Emulsions Microemulsions Miniemulsions

This chapter describes novel inkjet inks based on a variety of vehicles, and demonstrates several optical applications utilized by inkjet inks. It aims to provide a general description of inks which are based on unique components and structures, mainly micellar systems, polyelectrolyte complexes, microemulsions, miniemulsions, emulsions, liquid crystals, and interesting phase... 

There are four main types of liquid-phase heterogeneous free-radical polymerization microemulsion polymerization, emulsion polymerization, miniemulsion polymerization and dispersion polymerization, all of which can produce nano- to micron-sized polymeric particles. Emulsion polymerization is sometimes called macroemulsion polymerization. In recent years, these heterophase polymerization reactions have become more and more important... 

Emulsion A dispersion of droplets of one liquid in another immiscible liquid in which the droplets are of colloidal or near-colloidal sizes. The term emulsion may also be used to refer to colloidal dispersions of liquid-crystals in a liquid. See also Macroemulsion, Microemulsion, Miniemulsion. 

Taking into account all of the above mentioned applications, the synthesis of magnetic latex will be discussed in two parts first, the preparation of iron oxide nanoparticles and, second, the preparation of magnetic latex. Depending on the aim of researchers, many polymerization techniques are applied such as suspension, dispersion, emulsion, microemulsion and miniemulsion polymerization in combination with controlled radical polymerization techniques like atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) and nitroxide-mediated radical polymerization (NMP). The preparation of hybrid magnetic latex by emulsion polymerization will be the focus of this review. 

For the preparation of hybrid magnetic latexes, different monomers can be polymerized in heterogeneous reaction systems in the presence of magnetic particles. Several polymerization techniques, namely suspension, dispersion, emulsion, microemulsion and miniemulsion are prevalent. 

A better criterion in defining a microemulsion could be its fluidity. In effect, the viscosity of (macro)emulsions and suspensions is known to increase as the fragment size decreases, and thus it is expected that an emulsion with extremely small drop size, an internal phase content greater than 20-30%, and a monodispersed distribution (as expected in a microemulsion) would be quite viscous. However, systems with such a high viscosity have been called gel emulsions or miniemulsions because the authors preferred to elude the label microemulsion in order to avoid confixsion with single-phase microemulsions [5-7]. 

Dispersed polymers are also produced by inverse emulsion polymerization, miniemulsion polymerization, dispersion polymerization and microemulsion polymerization. 

Inverse (or water-in-oil) emulsions (315, 401) are emulsions in which an aqueous phase is dispersed within a continuous organic phase. This system is essentially the inverse of a conventional emulsion, hence the name inverse emulsion. The organic phase is typically an inert hydrocarbon (such as mixed xylenes or low-odour kerosenes), and the aqueous phase contains a water-soluble monomer such as acrylamide (268). The aqueous phase may be dispersed as discrete droplets or as a bicontinuous phase (335), depending upon the formulation and conditions of the inverse emulsion. The hydrophilic-lipophilic balance (HLB) value of the stabiliser determines the form and stability of an inverse emulsion, with HLB values of less than 7 being appropriate for inverse emulsions. Steric stabilisers such as the Span , Tween , and Plutonic series of nonionic surfactants are usually used in preparing inverse emulsions. Inverse emulsions, suspensions, miniemulsions (199), and microemulsions have been prepared, primarily as a function of the stabiliser concentration. Commercial products produced by inverse emulsion polymerisation include polyacrylamide, a water-soluble polymer used extensively as a thickener. 

Bulk or mass polymerization" Gas-phase pol3mierization Precipitation polymerization Suspension polymerization Microsuspension polymerization Dispersion polymerization Emulsion polymerization Miniemulsion polymerization Microemulsion polymerization... 

The potential of microemulsions in technological applications, however, has not been fully exploited. There are many established industrial activities effectively being carried out with emulsions, for instance polymerization reactions in micellar, emulsion, and miniemulsion environments. Technological aspects involved in this type of activity have been discussed in a series of review articles published by Capek [3-6], but the role of microemulsions has yet been restricted to academical investigations, of which works reported by Kaler et al. are a good example [7-10]. 

A broad range of polymers are produced by polymerization in heterogeneous media, including polyolefins manufactured by slurry (high density polyethylene and isotactic polypropylene) and gas phase (linear low density polyethylene and high density polyethylene) polymerization coatings and adhesives produced by emulsion and miniemulsion polymerization flocculants obtained by inverse emulsion and microemulsion polymerization poly(vinyl chloride) (PVC) and polystyrene produced by suspension polymerization and toners synthesized by dispersion polymerization. As a whole, they represent more than 50% of the polymer produced worldwide [1]. 

Upon addition of the initiator, the polymerization reaction proceeds, the characteristics of the products depending on the initial monomer dispersion. Thus, in the case of the microemulsion polymerization, small particles (20-60nm) are formed emulsion and miniemulsion polymerizations lead to polymer dispersions of similar size (most often 80-3(X)nm), but miniemulsion polymerization allows the production of composite particles not attainable otherwise. Suspension polymerization yields relatively large particles (50-1000pm). 

In the first section, various kinds of functional polymer, in particular the most used conductive polymer, conjugated polymer (CP), redox polymer, metallopolymer. Selection of the correct functional polymer depends on the desired properties of the resulting nanocomposites. The second part of the chapter focuses on the basic approaches used in the preparation of polymeric nanoparticles. As mentioned earlier, there are two basic approaches in the recent literature to synthesize the polymeric nanoparticles. In this section, we focus on the discussion of the common and widely used preparation methods for various kinds of polymeric nanoparticles. The polymerization method is based on the encapsulation of nanoparticles through heterogeneous polymerization in dispersion media. This method can be further classified into emulsion, microemulsion and miniemulsion. Polymer encapsulated nanoparticles can also be prepared directly from preformed polymer, where this approach is based on the specific interactions between nanoparticles and the preformed polymer, such as electrostatic interactions, hydrophobic interactions and secondary molecular interactions or self-assembly method. 

Heterogeneons polymerization system is a two-phase system where the starting monomer and the resulting polymer are in the form of a fine dispersion in an immiscible liquid medium. The processes can be classified as emulsion, microemulsion and miniemulsion techniques depending on the initial state of polymerization mixtnre, the kinetics of polymerization, the mechanism of particle formation and the size and shape of the final polymer particles. The nanoparticles sizes are sensitive to several parameters used during the synthesis process, such as amphiphilicity and molecular weight of encapsulation matrices, initial concentration of functional polymer and the miscibility of the functional polymer in aqueous media [44]. 

Microemulsion and miniemulsion polymerization differ from emulsion polymerization in that the particle sizes are smaller (10-30 and 30-100 nm respectively vs 50-300 inn)4" and there is no monomer droplet phase. All monomer is in solution or in the particle phase. Initiation takes place by the same process as conventional emulsion polymerization. 

Microemulsion and miniemulsion polymerization processes differ from emulsion polymerization in that the particle sizes are smaller (10-30 and 30-100 nm respectively vs 50-300 ran)77 and there is no discrete monomer droplet phase. All monomer is in solution or in the particle phase. Initiation usually takes place by the same process as conventional emulsion polymerization. As particle sizes reduce, the probability of particle entry is lowered and so is the probability of radical-radical termination. This knowledge has been used to advantage in designing living polymerizations based on reversible chain transfer (e.g. RAFT, Section 9.5.2)." 2... 

In this review we summarize and discuss the amphiphilic properties of polyoxyethylene (PEO) macromonomers and PEO graft copolymer molecules, the aggregation of amphiphilic PEO macromonomers into micelles, the effect of organized aggregation of macromonomers on the polymerization process, and the kinetics of radical polymerization and copolymerization of PEO macromonomer in disperse (dispersion, emulsion, miniemulsion, microemulsion, etc.) systems [1-5]. 

The radical polymerization in disperse systems may be divided into several types according to the nature of continuous phase and the polymerization loci the dispersion, emulsion, miniemulsion, microemulsion, suspension, etc. 

Microemulsion polymerizations follow a different mechanism from the conventional emulsion polymerizations. The most probable locus of particle nucle-ation was suggested to be the microemulsion monomer droplets [27], although homogeneous nucleation was not completely ruled out. The particle generation rate in microemulsion polymerization is given by an expression similar to Eq. (21), which was used for the miniemulsion polymerization of styrene [28] ... 

Emulsions made by agitation of pure immiscible liquids are usually very unstable and break within a short time. Therefore, a surfactant, mostly termed emulsifier, is necessary for stabilisation. Emulsifiers reduce the interfacial tension and, hence, the total free energy of the interface between two immiscible phases. Furthermore, they initiate a steric or an electrostatic repulsion between the droplets and, thus, prevent coalescence. So-called macroemulsions are in general opaque and have a drop size > 400 nm. In specific cases, two immiscible liquids form transparent systems with submicroscopic droplets, and these are termed microemulsions. Generally speaking a microemulsion is formed when a micellar solution is in contact with hydrocarbon or another oil which is spontaneously solubilised. Then the micelles transform into microemulsion droplets which are thermodynamically stable and their typical size lies in the range of 5-50 nm. Furthermore bicontinuous microemulsions are also known and, sometimes, blue-white emulsions with an intermediate drop size are named miniemulsions. In certain cases they can have a quite uniform drop size distribution and only a small content of surfactant. An interesting application of this emulsion type is the encapsulation of active substances after a polymerisation step [25, 26]. 

In Fig. 8 the calorimetric curve of a typical miniemulsion polymerization for 100-nm droplets consisting of styrene as monomer and hexadecane as hydrophobe with initiation from the water phase is shown. Three distinguished intervals can be identified throughout the course of miniemulsion polymerization. According to Harkins definition for emulsion polymerization [59-61], only intervals I and III are found in the miniemulsion process. Additionally, interval IV describes a pronounced gel effect, the occurrence of which depends on the particle size. Similarly to microemulsions and some emulsion polymerization recipes [62], there is no interval II of constant reaction rate. This points to the fact that diffusion of monomer is in no phase of the reaction the rate-determining step. 

As described above, the development of emulsion-based inks has evolved but major issues still limit their development. The microemulsion print quality is usually limited due to the ink penetration into the paper. As for the miniemulsions, better particle size control and improved emulsion stability are needed. In addition, more environmentally friendly solvents that have less smell, lower toxicity, and higher solubilizing power of the colorant need to be developed. 

A third type of emulsion process is the so-called microemulsion [123]. In microemulsions, the polymerization starts in droplets as well. However, these are thermodynamically stable and, in contrast to miniemulsions, they form spontaneously by gentle stirring. They consist of large amounts of surfactants or mixtures of them, and they possess an interfacial tension close to zero at the water/oil interface, with droplet sizes usually ranging between 5 and 50 nm. In... 

Amphiphilic lipopeptides with a hydrophobic paraffinic chain containing from 12 to 18 carbon atoms and a hydrophilic peptidic chain exhibit lyotropic meso-phases and good emulsifying properties. The X-ray diffraction study of the mesophases and of dry lipopeptides showed the existence of three types of mesomorphic structures lamellar, cylindrical hexagonal and body-centred cubic. Two types of polymorphism were also identified one as a function of the length of the peptidic chain and the other as a function of the water content of the mesophases. The emulsifying properties of the lipopeptides in numerous pairs of immiscible liquids such as water/ hydrocarbons and water/base products of the cosmetic industry showed that small amounts of lipopeptides easily give three types of emulsions simple emulsions, miniemulsions and microemulsions. 

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