Interface emulsion, definition

These figures are in approximate agreement with values calculated -with the aid of the Freundlich adsorption isotherm (see p. 134) but no definite conclusions may be drawn from them since the actual area of liquid-liquid interface in all probability was variable being dependent on the amount of emulsifying agent present. More recently the quantity of various soaps required to form a stable emulsion of kerosene in water has been determined by Grifiin (J.A.C.8. XLV. 1648, 1923) for sodium oleate, potassium stearate and potassium palmitate and by der Meulen and Riemann ibid. XLVI. 876, 1924) for sodium ricinoleate. 

The correlation between the stability of single O/W emulsion films, single drops under oil/water interfaces and real emulsions found in [514,516] also deserves attention. As revealed in the beginning of this Section the correlation between emulsions and emulsion films was studied in various aspects and always provide information about stability of such systems. Model studies of emulsion systems are worth further development especially if the correlation films/real emulsion is done at definite conditions which are as close as possible in both cases, for example, at equal capillary pressure, film size, emulsion dispersity, etc., as it is done in the correlation foam films/foam (see Chapter 7). 

To obtain a high selectivity, i.e., discrimination between the analytes and various unwanted matrix compounds, membrane extraction has a clear advantage over other sample preparation techniques, as all compounds that reach the analytical instalment must travel through the membrane. There is no direct connection and possibility for transferring compounds into the analytical instmment in other ways. This is not the case with other extraction techniques. With SPE, SPME, etc., there is a definite possibUity that matrix components are absorbed on the sorbing phase and subsequently being eluted into the extract. With LEE, such a transfer is less probable and it is generally considered that extracts after LLE are cleaner. The possible and common problem of the formation of emulsions at the phase interface with LLE, which is avoided with aU types of membrane extraction, is a source of contamination across the phase border. 

Some terms are used in other ways by other researchers, or in other countries, and may have legal definitions different from those given here. The distinctions drawn among light, heavy, extra-heavy, and bituminous crude oils were made on the basis of United Nations Institute for Training and Research (UNITAR)-sponsored discussions aimed at establishing such definitions (i-3). For terms drawn from the area of colloid and interface science, much reliance was placed on the recommendations of the lUPAC Commission on Colloid and Surface Chemistry (4), For important emulsion terms that are frequently used in industrial practice, the aim was to be consistent with the standard petroleum dictionaries such as references 5-7. 

Kj / y, where K is the surface dilationcil modulus, defined in 13.6.19). An alter-native Marangoni number was introduced by Edwards et al., who considered creep flow around an emulsion droplet. Their definition is Ma s K° /kar/, where a is the radius of the droplet, rj the bulk viscosity and fc (in s ) a rate constant, characteristic of the rate of supply of surfactants to the interface by transport from the bulk. The second definition rather applies to Gibbs monolayers it is a measure of the extent to which surface tension gradients can develop against the counteracting replenishment of the surface. 

Examples of industrial relevance for the first two combinations are the adsorption of pollutants from waste air or water onto activated carbon. Combinations three and four can be observed at the orientation of tensid molecules on water/air interfaces (foam formation, foam stabilization) or at the interface of two immiscible liquids, (e.g. oil and water, emulsion formation). This book deals mainly with the case of liquid molecules adsorbed onto solid surfaces. For this case the following definitions are made ... 

In contrast to the insignificant effect of surface-active impurities on emulsion stability, it has been found that the presence of two primary surfactant species, one soluble in water and the other in oil, can greatly enhance the stabihty of an emulsion system. The effect has been related to the production of very low inter-facial tensions and the formation of cooperative surfactant complexes that impart greater strength and coalescence resistance to the OAV interface. A broad definition of the term complex should be inferred in this context. It is not used, necessarily. 

Investigations of the effects of oil-soluble surfactants on the emulsification of paraffins in aqueous surfactant solutions led to the proposal that the formation of interfacial complexes at the oil-water interface could increase the ease with which emulsions could be formed and, possibly, explain the enhanced stability often found in such systems (Figure 9.9). By definition, an interfacial complex is an association of two or more amphiphilic molecules at an interface in a relationship that will not exist in either of the bulk phases. Each bulk phase must contain at least one component of the complex, although the presence of both in any one phase is not ruled out. The complex can be distinguished from such species as mixed micelles by the fact that micelles (and therefore mixed micelles) are not adsorbed at interfaces. According to the Le Chatelier principle, the formation of an interfacial complex will increase the Gibbs interfacial excess F/ [Eq. (9.2)] for each individual solute involved, and consequently, the interfacial tension of the system will decrease more rapidly with increasing concentration of either component. 

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