Hydrophile-lipophile balance temperature interfacial tension

The temperature (or salinity) at which optimal temperature (or optimal salinity), because at that temperature (or salinity) the oil—water interfacial tension is a minimum, which is optimum for oil recovery. For historical reasons, the optimal temperature is also known as the HLB (hydrophilic—lipophilic balance) temperature (42,43) or phase inversion temperature (PIT) (44). For most systems, all three tensions are very low for Tlc < T < Tuc, and the tensions of the middle-phase microemulsion with the other two phases can be in the range 10 5—10 7 N/m. These values are about three orders of magnitude smaller than the interfacial tensions produced by nonmicroemulsion surfactant solutions near the critical micelle concentration. Indeed, it is this huge reduction of interfacial tension which makes micellar-polymer EOR and its SEAR counterpart physically possible. 

Kunieda, H. and Shinoda, K. (1980) Solution behaviour and hydrophile-lipophile balance temperature in the Aerosol OT-isooctane-brine system-correlation between microemulsions and ultralow interfacial tensions. /. Colloid Interface Sci., 75, 601-606. 

Surfactants adsorb on liquid-air and oil-water interfaces and decrease surface and interfacial tensions and the corresponding works of adhesion. Thus, they facilitate the cleaning of various surfaces. Important characteristics in surfactant science, and for understanding their action in cleaning and other applications, include both parameters of the surfactants (CMC, Krafft point, hydrophilic/lipophilic balance) and of the (often aqueous) solution they are in (temperature, salts, co-surfactants, time). We will discuss all of these parameters in this chapter. 

When an 0/W emulsion is prepared using a nonlonlc surfactant of the ethoxylate type and is heated, then at a critical temperature (the PIT), the emulsion inverts to a W/0 emulsion. At the PIT the hydrophilic and lipophilic components of the surfactant are exactly balanced and the PIT is sometimes referred to as the HLB temperature. At the PIT the droplet size reaches a minimum emd the interfacial tension also reaches a minimum. However, the small droplets are unstable and they coalesce very rapidly. 

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