Differentiated surface group

The latexes were cleaned by ion exchange and serum replacement, and the number and type of surface groups were determined by conductometric titration. The molecular weight distributions of the polymers were determined by gel permeation chromatography. The stability of the latexes to added electrolyte was determined by spectrophotometry. The compositional distribution was determined by dynamic mechanical spectroscopy (Rheovibron) and differential scanning calorimetry, and the sequence distribution by C13 nuclear magnetic resonance. 

The film diffusion process assumes that reactive surface groups are exposed directly to the aqueous-solution phase and that the transport barrier to adsorption involves only the healing of a uniform concentration gradient across a quiescent adsorbent surface boundary layer. If instead the adsorbent exhibits significant microporosity at its periphery, such that aqueous solution can effectively enter and adsorptives must therefore traverse sinuous microgrottos in order to reach reactive adsorbent surface sites, then the transport control of adsorption involves intraparticle diffusion.3538 A simple mathematical description of this process based on the Fick rate law can be developed by generalizing Eq. 4.62 to the partial differential expression36... 

Chart 4.1 shows stearic acid, a molecule in which 16 CH2 groups form a long hydrophobic chain. The other end of the molecule terminates in a hydrophilic carboxylic acid group. When dissolved in a suitable solvent and spread on the surface of water, molecules may be compressed with the aid of a barrier. Figure 4.1 shows a plot of the surface pressure (differential surface tension) versus area occupied per molecule for stearic acid. The monolayer undergoes a number of phase transformations during compression the well-defined sequence can be viewed as the two-dimensional analogue of the classical transitions observed with pressure-volume isotherms. 

An interface may acquire an electrical charge by one or more of several mechanisms, the most common of which include (1) preferential (or differential) solution of surface ions, (2) direct ionization of surface groups, (3) substi-... 

FIGURE 5.1. The principle sources of surface charge in solids include (a) differential ion solubility phenomena, (h) direct ionization of surface groups, (c) isomorphous substitution of ions from solution, and (d) speciflc-ion adsorption from the solution phase (e) anisotropic crystal lattice structures. 

For typical aqueous colloidal dispersions, the particles may carry some charges most likely due to the preferential (or differential) dissolution of particle surface ions, direct ionization of particle surface groups, substitution of particle surface ions, specific adsorption of ions, and particle surface charges originating from specific crystal structures. 

Another fascinating area of dendrimer applications is based on their high surface functionality. No other class of synthetic or natural compounds contains so many reactive terminal groups per molecule as do the dendrimers. This provides major directions for possible exploitation. First, dendrimers can be modified in various ways with reagents of small molecular weight. It is thus possible to produce dendrimers with so-called ejt -modified or differentiated surfaces. For example, attachment of catalytic or biological receptor sites suggests many possible applications. Furthermore, the dendrimer interiors may be modified in many yet specific ways. Interior differentiated dendrimers with different combinations... 

Figure 10.11 Sources of surface charge in colloids, (a) Differential ion solubility (b) direct ionization of surface groups (c) isomorphous substitution (d) specific ion adsorption and (e) anisotropic crystals. Adapted from Myers (1999), with permission from John Wiley Sons, Ltd...

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