Moving-droplet mixing

Moving- and Oscillating-droplet Mixing by Electrowetting Most Relevant Citations... 

Figure 1.42 Schematic of the pivot point around which the droplet moves in a 2 x 3 mixer array (top row). Images of droplet mixing in a 2x3 array taken at various times (16 Hz switching frequency) [29] (by courtesy of RSC).

One of the requirements in MALDI-MS analysis is the use of a liquid matrix. The electrowetting-on-dielectric (EWOD) method has been used to move and mix droplets containing proteins and peptides with the liquid matrix, all of which were situated at specific locations on an array of electrodes. With this method, insulin (1.75 pM), insulin chain B (2 pM), cytochrome c (1.85 pM), and myoglobin (1.45 pM) have been analyzed [518]. 

The carrier gas moves solids and droplets at random, providing intimate mixing. The gas also prevents the material from sticking to the wall of tube. As the solid... 

M 14] [P I3]The fluorescent droplet is moved towards the non-fluorescent droplet and the coalesced droplet is held in place [97] (see also an initial experiment in [98]). By this action, the fluorescent droplet moves underneath the non-fluorescent one. From a top view, a homogeneous texture is yielded however, a vertically segregated fluidic system exists (see Figure 1.37). Mixing takes then place by diffusion and needs about 90 s to be completed. 

For a such case, linear arrays of electrodes may be used however, this will lead to extended structures when using, e.g., more than four electrodes. Instead of using such unidirectional motion, the droplet may be moved in circular fashion by a square-like 2x2 array of electrodes. Indeed, faster mixing times compared with simple droplet merging can be achieved, albeit not faster than for the respective four-electrode linear structure. Actually, a small portion of the droplet remains unmixed. This was explained as due to the droplet pivoting around the array center. For this reason, a non-symmetric array (2 x 3) was developed as mentioned below. 

At the liquid-liquid interface between a hydrocarbon oil and water under mixing, the molecules encounter unbalanced attraction forces, pull inwardly, and contract as other molecules leave the interface for the interior of the bulk liquid. As a result, spherical droplets are formed. Customarily, the boundaries between a liquid and gas and between two liquids are the surface and the interface, respectively. The interfacial tension (or interfacial free energy) is defined as the work required to increase the interfacial area of one liquid phase over the other liquid phase isothermally and reversibly. Moving molecules away from the bulk to the surface or interfacial surface requires work (i.e., an increase in free energy). Water molecules and hydrocarbon oil molecules at the interface are attracted to the bulk water phase as a result of water-water interaction forces (i.e., van der Waals dispersion y and hydrogen bonding y ), to the bulk oil phase due to the oil-oil dispersion forces, y 1, and to the oil-water phase by oil-water interactions, y )W (i.e., dispersion forces). As mentioned in Chapter 3, the oil-water dispersion interactions are related to the geometric mean of the water-water and oil-oil dispersion interactions. The interfacial tension is written as ... 

Pesticide movement away from the release site in the air is usually called drift. Pesticide particles, dusts, spray droplets, and vapors all may be carried offsite in the air. People who mix, load, and apply pesticides outdoors usually are aware of the ease with which pesticides drift offsite. People who handle pesticides indoors may not realize how easily some pesticides move offsite in the air currents created by ventilation systems and by forced-air heating and cooling systems. 

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