Phase inversion temperature preparation

Izquierdo, P., Esquena, J., Tadros, T.F., Dederen, C., Garcia, M.J., Azemar, N. and Solans, C. (2002) Formation and stability of nano-emulsions prepared using the phase inversion temperature method. Langmuir, 18 (1), 26-30. 

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. 

There are essentially two ways to prepare nanoemulsions. These are the phase inversion temperature (PIT) process and the high-pressure homogenization (HPH) process. 

In summary, the HLB method is only an empirical approach which has made it possible to organize a great deal of rather messy information on emulsion preparation, in order to choose candidate surfactants in trial and error laboratory work for suitable emulsion selection. There are other surfactant selection methods such as the phase inversion temperature (PIT) and the hydrophilic-lipophilic deviation (HLD) methods used for the same purpose in the emulsion industry, but these are outside the scope of this book. 

Consequently, the following four components were selected to prepare the photoresponsive emulsion system equal volumes of n-dodecane and 0.3 M NaNOs aqueous solution, the C12E4 surfactant, and an azobenzene-modified poly(acrylate). C12E4 is known to stabilize direct and inverse emulsions below and above the so-called phase inversion temperature (PIT here 24°C), respectively. Emulsions are unstable in the vicinity of the PIT, a temperature domain corresponding to the CTR of the light-responsive system. Emulsions made of equal oil and water volumes are directly below the PIT (and display a high electric conductivity because of the water continuum), but inverse (and of low conductivity) above the PIT (Khoukh et al., 2005). 

FIGU RE 4.4 Illustration of the preparation of a finely divided O/W emulsion from a coarse W/O emulsion using a heating-cooling cycle and the phase inversion temperature (PIT) principle. (From Forster [36]. Reprinted with permission of Blackwell Publishing Ltd.)... 

It is generally found that the same circumstances that affect the solution characteristics of nonionic surfactants (their cmc, micelle size, cloud point, etc.) will also affect the PIT of emulsions prepared with the same materials. For typical polyoxyethylene nonionic surfactants, increasing the length of the POE chain will result in a higher PIT for a given oil-aqueous phase combination (Fig. 11.12), as will a broadening of the POE chain length distribution. The use of phase inversion temperatures, therefore, represents a very useful... 

Formation and stability of nano-emulsions prepared using the phase inversion temperature method, Langmuir 18, 26-30 (2002). 

Two methods may be applied for the preparation of nano-emulsions (covering the droplet radius size range 50-200 nm). Use of high-pressure homogenisers (aided by appropriate choice of surfactants and cosurfactants) or application of the phase inversion temperature (PIT) concept. 

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. 

Resins are incorporated in Neoprene latex as solvent-cut emulsions, solventless pebble-milled dispersions, or sometimes as solvent-free emulsions prepared using invert emulsification techniques. In the latter case a resin with a melting point of 80°C (176 F) or lower is melted. Water and surfactants are added to the molten resin and the temperature of the mixture is decreased. Upon reaching a certain temperature, known as the phase inversion temperature, the water in molten resin emulsion spontaneously inverts to form a resin in water emulsion suitable for use in latex adhesives. A resin dispersion which can be prepared in this manner is shown in Table 16. This particular resin dispersion can be used to produce adhesives with moderate hot strength and good open time using the following recipe ... 

Thermal Phase Inversion Thermal phase inversion is a technique wFich rnav be used to produce large quantities of MF membrane econornicallv, A solution of polvrner in poor solvent is prepared at an elevated temperature. After being formed into its final shape, a sudden drop in solution temperature causes the polvrner to precipitate, The solvent is then w ashed out. Membranes rnavbe spun at high rates using this technique. 

HA and three different HA esters, supplied by Fidia Advanced Biomaterials SpA (Padua, Italy), were examined. HA esters were prepared by treating a quaternary ammonium salt of HA with an esterifying agent in a suitable aprotic solvent at a controlled temperature as described in detail elsewhere [2]. In this study we analyzed the following esters ethyl ester (HYAFF7), benzyl ester (HYAFFl 1), and dodecyl ester (HYAFF73 Figure 1). The materials used were both films and powders. Films were obtained by a phase inversion process from DMSO solutions as previously described [2,4]. 

In 1993 Bergbreiter prepared two soluble polymer-supported phosphines that exhibited an inverse temperature-dependent solubility in water [52]. Although PEG-supported phosphine undergoes a phase-separation from water at 95-100 °C, the PEO-poly(propylene oxide)-PEO supported catalyst was superior as it is soluble at low temperatures and phase-separates at a more practical 40-50 °C. Treatment of a diphenylphosphinoethyl-terminated PEO-PPO-PEO triblock copolymer... 

Phase inversion may be used to emulsify highly viscous substances such as bitumen (the viscosity of which can be as high as 10 Pa-s at room temperature) [134]. The most frequent industrial technique used to prepare bitumen-in-water emulsions consists of mixing hot bitumen (130°C) with an aqueous phase ( 60°C at... 

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