Thermodynamic parameters blends

The use of copolymers as surfactants is widespread in macromolecular chemistry in order to compatibilize immiscible blends. These additives are sometimes named surfactants , interfacial agents or more usually compatibi-lizers . Their effect on improving different properties is observed interfacial tension and domain size decrease, while there is an increase in adhesion between the two phases and a post-mixing morphology stabilization (coalescence prevention). The aim of the addition of such copolymers is to obtain thermodynamically stable blends, but the influence of kinetic parameters has to be kept in mind as long as they have to be mastered to reach the equilibrium. Introducing a copolymer can be achieved either by addition of a pre-synthesized copolymer or by in-situ surfactant synthesis via a fitted re-... 

Polymer miscibihty has been the subject of numerous studies. Pressure is a thermodynamic parameter that can affect the phase behavior of polymer mixture and that can be used to enhance the miscibility of polymers. This properly may have an important apphcation in controlhng microstructure. The phase behavior of blends and block copolymers under pressure has recently received significant attention 1-3). 

In polymer solutions or blends, one of the most important thermodynamic parameters that can be calculated from the (neutron) scattering data is the enthalpic interaction parameter x between the components. Based on the Flory-Huggins theory [41. 42], the scattering intensity from a polymer in a solution can be expressed as... 

The information provided in this Chapter can be divided into four parts 1. Introduction, 2. Thermodynamic theories of polymer blends, 3. Experimental methods, and 4. The characteristic thermodynamic parameters for polymer blends. Introduction presents the basic principles of the classical, equilibrium thermodynamics, describes behavior of the single component materials, then focuses on the two-component systems solutions and polymer blends. 

The 2D simulation has been carried out at the 50/50 iPP/EPDM blend composition (i.e., a near critical composition) following a temperature jump from a single phase temperarnre of 142°C to a temperature of 155°C, which is below the crystalmelting temperarnre, but it is above the LCST. The thermodynamic parameters used for the iPP/EPDM simulation are IT = 10, = 0.1, = 0.98, Xca = 0-8, k,p. 1,... 

Another experiment was carried out by quenching the 50/50 blend from the initial temperature of 127°C (i.e., the single phase) to a temperature of 11°C that lies underneath the liquidus line and the UCST spinodal. The same set of parameters for the iPP/EPDM blend was employed except for the thermodynamic parameter/g = 0.8 to account for the buried UCST immiscibility gap and the kinetic... 

The influence of PMMA content on the kinetic and thermodynamic parameters controlling the isothermal spherulitic growth and the overall crystallization rate of PEG from the molten blends has been analyzed on the basis of the modified Tumbul 1-Fisher equation ... 

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. 

Renewed interest in polymer blends has provoked a re-examination of the scattering laws for multicomponent systems, not only with a view to obtaining thermodynamic parameters, but also to assess the possibilities of removing the interference from the other components. This question has been particularly addressed by Jahshan and Summerfield and Koberstein they show that for a two phase system containing a proportion of deuterated material, essentially a three component polymer, then Eq. (14) should be written as ... 

GOM Gomez, C.M., Figuemelo, J.E., and Campos, A., Evaluation of thermodynamic parameters for blends of polyethersulfone and poly(methyl methaciylate) or polystyrene in dimethylformamide, Ro/ywzer, 39, 4023, 1998. 

It is also clear that activity of a filler should be related to any definite property of material. It was proposed to introduce the concept of structural, kinetic, and thermod3uiamic activity of fillers. Structural activity of a filler is its abihty to change the polymer structure on molecular and submolecular level (crystallinity degree, size and shape of submolecular domains, and their distribution, crosslink density for network pol3rmers, etc.). Kinetic activity of a filler means the ability to change molecular mobility of macromolecides in contact with a solid surface and affect in such a way the relaxation and viscoelastic properties. Finally, thermodynamic activity is a filler s ability to influence the state of thermodynamic equilibrium, phase state, and thermodynamic parameters of filled polymers — especially important for filled poljmier blends (see Chapter 7). 

Equilibrium melting point depression method was applied and a negative interaction parameter and energy density were formd. The negative value of the interaction parameter confirms a thermodynamically miscible blend. 

In the preceding chapter we have, based on the Flory-Huggins theory, discussed the basis for the phase behavior of polymer blends. Miscible polymer blends and polymer solutions have, even in the mixed one-phase system, spatial variations in the polymer concentration. These concentration fluctuations reflect the thermodynamic parameters of the free energy, as described in the Flory-Huggins model. 

Hobbs et al. [18] studied the morphology of different polymer blends using a transmission electronic microscope (TEM), and showed that the morphology, or the distribution pattern, of a polymer blend of three polymeric components depended on the thermodynamic properties of the polymer components under processing conditions. A thermodynamic parameter called the spreading coefficient of the polymer in the lowest amount was suggested to characterize the thermodynamic behavior of such a system, which can be calculated using the values of surface tension of the components. 

A series of pure low molar mass solutes with different polarities, such as alkanes, acetates, alcohols, formic acid, dimethyl amine and water were injected into the chromatographic colunm that contains the polymer blend. Their interaction with the stationary phase will reveal the effect of the chemical nature of the injected solutes on their miscibility with the blend. Several chromatographic quantities, illustrated in Equation 1 are precisely measured directly from the IGC experiment. These quantities will yield the specific retention volume. Kg". Kg" is the key term in the calculation of thermodynamic parameters and is commonly used to describe the chromatographic elution behavior of solutes. It is defined as ... 

The thermodynamics of blends of polymers of various flexibility and rigid molecules has been thoroughly treated from the theoretical point of view by Flory and Abe [126], who analyzed the phase equilibria as a function of various parameters, such as molecular structure, molecular mass, temperature, and concentration. The theoretical data indicate that systems constituted by rigid and flexible molecules are mainly heterophasic with hmited miscibility effects between the components. In general, it has been observed that the phase behavior of polymer/LC blends is affected by the chemical structure and concentration of the polymer, as well as by the intermolecular interactions with the LC component [127,128]. Studies on the thermodynamics and kinetics of phase transitions in polymer/LC blends have been reported for a few systems. These studies are of considerable interest due to the possibility of varying the stability range of the mesophase, as a function of composition, or even obtaining the formation of induced mesophases [129]. 

Note also the essential differenee between oligomer blends based on reactive and noncreative oligomers. Indeed, the formation of all-level structures of a ohemieally cured product in reactive oligomer blends (polymer-polymer blend) occurs concomitantly with the permanent variation of the chemical structure of the components (at least one of them), whereas the formation of materials from non-reactive components (e.g. solid materials) is not accompanied by any chemical transformations. This means that during the cure of reactive oligomer blends, both thermodynamic parameters of the system as a whole and those, characteristic of each of the components, do vary. Because of this, the equilibrium, that is, thermodynamically stable values of the parameters belonging to different structural levels vary during the course of the process, whereas in nonreactive blends these parameters are the fimction of the parameters of state only and are specified from the very start of the process. 

Mixing of Oligomer Blends Analysis of Thermodynamic Parameters... 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

---