Emulsification boundary

The hydraulic oil must provide adequate lubrication in the diverse operating conditions associated with the components of the various systems. It must function over an extended temperature range and sometimes under boundary conditions. It will be expected to provide a long, trouble-free service life its chemical stability must therefore be high. Its wear-resisting properties must be capable of handling the high loads in hydraulic pumps. Additionally, the oil must protect metal surfaces from corrosion and it must both resist emulsification and rapidly release entrained air that, on circulation, would produce foam. 

The resistance to fluid flow is a measure of the physical structure of the foam. In order to control the flow through a foam, ceU size, degree of reticulation, density, and other physical factors must be controlled. The control of these physical factors, however, is achieved through the chemistry and the process by which the foam is made. The strength of the bulk polymer is measured by the tensile test described above, but it is clear that the tensile strengths of the individual bars and struts that form the boundaries of an individual cell determine, in part, the qualities of the cells that develop. A highly branched or cross-linked polymer molecule will possess certain tensile and elongation properties that define the cells. The process is also a critical part of the fluid flow formula, mostly due to kinetic factors. As discussed above, the addition of a polyol and/or water to a prepolymer initiates reactions that produce CO2 and cause a mass to polymerize. The juxtaposition of these two reactions defines the quality of the foam produced. Temperature is the primary factor that controls these reactions. Another factor is the emulsification of the prepolymer or isocyanate phase with the polyol or water. 

Because of the availability of these new methods, devices, and purer materials, it has become more feasible to carry on effective research with adequate surface-chemical control of gas and liquid adsorption, wetting, adhesion, emulsification, foaming, boundary friction, corrosion inhibition, heterogeneous catalysis, electrophoresis, electrode surface potentials, and a variety of other subjects of interest in the surface-chemical and allied fields of research. In view of the present situation, serious investigators should now be able to report results in the scientific literature which will have much more value than ever before. There is no excuse for any investigator s taking such inadequate care in controlling surface composition or surface-active contaminants as was common in over 50% of the research publications in surface and colloid science in the past. 

One of the earliest uses of power ultrasound in processing was in emulsification. If a bubble collapses near the phase boundary of two immiscible liquids, the resultant shock wave can provide a very efficient mixing of the layers. Stable emulsions generated with ultrasound have been used in the textile, cosmetic, pharmaceutical, and food industries. Such emulsions are often more stable than those produced conventionally and often require little, if any, surfactant. Emulsions with smaller droplet sizes within a narrow size distribution are obtained when compared to other methods. 

At the oil-rich side, the phase behaviour is inverted temperature-wise as can be seen in the T( wA)-section provided in Fig. 1.7(c). Thus, the near-critical phase boundary 2 —1 starts at low temperatures from the lower n-octane-QoEs miscibility gap (below <0°C) and ascends steeply upon the addition of water. With increasing wA, this boundary runs through a maximum and then decreases down to the upper critical endpoint temperature Tu. The emulsification failure boundary 1 —r 2 starts at high temperatures and low values of wA, which means that only small amounts of water can be solubilised in a water-in-oil (w/o) microemulsion at temperatures far above the phase inversion. Increasing amounts of water can be solubilised by decreasing the temperature, i.e. by approaching the phase inversion. At Tu the efb intersects the near-critical phase boundary and the funnel-shaped one-phase region closes. 

From the above considerations, it can be concluded that T(wB)- and T(wA)-sections provide an easy method to determine the location of emulsification failure boundaries which are of particular interest if the optimal formulation for an industrial application has to be found. Furthermore, these sections yield the lower and upper temperature of... 

Figure 1.7 Vertical sections T(wb) and 7 (wA) through the phase prism which start at the binary water-surfactant (wb = 0) and the binary oil-surfactant (wA = 0) corner, respectively. These sections have been proven useful to study the phase behaviour of water- and oil-rich microemulsions, (a) Schematic view of the sections T wg) and T(wA) performed at a constant surfactant/fwater + surfactant) mass fraction ya and at a constant surfactant/(oil + surfactant) mass fraction 7b, respectively, (b) T(wb) section through the phase prism of the system FhO-n-octane-CioEs at ya = 0.10. Starting from the binary system with increasing mass fraction of oil wg, the oil emulsification boundary (2- 1) ascends, while the near-critical phase boundary (1 - 2) descends, (c) T(wA) section through the phase prism of the system EbO-n-octane-QoEs at 7b = 0.10. The inverse temperature behaviour is found on the oil-rich side With increasing fraction of water wA the water emulsification boundary (1 - 2) descends, whereas the near-critical phase boundary (2 —> 1) ascends.

Figure 1.19 Micrographs of microemulsion droplets of the o/w-type in the system II2O- n-octane-CnEs prepared near the emulsification failure boundary at ya = 0.022, wb = 0.040 and T = 26.1 °C. (a) Freeze-fracture direct imaging (FFDI) picture showing dark spherical oil droplets of a mean diameter = 24 9 nm in front of a grey aqueous background. Note that each oil droplet contains a bright domain of elliptic shape which is interpreted as voids, (b) The freeze-fracture electron microscopy (FFEM) picture supports the FFDI result. Each fracture across droplets which contain bubbles shows a rough fractured surface. (From Ref. [26], reprinted with permission of Elsevier.)...

Gradzielski, M., Langevin, D., Sottmann, T. and Strey, R. (1997) Droplet microemulsions at the emulsification boundary The influence of the surfactant structure on the elastic constants of the amphiphilic film. /. Chem. Phys., 106, 8232-8238. 

Initially, the decane and hexadecane microemulsion systems were studied at the emulsification boundary T m) to make an accurate comparison between the two systems. Deuterium-NMR relaxation using selectively deuterium-labeled surfactant is a useful method to detect variation of micelle size when changing composition and/or temperature. In a relaxation NMR experiment the combined motion of longitudinal (1/Ti) relaxation of the micelles and the transverse relaxation (I/T2) of the surfactants inside the film (internal diffusion) are measured. The measured parameters are therefore sensitive to the micellar size but essentially insensitive to intermicellar interaction. More information can be found in papers by Wennerstrom [133] and Halle [33]. At Tbpb the microemulsion droplets are generally spherical at infinite dilution [84]. The results from the relaxation measurements (expressed as l/r2-l/Ti) on the two systems are presented in Figure 3.3. 

Figure 3.8 Results from (a) dynamic light-scattering and (b) static light-scattering measurements performed at the emulsification boundary for different...

Figures.10 Axial ratios obtained for the different Ci2E5-alkane-H20 systems at the emulsification boundary for samples with 0 = 0.12 using NMR self-diffusion (downward...

Figure 3.22 The SAXS data at the emulsification boundary for the Ci2Es-water-decane system, where part of the oil is substituted with lidocaine of 1% lidocaine (circles) and 10% lidocaine (squares). The figure is adapted from and data taken from ref [114).

Figure 4.19. A-B block copolymers at the AB phase boundary. The effect is that of oil-in-oil surfactant emulsification.

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