Physical Chemistry of Emulsion Systems

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

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. 

As discussed in the section on physical chemistry of emulsion systems, the condition for kinetic stability is Gmax > 25kT when G ax < 5kT, flocculation occurs. Two types of flocculation kinetics may be distinguished Fast flocculation with no energy barrier and slow flocculation when an energy barrier exists. 

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. 

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. 

The structures of many food emulsions are complex and, often, several phases may exist. Such structures may exist under non-equilibrium conditions and the state of the system may depend largely on the preparation process employed, its prehistory and the conditions to which it is subjected. Unsurprisingly, therefore, fundamental studies on such systems are not easy, and in many cases one is content with some qualitative observations. However, due to the great demand of producing consistent food products and the introduction of new recipes, a great deal of fundamental understanding of the physical chemistry of such complex systems is required. 

Research on the modelling, optimization and control of emulsion polymerization (latex) reactors and processes has been expanding rapidly as the chemistry and physics of these systems become better understood, and as the demand for new and improved latex products increases. The objectives are usually to optimize production rates and/or to control product quality variables such as polymer particle size distribution (PSD), particle morphology, copolymer composition, molecular weights (MW s), long chain branching (LCB), crosslinking frequency and gel content. 

An interdisciplinary team of leading experts from around the world discuss recent concepts in the physics and chemistry of various well-studied interfaces of rigid and deformable particles in homo- and hetero-aggregate dispersed systems, including emulsions, dispersoids, foams, fluosols, polymer membranes, and biocolloids. The contributors clearly elucidate the hydrodynamic, electrodynamic, and thermodynamic instabilities that occur at interfaces, as well as the rheological properties of interfacial layers responsible for droplets, particles, and droplet-particle-film structures in finely dispersed systems. The book examines structure and dynamics from various angles, such as relativistic and non-relativistic theories, molecular orbital methods, and transient state theories. 

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... 

When applying the laws of dilute solution physical chemistry, it is generally presumed that the solute is miscible with (soluble in) the solvent in the mixture of interest. If this is not true, then the mixture is heterogeneous (in a phase sense) and must be treated accordingly. In colloid science, solubility plays an important role in the collapse of the colloidal structure of emulsions and dispersions by ripening. t is apparent from these observations that solubility is a fundamental property of all surfactant systems, and because the practical utility of a consumer product is dictated by its physical chemistry and colloid science [1], solubility is therefore also relevant to utility and performance. 

Alexander Florence is Dean of The School of Pharmacy at the University of London he was previously James P. Todd Professor of Pharmaceutics at the University of Strathclyde. His research and teaching interests are drug delivery and targeting, dendrimers, nanoparticles, non-aqueous emulsions, novel solvents for use in pharmacy and general physical pharmaceutics. He co-authored the book Surfactant Systems their Chemistry, Pharmacy and Biology with David Attwood. 

Based on the DLS measurements it is possible to find particle size distributions of polymers and proteins, particle aggregation phenomena, micellar systems and their stability, micro-emulsion technology, colloid behaviour, nucleation processes and protein crystallization. DLS is a non-destructive and convenient method and so it can find application in various branches of science. In chemistry it finds application in topics of colloids, polymers, emulsions, suspensions, nanoparticles, and in physics, applications such as in astrophysics and atmosphere physics and in biology it involves biophysics and biomedicine applications. 

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