Interphase regions

The performance of a product where adhesion plays a role is determined both by its adhesive and cohesive properties. In the case of silicones, the promotion of adhesion and cohesion follows different mechanisms [37]. In this context, adhesion promotion deals with the bonding of a silicone phase to the substrate and reinforcement of the interphase region formed at the silicone-substrate interphase. The thickness and clear definition of this interphase is not well known, and in fact depends on many parameters including the surface physico-chemistry of... 

Internal surfactants, i.e., surfactants that are incorporated into the backbone of the polymer, are commonly used in PUD s. These surfactants can be augmented by external surfactants, especially anionic and nonionic surfactants, which are commonly used in emulsion polymerization. Great attention should be paid to the amount and type of surfactant used to stabilize urethane dispersions. Internal or external surfactants for one-component PUD s are usually added at the minimum levels needed to get good stability of the dispersion. Additional amounts beyond this minimum can cause problems with the end use of the PUD adhesive. At best, additional surfactant can cause moisture sensitivity problems with the PUD adhesive, due to the hydrophilic nature of the surfactant. Problems can be caused by excess (or the wrong type of) surfactants in the interphase region of the adhesive, affecting the ability to bond. 

Restrained layers—coupling agents develop a highly crosslinked interphase region with a modulus intermediate between that of the substrate and the polymer. 

The interfacial zone is by definition the region between the crystallite basal surface and the beginning of isotropy. Due to the conformationally diffuse nature of this region, quantitative contents of the interphase are most often determined by indirect measures. For example, they have been computed as a balance from one of the sum of the fractional contents of pure crystalline and amorphous regions. The analysis of the internal modes region of the Raman spectrum of polyethylene, as detailed in the previous section of this chapter, was used to quantify the content of the interphase region (ab). 

A somewhat different liquid/liquid system is found in the solvent extraction of copper. We have studied the system using heptane/water. These solvents are so immiscible that, as shown in Fig. 15, there is probably no extensive interphase region but a more sharply defined interface. We have shown that for the oxime ligand, Acorga P50 [4], written as HL, the mechanism of the reaction is as in Scheme 2 (Albery et al., 1984 Albery and Choudhery, 1988). 

The concept sounds attractive, but there is a flaw in the explanation. Assuming an equilibrium situation between the two bulk phases and the interphase, complex formation at the interfacial region requires the same complexes are formed also in the bulk phases. Consequently, in order to produce a considerable amount of the mixed species MA, xBx in the liquid-liquid boundary layer some B must be dissolved in the aqueous, as weU as some A in the organic phase. Since by definition this condition is not met, the relative amount of M present at the interphase region as MAn xBx must be negligible. However, now the metal ion will be distributed between MA in the aqueous phase and MBp in the organic layer (n and p are the... 

The influence of process variables such as the temperature, pressure of H2 and CO on the hydroformylation reaction is well recognized by all researchers. However, other aspects, such as stirring speed, the shape and size of the stirrer, relative amounts of the aqueous and organic phases, etc. are usually overlooked by people working in laboratories far from the actual chemicals production. A few papers in the open literature deal with these questions, of which perhaps the most important concerns the location of the chemical reaction. Does it takes place in the bulk phases or at the interphase region ... 

Water-soluble l,3-bis(di(hydroxyalkyl)phosphino)propane derivatives were thoroughly studied as components of Pd-catalysts for CO/ethene (or other a-olefins) copolymerization and for the terpolymerization of CO and ethene with various a-olefins in aqueous solution (Scheme 7.17) [59], The ligands with long hydroxyalkyl chains consistently gave catalysts with higher activity than sulfonated DPPP and this was even more expressed in copolymerization of CO with a-olefins other than ethene (e.g. propene or 1-hexene). Addition of anionic surfactants, such as dodecyl sulfate (potassium salt) resulted in about doubling the productivity of the CO/ethene copolymerization in a water/methanol (30/2) solvent (1.7 kg vs. 0.9 kg copolymer (g Pd)" h" under conditions of [59]) probably due to the concentration of the cationic Pd-catalyst at the interphase region or around the micelles which solubilize the reactants and products. Unfortunately under such conditions stable emulsions are formed which prevent the re-use... 

Thus, in this case the solution side of the interphase acquires opposite and equal charge, qX (the charge per unit area on the solution side of the interphase). At equilibrium the interphase region is neutral ... 

Low, B.Y., Gardener, S.D., Pittman, C.U. and Hackell, R.M. (1994), A micromechanical characterization of graphite fiber/epoxy composites containing a heterogeneous interphase region. Composites Sci. Technol. 52, 589-606. 

The properties of any material are dependent on the particles present and the forces operating on the particles. Since these forces are different at the frontier than the forces in the bulk, the properties of the frontier region, the interphase region, will differ from the bulk properties. Thus, the uniform properties of the electrolyte are perturbed in the interphase region by the presence of another phase. 

Fig. 6.3. A schematic diagram to illustrate that in the interphase region (indicated by shading) there generally is net dipole orientation and net, or excess, charge density.

Fig. 6.4. A schematic representation of the charging of the solution side of an interface, (a) Shading indicates excess-charge density in the interphase region, (b) An exploded view shows that the positive charge in a lamina in the interphase exceeds the negative charge and there is a net, or excess, positive-charge density in the lamina.

When charges are separated, a potential difference develops across the interface. The electrical forces that operate between the metal and the solution constitute the electrical field across the electrode/electrolyte phase boundary. It will be seen that although the potential differences across the interface are not large ( 1 V), the dimensions of the interphase region are very small (—0.1) and thus the field strength (gradient of potential) is enormous—it is on the order of 10 V cm. The effect of this enormous field at the electrode/electrolyte interface is, in a sense, the essence of electrochemistry. 

There is a functional relationship between the charge on each phase (or the potential difference across the interface) and the structure of the interphase region. The fundamental problem of double-layer studies is to unravel this functional relationship. One has understood a particular electrified interface if, on the basis of a model (i.e., an assumed type of arrangement of the particles in the interphase), one can predict the distribution of charge (or variation of potential) across the interphase. 

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