Inverse temperature transitions inverted phase transitional

Inverted Phase Transitional Behavior of Inverse Temperature Transitions... 

As demonstrated in Figure 5.3 for several model proteins, essentially unlimited solubility occurs at low temperature, and phase separation (insolubility) occurs as the temperature is raised. Also, for our model protein composi-tions, - the curvature of the coexistence line is inverted, having the shape of a valley instead of a smooth mountain peak. Because of this we call the phase transition, exhibited by elastic-contractile model proteins, an inverse temperature transition. Even more compelling reasons exist for the inverse temperature transition label. 

Figure 5.3. Phase diagram for several elastic-contractile model proteins, showing an inverted curvature to the binodal or coexistence line (when compared with petroleum-based polymers) that is equivalent to the T,-divide, with the value of T, determined as noted in Figure 5.IB. Solubility is also inverted with insolubility above and solubility below the binodal line, that is, solubility is lost on raising the temperature whereas solubility is achieved by raising the temperature of most petroleum-based polymers in their solvents. Note that addition of a CHj group lowers the T,-divide and removal of the CH2 group raises the T,-divide. For these and the additional reason of increased ordering on increasing the temperature, the phase transitions of elastic-contractile model proteins are called inverse temperature transitions. (The curve for poly[GVGVP] is adapted with permission from Manno et al. and Sciortino et al. ).

Inverted Phase Diagrams of Hemoglobins A and S A Further Diagnostic of Inverse Temperature Transition Using the Spinodal Line... 

As a rule, the HLB number is sensitive to temperature variation. For most surfactants, HLB increases by raising the temperature, so that at a certain temperature a phase transition may take place. Thus, a w/o emulsion may invert into an o/w emulsion upon increasing the temperature. Around the phase inversion temperature, HLB == 7, which results in a rather unstable emulsion. 

A third class is phase inversion. Here, emulsions are made by starting with an emulsion in which the ultimate continuous phase is the dispersed phase and vice versa. Then by adding more and more dispersed phase, one can induce the emulsion to suddenly invert (catastrophic inversion). Alternatively, one can choose the surfactant system such that, for example, by a temperature change, the surfactant system changes from favouring the initial emulsion to favouring an inverted emulsion. This is called transitional phase inversion. 

To apply the phase inversion principle, the transitional inversion method should be used, as demonstrated by Shinoda and coworkers [11, 12] when using nonionic surfactants of the ethoxylate type. These surfactants are highly dependent on temperature, becoming lipophilic with increasing temperature due to dehydration of the poly(ethylene oxide) (PEO) chain. When an O/W emulsion that has been prepared using a nonionic surfactant of the ethoxylate type is heated, at a critical temperature - the PIT - the emulsion will invert to a W/O emulsion. At the PIT, the droplet size reaches a minimum and the interfacial tension also reaches a minimum, but the small droplets are unstable and coalesce very rapidly. Rapid cooling of an emulsion that has been prepared close to the PIT results in very stable and small emulsion droplets. 

---