Acid-base component

In addition to the acid—base components shown in Figure 9, various organic acids are often found. Many of these acids are by-products of the atmospheric oxidation of organic matter released into the atmosphere. Of special interest are formic, acetic, oxaUc, and benzoic acids, which have been found in rainwater in concentrations occasionally exceeding a few micromoles per Hter. 

The buffer capacity is a quantitative measure of the ability of a buffer to resist a change in pH. The more concentrated the acid-base components of the buffer, the higher its buffer capacity. 

The rest of the acids in seawater with pK values in the vicinity of 8-9, silicic acid and phosphoric acid, have low and variable concentrations (1-200 pmol kg ), but they must be considered in order to have a complete representation of the acid-base components of seawater. From the acid-base plot of Fig. 4.2 one can determine which species are most involved in the exchange of protons in seawater. Any constituent for which the lines are curved in the pH range 7-9... 

Storage under both neutral and acidic conditions causes ions such as Ca +, Al +, Na+ and to be released into solution [36,40]. Like fluoride, greater amounts of all of these species are released under acidic conditions [40]. For polyacid-modified composite resins, too, storage in acidic solutions, such as lactic acid, is associated with substantial shifts in pH towards neutral [43], showing that the capability of buffering storage media is conferred by the acid-base component of the polyacid-modified composite resin. 

Formation of at least part of the polysalt matrix from the acid-base components has been shown to reduce the efficiency of the polymerization process [19]. hi a study in which the application of the dental cure lamp was delayed for 20 min following mixing of the cement, the degree of conversion was found to be substantially reduced and the overall rate of polymerization to be lower than in systems that were irradiated immediately after mixing [ 19]. It is worth noting that conversion of HEMA to polymer is never particularly efficient in these systems, and that the maximum reported conversion in this study was only about 60%, and this was for a specific material, namely Fuji II EC (Fig. 7.2). 

The original contribution of van Oss et al. (11) to this held is the determination of the acid-base component of the surface free energy in terms of two parameters Y (Lewis) acid parameter of surface free energy Y (Lewis) base parameter of surface free energy. According to these authors, one can write ... 

According to van Oss et al. s surface thennodynamic approach, these non-electrostatic forces mu.st be related to the acid-base component of the interfacial tension between materials 1 and 2. The expression for the AB term in Eq. (4.3] is ttnally (between two spheres of radius a) (13. p. 80) ... 

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.

These equations result from assuming that the total surface eneigy can be split into the sum of components associated with different types of bonding, for example dispersion plus polar y (Eqs. 14 and 15), or Lifshitz-van der Waals y plus acid-base y (Eq. 16). The y and y terms are respectively the Lewis acid and Lewis base component of surface interaction. The acid-base component... 

Another formulation is by van Oss et al. (1987). They take the acid-base components in the surface tension to be... 

However, according to Fowkes [40], the geometric-mean expression could not be applied to the acid-base component of Wa. To determine the strengths of acidic and basic sites of polymer, Fowkes suggested using spectroscopic or calorimetric methods. 

In fact, since and coefficients are expressed in terms of enthalpy units, the parameter A can be considered equal to the variation of the enthalpy for acid-base interactions (-AH h) t the fibre-matrix interface. Moreover, Fowkes and Mostafa [2] have suggested that the contribution of the polar interactions to the thermodynamic work of adhesion could be generally neglected compared to both dispersive and acid-base contributions. They have also considered that the acid-base component of the adhesion energy can be related to the variation of enthalpy corresponding to the... 

The article on Surface energy components describes how surface energies of solids and thence the work of adhesion between adhesive and substrate could be calculated from an assumption that the surface energy is composed of the sum of a dispersion and polar component (Eqn. 9 therein). Practical measurements of surface tensions of liquids and of contact angles of liquids on solids were involved. In a similar way, solid surface energies and works of adhesion can be obtained from the assumption (Eqns. 3 and 4 above) that surface energy is made up of the sum of a Lifshitz-van der Waals and an acid-base component. The term is obtained using non-polar liquids in exactly the same way as the dispersion components, y, were obtained. This article is concerned with expressions that can be used to represent acid-base interactions and which can then be used in equations such as 3 and 4 and those derived from them. 

Fowkes method of evaluation of acid-base component... 

Fowkes was one of the first people to emphasize the importance of acid-base interactions in the context of adhesion. The volume of papers collected to honour his 75 birthday provides an important source of detailed information. Fowkes has argued that the acid-base component of the work of adhesion can be related to the molar enthalpy, for the acid-base reaction by... 

Some methods of evaluating the acid-base components have been discussed under Acid-base interactions introduction and Inverse gas chromatography. Here, the method introduced by Good, Chaudhury and van Oss, which involves acid-base surface... 

The surface energy parameters are defined by Eqn. 3 for the acid-base component of the work of adhesion between phases 1 and 2 ... 

Before the acid-base component of solid surface energy can be calculated, it is necessary to assume some arbitrary relation between the parameters of surface energy for one test liquid. Good chose to take... 

There are many reactions in organic chemistry. A large number of organic reactions can be categorized as acid-base reactions, or they will have an acid-base component or are loosely categorized as Lewis acids or Lewis bases. Recognizing this relationship provides a basis for understanding many reactions. 

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