Analysis thermal

Thermal methods are techniques in which changes in physical and/or 

When carrying out a thermal analysis procedure it is important to consider 

The apparatus required for TG analysis is shown in Fig. 36.1. TG is normally carried out on solid samples. Example operating conditions are as follows  

Identify tKe tart position digthe trac dseesEigT 6.2) ftW is- us ally indicated jay the.scale,b the tra .  

Using the Mr determine the y composition toss -with each region. r-- - = j 

Thermal analyses provide guidance as to at what temperature a resist film should be baked after coating. The PAB temperature must be below a deprotection temperature in the case of positive resists based on acid-catalyzed deprotection but should be preferably higher than its Tgto minimize the free volume in the film, as discussed earlier. 

Furthermore, in addition to the bulk thermal properties of polymers and resists, determination of Tg of film interfaces and of ultrathin films has become an important issue in thin film imaging (bilayer, 157 nm, and EUV). Various techniques have been employed, which include ellipsometry [481,482], positron annihilation spectroscopy (PALS) [483], QCM [484], scanning viscoelasticity microscope (SVM) [485],x-ray reflectivity [486,487], and thermal probe [488]. 

In thermal characterization, a controlled amount of heat is applied to a sample and its effect measured and recorded. In isothermal operations, the effect is recorded as a function of time at constant temperature. In a programmed temperature operation, the temperature is changed in a predetermined fashion, e.g., at a certain rate, and the effect is recorded as a function of temperature. 

The main thermal analysis techniques are differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). These methods are discussed in more detail in Section 6.3.8. 

Thermal analysis involves observation of the usually very delicate response of a sample to controlled heat stimuli. The elements of thermal-analysis techniques have been known since 1887 when Le Chatelier used an elementary form of differential thermal analysis to study clays (4), but wide application did not come until the introduction of convenient instrumentation by du Pont, Perkin-Elmer, Mettler and other sources in the 1960 s. Currently, instrumentation and procedures are commercially available for DTA, DSC, TGA, TMA, and a number of so-called hyphenated methods. Several methods are currently under study by ASTM committees for consideration as to their suitability for adoption as ASTM standards. 

Thermal analysis probes the enthalpy change of a reacting solid as a function of time, which is time-resolved calorimetry. In order to enhance the low solid state reaction rates of the reaction couples, the calorimeter has to operate at elevated tempera- 

Heat effects as such are rather unspecific, especially if the nature of the reactions taking place in the calorimeter is not known. The combination of thermal analysis with chemical analysis (for example with a thermobalance (DTG) or a mass spectrometer which register the rate of advancement of the reaction) enables us to arrive at specific caloric data (i.e., AH/A nt). Absolute values of AH are obtained by calibration only. 

DSC and related methods (differential thermal analysis, DTA) are of great practical importance. Therefore, one finds highly sophisticated commercial instruments for a variety of applications. DTA has been combined with in-situ emf and Knudsencell measurements. The interested reader is referred to the special literature on this subject [M.E. Brown (1988)]. 

Thermal analysis is an important technique for determining the physical and chemical properties of polymeric materials. It may be defined as a set of methods used to measure the physical or chemical changes of substances as a function of temperature. Some common thermal analysis techniques are given in Table 4.8.1. 

Thermal analysis is an essential tool to study the necessary thermal transitions in polymers, without which the processing and fabrication of polymeric materials is not possible. The thermal behaviour of a polymer has significant technological importance. For example, the T of rubber determines the lower limit of the use of rubber and the upper limit of the use of an amorphous thermoplastic. The most important techniques will be briefly discussed below. 

A thermal analysis unit, as discussed previously, is a valuable tool for both research work and qnality control. It can be used for the inspection of incoming lots of chemicals, and for batch-to-batch quality control in manufacturing. 

The thermal analysis of polymers is based on changes in the thermal properties of a polymer sample as its temperature is increased when it is subjected to continuous heating. These properties of polymer electrolytes are especially important from an industrial point of view. 

Dynamic mechanical analysis techniques permit measurement of the ability of materials to store and dissipate mechanical energy during deformation. DMA is used to determine the modulus, glass transition, mechanical damping and impact resistance, etc., of thermoplastics, thermosets, elastomers and other polymer materials. Information regarding the phase separation of polymers is also available by DMA [2]. In DMA, viscoelastic materials are deformed in a sinusoidal, low strain displacement and their responses are measured. Elastic modulus and energy dissipation are the measured properties. 

Stress-strain relationships are determined by DMA and temperature scans reveal glass transitions, crystallization and melting information. Blends of polypropylene and rubber have been studied by where the intensity of one of the two crystallization exotherms was used as a measure of the polypropylene domains and compared to the size determined by TEM cryomicrotomy and osmium tetroxide staining methods [25]. Isothermal annealing of PET above the crystallization temperature was shown to influence the morphology and increase thermal stability by combined SAXS and DSC analysis [26]. An excellent text edited by Turi [21] described the instrumentation and theory of thermal analysis and its application to thermoplastics, copolymers, thermosets, elastomers, additives and fibers. 

Testing procedure. Testing of thermal properties is a fairly standard procedure which is not discussed here. DSC was used for the studies on the effect of cooling rate on formation of spherulites in the presence of fillers. In order to assure the repeatability of conditions of the experiment, the instrument was calibrated with indium and tin standards. The TGA/DSC instrument was coupled with a mass 

Differential thermal analysis (DTA) is a technique in which the temperature difference between a substance and reference material is measured as a function of temperature or time while the substance and reference material are subjected to a controlled increase in temperature. Differential scanning calorimetry (DSC) is a technique in which the difference in energy inputs into the sample and reference material required to keep their temperatures equal is measured as a function of temperature while the substance and reference material are subjected to a controlled increase in temperature [70]. 

Classical DTA has been developed into heat-flux DSC by the application of multiple sensors (e.g., a Calvet-type arrangement) or with a controlled heat 

The purpose of differential thermal systems is to record the difference in the enthalpy changes that occurs between the reference and the test sample when both are heated in an identical fashion. Several publications are available concerning the theoretical aspects and applications of various thermal analysis techniques, including the DSC [71-74]. Commercial instruments are available from a number of companies including Perkin-Elmer, TA Instruments, Toledo-Mettler, SET ARAM, Seiko, and Polymer Laboratories. 

Another useful application of DSC is the determination of the specific heat (Cp) of substances as a function of temperature [71]. The specific heat is an important parameter in many thermodynamic and process design calculations. 

FIGURE 2.12. Schematic Representation of Heat-flux DTA and Power Compensation DSC 

FIGURE 15.6 (a) A linear temperature program, (b) Applying the temperature program in (a) to a sample that 

FIGURE 15.7 A representation of the results of the differential thermal analysis (a DTA curve) of a sample that melts at a particular temperature. 

FIGURE 15.9 A representation of a DSC curve for an exothermic process. Note that the y-axis is heat flow. 

FIGURE 15.10 A photograph of the interior of a small oven used for differential scanning calorimetry. The crucibles 

Differential thermal analysis (DTA) involves heating (or cooling) a test sample and an inert reference sample under identical conditions and recording any temperature difference which develops between them. Any physical or chemical change occurring to the test sample which involves the evolution of heat will cause its temperature to rise temporarily above that of the reference sample, thus giving rise to an exothermic peak on a DTA plot. Conversely, a process which is accompanied by the absorption of heat will cause the temperature of the test sample to lag behind that of the reference material, leading to an endothermic peak. 

The degree of purity of an explosive can be determined from DTA plots. Contamination of the explosive will cause a reduction in the melting point. Consequently, the magnitude of the depression will reflect the degree of contamination. A phase change or reaction will give rise to an endothermic or exothermic peak, and the area under the peak is related to the amount of heat evolved or taken in. 

The activation energy E can be calculated from the DTA plot using the Arrhenius equation as shown in Equation 6.16. 

AT is measured at several temperatures T, and In AT versus 1/Tis plotted. A straight line is obtained with a slope of —EjR. 

DTA will also provide information on the melting, boiling, crystalline transitions, dehydration, decomposition, oxidation and reduction reactions. 

In differential thermal analysis (DTA), a test sample and a comparison sample are heated at a constant rate. The temperature difference between the 

Differential scanning calorimetry, DSC, is a variant of differential thermal analysis. With DSC, the required heat for the transition is added or removed at the transition temperature. Thus, this method is particularly suited to quantitatively measuring heats of fusion or crystallization, as, for example, with crystallization at a given temperature. 

Ru(acac)3. We show here the thermal analysis (TA) data presented by these researchers that illustrate well the decomposition of the ligands at the two different temperatures 210 270°C (Figs. 10-12). 

notice how the exotherms for the heat flow data occur at the same 

Notice here that only two of the three (acac) ligands can interact with the surface protons, thus it appears that only 2/3 ° of the ligands can be lost by proton-assisted thermolysis. One of the samples, 1 wt% Ru(acac)3 appears to show a weight loss in the TG spectrum consistent with this prediction. It must be remarked that the data of this same sample agreed in the predicted and observed weight loss upon thermolysis (2.6%) whereas the other two samples showed different experimental and predicted weight losses. 

It is possible to use differential thermal analysis (DTA) and thermogravi-metric analysis (TGA) to evaluate the thermal properties of several types of polyurethane elastomers. For example, a typical elastomer prepared from MDI, a polyether and an aliphatic diamine extender will show from DTA two very small endothermic changes, one at 150°C and one at 205°C that is identical with the softening temperature. The polymer is found to melt at 2WC and exhibit weight loss in two steps, respectively, beginning at 280°C and 325X. 

Similar results can be obtained on a polymer prepared from MDI, polyester and aromatic diamine. In this case two small endothermic changes are obtained, one at 100°C that could be attributable to moisture, and one at 250°C which corresponds to polymer softening. The polymer decomposes in two steps, one beginning at 310°C and the other at 365°C, as TGA shows. 

Study of properties of materials with change in temperature is Thermal Analysis. Branches of thermal analysis are developed and named according to the study of various properties of the material. When on thermal treatment of a sample, heat is evolved, it is called Exothermic process and when heat is absorbed, known as Endothermic reaction. Possible processes of enthalpy changes and types of thermal reaction, i.e. exothermic or endothermic are listed in Table 6.4. 

Reaction process Adsorption Catalytic reactions Crystallisation Polymerisation Curing Desorption Melting Vapourisation Sublimation Desolvation (drying) Solid-solid transition Solid-liquid reaction Solid-gas reaction Solid-solid reaction Decomposition 

Main applications of thermal analysis are (1) Soil and clay analysis (2) Determination of Glass transition (3) Compositional effects on glass transition (4) Heat capacity determination (5) Characterization of polymer blends (6) Study the effects of additives added to polymer (7) Polymer degradation analysis (8) Crystallinity and crystallization rate study and (9) Reaction kinetic studies. 

Different types of thermal analysis developed are on the basis of (1) weight change, (2) energy change, (3) dimensional change and (4) evolved gas. They are grouped in Table 6.5. 

Thermo gravimetric analysis (TGA) Differential thermal analysis (DTA) Differential scanning calorimetry (DSC) Evolved gas analysis (EGA) 

Experimental determination of phase diagrams is convenient by using the thermal analysis method at which the temperature of the investigated sample is registered at its cooling by a constant rate of 2-5°C/min. Due to the thermal effects connected with the phase transformations (crystallization, polymorphic transformation), breaks appear on the cooling 

Curve No. 1 shows freezing of the pure component. On the curve, only one delay can be seen, which is caused by the evolution of the crystallization heat of the component. At melting temperature, this one-component system has no degree of freedom, since two phases coexist the solid compound and its melt k= l,/= 2, v = 0). The temperature of the system therefore stays constant until its whole solidification. In practice we can, however, observe at the end of the delay a temperature decrease caused by the transport of bigger heat amounts to the surroundings, than it could be evolved at crystallization of the compound. 

Curve No. 2 shows the cooling of the binary mixture with an arbitrary composition except of the eutectic one. On the curve, one break and one delay can be seen. The break is due to the start of the primary crystallization of one of the components. At primary crystallization, the binary system has one degree of freedom, as the solid component and the melt saturated with the component coexist (k = 2, f= 2, v = 1). Thus the cooling 

By thermal analysis of a sufficient number of samples, it is possible to construct a phase diagram of the investigated system. 

In differential scanning calorimetry (DSC), the sample is not heated at a constant rate, but a definite quantity of heat is either added or taken away isothermally. This method is particularly suited to measure the heats of fusion at crystallization or to follow the course of crystallization at a given temperature. 

Measurement of the weight change is called thermogravimetric analysis (TGA) whereas measurement of the thermal change accompanying the structural metamorphosis is called thermal analysis (TA). ALL CHANGEIS IN PHASE Involve a release or absorption of calories. One reason for this is that each solid has its own heat ciqiacity. That is, there is a characteristic heat content for each material which depends upon the atoms composing the solid, the nature of the vibrations within it, and its structure. The total heat content, or enthalpy, of each solid is defined by  

as we go from one solid to another, we see a change in caloric content. 

In 1821, Seebeck discovered that by joining two wires of different chemical composition together to form a loop (two junctions), a direct current (DC) would flow in the circuit, namely- 

Seebeck used antimony and copper wires and found the current to be affected by the measuring instrument (ammeter). But he also found that the voltage (EMF) was directly proportional to the difEerence in temperature of the two junctions. Peltier, in 1834, then demonstrated that if a current was induced in the circuit of 3.53., it generated heat at the junctions. In other words, the SEEBECK EFFECT was found to be reversible. Further work led to the development of the thermocouple, which today remains the primary method for measurement of temperature. Nowadays, we know that the SEEBECK EFFECT arises because of a difference in the electronic band structure of the two metals at the junction. This is Illustrated as follows  

In this diagram, we show the band model structure at the juncture of two metals, each of which has its own Fermi Level. Flow of electrons is indicated by the arrow. Since the height of the Fermi Level is proportional to temperature, then the EMF generated is a function of temperature also. It is thus apparent that a thermocouple (TC) will consist of a negative and a positive leg . 

Thermal methods are techniques in which changes in physical and/or chemical properties of a substance are measured as a function of temperature. Several methods of analysis are used  

Identify the start position of the trace (see Fig. 36.2) this is usually indicated by the scale on the trace. 

Identify any regions of decomposition these are where there is a rapid change in the vertical axis. Three distinct regions of decomposition can be identified in Fig. 36.2 (a) between the start and the first plateau there is a loss of 12.5% (stage 1) (b) between the first and second plateau a loss of 18.75% occurs (stage 2) and (c) between the second plateau and the final residue there is a loss of 29.75% (stage 3). 

The common methods of investigating the kinetics of explosive reactions are differential thermal analysis, thermogravimetric analysis and differential scanning calorimetry. 

Thermogravimetric analysis (TGA) has been used for characterizing the thermostability of polyaniline/ PE composite systems [41], The composite sample, prepared by in situ polymerization of polyanihne on a micropo-rous PE support, exhibited the kinetics of mass losses and thermal effects similar to pristine PE. The composite sample was thermally stable up to 250°C, showing a mass loss of no more than 3 to 4%. However, a gradual decrease in mass was observed beyond 255°C due to thermal destruction of both polyaniline and the PE support. The maximum mass loss was at about 470°C and a nearly non-distinguishable mass losses was seen from 500 to 800°C, where the carbonized residue was not more than 20% of the initial mass [41]. 

Moreover, DSC studies on polypyrrole coated ultra-high molecular weight PE fibers revealed an increase in crystallinity when the in situ polymerization temperature of polypyrrole was increased [29], The PE chains, which were restrained at lower temperatures, would have gained greater orientation when subjected to the higher polypyrrole polymerization temperatures resulting in increased crystallinity. 

When a substance undragoes a physical or chemical change, a corresponding change in enthalpy is observed. This forms the basis of the technique known as differential thermal analysis (DTA), in which the change is detected by measuring the enthalpy difference betw een the material under study and an inert standard. 

FIGURE 10.6 A DTA curve for quenched terylene showing the glass transition, melting endotherm, and a crystallization exotherm. 

It has long been considered that the most useful workhorse techniques, for a modestly equipped laboratory concerned with charcterising polymeric materials, are differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), wide and small angle X-ray diffraction (WAX and SAXS), thermogravimetric analysis (TGA) and optical and electron microscopy. 

This list has remained unchanged for nearly twenty years. A more ambitious laboratory should also be considering solid-state NMR, but this represents a quantum leap in cost and in interpretive skills. 

It will be noticed that three of the five essential techniques are concerned with thermal analysis (TA). In this chapter, all the main TA techniques are reviewed, but in order to keep to a reasonable length, examples will be selected only from the most important application areas. Some additional interesting applications will be presented from largely unpublished work from the Department of Chemistry, Loughborough University of Technology, UK. 

By way of introduction. Table 7.1 itemises the TA techniques covered in this chapter, together with their most important application areas. 

Classical adiabatic calorimetry, in which precise quanta of heat are applied and the temperature rise of the sample is noted under shielded conditions, is an extremely slow and laborious technique. By referring the temperature of a sample to that of an inert sample experiencing a closely similar heating profile, equivalent information can be obtained in a rapid scanning experiment. This has many advantages in that structures in the polymer are not annealed and changed during fast thermal scans. 

Solid-state CD and its derivatives could be analyzed using the TG method. Weigh 20 mg sample in the copple, and heat slowly (10°C/min) under protection of inert gas. The scan scope ranged from 0°C to 800°C. The thermal degradation kinetics, degradation temperature and thermal stability could be investigated through the analysis of TGA/DTA spectrum. 

The research papers which originated in the last couple of years in different countries in this field indicate that ED and Er are not generally reported and there is an emphasis on the study of comprehensive thermal behavior of explosives as a function of temperature or time by means of different thermal analytical techniques. Most commonly used methods of thermal analysis are differential thermal analysis (DTA), thermogravimetric analysis (TGA) or thermogravimetry and differential scanning calorimetry (DSC). 

Thermal Analysis Thermal analysis consists of a group of techniques where a physical property of an explosive is measured as a function of programmed temperature and the most common complementary techniques are listed in Table 3.5. 

Differential Thermal Analysis All materials emit or absorb heat when they are heated or cooled and the measurement of how these materials absorb or emit heat or energy with respect to time or temperature is done by thermal analysis. 

Derivative TG Rate of weight change Thermobalance or derivative thermobalance 

DTA Temperature difference between sample and reference material DTA apparatus 

Differenhal scanning calorimetry (DSC) conshtutes one of the most widely used techniques for the study of polymers, parhcularly those systems that crystallize. Although the term DSC is used in conjunchon with many different instruments, fundamentally, these can be divided into two categories heat flow instruments based upon differenhal thermal analysis (DTA) and those which are true power compensated instruments. 

In DTA, the temperature of the sample is compared with that of an inert reference as both are subjected to, ideally, idenhcal thermal programmes. To illustrate the principles, consider an experiment to investigate the melting behaviour of a material. In this, heat is supplied to both the sample and the reference and, as a consequence, the temperature of each will rise. As the sample melts, the thermal energy supplied by the instrument no longer raises its temperature but, rather, provides the necessary enthalpy of fusion. Since the temperature of the inert reference will continue to rise throughout this process, the temperature difference between the sample and the reference 

Despite the theoretical advantages of the power compensated approach, the associated instrumentation is much more complex and, therefore, there are circumstances where the simpUcity of DTA has much to recommend it. DTA requires just two thermocouples and can, therefore, be used under demanding conditions. For example, high-pressure DTA experiments have been used extensively to generate phase diagrams of polyethylene and related low molar mass compounds— high-pressure DSC is rather more complex. 

In the case of glassy systems, DSC can also be used to examine the discontinuity in the specihc heat capacity that is associated with the glass transihon. However, this transihon is generally broad and weak and, therefore, inferring Fg in this way can be difficult also, different authors choose to idenhfy Fg in different ways. As in the case of crystalUne polymers, polymer glasses are also never at equilibrium and, therefore, the form of the transihon that is 

Temperature modulated DSC (MDSC)2°2-204 jg another technique that has proved useful in the study of the glass transition - where, it has been claimed, the approach is capable of providing better resolution and sensitivity than conventional DSC.2° In this, a modulated temperature programme is superimposed upon the conventional heating ramp and the resulting heat flows are interpreted in terms of two heat capacities an in-phase storage heat capacity and an out-of-phase kinetic heat capacity. Various theoretical procedures have been proposed for this and there is little doubt that the approach can provide information that is complementary to conventional DSC.2 ° However, the technique does involve slow temperature scans (cf. high-speed DSC above) and the authors feel that there are areas where the additional data are not, at present, easy to interpret. 

NMR spectroscopy is quite conducive to the study of water relations. Radosta et al. (1989) discovered that the amount of monomolecular water bound to maltodextrin was independent of state (sol or gel), but was slightly dependent on temperature. 

NMR spectroscopy has been adapted to the study of relaxation, because the excited atoms return to their respective ground states at definite rates, depending on the nuclear environment (Gidley, 1992). Harris et al. (1995) presented a synopsis of the potential use and limitations of NMR applied to 

Thermal transitions and the characterizing intensities are indicated by inflections on a thermogram in a positive or negative departure from the 

and TG have become routine for monitoring polysaccharide solid-state transformations. Examples of important applications are hydra- 

In Synthesis and separations using functional polymers, D.C. Sherrington, P. Hodge Eds, John Wiley Sons Ltd., p. 1 (1988). 

Hosoya, K. Yoshizako, N. Tanaka, K. Kimata, T. Araki and J. Haginaka, Chem. Lett., 1437 (1994). 

Matsui, M. Okada, M. Tsuruoka and T. Takeuchi, Anal. Commun., 34, 85 (1987). 

Polymers chemistry and physics of modern materials, Blackie and Son Ltd. (1991). 

Advanced organic chemistry, John Wiley Sons (1992). 

and DTG are useful for detecting physical changes in addition to chemical degradation. Crystallization of amorphous drugs and polymorphic transitions (see Chapter 3) have been extensively studied using these methods.568-580-581 

The kinetics of degradation can be studied using isothermal calorimetry, that is, calorimetry performed at constant temperature. Recently, sensitive thermal conductivity microcalorimeters useful for detecting even small amounts of degradation at room temperature have become available. For example, the slow solid-state degradation of cephalosporins at a rate of approximately 1% per year was successfully measured by microcalorimetry.624 

Whereas microcalorimehy is most suitable for the study of degradations that result in relatively large enthalpy changes, such as those seen in the examples of oxidation and 

In addition to chemical degradation, microcalorimetry has been applied to the detection of physical changes in drug substances and excipients. An example is the change in the hydration of lactose.633 

In general, the decomposition of phosphonium-based ILs is accompanied by an endothermic temperature the only exceptions to date are the hexafluorophosphate salts. At a heating rate of 5 °C min a 510 J g exotherm beginning at 310 °C and with a maximum at 337 °C was noted [62]. In addition to the possible evolution of HF, the exothermic decomposition of hexafluorophosphate salts presents an added hazard when operating at or near the upper temperature limit. This is especially important to note when large volumes of such solvents are in service. 

Because of the wide range of alkyl substituents and anions, phosphonium salts can be very hydrophilic or hydrophobic this in turn determines the miscibility of various solvents as outlined in Table 2. At the one extreme are salts such as the tetrabutylphosphonium halides which are hygroscopic solids which will form 80-85% aqueous solutions and which are very insoluble in nonpolar solvents such as hexane. At the other end of the scale are such salts as trihexyl(tetradecyl)phospho-nium bistriflamide and hexafluorophosphate which are very hydrophobic and are totally miscible with nonpolar solvents. 

The compatibility of phosphonium ILs such as tetradecyl(trihexyl)phosphonium chloride - CYPHOS IL101 - with strong bases such as NaBH4, Grignard reagents and potassium metal, suggests that other applications which involve the use of alkali metals and even elemental phosphorus may be possible in phosphonium ILs. 

Toxicity data for ILs are still generally lacking. However, B. JastorfFetal. have recently reported structure-activity relahonship data on acetylcholinesterase inhibition for various classes of ILs [67]. Their conclusions indicated that ILs which contain imidazolium and pyridinium cations with longer alkyl substituents have EC50 values as low as 13 pM, where as phosphonium ILs containing bulky phosphonium cations such as tetradecyl(trihexyl)phosphonium have EC50 values of 2000 pM. 

MgNulty, F. Capretta, J. Wilson, J. Dyke, G. Adjabeng, A. Robertson, Chem. Commun. 2002, 1986. 

Heat is involved in most real-life processes. This permits heat—into or out of a system—to serve as a universal detector. In many cases, the heat into or out of a system can be measured nondestruc-tively. Heat transfer occurs in three ways conduction, convection, and radiation. Conduction occurs between solid materials when placed in contact with each other. Convection occurs when a hot material and a cold material are separated by a fluid (gas or liquid). Radiative heat transfer involves the emission and consequent absorption of electromagnetic radiation between a hot and cold material. 

Thermal Analysis Technique Principle Information Obtained 

TGA Measures change in weight with respect to temperature and time in an inert or reactive atmosphere Themnal stability, oxidative stability, kinetics, degradation, and shelf life. EGA when coupled to gas chromatography (GC), infrared (IR), and/or mass spectrometry (MS) for chemical composition and identification. 

DSC Monitors the difference In temperature between a sample and a reference material as a function of time and temperature In a specified atmosphere. Quantitatively measures heat absorbed or released by a material undergoing a physical or chemical change Glass transition, melt and phase change temperatures, heats of reaction, heat capacity, crystallinity, aging, degradation, and thermal history. 

Based on the kinetic results from the previous subsections, Dar (1999) estimated interior particle temperatures for FRRPP of styrene in ether. He used the same approach as the quasi-steady-state approximation in Section 2.2, which resulted in the use of the same differential equation and boundary conditions (Eqs. 2.2.1 and 2.2.2). The difference is that he employed a temperature-independent energy source term wherein the rate of reaction was based on the calculated derivative of monomer concentration with respect to time within a certain population of polymer-rich particles thus. 

The fact that LCST or even UCST behavior was not taken into account (a = 0 in Section 2.2) means that the maximum interior temperature obtained from this 

Polymerization reactions were occurring in the coils within the polymer-lean phase, in small particle globules, and in large particle agglomerated globules. Thus, 

A similar expression to Eq. (2.4.22) was used to calculate the rate of monomer consumption for the small particles, which were the collapsed globules. The difference is that model kinetic coefficients were used to calculate the derivative of the fractional conversion with time (dx/dt), which ended up to be 

For the rate of monomer consumption in the polymer-lean phase, the assumption is made that these are low molecular weight coils up to 30 monomer units long. Thus, 

Stephen B. Warrington, Anasys, IPTME. Loughborough University, Loughborough, United Kingdom (Chap. 26) 

GOnther W. H. Hohne, Dutch Polymer Institute, Eindhoven University of Technology, Eindhoven, The Netherlands (Chap. 26.2) 

Thermal analysis (TA) has been defined as a group of techniques in which a physical property of a substance and/or its reaction products is measured as a function of temperature while the substance is subjected to a controlled temperature programme [1]. The formal definition is usually extended to include isothermal studies, in which the property of interest is measured as a function of time. 

The definition is a broad one, and covers many methods that are not considered to fall within the field of thermal analysis as it is usually understood. The present chapter will be restricted to the major techniques as currently practiced. Since all materials respond to heat in some way, TA has been applied to almost every field of science, with a strong emphasis on solving problems in materials science and engineering, as well as fundamental chemical investigations. TA is applicable whenever the primary interest is in determining the effect of heat upon a material, but the techniques can also be used as a means of probing a system to obtain other types of information, such as composition. 

The aim of this chapter is to give an overview of the main TA methods and their applications. 

The characterization of melting behavior is particularly important when selecting a salt or co-crystal for a drug product, since processing steps, such as milling or micronization, can generate considerable heat which not all salt and 

Melting point analysis and binary phase diagrams are well suited for the characterization of neat salt and co-crystal forms however, neat forms comprise only part of the solid form landscape of a given salt or co-crystal. 

In addition to the aforementioned research methods, there are other methods, such as Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), the secondary ion mass spectrometry (SIMS), ionscattering spectroscopy (ISS), combined methods such as XPS-SIMS, and so forth. 

Each characterization technique has its own features. According to the purposes of characterization, one needs to choose a proper method for different polymers to achieve desired effects. With the rapid development of modern instruments, there will be more analysis methods for interface characterization of polymer matrix composites which will lead to clearer understanding of the structure and properties of polymers. 

The initial and boundary conditions pertaining to the given problem are specified as follows. The initial temperature is Tq (=298.15 K) for the whole laminate, and the ambient temperature of the environment is also Tq. The boundary conditions are specified by free convection between the surfaces of the specimen and the surrounding media. In the present case, air is the medium to which heat transfers from the composite. The temperature-dependent expressions of the heat transfer coefficients of air are directly invoked here. 

In the analysis, the front of deconsolidation can be defined straightforwardly according to the T of the matrix, at which it begins to melt and behaves in a rubber-like fashion. However, the definition of the front of reconsolidation must be somewhat arbitrary, since there is usually no definite distinction to identify when the melting matrix becomes fully liquid. One way to define the fully liquid state of a melting polymer is based on its viscosity. For instance, when the viscosity of the melt is significantly less than that at the T, the melt is then considered to be in a fully liquid state. Here we consider that a matrix becomes fully liquid when the ratio stated above is less than lO or 10 .  

The temperature dependence of viscosity is reported in detail in many studies here the form expressed by Eq. (15) is used and, again, for Cj and Cj, their universal values , C = 17.44 and Cj = 51.6, are employed. 

Suppose that the temperature of reconsolidation is r /,at which the viscosity of the thermoplastic melt is t7(7 ft). Then, in light of Eq. (15) we have 

FIGURE 6. TGA curve of poly(3-octylthiophene) synthesized by the Grignard reaction [27]. 

FIGURE 7. The effect of Fe and Cl impurities (both around 1 %) on the heat TGA stability of poly(3-octylthiophene). 

Differential scanning calometry, DSC, curves of P30T show one low temperature transition at -20°C corresponding to the glass transition temperature,Tg, and one high temperature transition at 165°C corresponding to melting of the polymer. 

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Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

Kissinger H E 1957 Reaction kinetics in differential thermal analysis Ana/. Chem. 29 1702... 

Theovent The 0x0 process Therapeutic agents Therapeutic enzymes Therapeutic lenses Therapeutic role Therbar Therm-8 Thermal analysis... 

Antioxidants have been shown to improve oxidative stabiHty substantially (36,37). The use of mbber-bound stabilizers to permit concentration of the additive in the mbber phase has been reported (38—40). The partitioning behavior of various conventional stabilizers between the mbber and thermoplastic phases in model ABS systems has been described and shown to correlate with solubiHty parameter values (41). Pigments can adversely affect oxidative stabiHty (32). Test methods for assessing thermal oxidative stabiHty include oxygen absorption (31,32,42), thermal analysis (43,44), oven aging (34,45,46), and chemiluminescence (47,48). 

Assessing the Thermal Stability of Chemicals by Methods of Differential Thermal Analysis, American Society for Testing and Materials, Philadelphia. 

Thermal Resistance and Flammability. Thermal analysis of PVA filament yam shows an endothermic curve that starts rising at around 220°C the endothermic peak (melting point) is 240°C, varying afitde depending on manufacture conditions. When exposed to temperatures exceeding 220°C, the fiber properties change irreversibly. 

A. B. Brennan and F. Rabbani, Morth American Thermal Analysis Sodety Conference Proceedings, VoL 20, 1991, pp. 164—170. 

Finally, the techniques of nmr, infrared spectroscopy, and thin-layer chromatography also can be used to assay maleic anhydride (172). The individual anhydrides may be analyzed by gas chromatography (173,174). The isomeric acids can be determined by polarography (175), thermal analysis (176), paper and thin-layer chromatographies (177), and nonaqueous titrations with an alkaU (178). Maleic and fumaric acids may be separated by both gel filtration (179) and ion-exchange techniques (180). 

Polypropylene molecules repeatedly fold upon themselves to form lamellae, the sizes of which ate a function of the crystallisa tion conditions. Higher degrees of order are obtained upon formation of crystalline aggregates, or spheruHtes. The presence of a central crystallisation nucleus from which the lamellae radiate is clearly evident in these stmctures. Observations using cross-polarized light illustrates the characteristic Maltese cross model (Fig. 2b). The optical and mechanical properties ate a function of the size and number of spheruHtes and can be modified by nucleating agents. Crystallinity can also be inferred from thermal analysis (28) and density measurements (29). 

Thermodynamic Properties. The thermodynamic melting point for pure crystalline isotactic polypropylene obtained by the extrapolation of melting data for isothermally crystallized polymer is 185°C (35). Under normal thermal analysis conditions, commercial homopolymers have melting points in the range of 160—165°C. The heat of fusion of isotactic polypropylene has been reported as 88 J/g (21 cal/g) (36). The value of 165 18 J/g has been reported for a 100% crystalline sample (37). Heats of crystallization have been determined to be in the range of 87—92 J/g (38). 

Temperature-risiag elution fractionation (tref) is a technique for obtaining fractions based on short-chain branch content versus molecular weight (96). On account of the more than four days of sample preparation required, stepwise isothermal segregation (97) and solvated thermal analysis fractionation (98) techniques usiag variatioas of differeatial scanning calorimetry (dsc) techniques have been developed. 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

A. R. McGhie, ia R. G. Liaford, ed.. Thermal Analysis Techniques in Electrochemical Science and Technology oJPoljmers-2, Elsevier Publishing Co., Inc., New York, 1990, p. 202. 

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