Molecular solubility

Then, the macromolecular characterization is necessary to obtain the molecular weight distribution of the polymeric material and the average molecular weights. For this purpose, the first important condition is to get a perfectly molecular soluble material which means to avoid aggregation and/or take off insoluble material. This point was previously discussed [12]. The polysaccharide must be isolated preferentially as a sodium salt form to be fully soluble in water or in presence of some NaCI used to screen electrostatic interactions. 

As the final products—polystyrene-h-polyivinylperfluorooctanoic ester)— form micelles in tetrahydrofuran (THF) as well as in DMF, there are not direct GPC data to characterize molecular parameter. For this reason, we employed esterification of the hydroxylated block copolymers with benzoylchloride as a model reaction to obtain a comparable product with molecular solubility that can easily be characterized by DMF-GPC. The GPC data from PSB-II—our largest and therefore most sensitive block copolymer—are summarized in Table 10.2. Results for all the other polymers are similar. 

Molecular solubility and diffusion. Treatise Mater. Sci. Tech. 17, 1-40. 

Generally, the phase diagram of surfactants has a triple point at which the solid, the dissolved, and the micellar phase coexist. The temperature at this triple point is the Krafft temperature (Tk). For most surfactants, the TK is below ambient temperature and, therefore, their CMC can be regarded as their molecular solubility. Everything said above about the CMC therefore holds true for aqueous solubility. However, TK of the cationic surfactants used in fabric softeners is above ambient temperature. The same is true for the individual 2-n-(p-sulfophenyl)-alkanes which are constituents of LAS. 

The molecular solubility term (b) depends on the chemical interaction between the solute (DMS) and the solvent (water). Because the internal energy of molecules is mass dependent, these chemical interactions should differ for the isotopically substituted DMS molecules and result in isotopic fractionation. However, in the case of DMS, the concentration in seawater is much larger than that in the atmospheric mixed layer, and Equation (3) reduces to (3a)... 

A polymer network or infinite network arises when all the polymer chains in a system are linked to each other or are crosslinked. The network as a consequence is not molecularly soluble since even a thermodynamically good ... 

Studying molecular properties of rigid-chain polymers by hydrodynamic methods, specific difficulties sometimes arise. Thus, many polymers with aromatic chains that are of great practical importance are molecularly soluble only in very aggressive media such as concentrated sulfuric acid. Hence, experiments in these systems require specific instruments ... 

Shelby J.E., Molecular solubility and diffusion, in Treatise of Materials Science and Technology, Academic Press, New York, (1979), Vol. 17. 

Today, silicates and zeolites are interesting carrier materials for heterogeneous catalysts. With [(Me3Si)3SiAlCl3] as a starting material the synthesis of modified alumosiloxanes seems feasible to yield molecular soluble carriers, hence catalysis in homogeneous phase seems possible. 

Due to micelle formation the total surfactant concentration undergoes an abrupt increase. Since true (molecular) solubility of surfactants, determined by the CMC, remains essentially constant, an increased surfactant concentration in solution is caused by an increase in a number of formed micelles. Micellar solubility increases with increase in temperature, and thus a continuous transition from pure solvent and true solution to micellar solution, and further to different liquid crystalline systems and swollen surfactant crystals (see below), may take place in the vicinity of the Krafft point. 

No significant breakthroughs in zero-valent rare-earth chemistry have been recorded in the last 10 years, and the reactivity studies are rather scarce. However, these molecules appear promising in the sense that they are the source of molecular, soluble zero-valent metals. In particular it would be very interesting to look at the chemistry of [(Ar )2R] to check whether these molecules could be the precursors to new complexes through controlled oxidation reactions. [(Ar )2Dy], which is stable, appears as a good candidate for this purpose. 

The topological transition (Fig. 1) from polymeric solids in compounds containing linked polyhedral homoatomic clusters to discrete molecular (soluble) clusters can be conveniently studied by using as examples compounds rich in elements of the main-groups 13 to 15. It is possible for main-group elements in the middle of the periodic table to form homoatomic molecules or ions with localized homonuclear 2c-2e bonds. At higher valence-electron concentrations, fewer bonding and more free-electron pairs are formed. As electron deficiency increases, however, the formation of delocalized bonds becomes necessary, a situation typical of elements on the left of the periodic table. 

The addition of electrolyte into a foamer solution reduces its molecular solubility and leads, as a result, to a sharp increase in the Wp value. On the other hand, in the concentration range studied, there is a transition of foam films from a higher thickness to common black films, and then to Newton black films [17]. Such a transition corresponds to an increase of the lifetime of the films as investigated by the Scheludko technique. 

A detailed consideration of the behavior and solubility of lipolytic products in aqueous systems not containing bile acids has two justifications. First, digestion is an aqueous process and significant intestinal absorption of certain lipolytic products may occur in the absence of bile acids, despite their low solubility. It is a reasonable assumption that such absorption occurs from a molecular solution, or at lest a nonmicellar solution, and we therefore seek information on molecular solubility or types of aggregation or both in aque-our systems. Second, behavior of lipolytic products in the absence of bile acids provides a framework from which to predict the behavior of these compounds when bile acids are added. 

The predominant form of monoglyceride present in intestinal content during fat digestion is the 2-isomer, which is unstable, slowly isomerizing to the 1-isomer. Few studies have compared the physical properties of the 1-and 2-isomers, but glyceryl monoethers, which are nearly isosteric and should have fairly similar physical properties, are prepared without difficulty. It would seem both feasible and interesting to examine the phase equilibria as well as molecular solubility of glyceryl 1- and 2-monounsaturated ethers. 

Although soaps are called soluble amphiphiles, the formation of micelles is in fact a manifestation of the low molecular solubility of the soap molecule. Micelle formation can only occur above the critical micellar temperature of the system. Below this temperature, soaps form a crystalline phase (which may or may not contain water depending on the history of the system). This means that the classification of a given lipid as a soluble or insoluble amphiphile is conditional upon the experimental temperature. 

Lucassen (54) has shown that the molecular solubility of the soap anion is about 5 x lO" moles greater than that of the corresponding fatty acid. Assuming that dimerization does not occur, one may describe the solubility of potassium soaps by the following equation ... 

At low concentrations, the bile acids are freely soluble in water and yield molecular solutions. The concentration at which molecular solubility is reached is termed the critical micelle concentration. Above this concentration, aggregation of the molecules occurs and micelles are formed. Hofmann and Small (6) have summarized the effects of temperature, electrolyte concentration, impurities, and the pH of the solution upon the critical micelle... 

Why does this occur Consider a solution in zone A at a temperature well above B. Under these conditions the individual molecules of amphiphile are freely distributed throughout the water forming a true solution. As the concentration of amphiphile is increased (moving toward zone Y) a point of maximum molecular solubility is reached at line BD. Any further addition of amphiphile results in the formation of micelles (zone Y). Therefore, concentration at which micelle formation first occurs BD) is the CMC. It is influenced slightly by temperature. 

Critical Micellar Concentration CMC) The concentration at which molecular solubility of a detergent is reached and molecular aggregation begins to occur. 

The first is a case of simple molecular solubility as discussed at the start of the topic. The product of these two constants must still be a constant ... 

The particle-mediated non-classical crystallization path makes crystallization more independent of ion products or molecular solubility. It can occur without pH or osmotic pressure changes, and opens new strategies for crystal morphogenesis. This is possible because the precursor particles can be formed independently and can be transported to the mineraUzation site so... 

Strategy Qassily each compound as ionic or molecular. Soluble ionic compounds are strong electrolytes. Classify each molecular compound as an acid, base, or neither. Molecular compounds that are neither acids nor bases are nonelectrolytes. Molecular compounds that are bases are weak electrolytes. Finally, classify acids as either strong or weak. Strong acids are strong electrolytes, and weak acids are weak electrolytes. 

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