Solute behaviour

This model is appropriate for random mixtures of elements in which tire pairwise bonding energies remain constant. In most solutions it is found that these are dependent on composition, leading to departures from regular solution behaviour, and therefore the above equations must be conhned in use to solute concentrations up to about 10 mole per cent. 

Solution Behaviour of Surfactants (eds. Mittal, K. L., Fendler, E. J.), Vol. 2, New York, Plenum Publishing Corp. 1982... 

The hydrophobic interaction results in the existence of a lower critical solution temperature and in the striking result that raising the temperature reduces the solubility, as can be seen in liquid-liquid phase diagrams (see Figure 5.2a). In general, the solution behaviour of water-soluble polymers... 

The different hydration numbers can have important effects on the solution behaviour of ions. For example, the sodium ion in ionic crystals has a mean radius of 0 095 nm, whereas the potassium ion has a mean radius of 0133 nm. In aqueous solution, these relative sizes are reversed, since the three water molecules clustered around the Na ion give it a radius of 0-24 nm, while the two water molecules around give it a radius of only 017 nm (Moore, 1972). The presence of ions dissolved in water alters the translational freedom of certain molecules and has the effect of considerably modifying both the properties and structure of water in these solutions (Robinson Stokes, 1955). 

The behaviour of most metallurgically important solutions could be described by certain simple laws. These laws and several other pertinent aspects of solution behaviour are described in this section. The laws of Raoult, Henry and Sievert are presented first. Next, certain parameters such as activity, activity coefficient, chemical potential, and relative partial and integral molar free energies, which are essential for thermodynamic detailing of solution behaviour, are defined. This is followed by a discussion on the Gibbs-Duhem equation and ideal and nonideal solutions. The special case of nonideal solutions, termed as a regular solution, is then presented wherein the concept of excess thermodynamic functions has been used. 

Expressing the concentrations of the components of a solution in terms of mole fractions or atom fractions is adequate only in some limiting cases of solution behaviour. A more... 

In order to understand polymer solution behaviour, the samples have to be characterised with respect to their molecular configuration, their molar mass and polydispersity, the polymer concentration and the shear rate. Classical techniques of polymer characterisation (light scattering, viscometry, ultracentrifugation, etc.) yield information on the solution structure and conformation of single macromolecules, as well as on the thermodynamic interactions with the solvent. In technical concentrations the behaviour of the dissolved polymer is more complicated because additional intramolecular and intermolecular interactions between polymer segments appear. 

A comparison of the solution behaviour of PS in both solvents, toluene and frans-decalin, reveals that the limiting power of the molar mass dependence of r 0 (3.35 and 3.28, respectively) is very close to the value of 3.4 observed in highly concentrated solutions and melts. The concentration dependence of r 0, however, is clearly different in each of the solvents ... 

Damas, C., Vannier, L., Naejus, R. and Coudert, R. (1999) Influence of structural modifications near the polar head of sodium carboxylates on their aqueous solution behaviour. Colloids and Surfaces A Physicochemical and Engineering Aspects, 152, 183-187. 

Abstract Protein-like copolymers were first predicted by computer-aided biomimetic design. These copolymers consist of comonomer units of differing hydrophilicity/hydro-phobicity. Heterogeneous blockiness, inherent in such copolymers, promotes chain folding with the formation of specific spatial packing a dense core consisting of hydrophobic units and a polar shell formed by hydrophilic units. This review discusses the approaches, those that have already been described and potential approaches to the chemical synthesis of protein-like copolymers. These approaches are based on the use of macromolecular precursors as well as the appropriate monomers. In addition, some specific physicochemical properties of protein like copolymers, especially their solution behaviour in aqueous media, are considered. 

Keywords Chemical synthesis Heterogeneous blockiness Physicochemical studies Protein-like copolymers Solution behaviour... 

In the researches performed by Tenhu and co-authors [19-21], it was shown that by means of chemical modification of the units with reactive pendant groups in thermoresponsive NiPAAm-containing copolymers one can prepare polymeric products, whose solution behaviour resemble in some aspects the behaviour predicted by the theory for protein-like copolymers. Scheme 1 presents the reaction used in these syntheses. 

It was found that in spite of the large excess of modifying amine (N-isopropyl-, -diethyl, -dipropyl, -diisopropyl, -n-hexyl, -cyclohexyl, -n-octyl), the extent of substitution did not exceed 5-10 molar %. For the case of the N-isopropyl derivative, i.e. [poly(AAm-co-NiPAAm)], the authors connected such results with the temperature-induced conformational transformation of partially hydrophobized copolymer acquiring the contracted conformation, "... which made it difficult for N-isopropylamine to react further with the amide groups [22], Unfortunately, no data on the solution behaviour of these interesting copolymers have been reported to date, although there is a high probability that they would demonstrate certain properties of the protein-like macromolecules. At least, in favour of similar supposition is supported by the results of our studies [23] of somewhat different PAAm partially hydrophobized derivative, whose preparation method is depicted in Scheme 3. 

Efforts at synthesis and studies of temperature-dependent solution behaviour of these chemically hydrophobized polyacrylamides are now in progress. However, it is reasonable to point out that in this case, contrary to the hydrophilization of the hydrophobic precursor, the problems associated with additional swelling of the globular core (as the modification proceeds) are absent however, the problem of the choice of working concentration for the precursor is still present since above the coil overlapping concentration the intermolecular aggregation processes at elevated temperatures can compete with the intramolecular formation of core-shell structures. 

As we close this section, we would also like to point out that the purposeful preparation of organosoluble copolymers exhibiting protein-like solution behaviour in organic media, has not, to the best of our knowledge, so far been reported, although attempts have been undertaken (e.g., the preparation of the partially fluorosiloxylated derivative of polyisoprene [25]). One may hope that the results of such studies will be published soon. 

Conformational and phase transitions can potentially be indicative of the primary structure of thermosensitive macromolecules. Indeed, depending on the relative location of H- and P-blocks, as well as on the variation of their length, the chains can either undergo conformational transition accompanied by phase separation, or they can exhibit only the conformational changes without macroscopic phase transitions, i.e. the behaviour observed in the case of protein-like HP-copolymers. Therefore, the solution behaviour of separated fractions of these NVCl/NVIAz-copolymers in an aqueous medium at different temperatures is very important. 

Unfortunately, data on the temperature-dependent solution behaviour of these fractions are not available to date, although it will be of considerable interest to compare, e.g., HS-DSC and NMR results for the bound and unbound fractions of poly(NiPAAm-co-NVIAz) over the temperature range characteristic of the conformational and phase transitions of NiPAAm homopolymers and copolymers. 

The activity coefficient of component i, y(-, is now defined as a measure of the deviation from the ideal solution behaviour as the ratio between the chemical activity and the mole fraction of i in a solution. 

Intratrack Reactions. Earlier It was noted that chemical reactions could occur between the species before they could diffuse away from each other. In the case of Irradiated water, for example, this will result In a greater yield of the molecular species, H2 and H202, and a lower yield of the radical species, 0H, e and H. Additionally, the amount of solute present In a short track or blob Is limited and this may conceivably alter the course of reactions. In other respects, once the radlolytlc species diffuse away from their place of origin Into the bulk of the solution, they follow conventional solution behaviour. However, even In homogeneous solutions there will be differences attributable to the three track entitles because of differences In the yields of molecular products formed by reactions between primary radicals and the yields of radical species which are able to escape out of the tracks. Thus It Is possible to consider the overall yield of products as the sum of the Individual yields from the three track entitles, duly adjusted for the relative contributions from each, giving a weighted average equivalent to the observed experimental yields (10,19). 

By using a thermodynamic model based on the formation of self-associates, as proposed by Singh and Sommer (1992), Akinlade and Awe (2006) studied the composition dependence of the bulk and surface properties of some liquid alloys (Tl-Ga at 700°C, Cd-Zn at 627°C). Positive deviations of the mixing properties from ideal solution behaviour were explained and the degree of phase separation was computed both for bulk alloys and for the surface. 

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