Capillary filling

Since the blocked gas inside of the capillary is dissolving in the liquid and then diffusing towards the exit of the channel, the meniscus of the liquid crosses the position l and goes deeper. This second stage of capillary filling with liquid is called diffusive imbibition and plays an important role in PT processes. The effect of diffusive imbibition upon PT sensitivity has been studied in [7]. 

Electroosmotic Mobility When an electric field is applied to a capillary filled with an aqueous buffer, we expect the buffer s ions to migrate in response to their electrophoretic mobility. Because the solvent, H2O, is neutral, we might reasonably expect it to remain stationary. What is observed under normal conditions, however, is that the buffer solution moves toward the cathode. This phenomenon is called the electroosmotic flow. 

Here, we will describe experimental studies on capillary filling of CNTs. Because of the focus of this chapter, we have taken examples from the work in our own laboratory certainly we may have inadvertently ignored other exciting work from other laboratories in the world. Still the preparation of a sample of purified and filled CNTs have yet to be developed, so that the study of filled tubes have been and can only be performed by electron microscopy and associated techniques. We have tried to describe in detail all the steps involved in the procedure of capillary filling, such as CNT production, opening, filling and final thermal processing. 

Our results indicate that the number of filled tubes is rather low, but the filled ones display astonishing narrow and very long filaments (2-.3 nm in diameter and several hundreds of nm in length) [32], If capillary filling is extremely efficient for these cases, it seems rather contradictory that filled tubes are so rare. We have not yet been able to identify the factors governing the exceptional capillary behaviour of only a few tubes. 

The capillary filling of CNTs is basically and usually described using macroscopic thermodynamic approximations. For example, Dujardin et al. [10] concluded that the surface-tension threshold value for filling a CNT was 100-200... 

DiGuilio and Teja have developed a two-wire technique to obtain absolute values of thermal conductivity. Quartz capillaries filled with liquid gallium served as insulated hot wires. They measured the thermal conductivity of the NaN0j-KN03 eutectic in the range 525-590 K with 1% accuracy. Radiation by the fluid was also accounted for. 

The mobilities of alkylpyridines were modeled and predicted in capillary zone electrophoresis.35 The model predicted that compounds adopt a preferred orientation, and additionally predicted mobilities of structural isomers to within 4%, a higher degree of accuracy than can be obtained from simple considerations of van der Waal s radius. Quantitative prediction of the mobilities of some pyridines, such as alkenylpyridines, was not possible. Mobilities of small solutes in capillaries filled with oligomers of ethylene glycol were related to solution viscosity and the diffusion coefficient.36... 

Cottet, H. and Gareil, R, Electrophoretic behavior of fully sulfonated polystyrenes in capillaries filled with entangled polymer solutions,. Chromatogr. A, 772, 369, 1997. 

G. Lippmann introduced the capillary electrometer to measure the surface tension of mercury (Fig. 4.10). A slightly conical capillary filled with mercury under pressure from a mercury column (or from a pressurized gas) is immersed in a vessel containing the test solution. The weight of the mercury column of height h is compensated by the surface tension according to the Laplace equation... 

The transport of many compounds takes place through interstices of polymer chains filled with aqueous medium [52], In such cases, the rate of mass transport is directly proportional to the degree of hydration of the membranes [53]. The most widely accepted method for determining the hydration of membranes is to equilibrate the membranes in water or buffer and weigh these membranes after blotting [54], In a newer method, the matrices to be studied are placed on a sintered glass funnel which is attached to a capillary filled with water. The absorption of water results in the movement of the capillary front [55],... 

It would therefore be of obvious importance to study the electrical behaviour of a surface liquid-air, since in that case we can determine changes in surface tension directly. Such experiments were already carried out by Quincke, who examined under the microscope the travel of a small air bubble in capillary filled with liquid, in an electric field. The method is therefore substantially cataphoresis, but has the drawback that there is only a minute thickness of liquid between the air surface and the glass wall, and that the portion of liquid film adjacent to the latter also travels in the electric field. Quincke found that air bubbles in water were negatively... 

Electrophoresis can be carried out using paper or a gel as the supporting medium. Typically, it can only be carried out in media compatible with water because buffers or salt solutions are required to carry the electric current required for separation. CE is carried out in a fused-silica capillary filled with buffer. 

The basic requirements of electrophoresis are a semi-conducting medium and an electric field. The semi-conducting medium can be a paper soaked in an electrolyte or a gel placed in an electrolyte. In the case of CE, it is a capillary filled with an electrolyte or a gel. The electric field is generated by applying a voltage difference over the capillary. 

Capillary gel electrophoresis (CGE) is a specialised form of CE that employs a fused silica capillary filled with an immobilised and cross-linked polyacrylamide gel. This gel contains a network of pores, which allows separation of ions based on differences in molecular size. CGE was applied to the separation of ionic alkylphenol ethoxy sulfates and... 

Several research groups used another interesting column technology as an alternative to the modification of the capillary surface. This method is inherited from the field of electrophoresis of nucleic acids and involves capillaries filled with solutions of linear polymers. In contrast to the monolithic columns that will be discussed later in this review, the preparation of these pseudostationary phases need not be performed within the confines of the capillary. These materials, typically specifically designed copolymers [85-88] and modified den-drimers [89], exist as physically entangled polymer chains that effectively resemble highly swollen, chemically crosslinked gels. 

Fig. 16. CEC separation of naphthalene (1), fluorene (2), phenanthrene (3), anthracene (4), pyrene (5),triphenylene (6),andbenzo(a)pyrene (7) using capillary filled with CIO alkyl substituted polyallylamine. (Reprinted with permission from [86]. Copyright 1997 Elsevier). Conditions capillary 50 pm i.d., 48 cm total length, 33 cm active length, field strength 400 V/cm, carrier concentration 20 mg/ml, mobile phase 60 40 methanol-20 mmol/1 borate buffer pH=9.3...

Suspecting that constant-flow conditions are not realized even for capillaries and that the effect is due most probably to the chamber volume instead of kinetic effects as explained by the earlier investigators, data were collected using empty capillaries and capillaries filled with glass powder. The results show that for glass-powder-filled capillaries, the minimum is absent (K8). 

Fig. 10.15 The methods for capillary filling of nanotubes involves dispersal of the agent in a liquid capable of flowing into the nanotube followed by subsequent evaporation of the solvent to leave particles inside the tube. Nanotubes have been filled with polystyrene spheres and palladium nanocrystals using this method (Reprinted from Kim et al., 2005. With permission from American Chemical Society Reprinted from Tessonnier et al., 2005. With permission from Elsevier) (See Color Plates)...

Another expression for AG may be obtained from consideration of the interfacial changes that occur as the capillaries fill. This takes the form ... 

Capillary Electrophoresis (CE) The CE instrument consists of a source/ sample vial, a destination vial and a small capillary filled with electrolyte joining the two vials. A voltage is applied and separates the sample according to size and charge, which is detected by UV absorbance. 

The reference electrode is connected with the cell via a glass tube (Luggin capillary) filled with electrolyte, and the narrowed orifice of the tube is placed about 0.1 to 0.3 mm in front of the side of the working electrode that faces the counter electrode. The potential between this point and the surface of the working electrode is measured with a high resistance voltmeter that makes contact with the silver wire of... 

FIGURE I Diagram of a capillary filled with an UV-absorbing BGE. A non-absorbing analyte will displace the UV-absorbing probe, resulting in a negative peak due to displacement of the probe (A). When the mobilities of the analyte and the probe are different, a non-symmetric peak will be observed (B). 

Inking Time — Pins may have different capillary fill and wetting rates depending upon surface characteristics and geometries. For example, inking times on quills are in the range of a few seconds, while it may not be necessary to keep solid pins in contact with a source plate for more than a second to allow uptake. 

Separation is carried out by applying a high potential (10-30 kV) to a narrow (25-75 pm) fused silica capillary filled with a mobile phase. The mobile phase generally contains an aqueous component and must contain an electrolyte. Analytes migrate in the applied electric field at a rate dependent on their charge and ionic radius. Even neutral analytes migrate through the column due to electro-osmotic flow, which usually occurs towards the cathode. 

Serotonin also constricts veins, and venoconstriction with increased capillary filling appears to be responsible for the flush that is observed after serotonin administration or release from a carcinoid tumor. Serotonin has small direct positive chronotropic and inotropic effects on the heart, which are probably of no clinical significance. However, prolonged elevation of the blood level of serotonin (which occurs in carcinoid syndrome) is associated with pathologic alterations in the endocardium (subendocardial fibroplasia), which may result in valvular or electrical malfunction. 

The 31P H NMR spectrum of the methanol solution, recorded using a capillary filled with acetone-d6 as lock, shows a signal at <5 27.8 ppm flanked by its 195Pt satellites ( p, P = 2707 Hz). 

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