Flow, pumping method capillary force

Methods available to control non-Newtonian flows are the same as for Newtonian flows, including pressure-driven flows via syringe pumps, capillary-driven flows, and electrokinetic flows. These methods and others are covered in more detail in other entries. In many cases the behavior of polymer solutions subject to a driving force is similar to that of the corresponding Newtonian solvent as long as the characteristic strain rate remains below the coil-stretch transition or De <2- Above this critical value, shear thinning and elasticity are important. 

By definition, a spontaneous capillary flow (SCF) occurs when a liquid volume is moved spontaneously by the effect of capillary forces—without the help of auxiliary devices such as pumps or syringes. Capillary systems can be either confined or open, i.e. the Uquid moves inside a closed channel or in a channel partially open to the air. On the other hand, composite channels—sometimes partly open or with apertures—are increasingly used, and spontaneous capillary flow is a convenient method to move liquids in such geometries. Some examples of SCF are shown in Figure 1.1. 

Forced-flow development. Forced-flow planar chromatography is a development technique wherein pressure is used to aid the mobility of the developing solvent. Examples of this are over-pressure layer chromatography (OPLC) and over-pressure thin-layer chromatography (OPTLC). In the latter a forced-flow technique is used to decrease the development time and thus speed up the separations. A pump controls the speed of the mobile phase. Theoretically, this method is faster than when movement of the solvent is due to capillary action alone (normal TLC) and can be used to advantage if slow-moving viscous solvents are involved as developing solvents. 

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