Interfacial acid-base function

The interfacial acid-base function theory was put forward the first time in 1962 by Fowks. This theory holds that the filler and polymer matrix of a composite material can be treated as a generalized acid or alkali. When the surfaces of the filler and polymer matrix have different acids or alkalis, they are easy to combine. The greater their difference in pH, the more easily they will combine. When the surfaces of the filler and polymer matrix have the same acid or alkali, the surface of the filler should be modified to change its pH value. The different surface pH values are beneficial to improve the bonding strength between the reinforced material and polymer matrix and improve the performance of filled plastics. 

With the above In mind, a° can be determined by colloid titrations, as described In sec. I.5.6e. To review the experimental ins and outs, consider (insoluble) oxides, subjected to potentiometric acid-base colloid titration. Basically the procedure Is that o° (at say pH , and c ) Is related to a° at pH" and the same Salt adding acid or base. The titration Is carried out in an electrochemical cell In such a way that not only pH" is obtainable, but also the part of the acid (base) that is not adsorbed and hence remains In solution. Material balance then relates the total amount (of acid minus base) adsorbed, a°A (where A is the interfacial area) at pH" to that at pH. By repeating this procedure a complete relative isotherm a°A as a function of pH Is obtainable. We call such a curve "relative" because it Is generally not known what <7° was In the starting position. 

Previous chapters have discussed comprehensively protein and DNA-based function and bioelectrochemical systems. Single- and multi-functional monolayers of proteins, DNA-based molecules, and enzymes, and of monolayers of amino acids and DNA-bases as their building blocks testify towards bioelectrochemical control at the nanoscale and sometimes singlemolecule levels. In these respects interfacial bioelectrochemistiy is undergoing a process similar to what has been the case in physical... 

Bell and SomorjaP proposed the concept of the interfacial active site involving the coupling of a metal center and a Lewis acid/base site to form adjacent centers. The latter sites are formed either in the oxide support or the added promoter. It was suggested that these active sites might be crucial in the conversion of the molecules with polar functional groups (such as CN, CS and NH). Close analysis of data presented in the above references " " shows that in all cases the character of interactions strongly resembles the presence of metal ion-metal nanocluster ensemble sites. 

Figure 7 Plots of potential energy of interaction as a function of the distance H between the surfaces of identical spherical particles with radius a = I pm. Top clasHcal DLVO theory. Bottom Exterxled DLVO approach. The following values were used for the calculations = 30 mV 1 1 electrolyte concentration 10 - M Mamaker constant = 2 X lO J acid-base component of the solid-liquid interfacial toiuon — 10 mJ/ni See text for details.

Specific interactions in binary blends of ethylene-vinyl acetate copolymer with various low molecular weight terpene-phenol tackifying resins (TPR) were systematically investigated, as a function of the composition of the blend and of the electron acceptor ability of the resin, by using attenuated total reflection FTIR spectroscopy. Molecular acid-base were evidenced between TPR hydroxyl groups and EVA carbonyl groups. Quantitative information on the fraction of acid-base bonded entities, the enthalpy and equilibrium constant of pair formation were obtained. A crystalline transition of the EVA copolymer was observed and discussed in terms of enthalpy and entropy considerations based on FTIR and calorimetric DSC investigations. Fundamental results are then summarised to predict the interfacial reactivity of such polymer blends towards acid or basic substrates. 16 refs. 

Surface chemistry (i.e., the number and the type of surface acid/base sites or grafted functionalities of different hydrophilicity) influences the hydrogen bond network structure in a relatively thick layer of interfacial water (3-10 nm or larger). Partial hydrophobization of a silica surface (e.g., by grafting of trimethylsilyl, TMS groups) affects the amounts of unfrozen... 

One method which has been used to characterize interfacial forces is based on specific donor-acceptor (acid-base) interactions between adhesive and substrate molecules. Here, functional groups in each material are assigned an acid or base strength, which then can be used to calculate expected bond strengths. Further discussion of this approach is delayed to a later section. 

The knowledge of both the strength of acid-base interaction, i.e., the enthalpy of interaction, and the number of moles of acid or base functional groups interacting per unit area across the interface allow the determination of the reversible acid-base work of adhesion. In the particular case of adhesion between solids, it rapidly appears (Israelachvili 1991) that the contribution of the polar interactions (Keesom, Debye) to the thermodynamic work of adhesion could be neglected compared with both dispersive and acid-base contributions as experimentally confirmed (Fowkes et al. 1984). The acid-base component of the work of adhesion can be related to the variation of enthalpy per mole of acid-base interfacial adducts interaction, follows ... 

In fuel cells, a membrane serves as an ionic conducting electrolyte, an interfacial environment for electrode reactions, an effective reactant separator, and a support for catalysts/electrodes. It is therefore essential that such a membrane exhibits, among other properties, optimized gas permeability. For this purpose, dense FBI membranes are prepared by solution casting. FBI dissolves in strong acids, bases, and a few organic solvents and membranes can be cast from their solutions accordingly. As the membranes are used in an acid-functionalized form to achieve proton conductivities. 

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