Calorimetric measurements, and

Table II shows the "heats of formation" of the conjugate phases, that is, the excess enthalpies for mixing the appropriate amounts of water and amphiphile (at the same initial temperature and pressure as the final system) to make a unit amount of the conjugate phase. Values labeled "calorimeter" and "phase volume," respectively, are based on the same set of calorimetric titrations. In the former case the phase composition was taken from the calorimetric measurements, and in the latter case the composition was taken from our phase-volume compositions. Literature values for the heats of formation are based on data from references 13-16.

Calorimetric measurements and morphological observations showed that PS-fr-PCL, PB-fr-PCL and PS-fc-PB-fc-PCL copolymers exhibit microphase separation and crystallization if the molecular weight is high enough. Only in PS-fc-PCL diblock copolymers, a shift of the PS glass transition to lower temperatures has been observed. In PS-fo-PB-fo-PCL, the crystallizable block (i.e., PCL) is covalently linked to a rubbery block and it has a free end. For these reasons there is no significant reduction in the melting temperature and... 

A combined application of direct calorimetric measurements and thermochemical investigations has made possible to obtain a number of important thermochemical quantities characterizing the interaction of the N—H bond of the amine with the epoxy ring 53). Combustion and evaporation enthalpies of phenylglycidyl ether and its condensation products with aniline and butylamine have been determined. Standard enthalpies of the formation of these compounds, strain energies of the epoxy ring in the phenylglycidyl ether molecule and — AH values for the three-phase states, which are most important for the determination of the true thermodynamic reaction characteristics, have been estimated. 

Figure 18.9 AtH as a function of temperature for the association reaction H+(aq) -I- OH (aq) = H20(1). The solid line gives the values obtained from calorimetric measurements and the dashed line gives the values obtained from the Marshall-Frank equation.

Titration calorimetry has been successfully employed in the determination of thermodynamic parameters for complexation (Siimer et al., 1987 Tong et al., 1991a). The technique has the advantage of employing direct calorimetric measurements and has been proposed as the most reliable method (Szejtli, 1982). It should be noted that the information derived from multistep series reactions is macroscopic in nature. In contrast to spectrophotometric methods that provide information concerning only the equilibrium constant(s), titration calorimetry also provides information about the reaction enthalpy that is important in explaining the mechanism involved in the inclusion process. 

Fig. 8.5 Hydrolysis of acetic anhydride investigated separately at Tr = 25°C (a) by calorimetry and (b) by infrared spectroscopy. Graph (a) shows measured and simulated reaction power graph (b) shows measured and simulated concentration-time curves of acetic anhydride. The simulated curve is from the kinetic parameters obtained from the calorimetric measurements, and is compared with the one determined by the IR measurements at 1139 cm-1. Reprinted in modified form with permission [18],...

The products used for the calorimetric measurements and for the synthesis of the MFI-type materials were high purity reagents 40% aqueous HF ( Prolabo) (n-C Hy NBr ( Fluka, purum, 99%) (0-0387)3N... 

The integration constant of this equation left undetermined by thermodynamics is therefore the sum of the vapour pressure constants of the individual reacting substances. In this way it is possible in principle to calculate chemical equilibria at all temperatures from thermal quantities (calorimetric measurements) and vapour pressure measurements with the individual reacting substances. 

These may be classified into three groups equilibrium measurements, calorimetric measurements, and computational methods. The first address surface free energy, the second surface enthalpy, and the third (usually) surface energy. 

The products used for the calorimetric measurements and for the synthesis of the MFI-type materials were high purity reagents 40%... 

We acknowledge the contribution of L. Hartmann to the measurements on iso-PMMA. We would like also to thank Y. Mikhailova, K.-J. Eichhom, and B. Voit for providing the hyperbranched polyesters, H. Huth and C. Schick for performing the AC-calorimetric measurements, and L. Haussler for... 

Pd hydride formation was routinely determined by chemisorption and calorimetric measurements and heats of formation of the g-phase hydride were consistently near 10 kcal/mole H2 absorbed, independent of support and crystallite size, which is in good agreement with literature values for bulk palladium. 

Julsrud (1979) proposed a thermodynamic model for cryolite-alumina melts based on cryoscopic and calorimetric measurements and considered the Al20Fg , Al20F , Al20FjQ, Al202F4, and Al202Fg species to be present in alumina saturated melts. 

Sobol and Selivanova [70SOB/SEL] prepared crystalline sodium diselenate, Na2Se207, by gradual heating of NaHSe04 to 475 K. Its standard enthalpy of formation was obtained from calorimetric measurements and three thermochemical cycles, see Appendix A. The mean ... 

Changes with negative AG are thermodynamically favoured. Eq. (2) permits the effects of finite temperature and pressure to be introduced by estimating changes in volume AV and entropy AS, or from the choice of chemical potential, since p=p(7 p). These contributions are discussed for a sample surface in Ref [17]. At equilibrium with reservoirs of A and B, pa and Pb of the surface are equal to those of the reservoirs, and so it is often convenient to use the reservoirs as the AG=0 reference. These chemical potentials may be calculated from First Principles or from calorimetric measurements and this is the focus of our discussion. 

The heat capacities of condensed phases are usually determined by calorimetric measurements, and of gases by calculation methods of statistical mechanics using molecular constants. 

The VTE and the Adam-Gibbs equations are useful because they permit the use of thermodynamic data, obtained by calorimetric methods, to describe molecular motions in undercooled liquids and glasses. Most investigations of pharmaceutical solids rely on calorimetric measurements, and for that reason their discussion is deferred until the fundamentals of the methods have been described in the following section. 

Table 4-7 Overview on calorimetric measuring and evaluation methods = possible...

Complex formation between AlBrj and sulphoxides has been investigated by dipole-moment and calorimetric measurements, and by i.r. spectroscopy. Stopped-flow pulse F.T. n.m.r. measurements have been used to monitor the exchange reaction (16), where DMSO = dimethyl sulphoxide and DMSO = pHeJdimethyl sulphoxide. ... 

The degree of crystallinity of polyamide fibers may be estimated from density determinations, calorimetric measurements, and infrared and x-ray data. Although not an absolute method, assessment of the degree of crystallinity from the density is a very facile, rapid, and precise procedure. It is independent of orientation or geometry of the sample, but requires dry samples that are free of voids and pigments. This method is based on the assumption that the density p or its reciprocal value and the specific volume V are represented by Equation 2.85 and Equation 2.86, respectively. 

Akaogi, M., and Navrotsky, A. (1984) The quartz-coesite-stishovite transformations new calorimetric measurements and calculation of phase diagrams, Phys Earth Planet. Int., 36, 124-134. 

The uncertainty level of this legacy varies considerably because of the fluctuating care given to the (mostly) calorimetric measurements and problems of reagent purity and reaction stoichiometry. Early on there have been successful efforts to systematize the database in terms of molecular structure (reviewed in detail by Cox and Pilcher [22]). As a result, one can compute a standard enthalpy of formation value for ordinary compounds (without strained rings, partially delocalized structures) that have not been studied experimentally with almost the same confidence that one can place in the experimental values themselves. 

A special problem arises if the molecular property measured in the course of the determination of the equilibrium constant is also dependent on the temperature. For example, the temperature dependence of the absorbance may render impossible the use of spectrophotometry in the determination of thermodynamic data from the equilibrium constants relating to various temperatures. In such cases AH may be obtained by means of a separate calorimetric measurement, and the entropy term is found in the usual manner from this AH value and from AG calculated from the equilibrium constants, relating to a single temperature ... 

Hill and Irving [Hi 69] used calorimetric measurements and Rao and Mathur [Ra 71] studied the temperature dependence of the equilibrium constants both groups found that the heat of the protonation of acetylacetone was higher in water-dioxane mixtures than in water. The heats of formation of the copper and nickel complexes, determined by the latter workers, reflect a similar tendency. 

Polymerization entropies can be determined in several ways via the temperature dependence of the equilibrium concentrations of the monomer, via the heat capacity, via the activation constants for polymerization and depolymerization, or via an incremental calculation method. The heat capacity serves to determine the entropy of polymerization because the quotient of specific entropy and specific heat capacity, (A5 /c ) is about unity at 298 K for polymers irrespective of their constitution. False results occur if, for example, monomer association in the vapor phase occurs, or if, with polymers, there is a physical transition in the temperature range between calorimetric measurement and equilibrium measurement. 

In certain cases, the entropy of polymerization can also be calculated using an increment method. A direct determination, for example, of from the heat capacity is possible, but this method can give incorrect values in some circumstances. Incorrect values are observed when a monomer associates in the vapor phase, or when physical transitions occur in polymers in the range of temperatures between calorimetric measurements and equilibrium measurements. If such effects are excluded, then the quotient S%s/Cp 298 is remarkably constant for the most dissimilar monomer-polymer systems (Table 16-10). Determination of the entropy of polymerization from the temperature dependence of the equilibrium concentrations of the monomer is relatively unambiguous. Alternatively, it can be determined from the Arrhenius parameters Ap of polymerization and A p of depolymerization [of equation (16-52)]. 

Gibbs energies of solution, AsoiG, are obtained from solubility or electromotive force (emf) measurements, Aso H from calorimetric measurements, and AsoiV from density determinations. The other quantities are obtained through the temperature dependence according to Eqs. (46b) and (46e). 

This system can give quite satisfactory calorimetric measurements and a number of successful designs have been based on this system, including two calorimeter cells by DuPont [143]. 

Strategies for controlling the copolymer composition and MWD of latices based on linear and non-linear copolymers, such as styrene/butyl acrylate copolymers and methyl methacrylate/n-butyl acrylate copolymers, are described. These strategies involve on-line procedures based on calorimetric measurements and open-loop processes employing a mathematical model for determining the trajectories of the manipulated variables, such as monomer feed flow rates and chain transfer agent. 35 refs. (3rd lUPAC-Sponsored International Symposium on Free-Radical Polymerization Kinetics and Mechanism, II Ciocco (Lucca), Tuscany, Italy, 3rd-9th June, 2001)... 

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