Soaps solid-phase properties

Some substances exist in more than one liquid form liquid crystals or anisotropic liquids, forming various types of mesomorphic phases (nematic, smectic, cholesteric). They share properties normally associated with both liquids and crystals. Sodium soaps have numerous mesomorphic states. Amorphous (metastable) phases of a substance may also display polymorphism. However, often the term polymorph is explicitly restricted to the solid phase and polymorphic transformations are restricted to transformations involving phases with different crystal structures which are part of a single component system such solid polymorphs form an identical liquid on melting. For example, phosphorous has many solid allotropes, which all revert to the same P4 form when melted to the liquid state. In contrast, for isomers the difference between them persists in the liquid phase. Polymorphs (allotropes) can be combined with other substances to give the same compounds isomers give different reaction products. 

A foam is a dispersion of gas bubbles in a relatively small volume of a liquid or solid continuous phase. Liquid foams consist of gas bubbles separated by thin liquid films. It is not possible to make a foam from pure water the bubbles disappear as soon as they are created. However, if surface active molecules, such as soap, emulsifiers or certain proteins, are present they adsorb to the gas-liquid interfaces and stabilize the bubbles. Solid foams, e.g. bread, sponge cake or lava, have solid walls between the gas bubbles. Liquid foams have unusual macroscopic properties that arise from the physical chemistry of bubble interfaces and the structure formed by the packing of the gas bubbles. For small, gentle deformations they behave like an elastic solid and, when deformed more, they can flow like a liquid. When the pressure or temperature is changed, their volume changes approximately according to the ideal gas law (PF/r= constant). Thus, foams exhibit features of all three fundamental states of matter. In ice cream, the gas phase volume is relatively low for a foam (about 50%), so the bubbles do not come into contact, and therefore are spherical. Some foams, for example bubble bath. 

Smectic" means soap in Greek since it tends to have mechanical properties akin to those of soaps. The simplest smectic phase is the smectic-A phase. This phase has traditionally been described as a system that is a solid in the direction along the director and a fluid normal to the director. A smectic-C phase is similar except that the density-wave vector makes a finite angle with the director. 

A wide variety of solid soap phases have been postulated but it is the four phases, a, o) and 6, which are of greatest interest in the soap-finishing processes of soap manufacture for their distinctive physical properties (Ferguson et aL, 1943). The a form is a... 

Lather volume depends upon the amount and the type of soap dissolved in the soap liquor during lathering. The mobility of the soap molecules, in addition to their surface properties, contributes to foaming. It is therefore possible that the soaps with very short chains (sodium caprylate and sodium caprate) may have an additional lather benefit. However, the proposed benefit should be restricted to low wash temperatures. The source of the short chain soaps is the coconut or palm kernel oil component of the fat charge. The amount of soap in solution in the wash liquor increases as the level of soluble soap in the bar increases. However, because the lather depends on the very short transient hydration period, it is the amount of soap which goes into solution over this period that is important. This amount also increases as the rates of dissolution of the solid soluble phases of the bar structure increase. 

While an increase in the electrolyte concentration in a soap liquor will always cause some reduction in lather it is believed that the gross reduction in lather often observed in high-electrolyte bars stems more from the influence of electrolyte on the types of solid soap phase content of the bar structure than from any subsequent influence which electrolyte may have on soap liquor properties. 

---