Active sheath flow

Pneumatically Controlled Flow Device Active Sheath Flow... 

Fig. 6 Active sample flow switching with sheath flow balance change, (a) Principle of flow switch [25], (b) Sorting of monodisperse oil-water emulsions [27], Reprinted with kind permission from [27] Copyright 2007 Chemical Biological Microsystems Society...

There has been a spate of recent activity associated with the formation and flow of aqueous droplets in channels surrounded by immiscible oil [10]. The typical configuration is similar to that used for flow cytometry in which a sample flow is injected into a co-fiowing sheath flow. In this chip-based manifestation, however, photolithography is used to fabricate a four-way intersection of channels and the sheath fluid is immiscible. Therefore, the water-oil interfacial tension results in the formation of droplets. Typically, the aqueous sample flow enters the intersection head-on and the two side channels... 

The first two components are the active surfactants, whereas the other components are added for a variety of reasons. The polyphosphate chelate Ca ions which are present (with Mg ions also) in so-called hard waters and prevents them from coagulating the anionic surfactants. Zeolite powders are often used to replace phosphate because of their nutrient properties in river systems. Sodium silicate is added as a corrosion inhibitor for washing machines and also increases the pH. The pH is maintained at about 10 by the sodium carbonate. At lower pH values the acid form of the surfactants are produced and in most cases these are either insoluble or much less soluble than the sodium salt. Sodium sulphate is added to prevent caking and ensures free-flowing powder. The cellulose acts as a protective hydrophilic sheath around dispersed dirt particles and prevents re-deposition on the fabric. Foam stabilizers (non-ionic surfactants) are sometimes added to give a... 

By far, the most common UME geometry is that of a microdisc inlaid in an insulating sheath but, unlike spherical electrodes, the surface of an iiflaid microdisc UME is not uniformly accessible as electrolysis at the edges of the microdisc diminishes diffusion to the disc centre. A rigorous mathematical treatment of the steady-state current at a microdisc is not possible but similar considerations to those described above apply. The faradaic current flowing at a microdisc UME during the electrolysis of a redox-active species contains contributions from a transient component... 

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