Phase diagrams sugar-water

Figure 1.14.4. Phase diagram for the solubility ot sugar in water. Note that when we were drawing a phase diagram for a pure substance, water or dry ice, the parameters that were varied were temperature and pressure. In this diagram, however, the phase diagram for a mixture, temperature and composition are the parameters being varied. Pressure is assumed to be constant.

Most water-soluble solids, like salts and sugars, show eutectic phase behavior, which means that they have phase diagrams of the type depicted for fructose. Some eutectic points are as in the table. 

Fig. 1 Phase diagrams of the sugar syrfactant wo-butanol/oil/water systems EMGD - diethylene glycol monoethyl ether, o/w - oil-in-water microemulsion, w/o - water-in-oil microemulsion, he. - becontinous microemulsion, LC - liquid crystals, 2F - two phase region...

In addition, the phase boundaries for these materials in the binary surfactant-water phase diagrams are often vertical or near-vertical this translates to temperature invariant phase behavior, which is a major attraction to formulators of surfactant-based products. A further attraction of sugar-based surfactants without ionic or ionizable functional groups is that their behavior is often very stable at high salt concentrations and in alkaline conditions. 

Phase diagrams similar to the above, but where a pure compound crystallises out, apply to compounds such as benzene and naphthalene. However, if we consider a different system where A is assumed to be sugar and B water, an interesting observation is made. 

Eutectic point (Tc) A single point on a temperature concentration phase (or state) diagram for a binary solution (e.g., water and sugars or salts) where the solution can exist in equilibrium with both crystalline solute and crystalline solvent. Under equilibrium conditions, cooling at Te results in simultaneous crystallization of solvent and solute in constant proportion and at constant temperature until maximum solidification has occurred (based on Fennema, 1996). 

---