Coalescence viscosity method

Studies of flow-induced coalescence are possible with the methods described here. Effects of flow conditions and emulsion properties, such as shear rate, initial droplet size, viscosity and type of surfactant can be investigated in detail. Recently developed, fast (3-10 s) [82, 83] PFG NMR methods of measuring droplet size distributions have provided nearly real-time droplet distribution curves during evolving flows such as emulsification [83], Studies of other destabilization mechanisms in emulsions such as creaming and flocculation can also be performed. 

A method of parallel plate mode was used to estimate the shear stress and viscosity of a foam [35], The lower plate was fixed and the upper one was rotated. In order to exclude the slip of the foam on the walls the plate was covered with a sand paper. To diminish the drainage and coalescence processes, the foam was produced from a solution with a high concentration of the foaming agent to which dodecyl alcohol was added. Proper linear... 

Interfacial Viscosity. In a clean system in which two pure liquids produce an interface, the viscosity of the interface should be the same as the bulk solution viscosity. However, surfactant or impurity adsorption at an interface can cause a resistance to fiow to occur that can be measured as the interfacial shear viscosity. This viscosity is defined as the ratio between the shear stress and the shear rate in the plane of the interface (12), Methods used to make these measurements include a viscous traction surface viscometer (J2), droplet-droplet coalescence (J3), the rotating ring viscometer (14), and surface laser light scattering (9). 

The validity of Frenkel s model is limited to Newtonian flow and can only be used to predict the early stage of the coalescence process, when the diameter of the two spherical particles remains nearly unchanged. The inadequacy of a Newtonian model in describing the coalescence of polymers was also demonstrated in other studies, as reviewed by Mazur, and has led to the development of models as well as alternative methods for the characterization of the coalescence behavior of polymers for rotational molding applications.Based on theoretical and experimental analyses of the coalescence phenomenon, the material properties of primary interest in the evaluation of resin coalescence behavior in rotational molding have been identifled as the resin viscosity, surface tension, and elasticity. 

In the present work, we summarize recent observations on the coalescence behavior of several oil-water-surfactant systems. We are particularly interested in the behavior exhibited by low tension systems and the role of bulk phase viscous effects and dynamic interfacial properties such as interfacial shear and dilatational viscosities. Also, a new experimental approach for conducting coalescence studies is described which involves tests in an inclined spinning drop device. This approach allows for coalescence tests under controlled conditions and provides an efficient method for quickly screening and evaluating different surfactant systems. 

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