Adsorbent self-potentials

Adsorption Potentials, Adsorbent Self-Potentials, and Thermodynamic Equilibria... 

The final contribution, the self-potential term Ogp, is the sum of all the above iateractions of adsorbed molecules with each other. 

In Figure 5, the heat of adsorption of CO2 increases slightly at the higher adsorbate loadings. This increase is due to the increasing self-potential contribution at the higher loadings. 

If we wish to study die adsorbent-adsorbate interactions we must undertake adsorption calorimetry or analysis of the isotherm data at very low surface coverage. It is only under these conditions that we can eliminate, or at least minimize, the adsorbate-adsorbate interactions. At higher coverage, an additional (self-potential) term, Em, must be added to E0 to allow for the latter interactions. 

B°d and C2D, have been evaluated using the Lennard-Jones 6-12 interatomic potential and for argon using the exp-six potential to describe adsorbate self-interactions. 

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. 

Modern theories of electronic structure at a metal surface, which have proved their accuracy for bare metal surfaces, have now been applied to the calculation of electron density profiles in the presence of adsorbed species or other external sources of potential. The spillover of the negative (electronic) charge density from the positive (ionic) background and the overlap of the former with the electrolyte are the crucial effects. Self-consistent calculations, in which the electronic kinetic energy is correctly taken into account, may have to replace the simpler density-functional treatments which have been used most often. The situation for liquid metals, for which the density profile for the positive (ionic) charge density is required, is not as satisfactory as for solid metals, for which the crystal structure is known. 

J. M. Tour, L. Jones II, D. L. Pearson, J. S. Lamba, T. P. Bur-gin, G. W. Whitesides, D. L Allara, A. N. Parikh, S. Atre, Self-Assembled Monolayers and Multilayers of Conjugated Thiols, a,co-Dithiols, and Thioacetyl-Containing Adsorbates. Understanding Attachments Between Potential Molecular Wires and Gold Surfaces, J. Am Chem Soc. 1995,112 9529-9534. 

In situ STM has been applied [326] to study the potential-induced self-organi-zation of a-cyclodextrin on Au(lll) surfaces in NaCl04 solutions. The adsorbed molecules formed an ordered array of a cylindrical structure in the potential range 0.20 to —0.15 V (versus SCE), while they were desorbed at potentials lower than -0.40 V. 

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