Absorption isotherms polymers

The usual way of representing polymer adsorption onto clay surfaces is to plot an isotherm showing the amount of polymer adsorbed in grams per gram of clay as a function of the equilibrium concentration of polymer in units of g cm 3. We have to be careful in comparing our results with standard isotherms because we are measuring the total amount of PEO inside the clay. This absorbed mass is not necessarily adsorbed onto the clay surfaces, but may be located in the interlayer solution. To reflect this difference, we have used the unusual nomenclature absorption isotherm rather than the usual adsorption isotherm in the presentation of the data. 

Brace et al. [92] investigated polymer/water interactions using SAW devices coated with either polyimide or cellulose acetate butyrate (CAB). In this study thermodynamic parameters were evaluated from the absorption isotherms, and transient responses to step changes in concentration were monitored. The transient responses observed were not consistent with Fickian diffusion, but could be described using a generalized relaxation equation containing two additive terms. Results under various conditions indicated that relaxation in the polymer system is much slower than diffusion of water. 

Fig. 10. Total number of panicles after styrene emulsion polymerizations as a concentration of free SD in the water phase before polymerization, initiators K,S20b (PPS) and dibenzoyl peroxide (BP). Other experimental conditions as in Fig. 9. Theoretical curves A-E calculated from the absorption isotherm, Eq. (107-108). Curves A-B, a = 4 g/dm . curves C-E, a = OA g/dm. (Reprinted by permission of J. Polym. Sci.)...

Another adsorption stndy was conducted for the two new chitosan derivatives that have been prepared from the reaction of cinnamoyl chloride (ChitoCin) and cinnamoyl isothiocyanate (ChitoThioCin) with chitosan. The modified chitosans were characterized to confirm their stractures. The metal uptake capacity of the two polymers was measured at different pH valnes as well as under competitive and non-competitive conditions. At pH 5.6, the (ChitoCin and ChitoThioCin) polymers exhibited higher capacity for Cu(II) (0.461-0.572 imnol/g) than the other metal ions nsed the capacities of the other metal ions are Fe(Ill) (0.235-0.341 imnol/g), Cr(III) (0.078-0.099 mmol/g), Co(II) (0.046-0.057 imnol/g) and Ni(ll) (0.041-0.053 imnol/g). Two absorption isotherms were examined for the absorption of metal cations with these two modified chitosan and it was fonnd that the adsorption mechanism fits the Langmuir isotherm better than the Frenndhch one. 

Evaluation of moisture absorptivity can be made by measuring the moisture absorbed against the relative vapor pressure, namely, moisture absorption isotherms. The moisture absorption isotherms of a polyacrylate-type superabsorbent polymer are shown in Fig. 3. 

Assuming a linear Henry-like absorption isotherm, for polymer membranes the permeability P. (molmm h Pa ) can be expressed as product of solubility S (mol Pa" m" ) and diffusivity D (m h ). For pore membranes, however, this simple relation is not valid because the limited pore volume the amount adsorbed does not increase linearly with the pressure (Henry-like behavior only for permanent gases at relative high temperatures) and the adsorption isotherm is usually curved (Langmuir-like). 

Langmuir type absorption isotherms are observed when only a limited number of dye sites are available inside the fibre. In this case the concentration of (fye in the polymer reaches a maximum limiting level as the concentration of dye in the dyebath is increased. This behaviour is typical of acid levelling dyes on wool and silk. " ... 

In synthetic fibers the number of ionic groups or dye sites is relatively small, and may have been introduced dehberately to make the base polymer dyeable. The restrictions on dye absorption are therefore very great the dye molecule must find an available specific site from among the limited number of sites in the fiber. This situation follows a Langmuir isotherm, where the reciprocal of dye in fiber 1 /DF is direcdy proportional to the reciprocal of dye in the dyebath 1 /HT. A plot of 1/against 1/H therefore gives a straight line. 

The absorption of vinyl chloride(VC) on surface-treated light-grade and nanoscale calcium carbonate was shown to obey the Langmuir isothermal equation in VC/calcium carbonate/water system. The absorption of VC on calcium carbonate was shown to increase with increase of the partial pressure of VC up to the saturation absorption and the absorption of VC on nanoscale calcium carbonate was greater than that of light-grade calcium carbonate at the same temp, and partial pressure of VC. The presence of calcium carbonate in VC suspension polymerisation system was found to influence the pressure/temp./ conversion(PTC) relationship of the reaction system. Based on the absorption of VC on calcium carbonate and VC distribution in vapour, water and polymer phases, a modified model to represent the PTC relationship of VC suspension polymerisation in the presence of calcium carbonate was proposed. 10 refs. 

For polymeric membranes filled with absorptive fillers, sorption in the filler occurs in accordance with the Langmuir adsorption isotherm while Henry s law governs that in the polymer matrix. This kind of sorption isotherm is designated as type-II isotherm. 

Compression molded samples of poly(vinyl acetate) also showed a mild temperature dependence in equilibrium absorption. The amount of water went from 4% at 23°C to 6% at 70°C. This polymer was the only one we tested that formed clustered water while stored Isothermally at room temperature. This clustering was obtained after 17h. as confimed by DSC and could be seen visually as a whitening of the polymer. 

Palaniappan and Narayana [168] studied the thermal stabilities of chemically prepared polyanilines in different acid media by isothermal heat treatments at 150°, 200°, 275° and 375°C in combination with EPR, electronic absorption and infra-red spectroscopic measurements. They also observed a three-step weight loss, the first step is attributed to the loss of water from the polymer salt starting at 110°C, the second, minor step is due to volatilization of acid ranging from 110°C to 275°C, and the polymer undergoes thermo-oxidative degradation of the polymer backbone in the third step above 275°C. The thermal stability was observed to be dependent on the doping counter-ion and no structural... 

An intriguing application of these Pd nanoparticles in basic research concerns the question of the solubility of H2 in such materials relative to bulk palladium [47]. Hydrogen concentration-pressure isotherms of surfactant-stabilized palladium clusters and polymer-embedded palladium clusters with diameters of 2, 3 and 5 nm were measured with the gas sorption method at room temperature. The results show that, compared to bulk palladium, the hydrogen solubility in the a-phase of the clusters is enhanced fivefold to tenfold, and the miscibility gap is narrowed. Both results can be explained by assuming that hydrogen occupies the subsurface sites of the palladium clusters. The Pd-H isotherms of all clusters show the existence of hysteresis, even though the formation of misfit dislocations is unfavorable in small clusters. Compared to surfactant-stabilized clusters, the polymer-embedded clusters show slow absorption and desorption kinetics. Moreover, evidence for a cubic-to-icosahedral transition of quasi-free Pd-H clusters by the hydrogen content was reported [47c]. 

In addition, since the SAW Is sensitive to minute perturbations occurring in thin films which are In Intimate contact with the surface, SAW devices can be used to monitor physical and chemical processes occurring In these overlayers. Based on this effect, SAW devices have recently found applications In the characterization of the properties of thin films (8-10). In this paper, we report on the utility of SAW devices to characterize (1) the surface area and pore size distribution of porous thin films based on Nj adsorption Isotherms and (2) diffusion coefficients (D) for thin polymer films based on absorption transients (l.e., mass absorbed as a function of time) as indicated by SAW velocity transients (l.e., SAW velocity... 

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