Differential solubility parameter

Solubility parameters are generally tabulated, together with the corresponding liquid molar volumes, only at 25°C. Although solubility parameters are themselves temperature-dependent, the combination of quantities in Eq. 70 is not. Differentiating Eq. 70 with respect to temperature gives — the excess entropy, a quantity which has been assumed to be zero in accord with the definition of a regular solution. Thus only data at 25°C are needed. Solubility parameters may be... 

Table I lists the final results of solvent-swelling conditions which resulted in selecting 2,2,4-trimethylpentane and styrene at —25°C for a differential solvent pair. The table also includes the published values for the solubility parameters (a/CED) of the elastomers and the solvents. This table indicates that for the elastomer systems Cl-butyl-cts-polybutadiene or Cl-butyl-SBR excellent differentiation can be obtained.

The system Cl-buty 1-natural rubber (or cw-polyisoprene) could not be resolved by differential solvent techniques because the polymeric solubility parameters were too similar. At one end of the spectrum—i.e., with styrene at — 25 °C—natural rubber could be highly swollen while restricting the chlorobutyl swell, but the reverse was not possible, as indicated by the swelling volumes in the trimethylpentane. As displayed in Table II, attempts to use a highly symmetrically branched hydrocarbon with a very low solubility parameter, served only to reduce both the swelling of natural rubber and chlorobutyl. (Neopentane is a gas above 10°C and a solid below — 20°C). Therefore, for this report the use of differential solvents in the study of interfacial bonding in blends was limited to systems of Cl-butyl and cw-polybutadiene or SBR. 

This approach to estimating solubilities and diffusion rates has not been applied to other classes of solutes, even though the solubility parameters can be easily estimated by group contribution methods and AHf and T can be determined by differential scanning calorimetry. 

The behaviour of the perfluorinated phases as discussed above illustrates the fact that the solubility parameter model, despite its charms, may only be used as a crude approximation. The occurrence of specific deviations from the general rule may at least be made plausible by differentiating between different kinds of molecular interactions, and by introducing so-called partial solubility parameters or partial polarities [303,312] (see also section 2.3.1). However, such an extension greatly increases the complexity of the model, without increasing its predictive value correspondingly. 

Displacement of glass transition temperatures of individual phases in a mixture of polymers determined by differential scanning calorimetry. This may be indicative of their limited interaction, despite the significant difference of the solubility parameters. 

The solubility parameter values of the polyesterimide (10.76 [182]), the novolae (10.7), and the resole (11.1), imply that these polymers should be thermodynamieally miseible beeause the differenee of these parameters between the polyesterimide and a phenolie resin is a small number. The theoretieally predieted miseibility of polyesterimide with novolae or resole appears to be bom out experimentally sinee differential thermal analysis shows a single glass transition temperature for all the blends, and seanning eleetron... 

Where the solubility parameter rule is in error is for natural rubber and polybutadiene. The differential in solubility parameters is around 0.6 but the two polymers are immiscible. Polybutadiene grade IISRP 1207 and an oil extended polymer such as IISRP 1712 have a differential of less than 0.1 and in this case the two elastomers are nearly fully miscible between the lower and upper critical solution temperatures. The blended elastomers mechanical properties then become a function of the filler type, distribution, vulcanization system, and any processing aids present. 

Solubility parameter estimation and differential scanning calorimetry (DSC) help assess the drugipolymer miscibility and determine drug loading. 

Pilin et al. (2006) extended the study on the effect of food grade plasticizer in PLA, as listed in Table 3.2. The solubility parameter 6 and interaction parameter x were used to evaluate the extent of compatibility of the PLA and the plasticizer. When the 6 of the components are close to each other or blend with X < 0-5, it can be considered that the mixture is miscible and no phase separation is expected. The differential scanning calorimetry results as shown in Table 3.3 indicate that the... 

In series of publications [25,27,29,35-40] several methods were used for eharaeterization of the microphase structure of the semi-IPNs studied. Small-angle X-ray seattering (SAXS), differential scanning calorimetry (DSC) [27, 35-37], dynamic mechanical thermal analysis (DMTA) [27, 30-32], dielectric relaxation spectroseopy (DRS), and thermally stimulated depolarization currents (TSDC) [25, 39, 40] measurements have shown that pure PCN is characterized by a typical homogeneous structure, but for segmented LPU the microphase separation on the level of hard and soft domains due to their thermodynamic immiscibUity was denoted. As for semi-IPNs, the destruction of the microphase separated morphology of LPU was observed and the microphase separation between PCN and LPU phases, expected from the difference of solubility parameters, was not found. 

In a paper by Bradford and Thodos (1966), 4 of the 16 references are to Hildebrand et ai, one to Chao and Seader, one to Prausnitz and Edmister, one to Frost and Kalkwarf, and the remainder to Thodos and his colleagues. The solubility parameter 5 is a temperature-dependent quantity, and when we are dealing with the difference between the 5a and 5s values, we are presented with differential effects. It was pointed out by the authors that the 5 value at 25°C has been assumed to be the same for other temperatures for utility purposes and represents a fictitious or empirical value. Data for n-hydrocarbons from methane to dodecane and for ethylene, propylene, 1,3-butadiene, cyclohexane, and benzene were given. 

The complexation of Pu(IV) with carbonate ions is investigated by solubility measurements of 238Pu02 in neutral to alkaline solutions containing sodium carbonate and bicarbonate. The total concentration of carbonate ions and pH are varied at the constant ionic strength (I = 1.0), in which the initial pH values are adjusted by altering the ratio of carbonate to bicarbonate ions. The oxidation state of dissolved species in equilibrium solutions are determined by absorption spectrophotometry and differential pulse polarography. The most stable oxidation state of Pu in carbonate solutions is found to be Pu(IV), which is present as hydroxocarbonate or carbonate species. The formation constants of these complexes are calculated on the basis of solubility data which are determined to be a function of two variable parameters the carbonate concentration and pH. The hydrolysis reactions of Pu(IV) in the present experimental system assessed by using the literature data are taken into account for calculation of the carbonate complexation. 

The present study is conducted under consideration of thus mentioned difficulties. The solubility measurement is applied to the present investigation, selecting the pH range 6 v 12 in which the carbonate concentration can be maintained greater than 5xl0 6 M/l. The carbonate concentration and pH of experimental solutions, both being mutually dependent in a given solution, are taken into account as two variable parameters in the present experiment and hence the final evaluation of formation constants is based on three dimensional functions. For calculation purpose, the hydrolysis constants of Pu(IV) are taken from the literature (18). In order to differentiate the influence of hydrolysis reactions on the carbonate complexation so far as possible, the calculation is based on the solubilities from solutions of carbonate concentration > 10-1 M/l and pH > 8. 

The value of Cs is the most critical parameter in determining the overall release rate from a given osmotic system. Indeed, its value will determine whether or not it is feasible to utilize an osmotic system to deliver a particular drug for a specified duration. The maximum release rate achievable is likely that seen with KC1. The relevant values for the parameters in Eq. (6) for OROS [10] are as follows A = 2.2 cm2, h = 0.025 cm, LpO = 2.8 X 10 6 cm2/(atm hr), Us = 245 atm, and Cs = 330 mg/mL. This translates to about 20 mg/hr or about 250 mg over a 24 hr period. This is for a highly water soluble drug with a high osmotic pressure differential. For drugs of moderate solubility—for example,... 

In summary, a number of parameters of outgrowth initiation, elongation, branching and cessation combine to generate axonal or dendritic geometry. These components can be modulated in vitro by a variety of soluble and substrate-bound factors, suggesting that, in vivo, control over morphological differentiation is multifactorial. 

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