Interfacial tension lowering

A Proposed Theory. In earlier publications (1-3), a theory was proposed to correlate solubilization rate, interfacial tension and size of the surfactant aggregate (1) the interfacial tension lowering between the oil-surfactant solution interface is a function of the rate of solubilization of oil, and (2) the rate of solubilization (AS/At) is a function of the effective volume for solubilization ... 

The factors determining the appearance of ordered cell-like motions were first investigated by Sternling and Scriven (S33) who considered the two-dimensional stability of a plane interface separating two immiscible semi-infinite fluid phases with mass transfer occurring between the phases. This system was shown to be unstable for mass transfer in one direction, but stable for transfer in the opposite direction. For an interfacial tension-lowering solute, instability... 

Of course, interfacial tension lowering alone may not be sufficient to stabilize an emulsion, in which case other interfacial properties must be adjusted as well. These simple calculations do, however, show how important the interfacial properties can become when colloidal-sized species are involved, as in the case of emulsions. 

A surfactant at low concentration in aqueous solution exists as monomers (free or unassociated surfactant molecules). These monomers pack together at the interface, form monolayer and contribute to surface and interfacial tension lowering. Although this phenomenon is highly dynamic (surfactant molecules arrive and leave the interface on a very rapid timescale), molecules at the interface interact with the neighbouring molecules very strongly which enables measurement of the rheological properties of the monolayer. 

It also appears that interfacial tension lowering between the CO2 and brine is beneficial. This allows brine displacement below Swc which provides additional mobility control by relative permeability effects without requiring large pressure drops. 

It has been mentioned above that foams can unfavourably affect the refining processes. Formation processes of non-aqueous foams are not well enough studied. In a vast review [264], comparison between aqueous and non-aqueous foams has been made. The stabilisation of non-aqueous foams (e.g. on a hydrocarbon basis) seems to be impossible with usual hydrocarbon surfactants because of the weak liquid-gas interfacial tension lowering gradients. Fluorinated or silicone-type surfactants can be used as eventually better stabilisers. These recommendations are, in our opinion, only applicable to the production of the so-called hardening foams (polystyrene foams, polyurethane foams etc.). 

FIG. 4 Interfacial tension lowering in the heptane/aqueous phase (pH 5.53) system by the addition of 5-nonylsalicylaldoxime (P50). 

Enhanced oil recovery by alkaline flooding was proposed some years ago as an inexpensive way to take advantage of the acid components that occur naturally in some crude oils [80,81]. The stabilization of oil-in-water emulsions can also be attained this way. In these cases the carboxylic acid contained in the crude oil adsorbs at the O/W interface, where it is neutralized into a carboxylic salt with surfactant properties such as interfacial tension lowering or emulsification. Fatty amines and their cationic counterparts at low pH are routinely used to stabilize asphalt emulsions for roads and pavement. 

Figure 18.1 Mechanism of displacement drying (a) roll-up of water droplet (b) water-solvent interfacial tension lowering, (a) Water contact angle increases due to adsorption of a hydrophobic surfactant, (b) Water break-up by lowering interfacial tension between bquid phases.

Water-solvent interfacial tension lowering [Figure 18.1(b)]—when the adsorption of a proper surfactant at the liquid-solvent interface results in a marked reduction of the water-displacement liquid tension. In effect, the skin on the water droplet is weakened, the droplet necks down in the presence of agitation, and a significant fraction of primary water droplets is broken away and floated to the surface of the solvent batch due to buoyant forces. 

The optimum surfactant formulation for a microemulsion system is dependent on many variables (i.e., pH, salinity, temperature, etc.). References [17,49] list some of the components in a typical formulation. The surfactants and co-surfactants must be available in large amounts at a reasonable cost. In addition, they should also be chemically stable, brine soluble, and compatible with the other formulation components. Common surfactants used are petroleum sulfonates and ethoxylated alcohol sulfates [50,51]. The degree of interfacial tension lowering depends on the... 

Cmc values are important in virtually all of the petroleum industry surfactant applications. For example, a number of improved or enhanced oil recovery processes involve the use of surfactants including micellar, alkali/surfactant/polymer (A/S/P) and gas (hydrocarbon, N2, CO2 or steam) flooding. In these processes, surfactant must usually be present at a concentration higher than the cmc because the greatest effect of the surfactant, whether in interfacial tension lowering [30] or in promoting foam stability [3J], is achieved when a significant concentration of micelles is present. The cmc is also of interest because at concentrations... 

Table 4.5 also shows the lowering of the interfacial tension at the interfaces between the aqueous and organic liquids, that is, the values of Aa = Oq - o(C). The difference between these values for the different systems was rather small however, a general trend is visible the higher the resistance to coalescence, the less the interfacial tension lowering. This agrees with the concept that resistance... 

Note The interfacial tension lowering at the corresponding interfaces is also shown. 

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