A review, with 38 refs. Double emulsions are emulsion-within-emulsion systems with promising applications. Attempts were made to find new amphiphiles to improve their thermodn. stability and to control the release of active matter or markers from double emulsions. The efforts to study the mechanisms of stabilization and release of water-sol. markers from W/O/W double emulsions are summarized, and the achievements in designing an ultimate synthetic graft-comb copolymeric amphiphile for the internal water-oil interface (the W/O emulsion) as well as for the external oil-water interface (the O/W emulsion) are presented. The amphiphilic polymers allow formation of small multicompartment emulsion droplets of W/O/W that are shear (homogenization) and mech. (centrifugation) resistant. The interface is covered with thick emulsifier layers that impart long-term stability. Addn. of controlled amts. of monomeric emulsifiers (Spans) will form reverse micelles in the oil phase, which are capable of transporting the markers via a diffusion-controlled mechanism from the inner to the outer interface. The tailor-made polymers are an excellent soln. to the 2 key problems that, so far, have prevented the use of double emulsions in certain industrial applications: stability and release. Agricultural formulations, based on stabilization by these polymers, have shown considerable advantages over other common techniques of encapsulating or entrapping active matter. [on SciFinder(R)]

A review, with 47 refs. Double emulsions have significant potential in many applications since, at least in theory, they can serve as an entrapping reservoir for active ingredients that can be released by a controlled and sustained transport mechanism. Many of the potential applications are in pharmaceuticals, cosmetics, and food. In practice, double emulsions are thermodynamically unstable systems with a strong tendency for coalescence, flocculation, and creaming. During the last decade much work was carried out to improve the stability and to control the release rates from double emulsions. The review will mention some of the more interesting studies making use of almost any possible combination and blend of monomeric emulsifiers, oils and stabilizers, polymerizable emulsifiers, macromol. surfactants both natural occurring and synthetic, increase viscosity of each of the phases, microspheres and microemulsions in the internal emulsions, etc. The presentation will stress also the most recent achievements in this area including: (i) the use of specially tailor-made polymeric emulsifiers to improve interface coverage and to better anchor into the dispersed phases; (ii) droplet size redn. by forming microemulsions or vesicles in the internal phase; (iii) an improvement in the understanding of the release mechanisms; (iv) the use of different filtration techniques to improve the monodispersibility of the droplets; and (v) use of various additives (carriers, complexing agents) to control the release via the reverse micellar mechanism. [on SciFinder(R)]

A review with 58 refs. discusses formation and stability of double emulsions employing polymeric and macromol. surfactants. Controlled release and transport mechanisms are discussed. [on SciFinder(R)]

A hydrocolloid, extd. from Portulaca Oleracea, comprises the compn. as shown: humidity 10-11%, fat 0. 5-0.6%, proteins 2.5-3.2%, nutritionable water sol. fibers 60-62%, nutritional non water sol. fibers 7.5-8.5% and total nutritional fibers 68-70%. To be more specific, the sugar contents in the fibers are as shown D-galactose: L-arabinose: L-rhamnose: D-xylose: D-galacturonic acid (40: 20: 5: 1: 31); and the compn. of the ash portion is as given with the unity mg/kg: 1400 Ca, 20,000 Mg, 60,000 K; 2,000 Na, 900 Fe, 460 S, 720 P, 60 Al. The mol. wt. of the fraction of the hydrocolloid has a distribution as shown: up to10000 daltons 34%; 10,000-100,000 daltons 12%; 100000-10000000 daltons 33%; 10,000,000-100,000,000 daltons 11%; \textgreater100,000,000 daltons 10%. In addn., the soly. in water, the viscosity, the surface tension and the interface tension of the hydrocolloid have been analyzed. The prepn. of hydrocolloid includes the steps of crushing Portulaca Oleracea in the presence of ethanol in a ratio of 1: 1 (wet plant: ethanol); drying the solid fraction and extg. with acetone; extg. the remainder with a mixt. of toluene: ethanol in a ratio of 1: 2; extg. the remainder with water; centrifuging the aq. fraction in order to remove the rest of the plant; adding ethanol to the aq. fraction in a ratio of ethanol: aq. soln. 3: 1; pptg. hydrocolloid. The prepn. of said emulsion comprises the steps of: dissolving the hydrocolloid in water at room temp. with stirring overnight; dripping the oil into the soln. and stirring in a homogenizer for 5 min for all the oil being dripped into the emulsion; continuing to stir for another 10 min. The hydrocolloid can be used in the following ways: being part of an emulsion; being part of a pharmaceutical prepn. which has effects on reducing the sugar level in the blood and the blood pressure. Further, the pharmaceutical compn. may be an emulsion. However, it may be any suitable tablet, capsule, soln., etc. [on SciFinder(R)]

Both hydrophobic emulsifiers and submicronial fat particles are needed to stabilize water-in-vegetable oil emulsions. Polyglycerol polyricinoleate (PGPR) is superior to glycerol monooleate and/or lecithin, but is incapable of stabilizing fluid emulsions for sufficient storage periods. Fluid emulsions, unlike margarine, exhibit high droplet mobility and are susceptible to flocculation and coalescence. Submicronial $\alpha$-form crystals of hydrogenated fat can be obtained in the oil phase by the flash-cooling process. The crystals are homogeneously almost mono-dispersed and exhibit insufficient stability against flocculation and phase sepn. The use of an emulsifier (PGPR) in the fat crystn. process was very helpful in decreasing the aggregation and flocculation processes. The $\alpha$-form (mixed with $\beta$'-form) submicronial crystals can stabilize water-in-oil emulsions only in the presence of food emulsifiers, provided the concn. of tristearin is limited to 1.0-2.0 wt% (to prevent phase sepn. and high viscosity) and the PGPR is added at sufficient concns. (PGPR/tristearin ratio of 2.0 or more). Ideally stable (for over 6-8 wk) fluid emulsions can be formed in systems composed of fat submicrocryst. hydrophilic particles and food-grade emulsifiers. These water-in-oil emulsions can serve as the basic prepn. for any food-grade water-in-oil-in-water double emulsion. [on SciFinder(R)]

The authors studied the nonionic system water/dodecane/butanol/ polyoxyethylene (10) oleyl alc., and water/dodecane/pentanol/ polyoxyethylene (8) lauryl alc. A pronounced increase in cond. may be the result of a microstructural change, not an inversion from W/O to O/W. Microstructural evolutions of two model systems along two different diln. lines, where the wt. ratios of surfactant/alc./oil are 2:1:1 and 4:3:3, resp., are similar. The inversion from W/O to O/W microemulsion should occur at a water content much higher than 20-30 wt%. (c) 1998 Academic Press. [on SciFinder(R)]

Sub-zero temp. DSC measurements were conducted to evaluate the behavior of water in non-ionic microemulsions. Two surfactant systems were studied. The first, based on ethoxylated fatty alc., octaethylene glycol mono n-dodecylether and also contg. water, pentanol and dodecane at a fixed wt. ratio of 1:1. The second system, based on oligomeric ethoxylated siloxanes, water and dodecanol as oil phase. In both systems it was found that in up to 30 wt.% of the total water content, all water mols. solubilize in the amphiphilic phase and are bound to the ethylene oxide (hereafter referred to as EO) head-groups. No free water exists in the surfactant aggregates' core. Up to three mols. of water are bound to each EO group. In the first system, the behavior changes significantly upon adding more water. The added pentanol allows further swelling and the water penetrates into the amphiphile structures and forms a reservoir of free water. Structures are deformed and grow from elongated channels (up to 15-20 wt.% water), via ill-defined (one-dimensional growth) local lamellar structures (up to ca. 60 wt.% water) to spherical normal, O/W micelles (at ≥85 wt.% water). In contrast, the oligomeric systems, due to geometrical restrictions of the amphiphiles and the nature of their curvature that prevents inversion, cannot further solubilize water in the surfactant aggregates' core, causing phase sepn. to occur. [on SciFinder(R)]

Proton NMR measurements were conducted on a U-type model quaternary nonionic microemulsion contg. varying amts. of water and having a fixed wt. ratio of surfactant [octaethylene glycol mono-n-dodecyl ether; C12(EO)8], cosurfactant (pentanol), and oil (dodecane). Chem. shift and T1 relaxation time data were used to obtain information about the microemulsion properties and structure. A slow exchange was obsd. between the hydroxyls of water, C12(EO)8, and pentanol in microemulsions contg. up to 10 wt% water. This is precedence of the hydroxyl-water interaction over hydration of the ethylene oxide (EO) groups of the surfactant. The fraction of bound water was calcd. from the chem. shift and T1 data. For the model system, chem. shift measurements indicated an inversion from W/O to O/W microemulsion at about 55-60 wt% water, in agreement with the microviscosity values evaluated from T1 data: 1.1 cP (55 wt% water) compared to 4.7 cP (30 wt% water) and 12.7 cP (10.7 wt% water). The irregularities in the monotonic dependence of the chem. shifts on water content in the microemulsion at 18 and 55 wt% water were interpreted to possibly reflect structural changes that took place in soln. [on SciFinder(R)]

Colloidal Pd prepd. in a water-org. microemulsion in the presence of the cationic surfactant aliquat 336 (trioctylmethylammonium chloride) is useful for the transfer hydrogenolysis of bromotoluene with sodium formate. The Pd catalytic activity is strongly dependent on the particle dimension, being highest for the smallest particles. The size of the particles is detd. by the prepn. conditions: coarser particles are formed at higher water contents and lower temps. The reaction obeys the mechanism of micellar catalysis. [on SciFinder(R)]