Inter facial tension

It is quite clear, first of all, that since emulsions present a large interfacial area, any reduction in interfacial tension must reduce the driving force toward coalescence and should promote stability. We have here, then, a simple thermodynamic basis for the role of emulsifying agents. Harkins [17] mentions, as an example, the case of the system paraffin oil-water. With pure liquids, the inter-facial tension was 41 dyn/cm, and this was reduced to 31 dyn/cm on making the aqueous phase 0.00 IM in oleic acid, under which conditions a reasonably stable emulsion could be formed. On neutralization by 0.001 M sodium hydroxide, the interfacial tension fell to 7.2 dyn/cm, and if also made O.OOIM in sodium chloride, it became less than 0.01 dyn/cm. With olive oil in place of the paraffin oil, the final interfacial tension was 0.002 dyn/cm. These last systems emulsified spontaneously—that is, on combining the oil and water phases, no agitation was needed for emulsification to occur. 

Change of differential capacityiC-C° Inter facial tension,... 

RECOVERY MECHANISMS. Being surface active, TFSAs lower oil-water inter facial tension, but not by the three orders of magnitude needed to increase the capillary number sufficiently to recover a substantial amount of incremental oil. Instead, TFSAs enhance the recovery of oil by changing the wettability of reservoir rock surfaces from oil-wet and intermediate wettability to strongly water-wet, and by coalescing emulsions in the near-wellbore region of the production wells. 

In the Will case, provided that there is enough surfactant but not too much, e.g., 1 wt. %, the system splits into three phases, i.e., a microemulsion in equilibrium with excess water and excess oil. At a higher surfactant concentration than the top vertex of the 3

single phase microemulsion often called WW behavior is attained. However, this occurrence generally requires a large amount of surfactant, e.g., 20 wt. %, which is in most practical cases too much for cost reasons. At a very low surfactant concentration, around the CMC, only two phases are in equilibrium, and the tension is not necessarily very low. Hence, the convenient surfactant concentration to carry out a phase behavior study is in the range 0.5-3 wt. % for which three-phase behavior and a very low inter facial tension is exhibited in most Will cases. 

Spreading coefficient as used here is surface tension of water minus surface tension of the oil minus inter-facial tension. 

However, if 10-min flotation treatments were used, oil recovery decreased drastically above a pH of 8. Further study revealed that low inter-facial tension develops in high pH water, given sufficient time. The 1-mm Strickland test did not allow enough time. 

York, Stubbs, and Tek (27C) have developed a theory for the breakup of thin liquid sheets as produced by tangential nozzles. A force balance between the inter-facial tension and aerodynamic forces is the basic concept, and the criteria for stability and instability are determined from it. Wave formation at the interface is of major importance in the subsequent breakup. 

For crew-cut micelles, Zhulina and Birshtein demonstrated that the dependence of the micellar parameters on Nb disappears and Rc scales as yl/3Nj(/3a and Z yNA, where y is the inter facial tension between the A and B blocks and a is the segment length [209]. 

Dynamic Interfacial Tension. Crude-oil-alkali systems are unusual in that they exhibit dynamic interfacial tension (Figure 11). A solution of 0.05 wt% sodium hydroxide in contact with David Lloydminster crude oil initially produces ultralow values of IFT. A minimum value is reached, after which IFT increases with time by nearly 3 orders of magnitude, measured in the spinning drop tensiometer. Taylor et al. (57) showed that dynamic inter-facial tension can also occur in crude-oil-alkali-surfactant systems. Figure 11 shows interfacial tension versus time for a solution containing 1 wt% sodium carbonate, and the same solution containing 0.02 wt% of Neodol 25-... 

Figure 11. Effect of caustic concentration on electrophoretic mobility and inter-facial tension of equilibrated sample of Huntington Beach crude...

MELROSE Solid-Fluid Inter facial Tensions... 

In several instance (98, 127), ADSA ultralow inter-facial-tension measurements are available for the same systems for which SDT has been performed. Ultralow interfacial tension measurements by ADSA were by means of an inverted sessile-drop set-up of Aerosol OT (AOT) in NaCI/water solution in an n-heptane matrix solution. 

Moreover, as shown in Figs 15a and 16a, the calculated y(t) agrees well with the measured dynamic inter-facial tension, in paticular at the lower concentrations. For larger concentrations, the deviation increases. It is possible that, at these concentrations, the adoption of a spherical symmetry for the model is no longer adequate, as the drop deforma-... 

CAMiller, RN Hwan, W Benton, T Fort Jr. Ultralow inter-facial tensions and their relation to phase separtion in micellar solutions. J Colloid Interface Sci 61 554—568, 1977. 

M Bourrel, A Graciaa, RS Schechter, WH Wade. The relation of emulsion stabihty to the phase behavior and inter-facial tension of surfactant systems. J CoUoid Interface Sci 72 161, 1979. 

The equilibrium interfaeial tension between water and oil is a measure of the adsorption of surface-active components to the interface and can be related to siuface excess by the Gibbs equation (183). However, in crude oil systems the activity/concentrations of the surfaee-aetive components are not easily determined. Indirect measures are applied. In most process conditions with short resident times, it is the dynamic inter-facial tension gradient that is important. Interfaeial tension also tells whether or not the demulsifier is surfaee active, and as will be shown later, this is important for demulsification. The interfaeial tension gradient is the... 

For even better results, drop profile analysis can be applied instead of measuring the contact angle directly (axisymmetric drop shape analysis, ASDA Fig. 4.20). This technique extracts experimental drop profiles from video images while slowly increasing or decreasing the droplet volume [42, 43]. The best fit of experimental data with theoretical assumptions based on the Laplace equation of capillarity allows one to calculate the surface/inter-facial tension and subsequently the contact angle. Also droplet radius, droplet volume, and the contact area are computed. ADSA can therefore reveal... 

The traditional mercury electrode is a drop that is periodically created and dispatched at the tip of a glass capillary that is immersed in an electrolyte solution. This is the so-called dropping mercury electrode (dme). Mercury flows from a reservoir through a capillary and forms drops because of its high inter-facial tension. The electrode can operate in the free dropping mode, or a mechanical knocker can... 

The above mentioned phenomena can be explained if we assume that condensation of the coacervate is associated with increase,of the interfacial tension coacervate / medium, conversely that "swelling reduces this inter-facial tension. (Compare p. 433,... 

The work of adhesion (see Wetting and work of adhesion. Contact angles and inter-facial tension) is a simple example of a concept that could be regarded as a fundamental measure of adhesion between two surfaces. 

Figure 2 summarizes the effect of NaCl concentration, oil chain length and surfactant concentration on the interfacial tension in this system. It is evident that ultralow interfacial tension minimum occurs at a specific salinity or specific oil chain length or specific surfactant concentration. Using light scattering, osmotic pressure, surface tension, dye solubilization and various other techniques, we have shown that the ultralow inter facial tension minimum in this system correlates with the onset of micellization in the aqueous phase and the partition coefficient of surfactant near unity (14). Baviere (15) has also shown that the partition coefficient is near unity at the salinity where minimum interfacial tension occurs. 

HTAB renders the glass surface more hydrophobic than does DTAB, but the interfacial tension against oil of both solutions is practically the same (9.6 rnNrn for DTAB, and 9.0 mNm for HTAB). Lerolat-100 in a concentration of 100 times the wets glass very well, but the inter facial tension against paraffin oil is 2 mNm" only. 

If the film is not too thin—a "thick thln-film rather than thin thin-film—the inter facial tension between it and contiguous fluid can be taken as independent of thickness (12). 

Static petroleum sulfonate adsorption on simulated reservoir solids is affected significantly by the composition of the microemulsion from which the sulfonate is adsorbed. Petroleum sulfonates which are preferentially oil-soluble tend to be adsorbed to a lesser degree from oil-external than from brine-external microemulsions under equivalent conditions. Since the cosurfactant component can be used effectively to obtain a desired microemulsion composition, sulfonate adsorption is affected significantly by the choice of cosurfactant. If an oil-external microemulsion is to be used in a flood, it is preferable to employ a glycol ether cosurfactant, rather than a simple alcohol, because of lower surfactant adsorption in addition, the glycol ether microemulsion would exhibit enhanced salt tolerance which would affect favorably its inter- -facial tension properties. 

Equivalent Alkane Carbon Number. (EACN) Each surfactant, or surfactant mixture, in a reference series will produce a minimum inter-facial tension (IFT) when measured against a different n-alkane. For any crude oil or oil component, a minimum IFT will be observed against one of the reference surfactants. The EACN for the crude oil refers to the n-alkane that would yield minimum IFT against that reference surfactant. The EACN thus allows predictions to be made about the interfacial tension behavior of a crude oil in the presence of surfactant. See references [JJ, 12]... 

Inter facial tension a is shown in Fig. 2 for various molecular weights as a function of AT = T - T. The interfacial tension decreases with increasing molecular weight at... 

Polymer Adsorption. The driving force for adsorption typically is the en-thalpic interaction between the interface and the polymer segments. Exceptions include aqueous solutions near hydrophobic substrates. In that case, the driving force may include the hydrophobic interaction between water and the surface. The enthalpic interactions may be of various forms such as hydrogen bonding, inter-facial tension, van der Waals attraction, polar interactions, and electrostatic attractions. This enthalpic interaction is offset by the loss in conformational entropy... 

---