Creams liquid crystal

FIG. 11. Transmission electron micrographs of freeze fractured oily droplets dispersed (a) in a hexagonal and (b) in a cubic liquid crystalline phase, bar 100 nm. From Mueller-Goymann, C., Liquid crystals in emulsions, creams and gels, containing ethoxylated sterols as surfactant, Pharm. Res. 1 154-158 (1984). 

Similar to Voltaren" Emulgel, oily droplets of an eutectic mixture of lidocaine and prilocaine are dispersed in a hydrogel to provide local anesthesia to the skin for injections and siugical treatment (Emla cream). A further possibility is the dermal administration of a liposome dispersion as a spray (Heparin PUR ratiopharm Spriih-gel "). After administration, water and isopropylic alcohol evaporate partially resulting in an increase of concentration and in a transition from the initial liposome dispersion into a lamellar liquid crystal [32]. The therapeutic effect appears to be influenced favorably by the presence of lecithins rather than by the degree of liposome dispersion. 

Usually the surfactant concentration in ointments and creams is significantly lower than in surfactant gels. Ointments are non-aqueous preparations, whereas creams result from ointments by adding water. The microstructure of both ointments and creams may consist of liquid crystals, as long as a liquid crystalline network or matrix is formed by amphiphilic molecules. In a liquid crystalline matrix, it is easier to deform the system by shear such formulations show plastic and thixotropic flow behavior on shear. In comparison to systems with a crystalline matrix which are usually destroyed irreversibly by shear, those with a liquid crystalline matrix exhibit a short regeneration time of... 

Mileller-Goymann, C. Liquid crystals in emulsions, creams and gels, containing ethoxylated sterols as surfactant. Pharm. Res. 1984,1, 154-158. 

Cetostearyl alcohol is used in cosmetics and topical pharmaceutical preparations. In topical pharmaceutical formulations, cetostearyl alcohol will increase the viscosity and impart body in both water-in-oil and oil-in-water emulsions. Cetostearyl alcohol will stablize an emulsion and also act as a co-emulsifier, thus decreasing the amount of surfactant required to form a stable emulsion. Cetostearyl alcohol is also used in the preparation of nonaqueous creams and sticks. Research articles have been published in which cetostearyl alcohol has been used to slow the dissolution of water-soluble drugs.In combination with surfactants, cetostearyl alcohol forms emulsions with very complex microstructures. These microstructures can include liquid crystals, lamellar structures, and gel phases. ... 

Good physical stability can, however, be obtained by developing a viscoelastic network in the continuous phase. The elastic component acts as a net that prevents the droplets from settling or creaming. Viscoelastic networks can be obtained with high-molecular-weight water-soluble polymers or lyotropic liquid crystals. 

We would like to note here that the silicone oils used have a lower density than the liquid crystal. As a result, the oil particles tend to cream and lie closer to the... 

Bingham-plastics resist a small shear stress, but flow easily imder larger shear stresses. Examples include toothpaste, jellies, some slurries, smectic liquid crystals, foams (shaving cream). 

Many natural and manufactured substances exist or have been processed as emulsions, including some foods, pharmaceuticals and cosmetics, coal, insecticides, and crude oil [1-4], Food emulsions are broadly defined as any system where there are at least two immiscible phases consisting of solids, liquids, gases, and/ or liquid crystals. Oil-in-water (O/W) emulsions (cream, dressings, etc.) are typically fluid and may contain a (partially) crystalline oil phase, whereas food-related water-in-oil (W/O) emulsions (butter, margarine, etc.) are typically soUd-like [5]. 

It is very often the commercial interest in novel materials which stimulates the growth in their study and eventual exploitation. This is certainly true in the case of thermotropic liquid crystals and their application in electro-optic displays. Indeed, the production of high-strength, high-modulus fibres has seen a wealth of interest in lyotropic main chain polymers. The use of lyotropic side chain polymers has, by comparison, been less well publicized. This is not to say that there are no applications. Alkyl polyoxyethylene surfactants attached to polysiloxane polymers have found uses in many personal care products such as liquid soaps, shampoos, skin creams, and hair mousses. Unfortunately the physical properties of these and other similar materials have been closely guarded secrets and the amount of information available in the literature is low. The limited data which does exist, however, provides us with some interesting structure - behaviour relationships. 

In 1770 C. W. Scheele showed that the natural product cream of tartar is a salt with a vegetable alkaline base (potash) supersaturated with a vegetable acid (tartaric). When he dissolved cream of tartar [potassium acid tartrate] in boiling water and added powdered chalk to the solution, the lime combined with part of the tartaric acid and gave a copious white precipitate. On evaporating the supernatant liquid he obtained crystals of soluble tartar [normal potassium tartrate] (9, 10). 

To ascertain if the precipitate is really cream of tartar, the following test, due to D6nig6s, is used When the crystalline precipitate has settled, the supernatant liquid is decanted off and the precipitate washed with a fine stream of alcohol into a dish, the excess of alcohol being then evaporated. Some of the remaining crystals arc introduced into a test-tube containing 3 c.c. of concentrated sulphuric acid and 3 drops of a resorcinol solution prepared by dissolving 2 grams of pure resorcinol in 100 cc. of water acidified with 5 CjC. of sulphuric acid. The solution is heated to 130-140° in presence of tartaric acid, a distinct carmine coloration is produced. 

The structure of whipped topping is thus completely different from that of whipped dairy or liquid imitation creams. In the latter systems the air bubbles appear to be covered in a monolayer of fat globules, which are rarely deformed and which protrude with a substantial part of their volume into the air phase of the bubbles. If large fat crystals are present, they are considered detrimental to foam stability, in contrast to whipped toppings6 (Figure 7). 

The flocculated fat globules of whipped cream contain fewer contact points, and the foam is therefore not as stiff as in toppings in which the aggregated crystal platelets have a large surface area, many contact points and thus increased stiffness. This means that an acceptable topping foam may be formed at a much lower fat content than is the case with liquid whipping creams. 

White mustard (Sinapis alba L.) honey is golden yellow when liquid and acquires a cream-yellow tinge when it crystallizes. 

Selenium is a steel gray or purplish powder, also fabricated into pellets, sticks, or plates. Selenium dioxide, selenous acid, and the alkali-metal selenites and selenates are colorless powders or crystals. Selenium chloride (reddish yellow), selenyl chloride (colorless or yellow) (bp, 176°C), and selenic acid (colorless) are liquids, whereas selenium tetrachloride is a cream-colored crystalline solid.1... 

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