Properties of emulsions

Apart from chemical composition, an important variable in the description of emulsions is the volume fraction, outer phase. For spherical droplets, of radius a, the volume fraction is given by the number density, n, times the spherical volume, 0 = Ava nl2>. It is easy to show that the maximum packing fraction of spheres is 0 = 0.74 (see Problem XIV-2). Many physical properties of emulsions can be characterized by their volume fraction. The viscosity of a dilute suspension of rigid spheres is an example where the Einstein limiting law is [2]... 

Additionally, mechanical (primarily shear), freeze—thaw, and thermal stabiHty the tendency to form sediment on long-term standing and compatibiHty with other dispersions, salts, surfactants, and pigments of acryHc dispersions are often evaluated. Details on the determination of the properties of emulsion polymers are available (60). 

Phospholipids are amphiphilic compoimds with high surface activity. They can significantly influence the physical properties of emulsions and foams used in the food industry. Rodriguez Patino et al. (2007) investigated structural, morphological, and surface rheology of dipalmitoylpho-sphatidylcholine (DPPC) and dioleoyl phosphatidylcholine (DOPC) monolayers at air-water interface. DPPC monolayers showed structural polymorphisms at the air-water interface as a function of surface pressure and the pH of the aqueous phase (Fig. 6.18). DOPC monolayers showed a... 

Rheological measurements were carried out to investigate the rheological properties of emulsions stabilized by different fat-water interfaces and the influence of fat droplets on the formation of the protein networks during a process of gelation. 

D. J. McClements, N. Herrmann, Y. Hemar 1998, (Influence of flocculation on the ultrasonic properties of emulsions theory), J. Phys. D Appl. Phys. 31, 2950. 

Table 7 Essential Properties of Emulsion Paint Biocides...

P Sherman. The flow properties of emulsions. J Pharm Pharmacol 16 1-25, 1964. 

In this study, mechanical properties of emulsion copolymers of viityl acetate and butyl aciylate, which consisted of a nonionic emulsifier (30 mol ethoxylated nottyl-phenol), an oligomeric stabilizator, and ammonium persulfate or potassium persulfate as initiators by changing monomer ratios from 90 10 to 10 90 for VAc BuA, were determined by differential scanning calorimeter. 

In this study, mechaiucal properties of emulsion copolymers of VAc and BuA were determined by differential scanning calorimeter (DSC). 

J.L. Salager Properties of Emulsions at the Onset of Catastrophic Phase Inversion in the Normal to Abnormal Inversion. In Proceedings of the 3rd World Congress on Emulsions l-F-185, Lyon, France (2001). 

In this section, we shall describe the bulk properties of emulsions that are due to surface tension only, as generally observed with surfactant-stabilized systems ... 

Shinoda K, Kunieda FI (1983) Phase Properties of Emulsions PIT and HLB. In Becher P (ed) Encyclopedia of Emulsion Technology, vol 1 Basic Theory, Chap. 5. Marcel Dekker, NY, pp 337-367... 

Anton RE, Castillo P, Salager JL (1986) Surfactant-oil-water systems near the affinity inversion. Part IV Emulsion inversion temperature. J Dispers Sci Technol 7 319 Minana-Perez M, Jarry P, Perez-Sanchez M, Ramirez-Gouveia M, Salager JL (1986) Surfactant-oil-water systems near the affinity inversion. Part V Properties of emulsions. J Dispers Sci Technol 7 331... 

Ye, A., Singh, H. (2000b). Influence of calcium chloride addition on the properties of emulsions stabilized by whey protein concentrate. Food Hydrocolloids, 14, 337-346. 

Dickinson, E. (1997). Properties of emulsions stabilized with milk proteins overview of some recent developments. Journal of Dairy Science, 80, 2607-2619. 

Viscosity is an important physical property of emulsions in terms of emulsion formation and stability (1, 4). Lissant (1 ) has described several stages of geometrical droplet rearrangement and viscosity changes as emulsions form. As the amount of internal phase introduced into an emulsion system increases, the more closely crowded the droplets become. This crowding of droplets reduces their motion and tendency to settle while imparting a "creamed" appearance to the system. The apparent viscosity continues to increase, and non-Newtonian behavior becomes more marked. Emulsions of high internal-phase ratio are actually in a "super-creamed" state. 

Disadvantages Many factors other than hydrophobicity influence emulsion properties. It is essential that researcher determine that this test actually correlates with desired property of emulsion. 

Farinato, R.S. and Rowell, R.L. 1983. Optical properties of emulsions. In Encyclopedia of Emulsion Technology, Vol. 1 Basic Theory, (P. Becher, ed.) Marcel Dekker, New York. 

In the broadest sense, stability of emulsions should be defined as maintenance of an initial state that was attained after homogenization of the two (or more) liquids (Sjoblom, 1996). The initial state of the emulsion can be defined by a set of internal parameters. The primary parameters used to describe the state of an emulsion are droplet size distribution and concentration, since the bulk properties of emulsions such as color, texture, and taste are primarily a function of these two colloidal parameters (McClements, 1999). In selected cases it may be necessary to include additional parameters such as pH and microbial load to further define the initial state of the emulsion. 

Conventional sensitometry is used to determine photographic sensitivity. Special sensitometers have been built which allow the photographic properties of emulsion coatings to be determined for exposures made under vacuum or a variety of atmospheres, pressures, and temperatures (13-15). 

The dielectric properties of water have been extensively used to determine moisture content in food systems. However, only veiy recently have we used the complex dielectric properties of emulsions in the microwave frequency region to characterize both emulsion type and water content [50-52], We have developed both a cavity resonance dielectrometer capable of operating at 8-11 GHz and an interference dielectrometer operating at 23.45 GHz. 

There are a number of physical-chemical properties of emulsions that are important to consider when developing an emulsion formulation for a drug. These include, but are not limited to, particle (droplet) size, viscosity, osmolarity, and zeta potential, which are used to monitor the physical stability of emulsions. Assays of potency and degradant levels are used to monitor the chemical stability of emulsions. 

Viscosity. This parameter can be monitored by standard rheological techniques. The rheological properties of emulsions, reviewed by Sherman (1983), can be complex, and depend on the identity of surfactants and oils used, ratio of disperse and continuous phase, particle size, and other factors. Flocculation will generally increase viscosity thus, monitoring viscosity on storage will be important for assessing shelf-life. 

Probable Effect of Different Variables on the Properties of Emulsion Formulation... 

Addad, J.P., ed., Physical Properties of Emulsions, John Wiley Sons, New York, 1996, pp. 1-17. 

Properties of Emulsions Since an emulsion is a colloidal system of liquid dispersed in liquid, therefore, its properties are common to those of colloidal solutions. 

Colloidal interactions form the basis of many of the properties of emulsions, as well as the changes observed in emulsions over time such interactions govern whether droplets remain as separate entities or aggregate. In this section, a brief overview of the predominant colloidal interactions of importance for the stability of emulsions of milk fat globules is given. 

Rheological properties of milk and cream are influenced by various processes (e.g., heat treatment, cooling or homogenization). McClements (1999) reported that the main factors that determine the rheological properties of emulsions can be divided into five groups ... 

Sherman, P. 1967a. Changes in the rheological properties of emulsions on aging. II. Viscosity changes in w/o emulsions at rates of shear from 0.133 sec-1 to 10.77 sec-1. J. Coll. Interface Sci. 24, 97-106. 

Studies [109,110] have shown that small changes in physical properties of emulsions can influence the elimination rate of these formulations from the blood. Indeed, an organ distribution study of stearylamine-based cationic or deoxycholic acid-based anionic nanosized emulsions and Intralipid, a well-known commercial anionic emulsion, containing 14C-CO was carried out following injection into the tail vein of male BALB/c mice (20-26g) at a volume of 5mL/kg [111, 112], Since CO... 

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