Interfacial component

Hoh et al. [4] used differential scanning calorimetry (DSC), FT-IR, and solid-state 13C-NMR to gain information about the epoxy/silane resin interphase. They used FT-IR to correlate the extent of reaction with the extent of interdiffusion as in the above studies. For both NMR and DSC studies, bulk models were used to study the molecular mobility of interfacial components. 

Fig. 9. Line shape analysis of the equilibrum 13C NMR spectrum of bulk polyethylene shown in Fig. 4. A crystalline component centered at 33.0 ppm, B crystalline-amorphous interfacial component at 31.3 ppm, C amorphous component at 31.0 ppm. The composite curve of the component lines is mostly superimposed on the experimental spectrum...

Fig. 30. Line shape analyses of the resonance lines of methine and methyl carbons in sPP/o-dichlorobenzene gel. A, B, and C indicate the crystalline, amorphous, and crystalline-amorphous interfacial components, respectively. (This figure was obtained by revising Fig. 7 in Ref. 25 whose horizontal chemical shift axis was somewhat shifted)...

Finally, the interfacial component mole fractions in each phase must add up to unity and satisfy the equilibrium relations. 

The intercept of Q vs. is therefore Q + hFAYq. A common application of chronocoulometry is to evaluate surface excesses of electroactive species hence it is of interest to separate these two interfacial components. However, doing so reliably usually requires other experiments, such as those described in the next section. An approximate value of nFATo can be had by comparing the intercept of the plot obtained for a solution containing O, with the instantaneous charge passed in the same experiment performed with supporting electrolyte only. The latter quantity is Qdi the background solution, and it may approximate Q for the complete system. Note, however, that these two capacitive components will not be identical if O is adsorbed, because adsorption influences the interfacial capacitance (see Chapter 13). 

Urdahl and Sjoblom studied stabilization and desta-bi-lization of water-in-crude oil emulsion (35). It was concluded that indigenous interfacially active components in the cmde oils are responsible for stabilization. These fractions would be the asphaltenes and resins. Model systems stabilized by extracted interfacially active components had stability properties similar to those of the crude oil emulsions. The same group studied the aging of the interfacial components (36).Resins and asphaltenes were extracted from North Sea crudes and exposed to aging under normal atmospherie and ultraviolet conditions. The FT-IR spectra showed that the carbonyl peak grew significantly as indi-... 

In the following discussions the published experimental findings are presented interrelatedly first in terms of internal oil chemistry at the interface and instabilities based on its composition, secondly in terms of effects of water chemistry, and thirdly in terms of demulsifier interaction. We include the activity of interfacial components involved in the structure of the protective skin, the behavior(s) of this structure with changes to water chemistry or solvency, or the effects of changes in film stmeture itself due to modification of relative proportions of interfacially active components. In some examples, developments in interfacial rheology, which is both a tool for understanding stable films and a means of rationalizing the effects of demulsifiers in demulsification, are discussed interrelatedly. Films may be sensitive to crude oil type, gas content, aqueous pH, salt content, temperature, age, and the presence of demulsifiers. Demulsifier performance is also influenced by many of these variables. 

Thus, the discussions that follow include several important factors. These are that (1) the activity of interfacial components is involved in the structure of the protective skin (2) the behavior of this structure changes with water chemistry or solvency due to mass transfer and interfacial dissipation effects (3) the changes in structure may be due to modification of the relative proportions of components and (4) for understanding stable films and as a means of measuring demulsification, one may adapt the new developments in interfacial rheology as tools. These are all factors considered in past studies and which are described in flie following sections. 

It is important to keep in mind that the AFM images visualize conditions in Langmuir films at the aqueous surface. Once again all interactions between an oil phase and interfacial components are lacking. In a real W/0 emulsion there are no guaranteees that all these components will be present at the W/0 interface due to solubility in the oil phase. Hence, results from an AFM study of LB films... 

The overall coalescence rate of a dispersion/emulsion in a separator is the most important design criterion. Unfortunately, this rate is a product of several complex mechanisms like binary coalescence, interfacial coalescence, and set-tling/creaming. Each of these mechanisms is further related to other even more complex processes/factors like hydrodynamic micro- and macro-motion, droplet size distribution, and interfacial components. In order to understand the overall coalescence rate one must also understand the interactions between these mechanisms. This makes it difficult to separate the overall rate into a sum of distinct rates, and is probably the reason why there exists no generalized coalescence model for concentrated dispersions with a sound theoretical foundation. 

The following will mainly focus on the effect and mechanisms that are associated with the hindering of film drainage by the interfacial components. 

Electrostatic stabilization occurs when the interfacial components are charged and the electric double layer between two or more droplets overlap. The resulting repulsive force counteracts further drainage of the film. Authors have, however, disregarded this repulsion as a significant stabilizing factor in describing water-in-crude oil stability (5, 6). 

Mechanical stabilization is a process where interfacial components act as particles, creating a mechanically stable film on the surface of the droplets. This film encapsulates the droplets and, due to its immobility and low solubility in both water and oil, creates a very stable emulsion. Asphaltenes, resins, wax particles, minerals, and clay are compounds believed to enhance the formation of mechanically stable films. 

All these mechanisms can be present when an emulsion is formed (although some are more predominant than others). This makes it very difficult to model emulsion stability as a function of fluid properties and interfacial components. 

Excellent Arrhenius behaviors were obtained for both and as indicated by the near-unity values of the linearity indices (R) [44], The activation energies were expected to be 20-25 kJ moE for the interfacial component and 50-70 kJ mol" for the charge-transfer component, respectively, for the anode/electrolyte interfaces... 

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