Adsorption equilibrium, copolymers

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

On the other hand, an attempt to accelerate the step of coordination of the substrate to the Cu catalyst was successful because it used the hydrophobic domain of the polymer ligand156 That was the oxidation catalyzed by polymer-Cu complexes in a dilute aqueous solution of phenol, which occurred slowly. The substrate was concentrated in the domain of the polymer catalyst and was effectively catalyzed by Cu in the domain. A relationship was found to exist between the equilibrium constant (Ka) for the adsorption of phenol on the polymer ligand and the catalytic activity (V) of the polymer-ligand-Cu complex for various polymer ligands K a = 0.21 1/mol and V = 1(T6 mol/1 min for QPVP, K a = 26 and V = 1(T4 for PVP, K a = 52 and V = 10-4 for the copolymer of styrene and 4-vinylpyridine (PSP) (styrene content 20%), and K a = 109 and V = 10-3 for PSP (styrene content 40%). The V value was proportional to the Ka value, and both Ka and V increased with the hydrophobicity of the polymer ligand. The oxidation rate catalyzed by the polymer-Cu complex in aqueous solutions depended on the adsorption capacity of the polymer domain. 

Maximum Cr(VI) removal has been observed at pH 1.0 and Cr(Vl) removal by CM-g-PMMA decreases with the variation of pH 1.0-10.0 at 100 mg/L initial Cr(VI) concentration. Total chromium in the equilibrium solution (after the adsorption was detected by the Diphenylcarbazide (DPC) method) indicates that some Cr(Vl) converts to Cr(III) during the adsorption and remains in the equilibrium solution along with the remaining Cr(Vl). Krishnani et al. [96] have made a similar observation for the adsorption of chromium on Ugnocellulosic substrates. At a low pH, lignin reportedly reduces hexavalent chromium into Cr(III), which is subsequently adsorbed contrary to the adsorption by CM-g-PMMA where the copolymer adsorbed chromium mainly as Cr(VI), while Cr(IlI), that is generated from the reduction of the Cr(Vl) at acidic pH still remains in solution. However, at pH 10 a negligible conversion of Cr (VI) to Cr(III) is reported. 

Finally, it should be noted that porous methyl methacrylate/DVB copolymers that exhibit some features of hypercrosslinked structures, but are directly wetted with water, retain no more than 50—60 mg/g phenol (at 250mg/L equilibrium concentration), which is many times less than the adsorption capacity of MN-200 at the same equhibrium phenol concentration [66]. 

The plasticizing effect of water on the Tg of polyacrylamide and its copolymer with acrylic acid is greater than that of most other polymers. The comparison is illustrated in Table 3, where ATg represents the suppression of the glass transition by the indicated amount of water. It is also interesting to note that polyacrylamide in its glassy bulk form contains a much higher equilibrium amount of water at room temperature conditions, since a glass usually has fewer adsorption sites than its crystalline counterpart. 

Tiberg, F., Malmsten, M., Linse, P. and Lindman, B., Kinetic and equilibrium aspects of block copolymer adsorption, Langmuir, 1, 2723-2730 (1991). 

We discuss variation of surface tension of blends and random copolymers with composition in terms of a generalized Langmuir adsorption isotherm. The partition coefficient in surface and bulk might be expressed by equilibrium of occupancy of the surface region by segments of types 1 and 2 as follows ... 

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