two H-bonds through both terminal OH-groups, PEG acts as a reversible crosslinker of PVP macromolecules. To characterise the hydrogen bonded complex formation between PVP ( M w=10 6) and PEG ( M w=400) we employed an approach described in the first two papers of this series that is based on the modified Fox equation. We evaluated the fraction of crosslinked PVP units and PEG chains participating to the complex formation, the H-bonded network density, the equilibrium constant of complex formation, etc. Based on the established molecular details of self-organisation in PVP–PEG solutions, we propose a three-stage mechanism of PVP–PEG H-bonded complex formation/breakdown with increase of PEG content. The two observed T gs are assigned to a coexisting PVP–PEG network (formed via multiple hydrogen bonding between a PEG and PVP) and a homogeneous PVP–PEG blend (involving a single hydrogen bond formation only). Based on the strong influence of coexisting regions on each other and the absence of signs of phase separation (evidenced by Optical Wedge Microinterferometry) we conclude that the PVP–PEG blend is fully miscible on a molecular scale.

Differential thermal analysis under quasi-isothermal, quasi-isobaric conditions (Q-DTA): Examinations using “transformation-governed heating control” and “self-generated atmosphere” (TGHC-SGA)

The course of conventional DTA or DSC curves is rather characteristic of the experimental conditions then of the transformation itself. The course of Q-TA T curves taken by the Q-DTA measuring technique is not deteriorated by these factors when using the “transformation-governed heating control” (TGHC). In this technique, namely, the temperature of the sample is governed by the transformation itself based on the feed-back principle so that the relay-switch system of the Q-DTA apparatus sensing the change of the Q-DTA t signal governs the heating control unit in a way, in which the transformation proceeds with a predetermined, very small and strictly constant rate by providing the suitable difference between the temperatures of the sample and the furnace. In order to normalise the experimental conditions, for decomposition reactions a particular, so-called “labyrinth crucible” should also be used, which provides a “self-generated atmosphere” already at the beginning of the reaction, and keeps the partial pressure of gaseous decomposition products constant at their maximum value of 100 kPa till the end of the transformation. This way, the unique normal characteristic temperature of reactions and transformations, together with reaction heat belonging to them can be measured, and the course of transformations free of every foreign influence can also be recorded.

Studying the Glass Transition by DSC and TMDSC

First, the principal features of the glass transformation process in polymers are reviewed, and then it is shown how they are manifest in conventional DSC, and the quantitative analysis of typical DSC data is discussed in terms of the Tool-Narayanaswamy-Moynihan (TNM) model. Subsequently, the way in which the glass transition is manifest in Temperature Modulated DSC is presented, and the effects of both experimental and material parameters are discussed. In conclusion, the two techniques are compared in terms of the information they provide about the glass transformation process.