Solubility parameter concept discussion

This leads to solubility parameter concepts (discussed later in this chapter), used by Hildebrand [3] to show that ... 

The above discussion demonstrates that the solubility parameter concept in combination with the gradient oven is a useful tool to select a convenient solvent, which could undergo a phase separation during the crosslinking reaction. 

The Flory-Huggins theory has been modified and improved and other models for polymer solution behavior have been presented. Many of these theories are more satisfying intellectually than the solubility parameter model but the latter is still the simplest model for predictive uses. The following discussion will therefore focus mainly on solubility parameter concepts. 

We now discuss how predictions of solubility and phase behavior can be carried out. Before proceeding with the equation of state approach, we present a brief discussion of the solubility parameter concept because solubility parameters continue to be presented in the literature as one means of correlating SCF-solute behavior. 

As will be discussed later, the intermolecular physical interactions, with their dispersion forces, dipole and hydrogen bond contributions, also play an essential role in describing the solvent power of a liquid. Modern solubility parameter concepts are based on these contributions. 

One closely related concept to 5 is the cohesive energy E, which is defined as the increase in the internal energy per mole of the system upon removal of all intermolecular interactions. When E is divided by the molar volume V, we obtain the cohesive energy density (ced), ElV, of the system. The solubility parameter is simply the square root of this cohesive energy density. A thorough discussion of the defliution of 5 and its relation to internal pressure may be found in the comprehensive review by Barton. ... 

Section 16.2 will discuss the concept and importance of the group-contribution (GC) approach in estimating two polymer properties, which are relevant for polymer solutions and blends the density and the solubility parameter. The GC technique is employed in several of the thermodynamic models discussed later in the chapter. 

The use of nanoparticles for oral appHca-tion is an intensively studied concept for the delivery of poorly soluble drugs, as discussed above. Particle uptake has been known for more than 50 years via M-cells as specialized phagocytic enterocytes, but also via lymphoid tissue and normal intestinal enterocytes [75, 76]. The kinetics of particle uptake and translocation depend on biopharmaceutical parameters like accessibility through the mucus and contact with the enterocytes, as well as on the physical properties of the particle like its size, particle charge, surfactant coating and, sometimes, targeting devices. 

Insufficient chemical resistance of a blend at times leads to its rejection for use in an aggressive chemical environment, although it possesses an excellent combination of mechanical properties. Thus chemical and solvent effects on polymer blends are important factors that frequently determine blends applicability. Attention has been given to chemical resistance of blends starting from the fundamental concept of the solubility parameters. Apart from the chemical and environmental restrictions, thermal resistance of a polymer blend is often a major criterion for its applicability. Thus, the thermal conductivity, heat capacity and heat deflection temperature of polymeric materials are discussed in separate sections. 

Coating and paint formulations, adhesives, polymer-plasticizer compatibility and solvent effects on plastic surfaces are only a few of the areas that can benefit from the Hansen solubility parameter theory. Hansen [1] extended the solubility concepts discussed in Chapter 4 to include resin and polymeric materials. The total solubility parameter of a polymer is the point in three-dimensional space where the three partial solubility parameter vectors meet as the center point of the idealized spherical envelope. The distance in space between the two sets of parameters (solvent and polymer) can be represented by the term, radius of interaction or R. The radius of interaction term is used to express the degree of mutual solubility. All of these solubility comparisons can be made by using computer spreadsheets that are described in Chapters 4, 19, and this chapter. 

Hansen solubility parameters are another potentially useful concept for determination of degree of compatibility and incompatibility of two materials. This concept is not discussed here because data on Hansen parameters of discussed additives are not available yet. ... 

In the second edition of this Handbook, Miron and Skeist stressed the importance of the solubility parameter in formulating adhesives for plastics. The concept of solubility parameter has been discussed in Chapter 1. Table 1 gives the solubility parameter for many plastics. Table 2 gives the solubility parameters of many solvents for plastics, along with their fractional polarities. 

Nirmalakhandan and Speece (1988a, 1988b, 1989) have used this index in conjunction with polarizability to correlate solubilities of some 470 compounds, with a standard error of 0.332 in log solubility. The correlation include three parameters, a modified polarizability parameter and two connectivity indices. For those familiar with connectivity indices, this method is very convenient, but for occasional use by those unfamiliar with these concepts, the method requires a considerable learning period. It is discussed more fully in Chapter 8. 

For other metals, such as Cd, Zn, Cu, and Ni, no simple sohd with properties simulating metal solubility in soils exists. Lindsay (1979) previously advocated the concept of a fictitious sohd phase called soil-Cu. There are a number of theoretical and semi-theoretical models that have been used to describe (ad)sorpfion of transition metals onto reactive surfaces (Fe, Mn or Al oxides soil organic matter). While probably more correct in a mechanistic sense than the solubility relations discussed below, these models have not proven to be particularly useful with intact soils because they contain a very complex assemblage of colloidal surfaces. Moreover, they do not seem to adequately predict increases in metal solubility with increases in total soil metal burden. This has led an increasing number of researchers to develop purely empirical models that describe trace-metal solubility as a function of simple soil parameters such as pH, organic matter content, and total metal content (e.g. McBride et al., 1997 Gray et al.,... 

In terms of micellar models, the cmc value has a precise definition in the pseudo-phase separation model, in which the micelles are treated as a separate phase. The cmc value is defined, in terms of the pseudo-phase model, as the concentration of maximnm solubility of the monomer in that particular solvent. The pseudo-phase model has a number of shortcomings however, the concept of the cmc value, as it is described in terms of this model, is very useful when discussing the association of surfactants into micelles. It is for this reason that the cmc value is, perhaps, the most frequently measnred and discussed micellar parameter [39]. 

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