Solubility parameter determination technique

Campion and Morgan developed the technique of reverse solubility parameter spectroscopy (RSPS)" to determine the 8 value for a liquid (e.g., an oU), from a series of swelling measurements using a range of elastomers of known 8. In this way, 8 for cmde Brent oU from the North Sea has been found to be 8.2 (cal cm ). ... 

Various models of SFE have been published, which aim at understanding the kinetics of the processes. For many dynamic extractions of compounds from solid matrices, e.g. for additives in polymers, the analytes are present in small amounts in the matrix and during extraction their concentration in the SCF is well below the solubility limit. The rate of extraction is then not determined principally by solubility, but by the rate of mass transfer out of the matrix. Supercritical gas extraction usually falls very clearly into the class of purely diffusional operations. Gere et al. [285] have reported the physico-chemical principles that are the foundation of theory and practice of SCF analytical techniques. The authors stress in particular the use of intrinsic solubility parameters (such as the Hildebrand solubility parameter 5), in relation to the solubility of analytes in SCFs and optimisation of SFE conditions. 

The determination of the strength of the Lewis acids MF , has been carried out in various solvents using the conventional methods. Numerous techniques have been applied conductivity measurements, cryoscopy, aromatic hydrocarbon extraction,53,84 solubility measurements,85-87 kinetic parameters determinations,52,88,89 electroanalytical techniques (hydrogen electrode),90-93 quinones systems as pH indicators,94-97 or other electrochemical systems,98 99 IR,100,101 and acidity function (//,) determinations with UV-visible spectroscopy,8 9 14 19 102-105 or with NMR spectros-copy.20-22,44-46,106-108 Gas-phase measurements are also available.109-111 Comparison of the results obtained by different methods shows large discrepancies (Table 1.2). 

Since the initial work of Smidsrod and Guillet numerous investigators have used I.G.C. to determine physicochemical parameters characterising the interaction of small amounts of volatile solutes with polymers Baranyi has shown that infinite dilution weight fraction activity coefficients, interaction parameters and excess partial molar heats of mixing can be readily determined with this technique. Partial molar heats and free energies of mixing, and solubility parameters of a wide variety of hydrocarbons in polystyrene and poly(methyl methacrylete) have been determined The temperature dependence of the interaction parameter between two polymers has also been studied... 

Determination of the polymer solubility parameter using the Guillet approach yields deceptively linear dependences compared to the scatter inherent in the experimental data. While the technique is more than adequate, compared with values obtained from more time consenting classical methods, one should be aware of the limitations of generating the linear dependence. 

The solubility parameter of Nafion membranes has been determined experimentally in a recent study (3) The samples which have been studied have an equivalent weight (EW) of either 1100 or 1200 (weight of polymer per sulfonic acid group). Since the samples are not soluble, the solubility parameter of the polymer can be determined only from the swelling technique (40 ... 

A linear programming technique is described which selects mixed solvents based on specifications of the ffo, 8p, end SH solubility parameters, evaporation rates, and other significant parameters of a solvent blend. Suggestions are made for setting the various restrictions and for setting procedures of data processing. For simpler cases of solvent selection, recourse to a computer is not necessary. Use of a solvent improvement cost factor, 8 J cost, then leads to optimum formulations since one can determine which solvents increase solubility at least cost. 8 is given by y/ 8P2 -(- 8H2. 

As mentioned in Section 3.7.1.2, there is a considerable scatter of solubility product values obtained in the molten KCl-NaCl eutectic using different methods of solubility determination. This disagreement in the solubility parameters may be explained by differences in the sizes of oxide particles whose solubility is to be determined. The difference in size causes the scatter of the solubility data according to the Ostwald-Freundlich equation and the employment of the isothermal saturation method, which implies the use of commercial powders (often pressed and sintered), leads to values which are considerably lower than those obtained by the potentiometric titration technique where the metal-oxides are formed in situ. Owing to this fact, the regularities connected with the effect of physico-chemical parameters of the oxides or the oxide cations should be derived only from solubility data obtained under the same or similar experimental conditions. However, this does not concern the dissociation constants of the oxides, since homogeneous acid-base equilibria are not sensitive to the properties of the solid phase of... 

The least sophisticated but most convenient technique illustrating polymer fractionation is fractional precipitation, which is dependent on the slight change in the solubility parameter with molecular weight. Thus, when a small amount of miscible nonsolvent is added to a polymer solution at a constant temperature, the product with the highest molecular weight precipitates. This procedure may be repeated after the precipitate is removed. These fractions may also be redissolved and fractionally precipitated. The shape of the distribution curve is then constructed from the fractional amount of each sample after chain length determination. 

Summary. The DCCLC technique is a very rapid, precise, and accurate method for determining aqueous solubilities and related parameters for PAHs. The agreement with solubilities and calculated solubility parameters, such as AHa, for which values have been previously reported in the literature helps to confirm the validity of this approach. In all cases replicate solubility measurements of the generated PAH solutions at constant temperature were better than 3% and in most cases better than 1%. Quantitative analyses of hexane extracts of the generated solutions by both GC and HPLC have agreed with the DCCLC values to within 3% in all cases. 

For the dimension 6 theoretical evaluation the following technique was used. As it has been shown in Ref. [24], Dj, value within the fiamework of two-dimensional (two-component) solubility parameter [14] can be determined according to Ihe Eq. (13). The solvents enumeration and corresponding to them 6 and values are adduced in Table 13. devalues were calculated according to the Eq. (80) and Eq. (11) of Chapter 1 at the condition d=1.0 and =2.0, since PC macromolecule is a linear one. 

The detailed comparative evaluation of experimental techniques and designs of equipment used for determination of enthalpy of evaporation can be found in the appropriate monographs. V alues of solubility parameters of solvents are presented in Subchapter 4.1. 

Luciani et al. (1998) critically examined the experimental methods used for the measurements of the interfacial coefficient in polymer blends as well as the theoretical models for its evaluation. A new working relation was derived that makes it possible to compute the interfacial tension from the chemical structure of two polymers. The calculations involve the determination of the dispersive, polar, and hydrogen-bonding parts of the solubility parameter from the tabulated group and bond contributions. The computed values for 46 blends were found to follow the experimental ones with a reasonable scatter of +/— 36 %. The authors mentioned also that since many experimental techniques have been developed for low-viscosity Newtonian fluids, most were irrelevant to industrial polymeric systems. For their studies, two were selected capillary breakup method and a newly developed method based on the retraction rate of deformed drop. 

The present study aims to understand the influence of solvent quality on the molecular-level friction mechanism of tethered, brushlike polymers. It involves complementary adsorption studies of PLL-,g-PEG by means of optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance with dissipation (QCM-D) as well as friction studies performed on the nanoscale using colloidal-probe lateral force microscopy (LFM). The adsorbed mass measured by QGM-D includes a contribution from solvent molecules absorbed within the surface-bound polymer fllm. This is in contrast to optical techniques, such as OWLS, which are sensitive only to the dry mass of a polymer adsorbed onto the surface of the waveguide.By subtracting the dry mass , derived from OWLS measurements, from the wet mass , derived from QCM-D measurements, it is therefore possible to determine the mass of the solvent per unit substrate area absorbed in the brushlike structure of PLL- -PEG, expressed as areal solvation, P. Areal solvation was varied by choosing solvents (aqueous buffer solution, methanol, ethanol, and 2-propanol) of different quality with respect to the PEG brush. The solvents were characterized in terms of the three-component Hansen solubility parameters, and these values were compared with measured areal solvation of the PEG brush. 

At this point, mention should be made of the reversed-flow gas chromatography technique, a version of IGC that has been applied successfully to the measurement of activity coefficients in polymer solutions [78], and also for determining Flory-Huggins interaction parameters and solubility parameters in polymer-solvent systems [79]. 

The Hildebrand solubility parameter is readily obtained for liquids by inserting the appropriate experimentally determined quantities into eq. (4.70). Polymers degrade prior to vaporization and their solubility parameter values are determined indirectly by one of two essentially different techniques. In the first technique, the polymer is lightly crosslinked and then treated with a number of solvents with different solubility parameters. The best solvent, the one which swells the polymer the most, is then the one which has a solubility parameter which resembles the solubility parameter of the polymer (Fig. 4.14). The other technique involves the measurement of the intrinsic viscosity of solutions of the polymer in a number of solvents of different solubility parameters. 

The parameters of the system must be evaluated and the appropriate values must be used in tiie model. Some parameters can be obtained independently of the mathematical model. They may be of a basic character, like tiie gravitation constant, or it may be possible to determine them 1 independent measurements, Uke, for instance, solubility data fi om solubility experiments. However, it is usually not possible to evaluate all the parameters from specific experiments, and many of them have to be estimated by taking results from the whole (or a similar system), and tiien using parameter-fitting techniques to determine which set of parameter values makes the model best fit the experimental results. For example, a complex reaction may involve ten or more kinetic constants. These constants can be estimated 1 fitting a model to resnlts from a laboratory reactor. Once the parameter values have been determined, they can be incorporated into a model of a plant-scale reactor. 

Hansen defined solvent as a point in three-dimensional space and solutes as volumes (or spheres of solubihty). If a solvent point is within the boundaries of a solute volume space then the solute can be dissolved by the solvent. If the point characterizing the solvent is outside the volume space of a solute (or resin) such a solvent does not dissolve the solute. The solubility model based on this concept is broadly applied today by modem computer techniques using data obtained for solvents (the three components of solubility parameters) and solutes (characteristic volumes). A triangular graph can be used to outline the hmits of solubility and place different solvents within the matrix to determine their potential dissolving capability for a particular resin. 

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