Emulsification by PIT method

Shinoda, K. and Saito, H. (1969) Thestability of O/W type emulsions as functions of temperature and the HLB of emulsifiers the emulsification by PIT-method. Journal of Colloid and Interface Science, 30, 258-263. 

Shinoda, K. and Saito, H., The stability of O/W type emulsions as fimctions of temperature and the HLB of emulsifiers the emulsification by PIT-method, J. Coll. Interf. ScL 30, 258 263, 1969. Austad, T. and Milter, J., Surfactant flooding in enhanced oil recovery, in Surfactants, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L., Ed., Cambridge University Press, Cambridge, 2000, pp. 203 249. 

Shinoda K, Saito H (1969) Stability of o/w type emulsions as function of tempraatuie and HLB of emulsifier—emulsification by PIT method. J Colloid Interface Sci 30 258—265... 

For optimum stability, Shinoda and Saito (1969) suggest emulsification by the PIT method, in which the emulsion is prepared at a temperature 2-4°C below the PIT and then cooled down to the storage temperature (for O/W emulsions). This is because an emulsion prepared near the PIT has a very fine average particle size but is not very stable to coalescence. Cooling it down to a temperature considerably below the PIT increases it stability without significantly increasing its average particle size. 

In path 3 (Fig. 17) the initial system is set at SAD = 0 or at SAD slightly positive, and a formulation change shifts it to SAD = 0. This can happen by changing the temperature (emulsification by the PIT method) (215) or formulation, so that the siufactant passes from one phase to the other, often producing a spontaneous emulsification. Another way to trigger an easy emulsification is by adding an alkaline aqueous solution that reacts with carboxylic acids present in the oil phase and results in interfacial formation of surface-active substances (216). 

Microemulsions are used in many cosmetic products and are the focus of current industrial and university research. Common aspects of microemulsions in cosmetics are performance on oily soils product aesthetics which includes clarity and multiphase products adjusted flow behavior microemulsions as carrier and protective matrix for actives, and the use of intermediate microemulsions phases in the emulsification process by means of the phase inversion temperature (PIT) method (72). 

This is applied in the so-called PIT method of Shinoda et PIT stands for phase-inversion temperature. It is observed that many nonionic surfactants decrease in HLB number with increasing temperature. Below the PIT (which also depends on the composition of both phases), an 0/W emulsion tends to be formed, but above the PIT, a W/0 emulsion see further on for an explanation. At the PIT the interfacial tension is very small, and quite small droplets result. These are unstable to coalescence, but by rapidly cooling the emulsion after emulsification a stable 0/W emulsion having fine (h oplets can be obtained. The droplet break-iq) is presumably in regime TV and fairly small e values suffice. The method is widely applied in industrial practice. 

Shinoda also studied emulsions that were produced at temperatures below the PIT, at the PIT and above the PIT with rapid cooling to aid stability. Drop sizes of emulsions produced at the PIT were retained in the final cooled emulsion. Shinoda noted that emulsions with the finest drops were produced by emulsifying 2-4 C below the PIT and then cooling. Shinoda termed this emulsification method emulsification by the PIT method . The study also showed that emulsification by the inversion method , i.e. emulsification above the PIT as a W/O emulsion and then cooling, did not result in such small drops. 

FIGURE 21.3 Droplet size, at 40°C, as a function of surfactant concentration for samples with an OAV weight ratio (R ) fixed at 0.2, after emulsification by the PIT method. (From Morales, D. et al., Langmuir, 2003, 19, 7196-7200. With permission.)... 

At constant temperature, phase transitions (similar to those observed in the PIT method) may take place by changing composition during the emulsification process [23,14], that is, a phase inversion can be induced by a change in composition. Although PEO-type surfactants are not required in the PIC method, numerous investigations have used these type of surfactants for the preparation of direct (0/W) nano-emulsions [57,26,58,19,59,32] and reverse (W/O) nano-emulsions, reported for the first time by Uson et al. [27]. 

The conditions for obtaining O/W nano-emulsions with a minimum droplet size and consequently low polydispersity by phase inversion emulsification methods (PIT and PIC) can be summarized as follows A bicontinuous microemulsion or a lamellar liquid crystalline phase (D or L , respectively), with all the oil dissolved, must be formed immediately before reaching the final two-phase region where the nano-emulsions form. These are composition conditions necessary but not sufficient, because the kinetics of incorporation of oil to these phases or the coalescence of droplets can make the nano-emulsion droplet size also dependent on preparation variables such as mixing rate and aqueous phase addition rate for the PIC method, or cooling rate for the PIT method. 

These methods make use of the phase transitions that take place during the emulsification process. The so-called phase inversion temperature (PIT) method is widely used in industry [49,50]. This method, introduced by Shi-... 

It is, of course, not necessary to form an emulsion by mechanical dispersion of oil and water phases. One method that has been nsed to form oil-in-water emnlsions with small and uniform drops in a nonionic snrfactant system is to start with the surfactant phase near the PIT and cool it rapidly by perhaps 20°C to 30°C (Friberg and Solans, 1968 Forster et al., 1995 Sagitani, 1992). The capacity for solubilization of oil decreases dramatically npon cooling, and the excess oil nucleates as small drops from the supersaturated microemulsion. Provided that it solubihzes substantial oil, the lamellar liqnid crystalline can also be cooled in this manner to form oil-in-water emulsions (Forster et al., 1995). Spontaneous emulsification can also be prodnced by diffusion, as discussed in Chapter 6. 

Figure 7 depicts the case of a transition by cooling for a nonionic system, the so-called PIT emulsification method [64], because the formulation variable is temperature, and the FILD = 0 optimum formulation is attained at the phase inversion temperature. In this case the emulsion at a temperature above the PIT is W/O then as temperature decreases the microemulsion oil phase solubilizes more and more water and the water drops vanish. 

FIG. 3 Schematic representation of emulsification methods A, B (at constant temperature) and PIT (phase inversion temperature). (From Ref. 16 by permission of Langmuir, Copyright 2001, American Chemical Society.)... 

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