Span/Tween mixtures

Once relatively stable emulsions are identified, the loading of emulsifier can be reduced to fine tune the system. One needs to decide whether an o/w or a w/o emulsion is better for their particular application. As an example, if a 50 50 Span/Tween mixture was the best, then the required HLB would be 9.8 for this particular system. Having the HLB of the liquid then allows the formulator to search publications (22, 23) for emulsifiers or mixtures of emulsifiers that have chemical compositions compatible with the liquid in addition to having the appropriate HLB. The required HLB values of common organic liquids, oils, and waxes are also available in the literature. 

The influence of the HLB of Span-Tween mixtures on the stability of W/O and O/W systems has been studied by Boyd et al. [115] the rate of droplet coalescence was determined using a centrifugal photosedimentometer. Fig. 8.21 shows the sensitivity of coalescence rate to HLB near the critical HLB for inversion. The schematic representation (Fig. 8.22) of the polysorbate 40 and Span... 

ST68 Sonicated Span/ Tween surfactant mixture air Animal studies [19]... 

The use of pharmaceuticals in form of emulsions is of special interest. Thus, for example, o/w emulsions stabilised by surfactants, such as mono- and diglycerides, are successfully used as pseuo-doxime-proxetil protection from intestinal lumen hydrolysis through oral administration [128]. Multiple w/o/w emulsions stabilised by Tween 20/Span 20 or Tween 80/Span 80 mixtures contributed to a prolonged retention of cytarabine in one of the phases, and its gradual release ensured a prolonged action of the drug [129]. 

Anionic surfactants are the most commonly used type in the emulsion polymerization. These include sulfates (sodium lauryl sulfate), sulfonates (sodium dodecylbenzene sulfonate), fatty acid soaps (sodium or potassium stearate, laurate, palmitate), and the Aerosol series (sodium dialkyl sulphosuccinates) such as Aerosol OT (AOT, sodium bis(2-ethylhexyl) sulfosuccinate) and Aerosol MA (AMA, sodium dihexyl sulphosuccinates). The sulfates and sulfonates are useful for polymerization in acidic medium where fatty acid soaps are unstable or where the final product must be stable toward either acid or heavy-metal ions. The AOT is usually dissolved in organic solvents to form the thermodynamically stable reverse micelles. [22] Nonionic surfactants usually include the Brij type, Span-Tween 80 (a commercial mixture of sorbitol monooleate and polysorbate 80), TritonX-100[polyoxyethylene(9)4-(l,l,3,3-tetramethylbutyl)-phenyl... 

The O/W stabilizing ability of Tweens and Spans, widely used in the food and pharmaceutical industries, have been studied by a Japanese group [116, 117]. O/W emulsions prepared with Tween 20-Span 80 mixtures were unstable over the whole HLB range possible with these surfactants (4.3 to 16.9) the authors... 

Matsumoto and Sherman [190] have obtained an equation which describes the behaviour of benzene/water microemulsions stabilized by Tween 20/Span 20 mixtures with particle diameters in the range 54 to 125 nm. The volume (s) of benzene solubilized in micelles of excess emulsifier is considered and the equation takes the form. 

A mixture of 70% Tween 60 and 30% Span 65 gives optimum behavior in a given emulsion system. What composition mixture of sodium lauryl sulfate and cetyl alcohol should also give optimum behavior in the same system ... 

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. 

Concerning the SLN produced by hot homogenization as described by Olbrich et al. [19], as lipidic matrix Compritol ATO 888 or paraffin were used, as tenside a mixture of Tween 80 and Span 85 was used, and as charge carrier either EQ1 [N,N-di-(()-s(eaoryI e(liyI)-.V,A -di methylammonium chloride] or cetylpyridinium chloride were used. The resulting particles were characterized by size between 101 and 105 nm and showed zeta potentials around 40 mV at pH 7.4. 

Figure 7 indicates the phase behavior of SOW systems containing ternary nonionic surfactant mixtures that in turn contain a very hydrophilic surfactant (Tween 60 Sorbitan -i- 20 EO stearate), a very hpophihc surfactant (Span 20 Sorbitan monolaurate), and an intermediate (Tween 85 Sorbitan 20 EO trioleate or Nonylphenol with an average of 5 EO groups). The two intermediate surfactants correspond exactly to an optimum formulation in the physicochemical conditions, i.e., they exhibit three-phase behavior with the system 1 wt. % NaCl brine-heptane-2-butanol. As the intermediate hy-drophihcity surfactant is replaced by an equivalent mixture of the extreme ... 

While carrying out tests on mosquito larvicides in Florida, Burrell et al, (8) found that oils were not spreading properly on most of the waters in September, and that some type of inhibiting biological film had formed on these breeding areas after control operations had been initiated early in the summer. They compared the spreading properties of Triton X-100 and of a Span 20-Tween 20 mixture (equal parts when used in No. 2 fuel oil) the results are given in Table II. 

The solutions of surface-active materials were made up in distilled water to a concentration of 1.0 gram/dl. Mixtures of Span 80 and Tween 80 were used to obtain HLB-values of 8, 10, 12, ana 14 a mixture of Tween 20 and Tween 80 for 16 and a commercial product with the composition polyoxyethylene (40) sorbitan monolaurate gave an HLB... 

Fig. 7.21. Dependence of the lifetime of a foam from a Span-80 + Tween-80 mixture on octane...

Polysorbates are surfactants that are pegylated derivatives of sorbitan monoesters (i.e., monolaurate, monopalmitate, monostearate, monooleate, or monoisostearate) or sorbitan triesters (i.e., tristearate or trioleate) and are available in many grades. Poly-sorbate 80, also known as Tween 80, is a mixture of polyoxyethylene 20 sorbitan monooleates and is a yellow viscous liquid at room temperature. Sorbitan monooleate, also known as Span 80, is a yellow viscous... 

Spans, Tritons, and Tweens are series of nonionic surfactants. Some of these products do not represent specific chemical compounds but rather mixtures of similar compounds having different number of ethylene oxide segments and/or different lengths of hydrocarbon chain, and the apparent adsorption isotherm is a result of interaction of particular components of the mixture in solution and on the surface. 

Type C emulsions contain drops entrapped in a very large number of small internal droplets, and were prepared using a 3 1 Span 80 Tween 80 mixture. 

Surfactants also differ in the lowest interfacial tension they can give. For most amphiphiles, final y at the AW interface ranges between 35 and 42 mN m-1. At the triglyceride oil-water interface the variation is relatively larger, because y0 is smaller and T1 is, in first approximation, the same as for an A-W interface. Typical results are between 3 and 5 mN m but smaller values can be obtained for some mixtures of surfactants. An equimolar mixture of a Span and a Tween, for instance, can give a higher surface excess than either of them, and this then leads to a lower y. Addition of salt tends to give a lower y for ionic surfactants, as mentioned above a similar but smaller effect has been observed for several nonionics. 

Fig. 6.7 Interfacial tension y (a) and mean droplet diameter d (b), of a decane in water emulsions as a function of the HLB of the emulsifier mixture Span 80/Tween 80 (total 0.5 wt%)...

First, /3-CD is dissolved in 20% NaOH aqueous solution, then EPI is dropped in with stiring. The mixture reacts for 1.5 h at room temperature, and then 200 kerosene which contains emulsifier (n (tween 20) n (span 80) = 1 3) is added and vigorously mixed for 5 min to make the water phase disperse. Finally, the reaction system is heated up to 60° C, stirring speed is reduced while continuing to react for 8 h. The product is filtered and washed with diluted hydrochloric acid, methanol, distilled water and acetone, respectively. After wash, the product is dried imder vacuum. 

The liquid gelators, Span 80-Tween 80 also forms emulsion organogels and emulsion hydrogels by fluid-filled fiber mechanism. It has been reported that Span 80 (sorbitan monooleate) and Tween 80 (polyoxyethylene sorbitan monooleate) mixed in the ratio of 1 2 w/w forms organogel with better firmness and architecture as compared to the other surfactant mixture ratios.When water is added dropwise into the homogenous surfactant mixture and oil, it forms spherical reverse-micellar droplets. These droplets/fibers self-assemble to form three-dimensional architecture to immobilize apolar solvent. " Similarly, in case of hydrogels micellar structures are formed, which entraps the external liquid phase to flow and form hydrogel. 

Ponthieu etal. [176] used an aqueous solution of A1(N03)3.9H20 as the water phase dispersed in oil phases like xylene, hexane, heptane, decane or dodecane (volume ratio 1 10) in which surfactants like Tween 80 (not so effective). Span 20, 40, 80 and 85 were added. The mixture was ultrasonically agitated for emulsification, and ammonia gas bubbled through the emulsion to cause... 

Akinc and Celikkaya [169], on the other hand, synthesized yttrium oxide where the stock solution of yttrium (0.25 M) was prepared in a similar way this solution was dispersed in toluene as the continuous phase, containing a dissolved mixture of Span 60 (Sorbitan monostearate) and Tween 80 (the most satisfactory volume ratio was 2 1) as emulsifier. Triethanolamine was used as the precipitating agent, while methanol was used for breaking the emulsion. A standard emulsion formulation had 150 ml of the water phase dispersed in 430 ml of the oil phase, with 10 g of Span 60 and 8 ml of Tween 80. The spherical particles of Y2O3 obtained by calcination at 700 C had a size range of 0.2-2 pm, peaking at around 0.6 pm. In another work, Celikkaya and Akinc [192] destabilized the system after precipitation by addition into acetone. 

The practical potential of nonionic MLC was demonstrated by the use of micellar solutions of Brij 35 in the analysis of tobacco [18], Samples of smoking tobacco were extracted with an ueous solution of 30% Brij 35, and an aliquot of the extract was chromatographically separated without further preparation, with a 6% Brij 35 mobile phase. Comparison with an aromatic aldehyde standard mixture enabled verification of vanillin and ethylvanillin as two of the extract components. Brij 35 was chosen for this study over other nonionic surfactants (such as Tritons , Spans , Igepals or Tweens ) on the basis of its commercial availability, high purity, low cost, low toxicity, high cloud temperature, and low background absorbance, compared to the other types of surfactants mentioned. Brij 35 does not possess a strong chromophore and its absorption is minimal. 

---