Phase inversion temperature , emulsifier

The phase-inversion temperature (PIT) is defined as the temperature where, on heating, an oil—water—emulsifier mixture inverts from O/W to a W/O emulsion [23]. The PIT correlates very well with the HLB as illustrated in Fig. XIV-10 [72, 73]. The PIT can thus be used as a guide in emulsifier selection. 

At low temperature, nonionic surfactants are water-soluble but at high temperatures the surfactant s solubUity in water is extremely smaU. At some intermediate temperature, the hydrophile—Hpophile balance (HLB) temperature (24) or the phase inversion temperature (PIT) (22), a third isotropic Hquid phase (25), appears between the oil and the water (Fig. 11). The emulsification is done at this temperature and the emulsifier is selected in the foUowing manner. Equal amounts of the oil and the aqueous phases with aU the components of the formulation pre-added are mixed with 4% of the emulsifiers to be tested in a series of samples. For the case of an o/w emulsion, the samples are left thermostated at 55°C to separate. The emulsifiers giving separation into three layers are then used for emulsification in order to find which one gives the most stable emulsion. 

K. Shinoda and H. Aral The Correlation between Phase Inversion Temperature in Emulsion and Cloud Point in Solution of Nonionic Emulsifier. J. Phys. Chem. 68,... 

Just as solubilities of emulsifying agents vary with temperature, so does the HLB, especially for the non-ionic surfactants. A surfactant may thus stabilize O/W emulsions at low temperature, but W/O emulsions at some higher temperature. The phase inversion temperature (PIT), at which the surfactant changes from stabilizing O/W to W/O emulsions, is discussed in Section 3.6.1. 

Tornberg and Ediriweera, 1987). Phase inversion temperature (Shinoda and Saito, 1969) and emulsifying capacity (Swift et al., 1961) have been used to evaluate the effects of low molecular weight and protein emulsifiers, respectively. Unfortunately, it is not possible to measure the size of the large droplets present in unhomogenized water-in-oil emulsions because the droplets coalesce very quickly. The phase inversion temperature is not a relevant test, as it may not be related directly to the stability to inversion at the emulsification temperature. Furthermore, it has been stated (Matsumoto and Sherman, 1970) that water-in-oil emulsions do not exhibit a true phase inversion temperature, unlike oil-in-water emulsions. 

A method requiring much less mechanical energy uses phase inversion see also the discussion of phase inversion temperature in the section Emulsifying Agents )- For example, if ultimately a W/O emulsion is desired, then a coarse OAV emulsion is first prepared by the addition of mechanical energy, and the oil content is progressively increased. At some volume fraction above 60-70%, the emulsion will suddenly invert and produce a W/O emulsion of much smaller water droplet sizes than were the oil droplets in the original O/W emulsion. 

A complementary means of emulsifier selection, the phase inversion temperature (PIT), which employs a... 

Four different emulsifier selection methods can be applied to the formulation of microemulsions (i) the hydrophilic-lipophilic-balance (HLB) system (ii) the phase-inversion temperature (PIT) method (iii) the cohesive energy ratio (CER) concept and (iv) partitioning of the cosurfactant between the oil and water phases. The first three methods are essentially the same as those used for the selection of emulsifiers for macroemulsions. However, with microemulsions attempts should be made to match the chemical type of the emulsifier with that of the oil. A summary of these various methods is given below. 

Shinoda, K.andArai, H. (1964) The correlation between phase inversion temperature in emulsion and cloud point in solution of nonionic emulsifier. /. Phys. Chem., 68, 3485-3490. 

Data on the preparation of alkyd emulsions by the phase inversion technique were presented in [211]. This technique is accomplished by adding water to an alkyd/surfactant mixture under formation of a stable emulsion. The determination of surfactant s solubility in water and alkyd phases allows to calculate the quantity of water required for phase inversion. Effective emulsifiers are ethoxylated sulphates (2-3 EO groups) of C12 - Ch and C16 - Cig higher alcohols. With these surfactants, the emulsification becomes less dependent on the temperature than with nonionic surfactants. 

Figure 11 Cloud-point temperature of micellar solutions as a function of the ethylene oxide chain length the hydrophobic part is an alkyl chain with 8 ( ), 10 ( ), 12 ( ), or 16 ( ) carbon atoms. Data from Ref. 51. The sjunbols ( ) represent the phase-inversion temperature for a 1 1 cyclohex-ane-water emulsion containing 5% of commercial ethylene oxide based emulsifiers having dodecylalkyl chains as a hydrophobic group. (Data from Ref. 54.)...

The phase-inversion temperature, according to Shin-oda and Saito (17). The effective HLB value is strongly temperature-dependent (the emulsifier becomes less hydrophilic with increasing temperature) when ethoxylated surfactants are used. In an emulsion system, this can be followed by the phase-inversion temperature, which corresponds to the temperature at which the effective HLB is about 6. In food and feed applications, this is fairly rarely used as purely ethoxylated surfactants are seldom used in such systems. 

Since the cloud point of a surfactant is a structure related phenomenon, it should also be related to HLB, solubility parameter, cmc, and other parameters, as is found to be the case. Clearly, temperature can play an important role in determining surfactant effectiveness where hydration (or hydrogen bonding) is the principal mechanism of solubilization. Because of the temperature sensitivity of such materials, their activity as emulsifiers and stabilizers also becomes temperature sensitive. In particular, their ability to form and stabilize o/w and w/o emulsions may change dramatically over a very narrow temperature range. In fact, an emulsion may invert to produce the opposite emulsion type as a result of temperature changes. Such a process is termed phase inversion, and the temperature at which it occurs for a given system is its phase inversion temperature (PIT). 

The phase inversion temperature (PIT) of an emulsifier designates a point in the temperature scale where its hydrophilic and lipophilic properties exactly balance. This can serve as a measure of the hydrophile-lipophile balance especially for the non-ionic surfactants facile experimental determination of the PIT is obviously an advantage [38]. 

The selection of different surfactants in the preparation of EWs emulsion is still made on an empirical basis. This is discussed in detail in Chapter 6, and only a summary is given here. One of the earliest semi-empirical scales for selecting an appropriate surfactant or blend of surfactants was proposed by Griffin [49, 50] and is usually referred to as the hydrophilic-lipophilic balance or HLB number. Another closely related concept, introduced by Shinoda and co-workers [51-53, 58], is the phase inversion temperature (PIT) volume. Both the HLB and PIT concepts are fairly empirical and one should be careful in applying them in emulsifier selection. A more quantitative index that has received little attention is that of the cohesive energy ratio (CER) concept introduced by Beerbower and Hill [54] (see Chapter 6). The HLB system that is commonly used in selecting surfactants in agrochemical emulsions is described briefly below. 

PIT - Phase inversion temperature of emulsion based on non-ionic emulsifiers... 

Although HLB is an important tool in industrial studies related to emulsions, it does not account for changes of temperature, which can be very important For this reason, Shinoda and Arai introduced about 40 years ago the so-called phase inversion temperature (PIT), which is the temperature at which an emulsion based on nonionic emulsifiers will change from oil-in-water to watCT-in-oil. To carry out this experiment equal weights of oil and water are mixed with 3-5% surfactant to make the emulsion and then the emulsion is heated until an inversion is apparent. The PIT occurs for thermod5mamic reasons (for a temperature below PIT, the emulsifiCT is strongly polar, above PIT the emulsifier interacts much less with water). The temperature dependency... 

As an alternative, the mayonnaise can be produced using selected non-ionic emulsifiers. In this case, the emulsion has a phase inversion temperature of 30 °C. Explain what is meant by a phase inversion temperature and discuss whether the value provided for the mayonnaise can result in any practical problems. 

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