Phase-inversion emulsification technique

Colloid Polymer Science 278, No. 11, Nov.2000, p. 1103-8 PREPARATION OF WATERBORNE DISPERSIONS OF EPOXY RESIN BY THE PHASE-INVERSION EMULSIFICATION TECHNIQUE. II. THEORETICAL CONSIDERATION OF THE PHASE-INVERSION PROCESS... 

Baek et ah [79] used the phase-inversion emulsification technique in order to obtain epoxy resin microcapsules containing the flame retardant triphenyl phosphate... 

Silica nanoparticles could also be encapsulated with an epoxy resin to produce water-borne nanocomposite dispersions by using the phase-inversion emulsification technique [98]. Microscopy results indicated that all the siHca nanoparticles were encapsulated within the composites and uniformly dispersed therein. 

In a novel process, FIPI was also applied to the emulsiflcation of polymer melts in water, thus providing an alternative method to emulsion polymerization for the production of latexes. " " In fact, some thermoplastic melts (such as polyethylene) cannot be obtained through the emulsion polymerization route hence, the present technique is an example of PI providing a novel product form. To achieve the emulsiflcation of thermoplastics, it is necessary to operate near or above 100°C and at elevated pressures, which necessitates the use of polymer processing equipment fitted with a MFCS mixer at the outlet. It was found that molecular surfactants could not be used to obtain the initial (water-in-polymer melt) emulsion. Instead, hydrophobically modified water-soluble polymers were used as the surface active material. After the phase inversion in the MFCS mixer, the resulting emulsion was diluted to the level required. This also freezes the molten latexes. The important attributes of FIPI emulsification include a low level of surfactant use, low temperature processing, production of submicrometer particles with a narrow size distribution, and production of novel products. 

Mixtures containing 1 wt% of the pure nonionic surfactant C,2E5 in water were contacted with pure n-hexadecane and n-tetradecane at various temperatures between 25 and 60°C using the vertical cell technique. Similar experiments were performed with C,2E4 and n-hexadecane between about 15 and 40°C. In both cases the temperature ranged from well below to well above the phase inversion temperature (PIT) of the system, i.e., the temperature where hydrophilic and lipophilic properties of the surfactant are balanced and a middle phase microemulsion forms (analogous to the optimal salinity for ionic surfactants mentioned above). The different intermediate phases that were seen at different temperatures and the occurrence of spontaneous emulsification in some but not all of the experiments could be understood in terms of known aspects of the phase behavior, e.g., published phase diagrams for the C12E 5-water-n-tetradecane system, and diffusion path theory. That is, plausible diffusion paths could be found that showed the observed intermediate phases and/or spontaneous emulsification for each temperature. 

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. 

In this study, after a brief introduction to PI we provide the bases of a technique for the preparation of polymeric micro-porous materials, known as polyHIPE polymers (PHPs) which are now used extensively in PIM, and micro-reactor technology. These polymers are prepared through the high internal phase emulsion (HIPE) polymerization route. In order to control the pore size, the flow-induced phase inversion phenomenon is applied to the emulsification technique. The metalization of these polymers and formation of nano-structured micro-porous metals for intensified catalysis are also discussed. Finally, we illustrate the applications of these materials in chemical- and bioprocess intensifications and tissue engineering while examining the existence of several size-dependent phenomena. 

Nevertheless, there is another way to avoid the emulsion inversion at high internal-phase content, which is the dynamic emulsification technique which is discussed next. 

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 ... 

In this technique, a transition in the affinity is obtained by changing the water volume fraction, instead of changing the temperature. By successively adding water into oil, initially water droplets are formed in a continuous oil phase. Increasing the water volume fraction changes the spontaneous curvature of the surfactant from initially stabilizing a w/o microemulsion to an o/w microemulsion at the inversion locus. This transition is referred to as PIC. PIC method of emulsification involves... 

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