Polymer-solvent interactions definition

The polymer-solvent interaction parameter, which is a key constant defining the physical chemistry of every polymer in a solvent, can be obtained from electrochemical experiments. Definition and inclusion of this interaction was a milestone in the development of polymer science at the beginning of the 1950s. We hope that Eq. 47 will have similar influence in the development of all the cross-interactions of electrochemistry and polymer science by the use of the ESCR model. A second point is that Eq. 47 provides us with an efficient tool to obtain this constant in electroactive... 

Navard and Haudin studied the thermal behavior of HPC mesophases (87.88) as did Werbowyj and Gray (2), Seurin et al. (Sp and, as noted above, Conio et al. (43). In summary, HjPC in H2O exhibits a unique phase behavior characterized by reversible transitions at constant temperatures above 40 C and at constant compositions when the HPC concentration is above ca. 40%. A definitive paper has been recently published by Fortin and Charlet ( who studied the phase-separation temperatures for aqueous solutions of HPC using carefully fractionated HPC samples. They showed the polymer-solvent interaction differs in tiie cholesteric phase (ordered molecular arrangement) from that in the isotropic phase (random molecular arrangement). 

In Flory s theory (/< ), a polymer-solvent system is characterized by a temperature 0 at which (i) excluded-volume effects are just balanced by polymer-solvent interactions, so that os=l, (ii) the second virial coefficient is zero, irrespective of the MW of the polymer, and (iii) the polymer, of infinite molecular weight, is just completely miscible with the solvent The fundamental definition of the temperature is a macroscopic one, namely that for T near 0 the excess chemical potential of the solvent in a solution of polymer volume fraction v2 is of the form (18) ... 

The physicochemical properties of the solvent, which have an important effect on the breaking force, are not yet properly understood. Polymer—solvent interactions are always present, and definitely affect the tensile strength of the bonds involved, whereas the critical stresses calculated in Section 6.2, although entirely valid for gas-phase processes, are not applicable in solution without many restrictions. This is indicated by the fact that different polymers with the same chemical bonds along the main chain have different rate constants of degradation in the same solvent. The hydrodynamic and mechanical effects in the chain-scission process ate certainly far more involved than the simple stretching of chemical bonds to their point of rupture. 

Interpretation of the second and third virial coefficients, A2 and A3, in terms of Floiy-Huggins theory is apparent from Eq. (3.82). The second virial coefl[icient A2 evidently is a measure of the interaction between a solvent and a polymer. When A2 happens to be zero, Eq. (3.82) simplifies greatly and many thermodynamic measurements become much easier to interpret. Such solutions with vanishing A2 may, however, be called pseudoideal solutions, to distinguish them from ideal solutions for which activities are equal to the molar fractions. Inspection of Eq. (3.83) reveals that A2 vanishes when the interaction parameter X equal to. We should also recall that %, according to its definition given by Eq. (3.40), is inversely proportional to temperature T. Since x is positive for most polymer-solvent systems, it should acquire the value at some specific temperature. 

The most important effect of plasticization is the lowering of the Tg of the polymer, which was discussed in Section 6.D. Another effect of plasticization is that the activation energy for viscous flow of the solution at T>1.2-Tg is usually smaller than the activation energy of the pure polymer since ET)p Er S for most polymer-solvent combinations. Our preliminary calculations show that Equation 12.21 may often be preferable to Equation 12.19 for describing the behavior of Er SS, at least for Op l. This issue must, however, be considered in greater detail in order to reach more definitive conclusions. In particular, ET SS must be examined as a function of Op in the limit of Op—>1. Furthermore, the dependence of the behavior of ET SS as a function of Op on the strength of the interactions between the polymer and the solvent needs to be considered. 

It is known through Ref. [13], that the value /) is defined by interactions of macromolecular coil elements between themselves and interactions polymer-solvent. The regular solutions theory absence complicates the exact definition of interactions of the second group and therefore the following approximate expression was used for determination [15] ... 

As it has been noted above, the fractal dimension macromolecu-lar coil in solution is determined by two interactions groups interactions polymer-solvent and interactions of coil elements between themselves. Such definition allows to link between themselves the dimension and Flory-Huggins interaction parameter which was determined as follows [1] ... 

Coil-like macromolecules, however, may form a great many contacts with a substrate, and the shape of the adsorbed coil molecule may be very different according to polymer-substrate, polymer-solvent, polymer-polymer, and substrate-solvent interactions (Figure 12-5). The number and order of adsorbed segments leads to a definite macroconformation, and a definite macroconformation, in turn, determines the thickness of and polymer concentration in the adsorbed layer. 

The plots of Fig. 2 allow to make several conclusions. Firstly, as it was to be expected [6], the value Dj. of the branched polymers is controlled by two factors interactions polymer-solvent and interactions of coil elements among themselves. Secondly, the branching degree g is a prevalent parameter in the second factor definition — we do not observe any correspondence with linear analogs. The parameter e, determined according to the Eq. (21), can be used for the estimation of character of interaction of macromolecular coil elements among themselves. 

Hory X parameters are defined using a reference density, and their values depend on the value chosen. This density is denoted by poR in Eq. (33). In polymer-solvent systems, the solvent density is usually used for this, that is, poR = Pos. Less well appreciated is the fact that all Hory parameters have this dependence. For example, the xab in this expression depends on this choice. As a result, the value of xab would differ in different solvents, even for the same pair of polymers. In the absence of solvent, one must still specify the density used in the definition of the interaction parameter. For these reasons, por has been maintained here to sustain generality. 

This equation suggests that the enthalpic interactions produce a proportionate change in the excess entropy, and reveals that AHf and ASf (or alternatively x and xp) must have the same sign (i.e. either both positive or both negative). Equation (3.43) also provides an alternative definition of the theta temperature, as being the proportionality constant relating AHf to A5f. On this basis the origin of the variation of 6 from one polymer-solvent system to another is clearly evident. 

Self-assembled monolayers (SAMs) are molecular layers tliat fonn spontaneously upon adsorjDtion by immersing a substrate into a dilute solution of tire surface-active material in an organic solvent [115]. This is probably tire most comprehensive definition and includes compounds tliat adsorb spontaneously but are neither specifically bonded to tire substrate nor have intennolecular interactions which force tire molecules to organize tliemselves in tire sense tliat a defined orientation is adopted. Some polymers, for example, belong to tliis class. They might be attached to tire substrate via weak van der Waals interactions only. 

The definition of a hostile effect, proposed earlier, as an adverse interaction between polymer and solvent wherein the chemical and/or physical integrity of the polymer is affected without the resultant formation of a "regular solution" has been clearly shown. The need now arises for an improved method by which hostile effects can be predicted. Therefore, if one employs the generalized rule cited by Seymour (14) that compatabillty or solubility on the molecular level can be expected if 61-62 is less than 1.8H and that the swelling of polymers occurs when 6 -62 is equal to 3.2H (20), then one would expect some interaction between PVC and all of the solvents listed on Table I, with the possible exception of methanol and 1-butanol. 

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