Polymer emulsification technique

An aqueous colloidal polymeric dispersion by definition is a two-phase system comprised of a disperse phase and a dispersion medium. The disperse phase consists of spherical polymer particles, usually with an average diameter of 200-300 nm. According to their method of preparation, aqueous colloidal polymer dispersions can be divided into two categories (true) latices and pseudolatices. True latices are prepared by controlled polymerization of emulsified monomer droplets in aqueous solutions, whereas pseudolatices are prepared starting from already polymerized macromolecules using different emulsification techniques. 

Membrane emulsification techniques allow preparation of highly monodisperse microgel particles. The Shirasu porous glass (SPG) membrane with a pore size of 0.1-18pm was used to prepare uniformly sized water droplets containing chitosan in organic solvent, and polymer chains were crosslinked by glutaraldehyde [26],... 

Bodmeier, R., Chen, H. and Bhagwatwar, H., Polymer and wax microspheres prepared by emulsification techniques, Bull. Tech. Gattefosse, 1990, 83. 

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. 

Hatate, Y., Ohta, H., Uemura, Y., Ijichi, K., and Yoshizawa, H., Preparation of monodispersed polymeric microspheres for toner particles by the Shirasu porous glass membrane emulsification technique, J. Appl. Polym. Set, 64, 1107-1113, 1997. 

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... 

Hosoya K, Bendo M, T anaka N, Watabe Y, Ikegami T, Minakuchi H, Nakanishi K. 2005. An application of silica-based monolithic membrane emulsification technique for easy and efficient preparation of uniformly sized polymer particles. Macromol Mater Eng 290 753-758. 

Inversion ofMon cjueous Polymers. Many polymers such as polyurethanes, polyesters, polypropylene, epoxy resins (qv), and siHcones that cannot be made via emulsion polymerization are converted into latices. Such polymers are dissolved in solvent and inverted via emulsification, foUowed by solvent stripping (80). SoHd polymers are milled with long-chain fatty acids and diluted in weak alkaH solutions until dispersion occurs (81). Such latices usually have lower polymer concentrations after the solvent has been removed. For commercial uses the latex soHds are increased by techniques such as creaming. 

Although such polymer/LC composite films are usually prepared by emulsification and phase separation techniques, the resulting composites have a variety of morphological characteristics arising from differences in conditions and compositions during sample preparation. The polymer/LC composite films are mainly classified into four types ... 

Microfluidic techniques have been recently used for the synthesis of microgel particles with dimensions of 1-30 pm. In these methods, microfluidic devices are used that provide emulsification of polymer solutions followed by physical [27, 28] or chemical [29] crosslinking. 

Quintanar-Guerrero, D., Allemann, E., Doelker, E., and Fessi, H. (1998), Preparation and characterization of nanocapsules from performed polymers by a new process based on emulsification-diffusion technique, Pharm. Res., 15,1056. 

Emulsion Solvent Evaporation The basic concept of the emulsion solvent evaporation technique producing nanoparticles is very straightforward. The particles are formed as an emulsion of a polymer-surfactant mixture and dispersed in an organic solvent. The solvent is then evaporated to leave behind the individual emulsion droplets which form stable free nanoparticles [203], This method is far easier and more preferable over methods such as spray drying and homogenization and operates under ambient conditions and mild emulsification conditions. The size and composition of the final particles are affected by variables such as phase ratio of the emulsion system, organic solvent composition, emulsion concentration, apparatus used, and properties of the polymer [204],... 

Although water-immiscible solvents display low solubility in water, there is some amount of solubility. The solvent diffusion/emulsification method exploits this for the production of nanoparticles. In this technique, drug and polymer are dissolved in an organic, water-immiscible solvent that is emulsified into an aqueous solution containing emulsifiers and stabilizers. The emulsion is then diluted with water to increase the level of organic solvent, which can be dissolved in the... 

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. 

The microchannel emulsion technique has been extended to the formation of multiple emulsions [158-163], encapsulation [123, 158, 164—166], polymer bead formation [123, 125, 167-169], demulsification [116, 158, 170], and even microbubble formation [171]. New methods of stabilizing emulsions have also been investigated in this realm, including particle-stabilized [172] and protein-stabilized emulsions [173], with some work in emulsification without surfactants [135,146]. In the case of multiple emulsions, microchannel architecture can enable the formation of W/O/W emulsions in which two water droplets of different compositions can be encased in the same oil droplet [163]. 

There are many different applications of the DLS technique. The DLS method has been u.sed to determine the size of polymer lattices and resins and to monitor the grow th of particles during processes such as emulsification and polymerization. Micelles and microemulsions have been studied by DL.S methods. DLS is also widely applicable to the investigation of biopolymers and biocolloids. It has been used to study natural and synthetic polypeptides, nucleic acids, ribosomes, vesicles, viruses, and muscle fibers. 

---