Penetrant solubility

The parameters needed for these predictions of isotherms, X and are readily accessible The value of X can te estimated from a single measurement of the equilibrium penetrant solubility at a known high activity, assuming applicability of the Flory-Huggins equation. The plasticizing effectiveness, C TX may be estimated either experimentally or theoretically, as discussed in the next section. 

In the following sections the different thermodynamic models presented in the preceding text will be applied in the calculation of the penetrant solubility for both the cases of rubbery and glassy polymeric systems. Binary as well as ternary systems will be considered to show the ability of the models to represent observed isotherms in rubbers as well as in glasses, based on their equilibrium versions and non-equilibrium extensions, respectively. 

An important aspect for the understanding of the transport properties of such polymers is the study of their structure, down to the molecular level. Especially in the absence of swelling phenomena, when the penetrant solubility in the perlluoropolymer matrix is relatively low, as is usually the case for non-fluorinated hydrocarbon vapours, the main factor which determines the transport properties is the Free Volume (FV). Knowledge of the free volume is therefore often of great importance for the understanding of the transport properties of dense membrane materials. 

If the simple solution-diffusion model applies, the penetrant solubility can be calculated from P and D from the simple equation ... 

Bioisosteric replacement is often considered when tbe aims are to maintain enzyme potency wbUe optimizing additional properties, sudi as cellular penetration, solubility, metabolism, toxidty, and so on. This prindple is often referred to as multiobjective optimization (MOOP) or multiparameter optimization (MPO) [12]. There are many ways in which one can address multiple objectives, but it is important to understand the landscape of the trade-off surface between each of the important... 

Solubility increase mechanism depends on the interaction between the penetrants and nanofillers. The functional groups of nanofillers such as hydroxyl when occur on the surface of the inorganic nanofiller phase in rubber composites may interact with polar gases such as SO2. This condition can increase the penetrant solubility in the nanocomposite rubbers and, in turn, increase the gas permeability. The solubility increase mechanism model due to permeation coefficient parameter of gas, P is described using the Arrhenius equation ... 

Figure 2. Penetrant solubility in polysulfone and poly(dimethylsiloxane) at 35°C and infinite dilution. The lines through die data are the best fits of the data to Equation 4. The values of M for PDMS and PSF are l.TxlO" and 4.7x10- cm (STP)/(cm cinHg), respectively. The polysulfone data are from Ghosal et al. (77) and the authors laboratories. The poly(dimethylsiloxane) data are from Merkel etal.(31).

Gas condensability is often the most important effect in determining the relative solubility of different gases in a polymer. Consequently, equation 4 usually provides good estimates of solubility selectivity. Moreover, equation 4 indicates that while penetrant solubility will change from polymer to polymer, solubility selectivity changes little from one polymer to another, which contributes to the earlier observation that Oj and n-C4Hjo permeability, for example, varies much more from polymer to polymer than Oj/Nj and selectivity, respectively. Of course,... 

Based on the results in Figures 2 and 4, as penetrant size increases, penetrant solubility increases and diffusivity decreases. The effect of penetrant size on permeability reflects the interplay between these two factors. In soft, flexible. 

Most properties of the substituted polyacetylenes (PA), such as permeability to penetrants, solubility, and thermal stability are strongly related to the number and/or steric hindrance of die substituents 1-4). However, these properties cannot be related in a strai tforward fashion to the kind of substituents or to the mono- or doublesubstitution along the main chain. In fact, the configuration of the repeat units and, consequently, the chain conformation and packing have to be taken into account and might be responsible for the properties of Afferent polymers. For instance, it has been shown that structural differences originating from different cis/trans tactic ratio in... 

The results obtained in the previous section permit calculation of penetrant solubility in a glassy polymer as a function of temperature, penetrant fugacity and polymer density. Contrary to the situation for the equilibrium solubility calculation, the polymer density under pseudo- uilibrium conditions must be known in order to calculate the corresponding penetrant content. For pure penetrants, the comparison of model predictions with experimental isotherms is rather satisfactory for the cases in which volume dilation data are also available (i, 13),... 

In previous work (i, 13, 14) we considered the comparison between the predictions of the model and the experimental results for the solubility of pure gases and vapours in glassy polymers, and concluded that NELF is a definitely reliable model. In this work the comparison is extended to the case of solubility of mixed gases, by considering the solubility of CO2/C2H4 mixtures in PMMA reported Koros and co-workers 4,15, 76). The model correctly represents the value and the trend of the penetrants solubility when the partial pressure of the penetrants changes. The results are obtained via a completely predictive procedure the comparison is limited to the low pressure range since experimental data for the dilation of the... 

Solubility-Selective Membrane The solubility coefficient reflects how many gas molecules can be sorbed in polymer membranes. It depends on the condensability as well as the physical interactions of the penetrants with the polymer membrane. Solubility is determined by the concentration of the sorbed gas per unit polymer volume. Generally, the concentration as a function of pressure at constant temperature shows a sorption isotherm with a characteristic shape that is concave to the pressure axis. The solubihty-selectivity term in Eq. (24.3) is thermodynamic in nature and is governed by the relative polymer-penetrant interactions and the relative condensabihty of the penetrants. Solubility-selectivity terms contribute significantly to separations of condensable vapors and polar molecules. 

Diffusion has been related to the polymer fractional free volume, which is a measure of the theoretical volume of the polymer divided by the actual volume of the polymer, while the penetrant solubility depends on its condensabihty [9]. 

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