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. 

The drawbacks of the W/O emulsification method include the use of large amounts of oils as the external phase, which must be removed by washing with organic solvents, heat stability problems of drugs, possible interactions of the cross-linking agent with the drug, and, as with all nanoparticles prepared by emulsification techniques, a fairly broad particle size distribution. 

K. Kandori, K. Kishi, and T. Ishikawa Preparation of Monodispersed W/O Emulsions by Shirasu-Porous-Glass Filter Emulsification Technique. Colloid Surfaces 55, 73 (1991). 

Jafari, S.M., He, Y., Bhandari, B. (2007). Effectiveness of encapsulating biopolymers to produce sub-micron emulsions by high energy emulsification techniques. Food Research International, 40, 862-873. 

Pont, E. G. 1955. A de-emulsification technique for use in the peroxide test on the fat of milk, cream, concentrated and dried milks. Aust. J. Dairy TechnoL 10, 72-74. 

If we analyze different mechanical emulsification techniques and relate the pressure gradient to the work required W (energy input) we find that for most devices the mean radius of drops R scales with... 

There is some evidence to suggest that, depending upon the phase volume ratios employed, the emulsification technique used can be of greater importance in determining the final emulsion type than the H LB values of the surfactants themselves [434], As an empirical scale the HLB values are determined by a standardized test procedure. However, the HLB classification for oil phases in terms of the required HLB values is apparently greatly dependent on the emulsification conditions and process for some phase-volume ratios. When an emulsification procedure involves high shear, or when a 50/50 phase volume ratio is used, interpretations based on the classical HLB system appear to remain valid. However, at other phase-volume ratios and especially under low shear emulsification conditions, inverted, concentrated emulsions may form at unexpected HLB values [434]. This is illustrated in Figures 7.4 and 7.5. 

The distinguishing feature of membrane emulsification technique is that droplet size is controlled primarily by the choice of the membrane, its microchannel structure and few process parameters, which can be used to tune droplets and emulsion properties. Comparing to the conventional emulsification processes, the membrane emulsification permits a better control of droplet-size distribution to be obtained, low energy, and materials consumption, modular and easy scale-up. Nevertheless, productivity (m3/day) is much lower, and therefore the challenge in the future is the development of new membranes and modules to keep the known advantages and maximize productivity. 

The membrane emulsification technique is also employed for the preparation of microspheres starting from monomers such as methacrylates (methylmethacrylate, cyclohexyl acrylate, etc.), polyimide prepolymer, styrene monomer [81], and so on. 

Fig. 3. SEM images of various dry powders for inhalation, (a) Spray-dried particles (see Subheading 3.1.)- Reproduced from ref. 5. (b) Particles prepared by emulsification techniques (see Subheading 3.2.1.), Reproduced from ref. 10. (c) Particles prepared by supercritical C02 swelling (see Subheading 3.2.2.), The particles in panel b were the starting material for these particles. Reproduced from ref. 10. (d) TI particles (see Subheading 3.4.2.),...

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],... 

To get a better idea of how to formulate the nanosized emulsion delivery systems suitable for parenteral, ocular, percutaneous, and nasal uses, the reader is referred to more detailed descriptions of methods of nanosized emulsion preparation [6, 116], A hot-stage high-pressure homogenization technique or combined emulsification technique (de novo production) is frequently employed in order to prepare nanosized emulsions with desired stability even after subjection to autoclave sterilization. Therefore, the steps involved in this technique in making blank anionic and cationic emulsions were arranged in the following order ... 

A few food products have been on the market using cross-flow membrane emulsification. The method can make emulsions that have small droplets with a narrow size distribution. Thus, it is possible to make sauces with lower oil content than with conventional emulsification techniques. The technique of cross-flow emulsification is clearly the best developed process for small-scale, high-value applications it is an attractive process. 

Figure 6.10. Comparison of different mechanical emulsification techniques with US assisted emulsification, (r) toothed colloid mill, ( ) standard valve, ( ) sharpened edge valve, (o) Microfluidizet and ( ) US-assisted emulsification. (Reproduced with permission of Elsevier, Ref [32].)...

Membrane emulsification is a relatively new technique with specific advantages (simplicity, potentially less energy demands, less surfactant, and narrow droplet-size distributions) compared to conventional emulsification techniques [102]. Depending on the membrane hydrophilicity/hydrophobicity and the composition of the two liquid phases, O/W, W/0, or MW emulsions may be produced. Most often used, O/W membrane emulsification consists of the pressurization of oil (dispersed phase) through membrane pores at high pressure (Figure 6.26). The oil jet flows formed in the circulating continuous phase are... 

Liu, R., Ma, G.H., Meng, F.-T., and Su, Z.-G., Preparation of uniform-sized PLA microcapsules by combining Shirasu Porous Glass membrane emulsification technique and multiple emulsion-solvent evaporation method, J. Contrail. Ret, 103, 31, 2005. 

This emulsification technique aims to maximize membrane surface area. The internal phase of the droplets can be placed inside the pores of polymeric films, or inside hollow fibers. The membrane phase can contain surfactants or no surfactants for easy coalescence. This aspect of the liquid membrane system will be discussed in more detail in the application section. 

These observations suggest that the collapse of the gaseous thread - and the break-up of the stream of gas into bubbles - cannot be driven by interfacial stresses, as is the case in conventional emulsification techniques. 

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

Bezemer JM, Grijpma DW, Dijkstra PJ, Van Blitterswijk CA, Feijen J. Control of protein delivery from amphiphibc poly (ether ester) multiblock copolymers by varying their water content using emulsification techniques. J Control Release 2000 66 307-320. 

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. 

There is a type of melt-dispersion technology, which actually represents a combination of melt-dispersion and emulsification technique. Namely, a melt (dispersed phase) is fed into a vessel containing water (continuous phase) wherein mechanical stirring is used for dispersing it thus, mixing is performed simultaneously with cooling (Figure 25.2). 

As previously mentioned, in melt-emulsification technique, the process variables are agitation speed, melt and water temperatures, as well as the type and concentration of the surfactant. In addition, critical parameters are different for different carrier materials and the type of lipid plays an important role, that is, the rate of lipid crystallization, the lipid hydrophilicity, and the surface of lipid crystals. The literature dealing with the specific influence of the process parameters is limited and one of the studies was done by our research group. In these works, ethyl vanilline was... 

The total protein encapsulation efficiency is high in the microparticles produced by w/o/o emulsification technique, since oil is the outer processing medium and protein cannot diffuse into the processing medium. 

There are many industrial processes in which the formation of low internal phase or concentrated emulsions needs to be controlled in terms of formation, stability, destruction or prevention. Examples range from asphalt emulsions to personal care products, and to food products. Success in emulsion control requires achieving the right physical chemistry and also the right fluid mechanics. In addition to HLB (see Section 7.2.1), both the nature of the emulsification method and the oil-water ratio are critical in determining the produced emulsion type. It appears that the emulsification technique (applied shear and oil-water ratio) used can be of greater importance in determining the final emulsion type than the HLB values of the surfactants themselves. 

Some preparation methods specific to the formation of nanoparticle suspensions are provided in References [20,62,63]. Many such methods are simply conventional colloidal suspension preparation methods that have been extended to produce smaller particle sizes, but others involve novel approaches. Some ofthese involve making nanoemulsions as a first step. For example, membrane, microfluidic and nanofluidic devices have been used to make nanoscale emulsions of all kinds, as already noted earlier, and the emulsion droplets so generated can be used in turn to make sohd microparticles and nanoparticles. If the nanoparticles are intended to encapsulate other materials, then a double emulsification technique can be used, at elevated temperature, to prepare a multiple emulsion (i.e. 

Higashi et al. (22), described a new method of producing W/O/W multiple emulsions by a membrane emulsification technique. This method permits the formation of monodis-persed liquid microdroplets containing aqueous micro-... 

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. 

The above emulsification methods (perhaps except the Couette flow technique) have as a common feature that the final DSD is primarily determined by the interaction of turbulent eddies with interfaces. Note, however, that turbulence is hard to control and to maintain consistently throughout the whole reactor volume. From a practical point of view, it is almost impossible to predict the DSD after a scale-up based on laboratory-scale experiments. Emulsification techniques based on other principles are necessary to overcome these drawbacks. An alternative technique is the so-called membrane emulsification method where the liquid forming the disperse phase is pressed through a porous membrane. The other side of the membrane where the droplets are formed is in contact with the continuous phase. This concept is simple and it is assumed to be superior to the above techniques (35). The basic relationship of membrane emulsification (equation (8.10)) correlates the trans-membrane pressure required to start the drop-wise flow through the pores (ft) with the average pore diameter of the membrane (Dm) with being the contact angle of the mixture with the wall of the pore ... 

Omi, S., Preparation of monodisperse microspheres using the Shirasu porous glass emulsification technique. Colloid Surf A, 109, 97-107 (1996). 

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