Outer phase

An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

Apart from chemical composition, an important variable in the description of emulsions is the volume fraction, spherical droplets, of radius a, the volume fraction is given by the number density, n, times the spherical volume, 0 = Ava nl2>. It is easy to show that the maximum packing fraction of spheres is 0 = 0.74 (see Problem XIV-2). Many physical properties of emulsions can be characterized by their volume fraction. The viscosity of a dilute suspension of rigid spheres is an example where the Einstein limiting law is [2]... 

It was pointed out in Section XIII-4A that if the contact angle between a solid particle and two liquid phases is finite, a stable position for the particle is at the liquid-liquid interface. Coalescence is inhibited because it takes work to displace the particle from the interface. In addition, one can account for the type of emulsion that is formed, 0/W or W/O, simply in terms of the contact angle value. As illustrated in Fig. XIV-7, the bulk of the particle will lie in that liquid that most nearly wets it, and by what seems to be a correct application of the early oriented wedge" principle (see Ref. 48), this liquid should then constitute the outer phase. Furthermore, the action of surfactants should be predictable in terms of their effect on the contact angle. This was, indeed, found to be the case in a study by Schulman and Leja [49] on the stabilization of emulsions by barium sulfate. 

The multiple emulsion technique includes three steps 1) preparation of a primary oil-in-water emulsion in which the oil dispersed phase is constituted of CH2CI2 and the aqueous continuous phase is a mixture of 2% v/v acetic acid solution methanol (4/1, v/v) containing chitosan (1.6%) and Tween (1.6, w/v) 2) multiple emulsion formation with mineral oil (oily outer phase) containing Span 20 (2%, w/v) 3) evaporation of aqueous solvents under reduced pressure. Details can be found in various publications [208,209]. Chemical cross-linking is an option of this method enzymatic cross-linking can also be performed [210]. Physical cross-linking may take place to a certain extent if chitosan is exposed to high temperature. 

When the original compositions of the outer phases are different, the permselective membrane will prevent the complete leveling of these compositions. Some equilibrium component distribution between phases (a) and (p) will be established, and between points A and B a potential difference called the membrane potential (or transmembrane potential) (p will develop. This potential difference is determined by... 

Since the outer phases are similar, membrane potentials can be measured. 

FIG. 6 Schematic of the rotating diffusion cell. The reaction is usually followed by sampling the bulk solution of the outer phase using a suitable analytical technique. 

In accordance with this dynamic mechanical measurements show that the rubber partially forms the outer phase below 170 -190°C.8... 

Scheme 2.2 Graphical representations of the inner and outer phases of the chiro-RAM-TE support. G = grafting group (monoureido-monoisocyanate intermediate), obtained as previously described [61] (i) LiCl/dry DMSO, 80°C, 3 h. (ii) dry pyridine, 70°C, 12 h.

In the case of a polydisperse system the calculation of the particle size distribution is possible by using special transformation algorithms. For this purpose certain requirements need to be fulfilled, such as a spherical particle shape, sufficient dilution, and a large difference between the refractive indices of the inner and the outer phases. Since usually not all requirements can be fulfilled, the z-average is preferred as a directly accessible parameter rather than the distribution fimction depending on models. 

Shima, M., Kobayashi, Y., Fujii, T., Tanaka, M., Kimura, Y., Adachi, S. (2004). Preparation of fine W/O/W emulsion through membrane filtration of coarse W/O/W emulsion and disappearance of the inclusion of outer phase solution. Food Hydrocolloids, 18, 61-70. 

RANGE a NUMBER OF duase x PHASES PMA5t xU OUTER PHASE... 

The advantages derived from the use of microscopic liquid-liquid interfaces have been highlighted in Sect. 5.5.3, and different approaches to support such small liquidlliquid interfaces in pores, pipettes, and capillaries have been addressed. The theoretical treatment of ion transfer through these interfaces needs to consider the asymmetry of the diffusion fields inside and outside the pore or pipette (i.e., diffusion can be approximated as linear in the inner phase, whereas radial diffusion is significant in the outer phase, especially for small sizes) [36, 40, 42-44]. 

The transport rate of H + and OH ions from the transition region into the outer phases cannot exceed the rate of their generation. However, the generation rate of H + and OH ions in a bipolar membrane is drastically increased compared to the rate obtained in water due to a catalytic reaction [26, 27]. Therefore, very high production rates of acids and bases can be achieved in bipolar membranes. 

A. Passive binding of Fe(III)—Lm complex and Fe(III) to ligands (acceptor sites) of the outer membrane and the outer phase of the inner membrane. Fe(III)-Ln represents a soluble chelate complex of Fe(III) with a sufficiently low stability constant, e.g., polynuclear Fe(III)-sucrose complex(es). B. reduction of membrane-bound Fe(III) to Fe(II) by the respiratory chain at the level of cytochrome c/cytochrome a and energy-dependent active transport of Fe(ll) across the inner membrane. See text. This model is based on Refs. 23, 24, 27-32. 

It has been generally assumed that iron is transported across biological membranes in the ferrous form and that ferric iron would have to be reduced before it can be used by the organism. Thus, based on nutritional studies it has long been recognized that Fe(II) is1 more effectively absorbed than Fe(III), and this has been attributed to differences in the thermodynamic and kinetic stability of the complexes and chelates formed by these cations (for review, see Ref. 2). The experimental proof of a transport in the ferrous form has, however, not been given until quite recently in studies of iron transport in isolated mitochondria (23) as well as in enterobacteria (33). In rat liver mitochondria we have found that Fe(III) donated from a metabolically inert water soluble complex of sucrose interacts with the respiratory chain at the level of cytochrome c (and possibly cytochrome a) (23, 32) (Figure 1 B), which has a oxidation-reduction potential of around +250 mV (34) and is localized to the outer phase of the mitochondrial inner membrane (35). 

An important difference between particulate solids and emulsions is that in the solids two components can percolate the system at the same time, that is, two components can act as the outer phase simultaneously. In this case the system is known as a bicoherent system. 

For this purpose an electron transfer across the bilayer boundary must be accomplished (14). The schematic of our system is presented in Figure 3. In this system an amphiphilic Ru-complex is incorporated Into the membrane wall. An electron donor, EDTA, is entrapped in the inner compartment of the vesicle, and heptylviolo-gen (Hv2+) as electron acceptor is Introduced into the outer phase. Upon illumination an electron transfer process across the vesicle walls is initiated and the reduced acceptor (HVf) is produced. The different steps involved in this overall reaction are presented in Figure 3. The excited sensitizer transfers an electron to HV2+ in the primary event. The oxidized sensitizer thus produced oxidizes a Ru located at the inner surface of the vesicle and thereby the separation of the intermediate photoproducts is assisted (14). The further oxidation of EDTA regenerates the sensitizer and consequently the separation of the reduced species, HVi, from the oxidized product is achieved. In this system the basic principle of a vectorial electron transfer across a membrane is demonstrated. However, the quantum yield for the reaction is rather low (0 4 X 10 ). 

The situation is more complex in chloroplasts even when the hydrophylic pH indicator, cresol red, was utilized the -binding kinetics at the outer surface of the thylakoids did not correspond to the reduction of A, 3 (B), but was approximately 30-fold slower [279]. A faster equilibration of protons could be obtained only after harsh surface treatments such as mechanical disruption by sand grinding or detergents. Attempts in the evaluation of the kinetics of proton release in the inner thylakoid lumen have been made with the permeant pH indicator, neutral red, buffering the outer phase with BSA [272,280]. Initially the two kinetic phases observed seemed to match kinetically the rate of water and plastoquinol oxidation... 

Metal Ion Organic Phase Outer Phase Inner Phase Comments References... 

---