Highly concentrated emulsions

A. Z. Zinchenko, R. H. Davis 2002, (Shear flow of highly concentrated emulsions of deformable drops by numerical simulations),/. Fluid Mech. 455, 21. 

H.M. Princen Rheology of Foams and Highly Concentrated Emulsions I. Elastic Properties and Yield Stress of a Cyhndrical Model System. J. Colloid Interface Sci. 91, 160 (1983). 

In highly concentrated emulsions, the droplets are forced to deform, that is, they... 

H.M. Princen and A.D. Kiss Osmotic Pressure of Foams and Highly Concentrated Emulsions. 2. Determination from the Variation in Volume Fraction with Height in an Equilibrated Column. Langmuir 3, 36 (1987). 

H.M. Princen, M.P Aronson, and J.C. Moser Highly Concentrated Emulsions. II Real Systems. The Effect of Film Thickness and Contact Angle on the Volume Fraction in Creamed Emulsions. J. CoUoid Interface Sci. 75, 246 (1980). 

H.M. Princen Highly Concentrated Emulsions. I CyUndrical Systems. J. CoUoid Interface Sci. 71, 55 (1979). 

V.G. Babak, M. J. Stebe, A review on highly concentrated emulsions Physicochemical principles of formulation, J. Disp. Sci. Technol. 23 (2002) 1-15. 

In this review, the structure, properties, stability and applications of highly concentrated emulsions will be discussed in the first section. Following this, the use of HIPEs to generate novel polymer materials will be the focus of the second part. 

The purpose of this section is to give a brief overview of the rheology of highly concentrated emulsions and foams, in as simple terms as possible. For comprehensive reviews in this field, see Refs. 16 and 50. 

Another important rheological property of dry foams and highly concentrated emulsions is G, the shear modulus. Princen and Kiss [57] demonstrated that this property was dependent on < >, the volume fraction of the system. Previously, Stamenovic et al. [58] and, much earlier, Derjaguin and coworker [59], had derived an expression for the shear modulus of foams of volume fraction very close to unity. The value was found to depend on the surface tension of the liquid phase (in foams), for the particular case of (Jja 1. However, Princen demonstrated that the values of G obtained were overestimated by a factor of two. This error was attributed to the model used by Stamenovic and coworker, which failed to maintain the equilibrium condition that three films always meet at angles of 120° during deformation. 

The HLB temperature was found to be the most important factor in the formation of stable emulsions. In each case, w/o HIPEs [9,11,80] would only form at temperatures above the HLB temperature of the systems, while o/w HIPEs [14] formed below the PIT. The nature of the oil phase was also found to be of importance to the formation of stable w/o HIPEs [11] aromatic liquids, for example, did not produce highly concentrated emulsions. With aliphatic oils, the stability was observed to vary with chemical nature. This was due to the different HLB temperatures for each liquid. 

Non-aqueous HIPEs have received even less attention indeed, to date, there have been only two publications dealing with this subject, to the authors knowledge [124,125]. These describe the preparation of highly concentrated emulsions of jet engine fuel in formamide, for use as safety fuels in military applications. The emulsifier system used was a blend of two nonionics, with an optimal HLB value of 12. 

Highly concentrated emulsions are also evident in everyday applications. A classic example is mayonnaise, in which a large volume of vegetable oil is emulsified in a small amount of vinegar, using lecithin from egg-yolk as the emulsifier. In addition, HIPEs are most probably found in many cosmetic products, especially gels and creams. However, little information is available on products of commercial importance, so one can only speculate on their exact nature and composition. 

Polystyrene latexes were similarly prepared by Ruckenstein and Kim [157]. Highly concentrated emulsions of styrene in aqueous solutions of sodium dodecylsulphate, on polymerisation, yielded uncrosslinked polystyrene particles, polyhedral in shape and of relative size monodispersity. Interestingly, Ruckenstein and coworker found that both conversions and molecular weights were higher compared to bulk polymerisation. This was attributed to a gel effect, where the mobility of the growing polymer chains inside the droplets is reduced, due to increased viscosity. Therefore, the termination rate decreases. 

A rubber-like copolymer/carbon fibre composite material has also been prepared [170]. Carbon fibres were added directly to o/w highly concentrated emulsions of block copolymers, such as styrene/butadiene triblocks (SBS), in toluene, followed by precipitation in methanol, drying and hot-pressing. The surfactant was found to aid adhesion between the polymer and carbon fibres. The materials obtained had fairly even distributions of carbon fibres, good mechanical properties and conductivities which increased with increasing carbon fibre length. 

If both continuous and dispersed phases of highly concentrated emulsions contain monomeric species, it is possible to obtain hydrophilic/hydrophobic polymer composite materials. Polyacrylamide/polystyrene composites have been prepared in this manner [180], from both w/o and o/w HIPEs containing aqueous acrylamide and a solution of styrene in an organic solvent. 

The simplest and most common synkinons are non-branched, saturated fatty acids from C12 to C18 (trivial names lauroyl Cl2, myristoyl Cl4, palmitoyl or cetyl Cl 6, stearoyl Cl8) and their sodium, ammonium and potassium salts (also known as soaps ). Laurie, myristic, palmitic and stearic acids are barely soluble in water at 20°C (5.5, 2.0,0.7 and 0.3 mg/L) and 60°C (8.7, 3.4, 1.2 and 0.5 mg/L), each ethylene group lowering the solubility by a factor of 2-3. The solubilities of the corresponding sodium and potassium salts are, however, in the order of several grams per litre. Even in highly concentrated emulsions of soaps in distilled water ( 30% w/w), precipitation of solids is often not observed. Bivalent fatty acid salts, however, are just as insoluble as free fatty acids only 1.4 mg of calcium stearate dissolves in 1 L of water. ... 

Balinov, B., Linse, R, and Soderman, O. Diffusion of the dispersed phase in a highly concentrated emulsion emulsion structure and film permeation, /. Colloid Interface Sci., 182, 539, 1996. 

Concentrated emulsions or high internal phase emulsions (HIPE) are systems in which the volume fraction of the dispersed phase is larger than about 0.74, which is the close-packing volume fraction of monodispersed hard spheres. The dispersed soft entities of a concentrated emulsion are no longer spherical. They deform into polyhedra separated by thin films of continuous phase. The structure is thus analogous to a conventional gas-liquid foam with low liquid content. The structure, properties, stability, and applications of highly concentrated emulsions were recently reviewed by Cameron and... 

Kunieda H, John AC, Pons R, Solans C. Highly concentrated emulsions (gel emulsions) macro self-organizing structures. In Esumi K, Ueno M, eds. Structure-Performance Relationships in Surfactants. Vol. 70. Surfactant Science Series. New York Marcel Dekker, 1997 359-393. 

Princen HM. Rheology of foams and highly concentrated emulsions. I. Elastic properties and yield stress of a cylindrical model system. J Colloid Interface Sci 1983 91 160-175. 

Princen, H. M., Osmotic pressure of foams and highly concentrated emulsions. 

In practice, these high-concentration emulsions are diluted to 4 - 5% by oil content. 

H. Kunieda, A.C. Johns, R. Pons and C. Solans, Highly Concentrated Emulsions -Gel Emulsions Macro-Self-Organizing Structures, in [41], pp. 359. 

Pinsach J, de Mas C, Lopez-Santm J (2006) A simple feedback control of Escherichia coli growth for recombinant aldolase production in fed-batch mode. Biochem Eng J 29 235-242 Pons R, Erra P, Solans C et al. (1993) Viscoelastic properties of gel-emulsions their relationship with structure and equilibrium properties. J Phys Chem 97 12320-12324 Princen HM (1979) Highly concentrated emulsions. 1. CyUndtical systems. J Colloid Interface Sd 71 55-66... 

Princen HM, Kiss AD (1986) Rheology of foams and highly concentrated emulsions. III. Static shear modulus. J Colloid Interface Sci 112 427-437 Ramsaywak PC, Labb6 G, Siemann S et al. (2004) Molecular cloning, expression, purilication, and characterization of fructose 1,6-bisphosphate aldolase from Mycobacterium tuberculosis -a novel Class II A tetramer. Protein Expres Purif 37 220-228 Richard JP (1993) Mechanism for the formation of methylglyoxal from triosephosphates. Biochem Soc 121 549-553... 

Solans C, Pinazo A, Caldero G et al. (2001) Highly concentrated emulsions as novel reaction media. CoUoids Surf A 176 101-108... 

Pri ncen, H.H. Kiss, A.D. Rheology of foarns and highly concentrated emulsions. IV. An experimental study of the shear viscosity and yield stress of concentrated emulsions, J. Colloid Interface Sci., 128(1) 176-187, 1989. 

This technique is particularly useful for highly concentrated emulsion systems. We have used the digitized optieal imaging technique to study the microstructure of a number of... 

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