Calorimetry polymer thermodynamics

The thermomechanical data accumulated during the last years as a consequence of the improvement of the technique of deformation calorimetry contributed significantly to the understanding of thermodynamics and mechanisms of the reversible deformation of polymers in the glassy, semicrystalline and rubbery state. 

As to Eq. (7), it is to be remembered that AG, in a general case is a function of p. Therefore, the experimental dependencies of p on concentration, chain length of oligomer and temperature may be employed to find thermodynamic parameters only for a fixed value of p, e.g., for p = 0.5 using Eqs. (8 a- b). These equations have been taken by various authors to calculate the enthalpy and entropy of complex formation between simple synthetic oligomers and polymers 28). In a number of cases the correspondence between the values of complex formation enthalpy thus obtained and determined, either by calorimetry or by potentiometric titration 26), has been found satisfactory although it is obvious that in a general case these values do not necessarily coincide. 

A more recent development is temperature-modulated DSC (Jones etal, 1997), which is a particular example of the broader area of modulated calorimetry (Gmelin, 1997) and enables deconvolution of kinetic and thermodynamic processes during the reactive curing of polymer networks (Van Assche et al, 1997). This is discussed in more detail later (Section 3.2.3). 

NIN Ninni, L., Meirelles, A.J.A., and Maurer, G., Thermodynamic properties of aqueous solutions of maltodextrins from laser-light scattering, calorimetry and isopiestic investigations. Carbohydrate Polym., 59,289,2005. 

Bershstein VA, Egorov VM, Differential Scanning Calorimetry of Polymers, Ellis Harwood, 1994. McNaughton JL, Mortimer CT, Differential Scanning Calorimetry, Thermochemistry and Thermodynamics, Skinner HA ed., Butterworths, London, 1975. 

The infortnation provided in this chapter can be divided into four parts 1. introduction, 2. thermodynamic theories of polymer blends, 3. characteristic thermodynamic parameters for polymer blends, and 4. experimental methods. The introduction presents the basic principles of the classical equilibrium thermodynamics, describes behavior of the single-component materials, and then focuses on the two-component systems solutions and polymer blends. The main focus of the second part is on the theories (and experimental parameters related to them) for the thermodynamic behavior of polymer blends. Several theoretical approaches are presented, starting with the classical Flory-Huggins lattice theory and, those evolving from it, solubility parameter and analog calorimetry approaches. Also, equation of state (EoS) types of theories were summarized. Finally, descriptions based on the atomistic considerations, in particular the polymer reference interaction site model (PRISM), were briefly outlined. 

There are many techniques for probing the chemical and physical properties of a solid surface to predict the tending of organic polymers to solid surfaces. The electronic structure of solid surfaces has been studied by measuring the thermodynamic interaction of the solid surface with simple liquids of known molecular structure. Experimental techniques for measuring the thermocfynamic interaction between solid and liquid include contact angle measurement, calorimetry, and gas chromatography. Some of these techniques are discussed below. Specific techniques related to characterization of carbon fiber surfaces are also discussed. 

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. 

To determine crystallinity in a semicrystalline polymer, diffraction, thermodynamic, and spectroscopic methods can be used. Diffraction method is mainly used with waxd methods. Thermodynamic methods include dilatometiy, differential scanning calorimetry (dsc), etc, while ir and nuclear magnetic resonance (nmr), and other spectroscopic methods can also be used. 

For many years, the thermodynamic description of macromolecules lagged behind other materials because of the unique tendency of pol5nneric systems to assume nonequilibrium states. Most standard sources of thermodynamic data are, thus, almost devoid of polymer information (1-7). Much of the aversion to include polymer data in standard reference sources can be traced to their nonequilibrium nature. In the meantime, polymer scientists have learned to recognize equilibrium states and utilize nonequilibrium states to explore the history of samples. For a nonequilibrium sample it is possible, for example, to thermally establish how it was transferred into the solid state (determination of the thermal and mechanical history). More recently, it was discovered with the use of temperature-modulated differential scanning calorimetry (TMDSC) that within the global, nonequilibrium structure of semicrystalline polymers, locally reversible melting and crystallization processes are possible on a nanophase level (8). 

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