Primary surface properties

In discussions of the surface properties of solids having a large specific surface, it is convenient to distinguish between the external and the internal surface. The walls of pores such as those denoted by heavy lines in Fig. 1.8 and 1.11 clearly comprise an internal surface and equally obviously the surface indicated by lightly drawn lines is external in nature. In many cases, however, the distinction is not so clear, for the surfaces of the primary particles themselves suffer from imperfections in the forms of cracks and fissures those that penetrate deeply into the interior will contribute to the internal surface, whereas the superficial cracks and indentations will make up part of the external surface. The line of demarcation between the two kinds of surface necessarily has to be drawn in an arbitrary way, but the external surface may perhaps be taken to include all the prominences and all of those cracks which are wider than they are deep.,The internal surface will... 

Having said this, it was felt therefore that there is a need for a book addressing analysis and characterisation of polymers from the point of view of what we wish to call the primary analytical question. Many excellent textbooks and reference works exist which address one or more individual analytical techniques, see, for example, references [1-10]. These books form the basis of the knowledge of the technique expert. They also contain many excellent and varied examples on successful applications of analytical techniques to polymer analysis and characterisation. There are also books which address the multitude of analytical techniques applied in polymer analysis, see, for example, references [11-24], However, a synthetic chemist may wish to know the constitution of his/her polymer chain, a material scientist may want to find out the reasons why a fabricated sample had failed. What technique is best or optimal to study chain constitution will depend on the situation. Polymer failure may result from morphological features, which needs to be avoided, a contaminant, a surface property degradation, etc. When a sample has been processed, e.g., a film blown, molecular orientation may be the key parameter to be studied. A formulation scientist may wish to know why an additive from a different supplier performs differently. It is from such points of view that polymer analysis and characterisation is addressed in this book. 

In polymer blends, or mixtures, the primary question is whether one of the components segregates preferentially to the surface. One of the reasons this is of interest is because most commercial polymers contain more than one component and a surface segregation of one of the components from a miscible mixture during, for example, extrusion of the material, could affect the surface finish of the product. Because polymer blends are generally dense liquids, from the previous discussion it is clear that packing effects are expected to dominate the surface properties. 

The respirable powders of a DPI cannot be characterized adequately by single-particle studies alone bulk properties must also be assessed since they contribute to ease of manufacture and affect system performance. Primary bulk properties include particle size, particle size distribution, bulk density, and surface area. These properties, along with particle electrostatics, shape, surface morphology, etc., affect secondary bulk-powder characteristics such as powder fiow, handling, consolidation, and dispersibility. 

In all above mentioned applications, the surface properties of group IIIA elements based solids are of primary importance in governing the thermodynamics of the adsorption, reaction, and desorption steps, which represent the core of a catalytic process. The method often used to clarify the mechanism of catalytic action is to search for correlations between the catalyst activity and selectivity and some other properties of its surface as, for instance, surface composition and surface acidity and basicity [58-60]. Also, since contact catalysis involves the adsorption of at least one of the reactants as a step of the reaction mechanism, the correlation of quantities related to the reactant chemisorption with the catalytic activity is necessary. The magnitude of the bonds between reactants and catalysts is obviously a relevant parameter. It has been quantitatively confirmed that only a fraction of the surface sites is active during catalysis, the more reactive sites being inhibited by strongly adsorbed species and the less reactive sites not allowing the formation of active species [61]. 

Adsorption influences all phenomena depending on surface properties, since it constitutes the primary step for every catalytic reaction involving solid catalysts. According to the relationship ... 

Moreover, both river induced up-welling and river discharge of nutrients create a fertile environment which enhances the primary production of organic matter in off-shore direction of estuaries. It can be predicted from these observations that heterogeneous reactions between dissolved and both mineral phase and biota will be predominant in estuaries and coastal zones. These reactions will primarily affect those elements and compounds which are located at the particulate surface. The determination of surface properties of particles appear to be an important key to understand the interactions of trace elements and organic compounds between particulate and dissolved phases in estuarine and coastal systems. 

Another interesting modification of glass surfaces was introduced by Beier and Hoheisel.23 They synthesized a flexible, dendritic linker system that enables covalent immobilization of oligonucleotides and PNAs with high loading capacity in a controlled manner. This method facilitates the modulation of surface properties such as hydrophobicity and charge. The synthesis of the linker system involves two consecutive reactions an acylation of surface-bound amine groups with acid chloride (4-nitrophenyl-chloroformate or acryloylchloride) and subsequent reaction with an amine. A bis-amine results in a linker system, while a polyamine produces a dendritic structure (Fig. 14.3). Because polyamines possess primary and secondary amine... 

The advent of the atomic force microscope has allowed surface properties at nearly molecular length scales to be measured directly for the first time. Recently, a method has been proposed whereby a small ( 3.5 /nn) particle is attached to the cantilever tip of the commercially available, Nanoscope II AFM [67,68]. The particles are attached with an epoxy resin. When the cantilever tip is placed close to a planar surface, the AFM measures directly the interaction force between the particle and the surface. A primary difference between this technique and the surface forces apparatus (SFA) is the size of the substrates, since the SFA generally requires smooth surfaces approximately 2 cm in diameter. Other differences are discussed by Ducker et al. [68]. For our purposes, it suffices to note that the AFM method explicitly incorporates the particle-wall geometry that is the focus of this chapter. 

As an extension of that work we have investigated the surface properties of goethite (aFeOOH). The primary concerns of this work are to evaluate the effect of the major ions of seawater on the titratable charge of aFeOOH and to quantitatively evaluate the capacity of the solid for these ions. 

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