Emulsions physical chemistry

Narsimhan, G. Emulsions" in Physical Chemistry of Foods, ed. Schwartzberg, H.G. and Hartell, R.W., Maicel-Dekker Inc. (1992). 

The range of monomers which can be employed is largely dictated by the physical chemistry of the emulsion system. For instance, monomers must be sufficiently hydrophobic to allow the formation of stable w/o HIPEs. In addition, most systems which have been studied have used polymerisation methods which require either an initiation step, or addition of a catalyst. This is due to the fact that the first step in the preparation of the polymer is the preparation of HIPE this can only proceed satisfactorily in the absence of any significant degree of polymerisation. Thus, it can be seen that radical addition polymerisation is suitable for the synthesis of PolyHIPE polymers, whereas condensation polymerisation can be more problematical. Also, the latter reactions often generate water as the by-product, hence the aqueous component of the HIPE is inhibiting to the polycondensation. 

What is necessary for a collision to be followed by a coalescence What is the mechanism of coalescing These are questions that have fascinated many scientists and engineers both in the field of the physical chemistry of emulsions and foams and in the engineering field of agitated dispersions. 

J.T. Davies, A quantitative kinetic theory of emulsion type, I, Physical chemistry of the emulsifying agent, in J.H. Schulman (Ed.), Proceedings of the 2nd International Congress of Surface Activity, Butterworths, London, 1957, pp. 426-438. 

Figure 9.22 Storage and loss moduli G and G" for a water-in-oil emulsion containing 99% water, 0.5% C10H22 oil, and 0.5% trethylcnc glycol dodecyl ether (C12EO3) surfactant at 40°C. The droplets are around a micron in size. The closed circles ( ) are for the first experimental run, while the open circles (Q) are for a repeat run. The solid and dashed lines are fits of the Maxwell model to the first and second runs, respectively. The fitted modulus Goo is 216 Pa for both runs, while the fitted relaxation times are 2.7 sec and 4.3 sec. (Reprinted with permission from Pons et al.. Journal of Physical Chemistry 97 12320 Copyright 1993, American Chemical Society.)...

No attempt has been made to include every term that may be encountered in dealing with petroleum emulsions. Some basic knowledge of underlying fields such as physical chemistry and chemical engineering is assumed. Many named emulsions and phenomena (such as Pickering emulsions) have been included, but named equations and constants have generally not been included. 

Washington, C. King, S.M. Heenan, R.K. Structure of block copolymers adsorbed to perfluorocarbon emulsions. Journal of Physical Chemistry 1996, 100, 7603-7609. 

Surfactants find apphcation in almost all disperse systems that are utilised in areas such as paints, dyestulfs, cosmetics, pharmaceuticals, agrochemicals, fibres, and plastics. Therefore, a fundamental understanding of the physical chemistry of surface-active agents, their unusual properties, and their phase behaviour is essential for most formulation chemists. In addition, an understanding of the basic phenomena involved in the application of surfactants, such as in the preparation of emulsions and suspensions and their subsequent stabilisation, in microemulsions, in wetting, spreading and adhesion, is vitally important to arrive at the correct composition and control of the system involved [1, 2]. This is particularly the case with many formulations in the chemical industry mentioned above. 

Physical Chemistry of Emulsion Systems 1165 For a perfectly spherical droplet rj = rj = r and... 

The preparation of polymer latices is a more lengthy process and requires more specialised apparatus and laboratory facilities. A student experiment for the preparation of polystyrene latex by emulsion polymerisation (sec Chapter 4) is described by M. W. J. Eskcr and J. H. A. Picper in Physical Chemistry Enriching Topics from Colloid and Surface Chemistry , cd. H. van Olphen and K. J. Mysels, Theorex, California, 1975. 

A. W. Adamson, Physical Chemistry of Surfaces , 4th Edn., Wiley-Interscience, New York, London, Sydney, Toronto, 1982, Ch. XII. This chapter deals with emulsions and foams and, inter alia. with soan films. 

If the product of a polymerization is a latex then the process of polymerization can be considered, either in part or in full, as an emulsion polymerization. The advantage of doing so is that the physical chemistry of emulsion polymerization, combined with the appropriate polymer chemistry allows, in many cases, fuller understanding of the unconventional emulsion polymerizatiotL... 

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. 

It would appear that, fi-om fundamental tenets of physical chemistry, the demulsifier strueture and ehemistry determine the degree of interfacial activity and the HLB. In addition, its molecular weight governs viseosity and diffu-sivity as well as its solubility. The overall struetural configuration determines the elastieity and viseosity at an interface or in solution. However, earrier solvents play a major role in the demulsifier eonfiguration as well as in compatibility with the eontinuous oil phase and at the oiEwater interface. These faetors all apply in the demulsifieation of erude oils and bitumen emulsions. 

In this chapter, we have attempted to review and summarize the state of knowledge of the mechanisms of stabilization of W/0 emulsions by asphaltenes. This has necessarily taken us into flic realm of asphaltene chemistry, physical chemistry, adsorption at interfaces, film structure, and film rheology. The self-assembly of asphaltenes at oil-water interfaces into a physically crosslinked, mechanically strong. 

Tadros, Tharwat F. Applied Surfactants Principles and Applications. Weinheim, Germany Wiley-VCH Verlag, 2005. Author covers a wide range of topics on the preparation and stabilization of emulsion systems and highlights the importance of emulsion science in many modern-day industrial applications discusses physical chemistry of emulsion systems, adsorption of sm-fectants at liquid/liquid interferes, emulsifier selection, polymeric surfectants, and more. 

Thickening agents based on aqueous emulsion polymer chemistry were first developed [9] in the late 1950s and represent another important class of thickening agents. In this physical form, a monomer composition is chosen that provides a balance between the hydrophilic nature of a carboxylic acid monomer (such as acrylic, or more usually methacrylic acid) and a hydrophobic alkyl (meth)acrylate monomer (such as methyl methacrylate, ethyl acrylate, butyl acrylate or mixtures of such species). Whilst the carboxylic acid is in the free-acid form the overall composition is balanced to sufficiently hydrophobic to be water immiscible. This allows the monomer mixture to be reacted using a conventional oil-in-water emulsion polymerisation technique. 

Tse, K.Y. and Reineccius, G.A. (1995) Methods to predict the physical stability of flavor-cloud emulsion. In C.T. Ho, C.T. Tan and C.H. Tong (eds), Flavor Technology Physical Chemistry, Modification, and Process. American Chemical Society, Washington, DC, p. 173. 

The physical chemistries behind these processes are complex the rate of development is dependent on many factors which include the nature [25] of the catalytic speck itself, its size, the reduction potential (See electrochemical explanations, for example [26, 27]) of the developer composition and the agitation of the process [28] to prevent undue concentration depletion. It also depends on the stage of the development process typical negative emulsion systems are characterised by a slow initial rate (often referred to as an induction period) followed by a rapid acceleration and a final slowing as reagents are depleted. Many different compounds have been explored as developers alone and as combinations. Some combinations provided advantages in rates of development [29] compared to... 

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