LANGMUIR SORPTION

The uptake of anionic dyes from acidified solutions by polyamides has traditionally been treated as Langmuir sorption on sites usually identified with the terminal amino-groups of the polymer75,76). It was also early realized that additional sorption can occur at sufficiently low pH, known as overdyeing 75,76). 

The data shown in Figure 8 illustrate the reduction in permeability of polycarbonate to CO2 caused by competition between isopentane and CO2 for Langmuir sorption sites (33) ... 

Table l. Selected properties and Tween 80 Langmuir sorption parameters for Ottawa 20-30 mesh sand, Ottawa F-70 sand and Wurtsmilh aquifer material. 

Figure 2.28 An illustration of the two components that contribute to gas sorption in a glassy polymer according to the dual sorption model. Henry s law sorption occurs in the equilibrium free volume portion of the polymer. Langmuir sorption occurs in the excess free volume between polymer chains that exists in glassy polymers...

For a Langmuir sorption isotherm the net sorption rate can be written... 

FIGURE 5.20 Langmuir sorption isotherm of Br2 on cotton fibers. 

FIGURE 9.4 Dependence of constants (a, b, and c present Henry constant, sorption affinity constant, and Langmuir sorption capacity respectively) of the model of dual-mode sorption of hydrocarbons by glassy polyphenylene oxides on boiling temperatures of hydrocarbons Z), is pDMePO, poly-2,6-dimethyl-l,4-phenylene oxide o is pDPhPO, poly-2,6-diphenyl-l,4-phenylene oxide is pDMePO/pDPhPO copolymer (97.5/2.5% mol) v is pDMePO/pDPhPO copolymer (75/25% mol). (From analysis of results presented in Lapkin, A.A., Roschupkina, O.P., and Ilinitch, O.M., J. Membr. Sci., 141, 223, 1998.)... 

The modeled pattern in Figure 11 shows the observed concentration trends, but, clearly, it does not match the details. Notably, the predicted As peaks arrive too early and they are too small. The column experiments of Isenbeck-Schroter (1995) and Darland and Inskeep (1997) required kinetic reactions for Freundlich or Langmuir sorption isotherms for As, but a kinetic model appears to spread out the As concentrations in Figure 11 only, and it does not shift the position of the peak to later arrival times. Therefore, other reactions might explain the discrepancy. 

Equally disturbing is that sorption parameters (i.e., Langmuir sorption parameters) obtained from batch and thin-disk methods are different (Miller cl al., 1989). This was attributed to the fact that batch systems are closed whereas flow systems arc open so that the competitive antecedent solute species is removed, ll is apparent that much more work needs to be done on... 

Howsmon, G.J., andN.A. Peppas, "Mathematical Analysis of Transport Properties of Polymer Films for Food Packaging. VI Coupling of Moisture and Oxygen Transport Using Langmuir Sorption Isotherms", J Appl Poly Sci 1986, 31, pp 2071-2082. 

The transfer rate in the mixed side-pore model is proportional to the difference in concentration between the flowing-water and immobile-water phases. The transfer-rate constant kgA is a characteristic-rate parameter for diffusion in the immobile-water phase. Without the Freundlich sorption mechanism, this third model is the same as the dead-end pore model developed by Coats and Smith (19). The Freundlich sorption isotherm was included by van Genuchten and Wierenga (18) in their study, but they solved for the linear case only. Grove and Stollenwerk (20) described a similar model but included Langmuir sorption and a continuous immobile-water film phase. 

FIGURE 20.4-7 Langmuir sorption capacity C as a function of temperature for several polymer-penetrant syatems. Note diet C disappears near Tg in the same fashion as Vg — Vt does in Fig. 20.4-5.26... 

Langmuir Sorption Capacity of Glassy Polymare. J. Polym. Sci. Polym. Phys. Ed., 19, 1655 (1981). 

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