Role of acid-base interactions

For the sake of completeness, it is worthwhile to briefly discuss role of acid-base interactions in adhesion. In this context, the term acid refers to a Lewis acid (an electron acceptor) and a Lewis base (electron donor), rather than the more conventional acid and base definitions. The role of acid-base interactions in adhesion is discussed in detail by Lee [105]. 

Basic Mechanisms of Adhesion Acid-Base Interactions. The understanding of polymer adhesion has been greatly advanced in recent years by the recognition of the central role of acid-base interactions. The concept of an acid was broadened by G. N. Lewis to include those atoms, molecules, or ions in which at least one atom has a vacant orbital into which a pair of electrons can be accepted. Similarly, a base is regarded as an entity which possesses a pair of electrons which are not already Involved in a covalent bond. The products of acid-base interactions have been called coordination compounds, adducts, acid-base complexes, and other such names. The concept that... 

Although Eq. 11 tries to take into account the effect of polar interactions, the role of acid/base interactions in adhesion became clear and theories describing them have been more and more accepted [35]. The boimdary case of such interactions is the formation of covalent bonds between the surfaces. Such interactions cannot be described by Eq. 11. As a consequence Fowkes [36] suggested that the reversible work of adhesion should be defined as ... 

J.C. Berg, Role of acid-base interactions in wetting and related phenomena, in J.C. Berg (Ed.), Wettability. Surfactant Science Series 49, Marcel Dekker, New York, 1993, pp. 75-148. 

The aim of the present contribution is to review the role of acid-base interactions in adsorption, wetting, and adhesion, and the methodologies and techniques to characterize the acid-base properties of materials. Examples have been selected from the authors research work and from a survey of the literature. This chapter is organized into the following three sections definition, properties, and strength of acid-base interactions theory of acid-base interactions in adhesion and experimental assessment of acid-base properties of polymers and other materials. 

Most of the acid-base concepts, developed for solution chemistry, are applied to solid acids and bases. The present lectures, however, concern the acid-base catalytic properties of zeolites and their modification. Consequently, for clarity, attention is focussed on catalytic sites which results in somewhat restrictive definitions of acid-base interactions. In a comprehensive picture of zeolite catalysis several features other than the nature of particular sites can strongly influence overall activity and selectivity. These other features (2f) which include the wider implications of sorbate-sorbent interactions, both locally and globally, and the role of diffusion, are not considered here. 

It is important to emphasize that spectroscopic evidence shows that water transforms the Lewis acid sites of sulfated zirconia into Bronsted acid sites [80]. At the same time, water promotes isomerization reactions over sulfated zirconia for a moderate extent of catalyst dehydration. Similarities were reported between the effect of rehydration on the isomerization activity of sulfated zirconia [81] and on that of other oxide catalysts [49] that are consistent with the role of surface donor sites in hydrocarbon isomerization reactions. However, when spectroscopic methods using basic probes were used to compare sulfated zirconia and zeolites in terms of the strength of their acid sites, the results were inconsistent with all catalytic data. These findings illustrate the danger of comparing the acidity of catalyst systems that differ in structure and composition, such as zeolites and sulfated zirconia in these systems the "catalytic" and the "physicochemical" scales for the strength of acid-base interaction may contain significantly different parameters. 

During previous studies, the role of acid/base chemistry of the pigment was not thoroughly explored. The ammonia adsorption study indicates that the surface does have some acidic characteristic towards NH3. Ammonia has a relatively low pKb value in comparison with typically amine additives for polymer systems. As such, any acidic surface on the pigment would have some interaction with the ammonia. A HALS additive may not have the same level of interaction with a pigment surface due to higher pKb values. 

Steric interactions between bulky substituents such as t-Bu, leading to larger C-E-C bond angles, obviously affect the Lewis basicity caused by the increased -character of the electron lone pair. However, the strength of the Lewis acid-base interaction within an adduct as expressed by its dissociation enthalpy does not necessarily reflect the Lewis acidity and basicity of the pure fragments, because steric (repulsive) interactions between the substituents bound to both central elements may play a contradictory role. In particular, adducts containing small group 13/15 elements are very sensitive to such interactions as was shown for amine-borane and -alane adducts... 

The important role of thermodynamics in complex formation, ionic medium effects, hydration, solvation, Lewis acid-base interactions, and chelation has been presented in this chapter. Knowledge of these factors are of great value in understanding solvent extraction and designing new and better extraction systems. 

The measurements have indicated a linear relation between P (or dP) and pK. The following components were used C H COOH, CH JCOOH, OH,C1COOH, CHCljCOOH, CClgCOOH, N-methylpyperidine, diethylamine, ethylamine. The majority of systems contained benzene as solvent and in two cases dioxan solution was used in order to test the stability of complexes with hydrogen bond, and to confirm the absence of their additional association. The attention was paid to the role of the so-called polar hydrogen bond in acid-base interactions. 

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