Properties Derived from Calorimetry

PROPERTIES DERIVED FROM CALORIMETRY 7.5.1. The Measurement of Thermodynamic Properties... 

In the system Th(IV)-H20 three sets of thermodynamic quantities can be derived from experimental data (1) the hydrolysis constants l°gio j3° and log10 /34 of ThOH3+ and Th(OH)4(aq), respectively, have been determined potentiometrically by several authors over a wide range of ionic strength (for references see Hummel et al. 2002) (2) the thermodynamic properties of Th02(cr) have been determined by calorimetry, and thus a solubility product logio K°s 0 (cr) for... 

Using differential scanning calorimetry (DSC) (or, less directly, differential thermal analysis (DTA)) (see Section 2.8.5., above) it is possible to measure several of the thermodynamic properties of solids and of solid state reactions. The DSC response is directly proportional to the heat capacity, Cp, of the sample, so that by use of a calibrant it is possible to obtain values of this fundamental thermodynamic property, at a particular temperature, or as an average over a specified temperature range. Other thermodynamic properties are readily derived from such measurements ... 

The compounds, derived from L-threonic acid and various biological metal elements, facilitate the combination of the metal ions with amino acids or proteins and improve the efficiencies of the absorption and utilization of these metal ions in the humw body. Qing and coworkers investigated the thermodynamic properties of copper L-threonate hydrate by adiabatic calorimetry and combustion calorimetry [158]. 

The thermodynamic properties of several cyanoacrylate polymers have been determined using precision adiabatic and isothermal calorimetry (52-55). The Gibbs free energy AGq estimated from the enthalpy Aifo and entropy ASq of the bulk polymerization of various monomers showed that polymerization is thermodynamically feasible over the temperature range -270 to - -160°C at standard pressure. Ceiling temperatures Tc for polymerization were derived from the thermodynamic data and represent the upper temperature limit of polymerization. 

This paper concerns the preparation and the thermomechanical properties of environmentally compatible polymers derived from saccharides and lignins at our laboratory. The above research results have been obtained over the last several years. The environmentally compatible polymers include polyurethane (PU) and poly(8-caprolactone) (PCL) derivatives. PU derivatives were prepared from saccharides and lignins. PCL derivatives were synthesized from lignins, saccharides, cellulose and cellulose acetate. The thermal properties of the above polymers were studied by differential scanning calorimetry (DSC), thermogravimetry (TG) and TG-Fourier transform-infrared spectrometry (FTIR). Mechanical properties were measured by mechanical testing. 

Kujawa and Winnik [209] reported recently that other volumetric properties of dilute PNIPAM solutions can be derived easily from pressure perturbation calorimetry (PPC), a technique that measures the heat absorbed or released by a solution owing to a sudden pressure change at constant temperature. This heat can be used to calculate the coefficient of thermal expansion of the solute and its temperature dependence. These data can be exploited to obtain the changes in the volume of the solvation layer around a polymer chain before and after a phase transition [210], as discussed in more detail in the case of PVCL in Sect. 3.2.2. 

The enthalpies of phase transition, such as fusion (Aa,s/f), vaporization (AvapH), sublimation (Asut,//), and solution (As n//), are usually regarded as thermophysical properties, because they referto processes where no intramolecular bonds are cleaved or formed. As such, a detailed discussion of the experimental methods (or the estimation procedures) to determine them is outside the scope of the present book. Nevertheless, some of the techniques addressed in part II can be used for that purpose. For instance, differential scanning calorimetry is often applied to measure A us// and, less frequently, AmpH and AsubH. Many of the reported Asu, // data have been determined with Calvet microcalorimeters (see chapter 9) and from vapor pressure against temperature data obtained with Knudsen cells [35-38]. Reaction-solution calorimetry is the main source of AsinH values. All these auxiliary values are very important because they are frequently required to calculate gas-phase reaction enthalpies and to derive information on the strengths of chemical bonds (see chapter 5)—one of the main goals of molecular energetics. It is thus appropriate to make a brief review of the subject in this introduction. 

The method is based on classical nucleation and growth equations for amorphous materials and a derived expression for AG based on the expressions of Turnbull,Hoffman, and Thompson and Spaeten. Using the calculated AG value, published material property data such as modulus and surface energy, and the measured crystallization or glass transition temperature (T ) obtained from differential scanning calorimetry (DSC), analytical expressions for nucleation rate and growth rate can be written. These expressions are then used as the basis for a pixel-by-pixel modeling approach for visualization of the microstructural evolution of the cross-section of a thin... 

Various calorimetric methods can be used to characterize carbon surfaces from different viewpoints the application of these techniques to carbons has been recently reviewed in detail [35], and only a brief outline will be presented here. Adsorption calorimetry has been used to investigate surface chemical properties more irequently than to characterize porosity in carbons. Terzyk et al. [36] have compared a number of techniques, including benzene adsorption calorimetry, to characterize the microporosily of cellulose-derived carbonaceous films where the majority of micropores possessed the same diameter. The determination of pore size based on the enhancement of potential energy in micropores... 

Many cellulose derivatives form lyotropic liquid crystals in suitable solvents and several thermotropic cellulose derivatives have been reported (1-3) Cellulosic liquid crystalline systems reported prior to early 1982 have been tabulated (1). Since then, some new substituted cellulosic derivatives which form thermotropic cholesteric phases have been prepared (4), and much effort has been devoted to investigating the previously-reported systems. Anisotropic solutions of cellulose acetate and triacetate in tri-fluoroacetic acid have attracted the attention of several groups. Chiroptical properties (5,6), refractive index (7), phase boundaries (8), nuclear magnetic resonance spectra (9,10) and differential scanning calorimetry (11,12) have been reported for this system. However, trifluoroacetic acid causes degradation of cellulosic polymers this calls into question some of the physical measurements on these mesophases, because time is required for the mesophase solutions to achieve their equilibrium order. Mixtures of trifluoroacetic acid with chlorinated solvents have been employed to minimize this problem (13), and anisotropic solutions of cellulose acetate and triacetate in other solvents have been examined (14,15). The mesophase formed by (hydroxypropyl)cellulose (HPC) in water (16) is stable and easy to handle, and has thus attracted further attention (10,11,17-19), as has the thermotropic mesophase of HPC (20). Detailed studies of mesophase formation and chain rigidity for HPC in dimethyl acetamide (21) and for the benzoic acid ester of HPC in acetone and benzene (22) have been published. Anisotropic solutions of methylol cellulose in dimethyl sulfoxide (23) and of cellulose in dimethyl acetamide/ LiCl (24) were reported. Cellulose tricarbanilate in methyl ethyl ketone forms a liquid crystalline solution (25) with optical properties which are quite distinct from those of previously reported cholesteric cellulosic mesophases (26). 

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