Shinoda phase inversion temperature

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,... 

Shinoda K, Aral H (1967) The effect of phase voliune on the phase inversion temperature of emulsions stabilized with nonionic simfacatnts. J Colloid Interface Sci... 

The interfacial tension y at the planar interface has a minimum near the temperature Indeed, at the latter temperature r is small, A/jt0 = 0 and because d ij w/d J and dfi /dT have opposite signs and s is also small (because T is small), dy/d I 0. The temperature T0 is provided by Eq. (25) and is independent of the concentration of surfactant. In other words, the two minima of Fig. 4 which correspond to the phase inversion temperatures of a macroemulsion (the curve with a positive minimum) and microemulsion (the curve with a negative minimum) are the same. When emulsions are generated from a microemulsion and its excess phase, the emulsion is of the same kind as the microemulsion, the phase inversion temperature is obviously located in the middle of the middle phase microemulsion range and the above conclusion remains valid. The above results explain the observation of Shinoda and Saito [6,7] that the phase inversion temperature (PIT) of emulsions can be provided by the ternary equilibrium phase diagram. 

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. 

Shinoda and Kuineda [8] highlighted the effect of temperature on the phase behavior of systems formulated with two surfactants and introduced the concept of the phase inversion temperature (PIT) or the so-called HLB temperature. They described the recommended formulation conditions to produce MEs with surfactant concentration of about 5-10% w/w being (a) the optimum HLB or PIT of a surfactant (b) the optimum mixing ratio of surfactants, that is, the HLB or PIT of the mixture and (c) the optimum temperature for a given nonionic surfactant. They concluded that (a) the closer the HLBs of the two surfactants, the larger the cosolubilization of the two immiscible phases (b) the larger the size of the solubilizer, the more efficient the solubilisation process and (c) mixtures of ionic and nonionic surfactants are more resistant to temperature changes than nonionic surfactants alone. 

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. 

In determining the emulsification temperature for emulsions stabilised with EO containing nonionics, the consideration of the phase inversion temperature (PIT or HLB-temperature) suggested by Shinoda and co-workers [193] can be also important in order to select the surfactant of optimum HLB. The PIT of an emulsion depends not only on the structure of surfactant(s), but also on many other parameters, such as the surfactant concentration, nature of the oil, phase ratio, or the presence of salts. The lowest interfacial tension at the PIT is the important factor for obtaining emulsions with small average droplet size and hence good stability. 

Figure 14 (right) indicates the variation of the emulsion drop size along a formulation scan, which here is a temperature scan with a non ionic surfactant. Optimum formulation, here optimum temperature T, essentially corresponds to Shinoda s phase inversion temperature (PIT) (80) where the surfactant affinity switches from hydrophilic to lipophilic. 

Nevertheless, it is now understood that HLB essentially depends on the surfactant, while the phase behavior and emulsion properties are also related to the water and oil phase nature, as well as to the temperature (100). The temperature was the preferred variable in the case of nonionic surfactants which are very sensitive to it, and an experimentally based concept was first introduced by Shinoda to quantify the formulation, i.e., the phase inversion temperature (PIT) (105, 106). It is known that the hydrophilicity of a nonionic surfactant decreses when temperature decreases. In water solution there exists a temperature at which the surfactant is no longer soluble and thus produces a separate phase. This so-called cloud point occurrence is related to the Shinoda PIT, which is essentially the same phenomenon, but in the presence of an oil phase whose nature could facilitate this separation and make it happen at a lower temperature. Although the PIT is limited to the liquid water temperature range of nonionic surfactants, its introduction was an important milestone because it was related not only to the surfactant, but also to the whole physicochemical environment (107), a feature that was shown to be essential by Winsor. 

The phase-inversion temperature (PIT) is the temperature at which the continuous and dispersed phases of an emulsion system are inverted (e.g. an o/w emulsion becomes a w/o emulsion, and vice versa). This phenomenon, introduced by Shinoda (16), occurs for emulsion systems containing non ionic surfactants, and can be a valuable tool for predicting the emulsion behaviour of such systems. The phase inversion occurs when the temperature is raised to a point where the interaction between water and the nonionic surfactant molecules decreases and the surfactant partitioning in water decreases. Hence, surfactant molecules... 

If we take also into consideration the work of Shinoda and others (9,10) on the composition of emulsions and microemulsions, we see a drastic change of the composition at a given temperature, the phase inversion temperature PIT. The problems connected with the thermostatting of the measurement apparatus may then easily be imagined. 

The second intent to numerically characterize the formulation concept was the so-called phase inversion temperature (PIT), originally introduced by K, Shinoda in 1964 as the temperature at which a polyeihoxylated nonionic surfactant. switched Its dominant afhnity from the aqueous phase to the oil phase to produce a change in emulsioa type. This was both easy to determine experimentally and simple to understand as far as the related phenomenology was concerned (48-50). 

For nonionic surfactants, particularly those of the ethoxylate type, a selection can be made based on the hydrophUic-lipophilic balance (HLB) concept (Chapter 6). A closely related system developed by Shinoda and his collaborators is based on the phase inversion temperature (PIT) concept. This is also described in detail in Chapter 6. 

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. 

The phase inversion temperature (PIT) concept which has been developed by Shinoda [95,96] is closely rated to the HLB balance concept described above. Shinoda and coworkers found that many 0/W emulsions stabilized with nonionic surfactants undergo a process of inversion at a critical temperature (PIT). The PIT can be determined by following the emulsion conductivity (small amount of electrolyte is added to increase the sensitivity) as a function of temperature. The conductivity of the 0/W emulsion increases with increasing temperature until the PIT is reached, above which there will be a rapid reduction in conductivity (W/0 emulsion is formed). 

Shinoda and Takeda [7] reported that added salts in water alter the HLB and, consequently, the cloud point of nonionic surfactants. Consequently, this is also reflected in a change of emulsion PIT (phase-inversion temperature). This effect is explained by the... 

The second intent to numerically characterize the formulation concept was the so-called phase-inversion temperature (PIT), originally introduced by Shinoda in 1964 as the temperature at which a nonionic surfactant switched its dominant affinity from the aqueous phase to the oil phase. This inversion occurred in a so-called phase transition process that was both easy to determine experimentally and simple to understand as far as the associated phenomenology was concerned [107,108]. Later, it was related to the temperature at which the emulsion inversion takes place [57,58,109], which is the same in most cases, with scarce exceptions and with no real significance [110]. It was finally fine-tuned again and renamed the HLB temperature [111], as a way of stating that it was the temperature at which the hydrophilic and lipophilic tendencies of the surfactant were balanced (i.e., whenever a Winsor Type III system is occurring). 

O/W emulsions stabilized with non-ionic surfactants tend to form W/O emulsions at elevated temperatures as the surfactant molecules dehydrate and become more lipophilic. The phase inversion temperature (PIT) can thus be ascertained by experiment. Arai and Shinoda [39] have found that the PIT of emulsions in which the oil phase consists of oil mixtures can be expressed as... 

Figure 8.6 The effect of the mixture of n-heptane with various oils on the phase inversion temperatures of emulsions stabilized with 3 % w/w in water of polyoxyethylene (9.6) nonyl phenyl ether. From Arai and Shinoda [39] by permission of Academic Press.

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... 

It is now well established that the choice of emulsification conditions is an important consideration in determining the ultimate drop size (and hence stability) of an emulsion. Using nonionic surfactants, Shinoda and Saito demonstrated that emulsification at the phase inversion temperature (PIT) followed by cooling led to the formation of stable O/W emulsions of small drop size. Emulsification at temperatures higher than the PIT, initially producing W/O emulsions, resulted in very stable emulsions on subsequent cooling. The inversion process, forming a... 

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. 

The effect of additives in the water and oil phases. Although the exact mechanism by which various additives affect the phase inversion is not fully understood, their presence in nSOW systems has been shown to affect the PIT as well as the emulsion inversion point, EIP. " The phase inversion temperature varies with the amount and chemical type of additives in the water phase. Shinoda and Takeda showed that inorganic salts can affect the PIT more strongly than their parent acids. Also, they showed that the effect of fatty acids and alcohols on the PIT for 1 1 volume ratio paraffin-water systems was independent of the chain length of the acid or alcohol. 

The condition for which die hydrophilic and lipophilic properties are exactly balanced and die surfactant films have no spontaneous tendency to curve in either direction has been called the phase inversion temperature (PIT) or hydrophile-lipophile balance (HLB) temperature by Shinoda and Friberg for the case of nonionic surfactants for which temperature is usually the variable of greatest interest (see Section 12.2). For ionic surfactants it is more common to speak of optimal conditicms, e.g. optimal salinity. ... 

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