Interfaciai tension

Variation In interfaciai Tension of a Mercury-1.0 N CsCi Interface with Potential Difference... 

Variation in Interfaciai Tension of an Hc/CsCi Interface with CsCI Concentratioir... 

ARNEODOETAL. Interfaciai Tension Behavior of Citrus Oils... 

Interfaciai Tension Procedure. IFT measurements were made by the Wilhelmy plate method. The apparatus was the same as that described previously (2). A standard protocol was followed for all IFT determinations. The desired interface was formed at a specified temperature by partially filling a thermostatted sample holder with the desired aqueous phase. This phase, distilled water (mono triple) or a supernatant aqueous phase isolated from a complex coacervate system, completely covered the Wilhelmy plate (roughened platinum). The desired citrus oil was carefully layered onto the aqueous phase. It had been preheated (or cooled) to the same temperature as the aqueous phase. Once the citrus oil/aqueous phase interface was formed, the Wilhelmy plate was drawn completely through the interface and into the oil phase where it was zeroed. 

Figure 18 Interfaciai tension of sunflower oil/water with and without protein (0.25% skimmed milk) in the water phase, and with and without 0.1% emulsifier (saturated monodiglyceride) in the oil phase. The two-phase systems were heated to 40°C for 1 hour, cooled to 5°C and reheated again to 40°C. Symbols O = Oil W = Water P = Protein E = Emulsifier. Reproduced from reference44, courtesy of The American Institute of Chemical Engineers 1990 AlChE. All rights reserved.

Here ft is a correction factor to allow for the complex shape of the liquid just before break-away and for the non-vertical surface tension forces. Tabulations of ft are given in the literature. Again zero contact angle is required (attainable with an extremely clean ring) and the ring must lie flat on a quiescent liquid surface. For interfaciai tension measurements the ring must be preferentially wetted by the lower liquid. 

At the interface between two condensed phases, the dissimilar molecules in the adjacent layers facing each other have potential energies greater than those of similar molecules in the respective bulk phases. This is due to the fact that cohesive forces between like molecules tend to be stronger than adhesive forces between dissimilar molecules. Thus the interfaciai tension is the force per unit length existing at the interface between two immiscible or partially miscible condensed phases and the interfaciai free energy is the work required to increase the interface by unit area. 

Figure 4.37. Computed interfaciai tension at the water-decane interface in the presence of CjQ - p SOgNa". Influence of branching. Temperature 25 C. (Redrawn after van Os et al., loc. cit.)...

Surface and Interfaciai Tension Measurement, Theory, and Applications, edited by Stanley Hartland... 

Figure 4.10. Schematic representation of the interfaciai tension measurements by the capiiiary breakup method is the initiai diameter of the fiber, b and a are the maximum and minimum diameters observed during the break-up process, respectiveiy.

In 1960, Blair [59] and Dodd [68] published key studies on water-in-crude oil emulsions and their films (see [1-6] for references). Using a Cenco surface film balance to study the water-oil interface, Blair showed that the principal source of stability arises from the formation of a condensed and viscous interfaciai film by adsorption of soluble material from the petroleum phase, such film presenting a barrier to coalescence of the dispersed droplets. This primary film may be augmented by secondary adsorption of large particles or micelles originally suspended in the petroleum. The classical picture of emulsion stabilization by an adsorbed monolayer yielding low interfaciai tension values does not seem to be an accurate one in this case. It appears that a primary adsorbed layer is initially formed, almost certainly comprised of asphaltenes, and a secondary layer superimposes on this primary layer and is likely comprised of asphaltenes, wax particles, and possibly... 

The surface light scattering method has been used to show that the low interfaciai tensions in the Winsor I and II systems (O/W microemulsion in equilibrium with excess oil and W/O microemulsion in equilibrium with excess water, respectively) are due to the large surface pressure of the surfactant monolayer coating the interface, which almost balances the bare oil/water interfaciai tension [36,37]. Schulman and Montagne [38] proposed early that the low interfaciai tensions in microemulsion systems should be associated with these large surface pressures tt, i.e., 7 = 70 - tc 0. In other models, the origin of the low interfaciai tensions was attributed to the vicinity of critical points [39,40]. 

Overbeek and coworkers [41] studied oil-water-alcohol-surfactant mixtures close to the cmc and showed that ultralow interfaciai tensions could be obtained as well in their systems. They determined the monolayer composition from the 7(c) curve below the cmc. Similar work on ternary oil-water-surfactant mixtures was reported by Aveyard et al. [42]. In these studies, ) was measured by using a spinning drop tensiometer. 

On the other hand, it was discussed in the previous chapter that formulation can greatly influence interfaciai tension, a crucial factor in the determination of the breakup-coalescence dynamic equilibrium and thus the drop size average and distributicHi. Consequently, it is no wonder that—la.st but not least—the... 

E. Ruckensiein. The surface of tension, the natural radius, and the interfaciai tension in the thermodynamics of nticrocmulsions.. Colloid Interface Sci.. 114 173- 179, 1986. 

Table 3 Interfaciai Tensions of Low Molecular Weight Cheinica Additives ...

Interfaciai tension Interfaciai tension Interfaciai tension ... 

Uses interfaciai tension modifier for minimizing crawiing, fish-eyes and cratering in soiv.-based coating systems, UV-cured automotive OEM ciear coats, anticorrosive primers, piastic ciear coats, marine topcoats, wood furniture coatings Features Siiicone-free... 

Uses Interfaciai tension modifier for minimizing crawling, fish-eyes and cratering in low VOC aq. coatings, UV-cured automotive OEM clear coats, anticorrosive primers, plastic clear coats, marine topcoats Regulatory FDA cleared NV components Properties Sp.gr. 1.01 dens. 8.4 Ib/gal vise. (G-H) C-G flash pt. 50.5 C surf. tens. 29 dynes/cm (0.5%) 77.5% solids, 16.7% water, 5.8% ethyl alcohol... 

Figure 6 Evolution of interfaciai tension for Leduc crude oil (a), 100 ppm Duomeen C in the oleic phase (o), and 100 ppm Aerosol OT in the aqueous phase (a). 

Based on measurement of time-dependent interfaciai tension, we have defined an apparent spreading rate as given in [5], which served to... 

Figure 7.3 Evolution of the interfaciai morphoiogy due to crowding of the interface by interfacial copolymers and consequent decrease ofthe interfaciai tension (a) interfaciai roughening (b) formation of pinch-offs and (c) formation of micro-emulsions on the continuous phase.

Table 19. Effect of Spreading Coefficients (interfaciai Tensions) on Mixed Particie Morphoiogy ...

It is advantageous to reduce AGi hy n x and to ascribe the change in the free energy per unit area of seed particles to interfaciai tension. This leads to equation 46. 

The mil king of an emulsion involves many nonequilihrium features, at least from the mechanical point of view. Actually the product of the interfaciai tension by the produced surface area y AA, which is the interfaciai energy, is always much smaller than the mechanical energy put into the system by the stirring device. A significant characteristic is the way and the efficiency in which the energy is provided to the drop so that breaking is favored over coalescence. This has to do not only with the device but with formulation and eventual transient events. 

The role of the surfactant as the essential ingredient in the formation and persistence of an emulsion is associated with several nonequilibrium proces.ses. When the drops are formed by effect of mechanical shearing the presence of surfactant reduces the interfaciai tension, so that breaking is favored. On the other hand, the adsorption of surfactant onto the freshly produced interface results in a repulsion that prevents the iiuiiiediaie coalescence of neighboring Jioplets. Thus, the surfactant plays a role in both the breaking and coalescence steps, i.e.. the dynamic balance that determines the drop size. 

Thermophoresls, Figure 1 The thermophoretic motion of a smaii particie in a temperature gradient as the resuit of interfaciai tension due to the diffusive iayer around the particie see Ruckenstein [8]... 

Schematic representation of iow (left) and high (right) static contact angies, 6o. Interfaciai tensions are represented by arrows and termed yu (S = soiid, L = iiquid, V = vapor/surrounding fiuid phase)...

Spinning Drop Suitabie for iow interfaciai tensions. The diameter of a drop within a heavy phase is measured when both are being rotated. 

Pendent Drop Surface and interfaciai tensions are measured by this method. 

Drop Volume A method employed for determining interfaciai tension as a function of time (interface age). The time between two consecutive drops is measured when liquid of one density is pumped into a second liquid of a different density. 

Uses Surface tension reducer, interfaciai tension reducer, wetting agent, dispersant, emuisifler, penetrant, soiubiiizer for cosmetics, detergents, agric., mining prods., textiies emuisifler, dispersant for water treatment, paints, inks, poiymer-ization... 

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