Water-in-silicone oil emulsion

ZeUsko, R, Brook, M. A. Stabilization of a-Chymottypsin and Lysozyme Entrapped in Water-In-Silicone Oil Emulsions, Langmuir 2002,18, 8982-8987. 

Keywords water-in-silicone oil emulsion, enzyme stability, protein release... 

Summary Water-in-silicone oil emulsions, stabilized by silicone-polyether surfactants, are marginally permeable to polar, but uncharged, molecules such as phenolphthalein and crystal violet. However, charged compounds, including these compounds in basic and acidic pH regimes respectively, and proteins transfer much less readily from the internal water phase to external bulk water. Transfer experiments were followed colorimetrically. These experiments shed light on the possible mechanisms by which proteins may be released from these emulsions in bioactive form simple breaking of the emulsion does not appear to be the mechanism of action. 

Applications in the biological area include stabilization of water in silicone oil emulsions by peptide-silicone hybrid polymers and the mitigation of reactive human cell adhesion on PDMS by immobilized... 

Sakai, K. Ikeda, R. Sharma, S. C. Shrestha, R. G. Ohtani, N. Yoshioka, M. Sakai, H. Abe, M. Sakamoto, K., Active Interfacial Modifier Stabilization Mechanism of Water in Silicone Oil Emulsions by Peptide-Silicone Hybrid Polymers. Langmuir 2010, 26, 5349-5354. 

In order to establish the extent to which the native conformation of the protein is retained when in contact with functional silicones, proteins are entrapped within water-in-silicone oil emulsions and their biological activity assessed. The objective is to elucidate the nature of the interaction between the biological and synthetic polymers, the role of different polar groups on the silicones, the denaturation rate of the proteins in contact with the functionalised silicones, and the role of different polar groups on the silicone polymer. Through the use of modified silicones in conjunction with proteins at these water-oil interfaces, it may possible to increase the stability of not only the interface, but of the protein as well. The results presented, combined with the ability to entrap more than one protein in the emulsion droplets at time, offers a great potential for using these systems as delivery vehicles in oral vaccinations. 9 refs. 

No systematic studies of the use of silicone surfactants as emulsifiers have yet been published. Silicone polyoxyalkylene copolymers with relatively high molecular weight and a high proportion of silicone are effective water-in-silicone oil emulsifiers and a recent study of these copolymers suggests that they stabilize emulsions by a solid-particle mechanism [68]. This type of silicone surfactant has been used to prepare transparent water-in-oil emulsions (often with an active ingredient in the internal phase) for use as deodorants or antiperspirants as well as cosmetics and other personal care products. Their use as drug delivery vehicles has also been claimed. These copolymers can also be used to prepare multiple emulsions not requiring a two-pot process. 

Kinetics. Emulsions have long been used to determine crystal nucleation kinetics, i.e., to find values of Acat and of /het or /hom as a function of supersaturation or other conditions. The material is emulsified in a suitable medium, e.g., water in silicone oil or oil in water, with a suitable surfactant, and the droplet size distribution is determined. To obtain useful results, a series of emulsions differing in average droplet size should be made. The emulsions are cooled to various temperatures Tc below Teq, and after a given time the amount of crystalline material is determined, e.g., by a change in density, or from the heat of fusion, or by means of some spectroscopic method. The same method is applied to the bulk material starting at Tc, and from the ratio of the results the value y is calculated,... 

Silicones give a imique diy-lubrieity feel to surfaces sueh as textiles, hair, and skin [38], That is why graft polysiloxane-poly(oxyalkylene) copolymers are used for making water-in-silicone oil (w/o) emulsions for personal care products [52]. The question of how to solubilize polymeric silicone oils, preferentially in microemulsions, is of high technological importance... 

The study of inverse adhesive emulsions has revealed the same features as direct emulsions [112,113]. Here again, it was shown that adhesion is favored when the surfactant becomes less soluble in the continuous phase [113]. This can be tested experimentally by using binary mixtures of oils, one in which the surfactant is soluble and another one in which the surfactant is insoluble. For example, water droplets can be stabilized in mineral oil by sorbitan monooleate (Span 80). This surfactant is soluble in dodecane whereas it is not in silicon oil. The affinity of the surfactant for the organic solvent can be tuned by mixing dodecane and silicon oil. As shown in Fig. 2.38, the energy of adhesion between water droplets strongly varies as the ratio of the mixture is changed. A sharp rise is noted as the surfactant... 

Type Silicone oil emulsion in water Appearance White liquid Density 3.5 lbs./gallon Solubility Readily disperses in water... 

The system was originally developed to formulate sun oils (solutions of ultraviolet absorbers in emollients) but has been rapidly extended, with the incorporation of basic emulsion technology, to cover oil-in-water lotions. Subsequently, the system has been further expanded to incorporate water-in-oil, oil-in-water, and water-in-silicone creams and lotions. It can now be used to formulate all types of skin care products, not just sun care products. The system won second prize in the UK DTI Manufacturing Intelligence Awards in 1991. It is the only system for which the developers have given details of costings and quantitative benefits. 

Viscoelastic and viscosimetic measurements have been performed on model systems and on commercial products [29]. Water-in-silicone emulsions have been prepared, in which the oil phase consisted of decamethylcyclopentasiloxane (cyclomethicone, D5) and the surfactant used was a branched type silicone copolymer. The interfacial rheology study of such surfactants revealed that the ability of these eopolymers to effectively stabilize water-in-D5 emulsions is a result of a process involving the nucleation, growth, and accumulation of surfactant-rich particulates at the D5/water interface [55]. 

Oil-in-oil emulsion systems display a relatively strong ER effect. Examples of such ER active emulsions are chlorinated paraffin/polydimethylsiloxane [11], castor oil/polydimethylsiloxane [13], urethane-modified polypropylene glycol/dimethylsiloxane [12] etc.. The ER effect in emulsions is attributed to the stretched droplets that Ibrm fibrillation chains along the direction of the electric field. This is a typical feature for any emulsion system in which the two liquids have a quite different dielectric constant and conductivity. Figure 17 shows the water droplet chains formed in a supercritical fluid carbon dioxide medium under a 60 Hz ac field of a very low field strength, Emax=IO V/mm [115]. A synergetic effect is observed in an system composing of polyanilines dispersed in a chlorinated paraffin/silicone oil emulsion [107],... 

Bibette et see similar effects in silicone oil-in-water emulsions stabi-... 

Uses Emollient, foaming agent for skin cleansers and hair prods, rheology control agent for gel str, in water-in-silicone emulsions emulsifier for silicone oils Regulatory JCIC registered Canada DSL listed... 

Uses Emulsifier for waler-in-oil and water-in-silicone emulsions can be used in a wide range of personal care applications such as skin care, color cosmetics, sun care, hair care, and antiperspirants and deodorants Features Designed to prepare clear gels Regulatory SARA 311/312 Acute/Fire Hazard... 

An example of the first type is the emulsion stabiliser as exemplified by sodium oleyl sulphate, cetyl pyridinium chloride and poly(ethylene oxide) derivatives. For a number of applications it is desirable that the latex be thickened before use, in which case thickening agents such as water-soluble cellulose ethers or certain alginates or methacrylates may be employed. Antifoams such as silicone oils are occasionally required. 

Fig. 18. Comparison of results from various particle systems for stirred vessel with baffles and bubble columns Activity a/ao of Acylase resin after t = 300 h, equilibrium drop diameter dg of silicon oil-water-surfactant emulsion and reference floe diameter dpv of floe system in dependency on specific power P/V H/D = 1 D = 0.15 m 0.4 m...

The most widely studied deformable systems are emulsions. These can come in many forms, with oil in water (O/W) and water in oil (W/O) the most commonly encountered. However, there are multiple emulsions where oil or water droplets become trapped inside another drop such that they are W/O/W or O/W/O. Silicone oils can become incompatible at certain molecular weights and with different chemical substitutions and this can lead to oil in oil emulsions O/O. At high concentrations, typical of some pharmaceutical creams, cosmetics and foodstuffs the droplets are in contact and deform. Volume fractions in excess of 0.90 can be achieved. The drops are separated by thin surfactant films. Selfbodied systems are multicomponent systems in which the dispersion is a mixture of droplets and precipitated organic species such as a long chain alcohol. The solids can form part of the stabilising layer - these are called Pickering emulsions. 

Eigure 4.2. The E dependence of the storage G (solid symbols) and loss G" (open symbols) moduli of a mono-disperse silicon oil-in-water emulsion stabilized with SDS, with radius a = 0.53 jam, for three volume fractions from top to bottom (j> = 77%, 60%, and 57%. The frequency is 1 rad/s the lines are visual guides. (Adapted from [10].)... 

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