Some Practical Capillary Systems

While many practical capillary systems do not lend themselves to direct analysis according to the simple concepts presented above, there are areas in which those principles, along with some intuition and a dollop of luck, can be constructively employed to analyze and predict capillary phenomena. Several areas in which various degrees of success have achieved are wetting and repellency of woven fibers, paper products, porous solids, wicking, and cleaning action in detergent baths. Approaches to some of those problems will be briefly discussed below. 

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Microchips offer various possibilities for the performance of analytical assays they comprise a capillary system, to which electric fields can be applied, which is the principle of capillary electrophoresis (CE). Thus, capillary electrophoretic separation assays can be transferred to microchips leading to the accelerated separation of compounds, in particular of carbohydrates, amino acids, peptides, proteins, and nucleic acids. In Table 3, some representative assays are summarized with special emphasis on the practical applications. 

Adsorption from liquids is less well understood than adsorption from gases. In principle the equations derived for gases ought to be applicable to liquid systems, except when capillary condensation is occurring. In practice, some offer an empirical fit of the equilibrium data. One of the most popular adsorption isotherm equations used for liquids was proposed by Freundlich 21-1 in 1926. Arising from a study of the adsorption of organic compounds from aqueous solutions on to charcoal, it was shown that the data could be correlated by an equation of the form ... 

This demonstration, that the combination of surfactants and silica can produce mesoporous materials resembling zeolites in terms of uniform pores and well-defined structure stimulated a systematic exploration of the new area. The behavior of surfactant system was exploited to vary pore size of the generated materials and to produce novel discrete structures. An in-depth characterization showed some remarkable and unprecedented physical properties, such as adsorption of gases with capillary condensation in the mesopore region [12], A comprehensive catalytic testing showed potential for practical applications in hydrocarbon conversion and other processes [7,9]. 

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