Forced flow-through type capillary

The macromolecules in solution may be subjected to the action of some mechanical stresses resulted from several types of stresses applied, such as ultrasonation [797,798], cryolysis [799,800], laminar or turbulent flow through thin tubes [801,802], ultrahigh speed stirring [803-806], flow between two concentric cylinders which rotate in opposite directions [210], forced flow through the capillaries [798-814]. 

This shearing in turn creates a hot melt deformation, or stress. The stress required to bring about a shearing type of a hot melt deformation (a required force divided by the area over which it works) is called shear stress (t, see below). In case of capillary flow, apparent shear stress is the measured resistance to the flow through a capillary die. 

Finally increase in n shown by several systems during postdrying (3) (see Table I) stems from subterranean absorption processes e.g. interconnection of partially filled pores and localized surface fibre wicking. The values of n which in several cases are close to the theoretical value, 0.5, for a Lucas-Washbum type capillary model, suggest that the condition of flow through completely filled and interconnected capillaries to supply the spreading front, is ultimately attained. This final stage reflects lag in the equilibration of bulk and surface capillary forces. 

Hi) By streaming potential A third type of electrokinetic phenomenon observed is the development of a streaming or flow potential when a hquid like water is forced to flow through a Uiss capillary. A potential develops on either side of the capillary at its two ends (see figure 3.10). 

Capillary Viscometers sed for concentrated solutions or polymer melts and described just above, the other, described here, used for measuring dilute-solution viscosities. The most widely used of the latter types employ a glass capillary tube and means for timing the flow of a measured volume of the solution (e.g., polymer in solvent) through the tube under the force of gravity. This time is then compared with the time taken for the same volume of pure solvent, or of another liquid of known viscosity, to flow through the same capillary. Relevant tests are from ASTM (www.astm.org). See also Dilute-Solution Viscosity and Viscometer. 

Solution (Wet) Spinning. In the most widely used solution spinnerette system (60) the spinnerette consists of two concentric capillaries, the outer capillary having a diameter of approximately 400 ]Am and the central capillary having an outer diameter of approximately 200 ]lni and an inner diameter of 100 ]lni. Polymer solution is forced through the outer capillary while air or Hquid is forced through the inner one. The rate at which the core fluid is injected into the fibers relative to the flow of polymer solution governs the ultimate wall thickness of the fiber. Figure 19 shows a cross section of this type of spinnerette. 

If a liquid is used as die mobile phase, the technique used is liquid chromatography (LC). The solid adsorbent is constrained in a tube or column through which the liquid mobile phase flows. Any number of solvents, buffer solutions, or supercritical fluids can be used as liquid mobile phases. High-pressure liquid chromatography (HPLC) is used if pressure is needed to force die liquid phase through the tube. If the liquid phase moves over a thin adsorbent surface propelled by capillary action, die technique used is thin-layer chromatography (TLC). In general, two types of surfaces are used as the solid phase. 

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