The Application of Modulated Temperature Power Compensation DSC to the Characterisation of Polymer Blends

A modulated temperature power compensated differential scanning calorimeter, MTDSC, has been built from a standard Perkin-Elmer DSC model-2 such that a computer generated voltage has been applied to induce a sinusoidal change in sample temperature superimposed on a linear heating rate. The effect of amplitude of the temperature fluctuation, modulation period and block temperature on the reversibility has been assessed from the Lissajous diagram of heat flow vs. sample temperature. From their reproducibility and symmetry the most effective conditions for operating the MTDSC has been deduced. The specific heat of sapphire has been measured using these operational conditions for comparison with conventional DSC. Phase separated blends of polycarbonate (PC) and polyethylene terephthalate (PET) have been analysed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Greater insight into the MTDSC technique involving fundamental sinusoidal heat flow equations

Summary Modulated temperature DSC was investigated, comparing data found experimentally to that derived from theory. Deviation from theory was found with regard to the amplitude of the modulated heat flow signal when large modulation amplitudes were employed in the experiment. These deviations were determined to be dependent on the absolute temperature and it was concluded that further investigation of the heat flow signal obtained during MTDSC experiments is required.     

Modulated‐temperature differential scanning calorimetry study of temperature‐induced mixing and demixing in poly(vinylmethylether)/water

The heat capacity or reversing heat flow signal from modulated‐temperature differential scanning calorimetry can be used to measure the onset of phase separation in a poly(vinylmethylether)/water mixture, clearly showing the special type III lower critical solution temperature demixing behavior. Characteristic of this demixing behavior is a three‐phase region, which is detected in the nonreversing heat flow signal. Stepwise quasi‐isothermal measurements through the phase transition show large excess contributions in the (apparent) heat capacity signal, caused by demixing/remixing heat effects on the timescale of the modulation (fast process). These excess contributions and their time‐dependent evolutions (slow process) are useful in understanding the kinetics of phase separation and the morphology (interphase) development. Care has to be taken, however, in interpreting the heat capacity signal derived from the amplitude of the modulated heat flow because nonlinear effects lead to the occurrence of higher harmonics. Therefore, the raw heat flow signal for quasi‐isothermal demixing and remixing measurements is also examined in the time domain. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1824–1836, 2003     

Dependence of the preexponential factor on temperature

Summary The dependence of the preexponential factor on the temperature has been examined and the errors involved in the activation energy calculated from isothermal and non-isothermal methods without considering such dependence have been estimated. It has been shown that the error in the determination of the activation energy calculated ignoring the dependence of Aon Tcan be rather large and it is dependent on x=E/RT, but independent of the experimental method used. It has been also shown that the error introduced by omitting the dependence of the preexponential factor on the temperature is considerably larger than the error due to the Arrhenius integral approach used for carrying out the kinetic analysis of TG data.     

As-As dimerization, Fermi surfaces and the anomalous electrical transport properties of UAsSe and ThAsSe

A temperature dependent electron diffraction study has been carried out on UAsSe to search for evidence of As-As dimerization at low temperature. A highly structured characteristic diffuse intensity distribution, closely related to that recently reported for ThAsSe, has been observed at low temperature and interpreted in terms of a gradual charge density wave type phase transition upon lowering of temperature involving disordered As-As dimerization within (001) planes. Plausible models of the proposed As-As dimerization have been obtained using a group theoretical approach. Electronic band structure calculations of ThAsSe and UAsSe have been used to search for potential Fermi surface nesting wave-vectors. The results are in good agreement with the experimentally observed diffuse intensity distributions in both cases.     

Modulated temperature DSC measurements relating to the cold crystallization process of poly(ethylene terephtalate)

The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.Dedicated to Professor Wunderlich on the occasion of his 65th birthday     

Theory and Applications of Modulated Temperature Programming to Thermomechanical Techniques

The application of modulated temperature programs to thermomechanical analysis can be used to separate the reversible nature of thermal expansion from irreversible deformation arising from creep under the applied load or changes in dimensions due to relaxation of orientation. The effect of experimental variables and calibration are described. Modulated temperature TMA allows the time-dependent nature of thermal expansivity to be studied. Measurements made under compression afford a means of measuring the thermal expansivity of soft specimens independently of initial load. Application of these principles to scanning thermal microscopy leads to a novel method of generating image contrast based upon local changes thermal expansivity of a specimen. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat Transfer in a Disc-Type DSC Apparatus IV. Applicability of the coupled cells model to periodic temperature modulation

The application of non-linear heating programs to a heat-flux DSC apparatus has attracted much attention. On the basis of thermodynamics, the change in enthalpy of a sample during a temperature change ΔT is due, on the one hand to the true heat capacity of the sample ΔT C_pξ and on the other, to the enthalpy of some transformation occurring in the sample Δ_rH Δξ. These contributions can be separated on the basis of the kinetics of the transformation. The coupled cells model of a disc type, heat flux DSC apparatus has been tested, using true heat capacities and a sine modulation of the temperature of the furnace around a constant temperature. In the range from 2 to 60 mHz, the amplitude and phase shift of the calorimetric signal were measured at several frequencies. Theoretical equations, based on the model, and using the thermal Ohm's law explains the results with a reasonable accuracy. A non-linear DSC experiment affords two ways of determination of the heat capacity of a sample making possible a distinction between the enthalpic effect and heat capacity. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Theoretical Approach to Temperature Modulated Power Compensation DSC

The steady state of temperature modulated power compensation DSC has been theoretically investigated for measurements of complex heat capacity, taking accounts of heat capacities of heat paths, heat loss to the environment, and mutual heat exchange between the sample and the reference material. Thermal contact between the sample cell and the cell holder is also taken into accounts. Rigorous and general solutions are obtained. From these solutions application of the technique to heat capacity measurements is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Melt Behaviour of Poly(p-xylylene) (PPX) Coated Gel-spun UHMW-PE Fibers As Revealed by Temperature Modulated DSC

The method of temperature modulated DSC has been applied to obtain additional information about the effect of constraints on the melting behaviour of gel-spun ultra high molecular mass polyethylene (UHMW-PE) fibers coated with a high temperature stable poly(p-xylylene) (PPX) polymer. The underlying signal, corresponding to the normal DSC signal, reveals two endothermic peaks for the coated PE fibers. A shift in the underlying and magnitude signal from 142 to 145°C at 0.1 K min^–1 , a relative small magnitude signal, together with a vanishing step-like change in the phase signal with increasing PPX coating layer thickness characterize the constraints in terms of a hindrance of the melting of the unconstrained orthorhombic crystal fraction. The time constant of the melting process can be estimated as larger than the reciprocal angular frequency 1/ω=5 s of the modulation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reversibility of the low‐temperature transitions of polytetrafluoroethylene as revealed by temperature‐modulated differential scanning calorimetry

Temperature‐modulated differential scanning calorimetry reveals distinct differences in the kinetics of the low‐temperature phase transitions of polytetrafluoroethylene. The triclinic to trigonal transition at 292 K is partially reversible as long it is not complete. As soon as the total sample is converted, supercooling is required to nucleate the reversal of the helical untwisting involved in the transition. The trigonal phase can be annealed in the early stages after transformation with a relaxtion time of about 5 minutes. The dependence of the reversing heat capacity on the modulation amplitude, after a metastable equilibrium has been reached, is explained by a non‐linear, time‐independent increase of the heat‐flow rate, perhaps caused by an increased true heat capacity. The order‐disorder‐transition at 303 K from the trigonal to a hexagonal condis phase is completely reversible and time‐independent. It extends to temperatures as low as the transition at 292 K or even lower. Qualitatively, the thermal history and crystallization conditions of polytetrafluoroethylene do not affect the transition kinetics, that is, melt‐crystallized film and as‐polymerized powders show similar transition behaviors, despite largely different crystallinities. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 750–756, 2001     

Reversible and irreversible heat capacity of poly(trimethylene terephthalate) analyzed by temperature‐modulated differential scanning calorimetry

The heat capacity of poly(trimethylene terephthalate) (PTT) has been analyzed using temperature‐modulated differential scanning calorimetry (TMDSC) and compared with results obtained earlier from adiabatic calorimetry and standard differential scanning calorimetry (DSC). Using quasi‐isothermal TMDSC, the apparent reversing and nonreversing heat capacities were determined from 220 to 540 K, including glass and melting transitions. Truly reversible and time‐dependent irreversible heat effects were separated. The extrapolated vibrational heat capacity of the solid and the total heat capacity of the liquid served as baselines for the analysis. As one approaches the melting region from lower temperature, semicrystalline PTT shows a reversing heat capacity, which is larger than that of the liquid, an observation that is common also for other polymers. This higher heat capacity is interpreted as a reversible surface or bulk melting and crystallization, which does not need to undergo molecular nucleation. Additional time‐dependent, reversing contributions, dominating at temperatures even closer to the melting peak, are linked to reorganization and recrystallization (annealing), while the major melting is fully irreversible (nonreversing contribution). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 622–631, 2000     

Temperature Calibration of TMAs Using Modulated Temperature and Curie Temperature Reference Standards

This article presents the concept of calibrating temperature in thermomechanical analyzers (TMA) using reference standard magnetic materials whose Curie temperatures are well-known. This concept has not been tested experimentally to the best of the author's knowledge. Electrical current applied to a unifilarly wound furnace results in the furnace acting as an electrical inductor. A magnetic material sample located within such a furnace practically constitutes a solenoid core. A modulated temperature program directly results in a corresponding varying force exerted by the sample against the TMA probe, if the probe's axis and the central induced magnetic field line of force are coaxial, and, furthermore, if the direction of the central magnetic field line of force and the expansion direction of the probe are identical. If a sample undergoes a Curie transition, then the force which the sample exerts against the probe will diminish to zero as the transition goes to completion. Using a modulated temperature program throughout this phase transition allows determination of transition completion, by observation of the point at which the force required to maintain the sample's physical position reaches a steady state from it's previously non-steady state. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature Control Modes in Thermal Analysis

Now we can use several temperature control modes, i.e., the isothermal run including stepwise heating and cooling, constant rate heating (or cooling), temperature control for sample thermal history, sample controlled thermal analysis (SCTA or controlled-rate thermal analysis, CRTA), temperature jump, rate jump, temperature modulation and repeated temperature scanning. Their advantages and drawbacks are reviewed with some illustrative examples, especially for application to kinetic analysis. The combined use of these varieties of temperature control mode is recommended by showing examples. Temperature modulation and repeated temperature scanning are discussed in comparison with temperature modulated DSC, and common and analogous points are elucidated. In relation to this, the possibility that an imaginary part of overall reaction rate constant in complex reaction is postulated. Finally,these modes are classified and tabulated from two viewpoints and other possible modes are shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prediction of solvent activities using the UNIFAC-FV model

A UNIFAC group contribution method with an explicit temperature dependent free volume term has been developed. The systems used in the development were benzene-polyethylene oxide from 319 to 423 K and n-hexane—n-hexadecane from 303 to 333K. The addition of temperature dependence to the proportionality factor in the free volume expression decreased the average error in prediction of the solvent activities from 15% to 6%.     

Obtaining Modulated Temperature DSC Curves Through a Non-conventional DSC Method

The DSC curve obtained in conventional equipment usually only shows the resultant thermal effect due to simultaneous phenomena, which may occur during isothermal or dynamic analyses. This does not allow one to identify the processes properly and may cause an erroneous interpretation of the resulting curves. Modulated DSC equipment enhances the operating conditions and the analysis capacity of conventional DSC by superimposing a sinusoidal temperature modulation on the linear temperature control. Thus reversing and non-reversing heat flow curves are obtained, which are, respectively, the heat capacity and kinetic components of the DSC curve. Therefore, events that are related to these components can be separately analyzed. A method to obtain curves similar to the MDSC reversing and non-reversing components was developed using conventional DSC equipment in a non-conventional way. It was applied to analyze samples of poly(ethylene terephthalate) (PET) taken from bottles of mineral water. The second PET crystallization step that occurs during its melting was quantified and an apparent initial crystallinity was obtained from the resulting data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of Temperature Modulated Relative Dilatometry. Temperatures of adhesion degradation

Application of temperature modulated dilatometry (TM DIL) to investigation on degradation of the adhesion between ceramic films and the substrate is presented. Layers of titanium nitride deposited by plasma assisted physical vapour deposition (PA PVD) methods on the Armco iron substrates were tested. This paper shows that the TM DIL method is helpful in determining the usefulness of the titanium nitride covering of the cutting tools and machine parts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Applications of Micro-Thermal Analysis

Micro-thermal analysis combines the imaging facility of scanning probe microscopy with the ability to characterize, with high spatial resolution, the thermal behavior of materials. A sample may be visualized according to its surface topography and also its relative thermal conductivity. Areas of interest may then be selected and localized thermal analysis (TMA and modulated temperature DTA) performed. Applications of this new technique to study semiconductors, polymer blends and biological specimens are described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of temperature on metal-organic frameworks

Reaction temperature is one of the key parameters in the synthesis of metal-organic frameworks （MOFs）. Though there is no convergence with regard to the various experimental parameters, reaction temperature has been found to have remarkable influence on the formation and structure of MOFs, especially toward the control of topology and dimensionality of the MOF structures. Theoretically, the reaction temperature affects directly the reaction energy barrier in reaction thermodynamics and the reaction rate in the reaction kinetics. This review aims to show the influence of reaction temperature on crystal growth/assembly, structural modulation and transformation of MOFs, and to provide primary information and insights into the design and assernblv of desired MOFs.