Multiple droplets

Figure 3.29. Interaction of multiple droplets impinging on a non-flat surface (Re = 76229, We = 33897, s/Do=033, X/D0=2.8). From top to bottom t/(D,/ii0) = 0, 0.8, 1.6. (Reprinted from Ref. 389, 1995, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X51GB, UK.)...

Figure 3.30. Schematic showing the impact phenomena of multiple droplets on a substrate surface spreading pattern at low impact velocities (fop) and splashing mechanism at high impact velocities (bottom).

Figure 1.43 Multiple droplet motion and fusion on an 8 x 8 array fluid processor with 30 pm electrodes, (a) Four droplets of varying size, three on one line and one separate large droplet (b) spontaneous fusion of the middle droplet on the line with the large droplet (c) spontaneous fusion of the upper droplet on the line with the large droplet ...

Recently Di Stefano and coworkers (24) have found with o/w/o systems that the nature of the internal droplets depended on the rate of agitation used in preparation, agitation rates of 212 rpm forming types A or B systems and 425 rpm a type C emulsion. These systems were unusual in that the multiple droplets were extremely... 

As soon as the mobile phase reaches the first coil unit, the two phases interact to establish the hydrodynamic equilibrium where one phase with less wall surface affinity is split into multiple droplets which oscillate synchronously with the coil rotation. While continuous pumping of the mobile phase keeps breaking this equilibrium state at the head end of the coil, the two phases can quickly react to restore the equilibrium by readjusting their relative volumes in each coil unit. Thus the stationary phase pushes newly introduced excess amounts of the mobile phase toward the tail end of the coil. 

Fig. 10 Multiple-droplet sorting device using flexible high-aspect ratio PDMS walls [34], (a) Structure of the multimode droplet sorting device, (b) Principle of multimode droplet sorting, (c) Photograph of droplet sorting (Mode 3)...

From Equation 1, it is apparent that by reducing the interfacial tension, or by increasing the shear rate, the critical droplet size decreases, Since the Taylor approach is only applicable to a single droplet suspended in a Newtonian fluid, multiple droplet interactions and non-Newtonian viscosities are not considered. Despite these drawbacks, the Taylor approach remains one of the most commonly used models for predicting the sizes of dispersed droplets during shear. 

A stable W/O emulsion (the primary emulsion) is emulsified in water using surfactants appropriate to the stabilization of an oil-in-water emulsion. The emulsification of the primary emulsion is a critical stage as excess turbulence will cause the coalescence of the multiple droplets. Ultrasound and high shear mixers cannot, therefore, be used at this stage. A typical size distribution of internal (aqueous) and multiple (oil) drops is shown in Fig. 8.26. One of the difficulties in recording the size data of these systems is that oil droplets may be empty or contain one, two or more droplets. Davis et ai [146] used a Coulter counter to size the external oil droplets in multiple systems and the same group [147] used a... 

Florence and Whitehill [150,151] have described three types of multiple W/O/W emulsions, categorized according to the predominance of the multiple droplet type (Fig. 8.28). Using isopropyl myristate as the oil phase, 5 % Span 80 to prepare the primary W/O emulsion and various surfactants to prepare the secondary emulsion, three main emulsion types were observed. 

When droplet deformation occurs, the Laplace pressure of the deformed droplet will be a function of the radius along the droplet surface. In the extreme cases, as a droplet becomes elongated and cylindrically shaped, the Laplace pressure is reduced to a half that of the original spherical droplet. For multiple emulsions, the Laplace pressure exists in both the inner and multiple droplets. However, because the size of the inner droplets is much smaller, the Laplace pressure on the stability of the inner droplets is much greater than that on the multiple droplets. 

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