Glass liquid meniscus

It is important, however, to remove the protein layer from the surface over which the air/liquid meniscus is displaced during the measurement so as to assure that the conditions of flow with and without the layer in the capillary are totally comparable. Using this method we find that in the case of bovine serum albumin very thick layers are formed layers whose thickness grows in direct proportionality to albumin concentration up to 15% w/v, at least. We also find a reversible doubling of layer size as temperature is raised from 7.7 to 15°C in the case of triple helical soluble collagen adsorbed end on to glass. 

The most common laboratory instrument used to measure gas pressure is a manometer, a glass U-tube partially filled with a liquid (Figure 11-1). Mercury is the most commonly used liquid, because it is fairly nonvolatile, chemically inactive, and dense, and it does not dissolve gases or wet (adhere to) glass. Because mercury does not wet glass, its meniscus will curve upward instead of down, and its position is recorded as that of the horizontal plane tangent to the top of the meniscus. 

Liquid evaporation was employed for liquid pumping in Si-glass microchannels. With hydrophobic patterning at the outlet reservoir, the evaporation rate at the liquid meniscus was controlled to produce a flow rate of 5 nL/min. The hydro-phobic region was patterned by an A1 mask using a silane solution (FDTS) [146]. 

This means that when a glass tube of a hair-line diameter is dipped in water, the liquid meniscus will rise to the very same height. The magnimde of rise is rather large, i.e., 3 cm if the bore is of 1 mm for water. This equation also explains what happens when liquid drops are formed at a faucet. Although it may not be obvious here, the capillary force can be very dominating in different processes. The capillary phenomenon thus means that it will play an important role in all kinds of systems where liquid is in contact with materials with pores or holes. In such systems the capillary forces will determine the characteristics of liquid-solid systems. Some of the most important are as follows ... 

Equation (670) is known as the Washburn equation. The rc term can also be eliminated from Equation (670) by using a completely wetting liquid giving 9=0, and measuring the increase of the liquid level in the powder column by time. In the practical wicking method, the powder is filled inside a glass capillary tube, the bottom of this tube is brought into contact with the test tube, and the increase of the liquid meniscus with time is followed by a cathetometer. 

Jurin s law describes the spontaneous ascent of a liquid up a fine capillary tube (radius R < n ) (see Fig. 1.10). Dip the end of an extremely clean glass capillary tube (cleaned with sulfochromic acid) into water. The water will rise up to a height h and, as the water totally wets the glass, the meniscus will be hemispherical. The pressure at point A, just inside the liquid, can be calculated using Laplace s formula. If Pq is the outside pressure, then... 

Perhaps the best discussions of the experimental aspects of the capillary rise method are still those given by Richards and Carver [20] and Harkins and Brown [21]. For the most accurate work, it is necessary that the liquid wet the wall of the capillary so that there be no uncertainty as to the contact angle. Because of its transparency and because it is wet by most liquids, a glass capillary is most commonly used. The glass must be very clean, and even so it is wise to use a receding meniscus. The capillary must be accurately vertical, of accurately known and uniform radius, and should not deviate from circularity in cross section by more than a few percent. 

Consider an experiment in which liquid carbon dioxide is introduced into an otherwise evacuated glass tube, which is then sealed (Figure 9.4, p. 232). At 0°C, the pressure above the liquid is 34 atm, the equilibrium vapor pressure of C02(Z) at that temperature. As the tube is heated, some of the liquid is converted to vapor, and the pressure rises, to 44 atm at 10°C and 56 atm at 20°C. Nothing spectacular happens (unless there happens to be a weak spot in the tube) until 31°C is reached, where the vapor pressure is 73 atm. Suddenly, as the temperature goes above 31°C, the meniscus between the liquid and vapor disappears The tube now contains only one phase. 

One result of adhesive forces is the curved surface of a liquid, called a meniscus. As Figure 11-18 shows, water in a glass tube forms a concave meniscus that increases the number of water molecules in contact with the walls of the tube. This is because adhesive forces of water to glass are stronger than the cohesive forces among water molecules. 

Tears-of-Wine The surface motion of mixed liquids was described in ancient times [29], and scientifically in a paper by James Thompson, the brother of Lord Kelvin [30] in 1855. Recently Neogi [31], and Cazabat [32] reported on the formation of ordered stmctures in evaporating solutions of two liquids. The meniscus of wine in a glass is drawn upward on the glass surface and forms a thin film. Due to its... 

Note that if 0 > 90° (e.g. mercury on glass), the liquid will actually fall below the reservoir level and the meniscus will be curved in the opposite direction. 

The Cannon-Fenske viscometer (Fig. 24b) is excellent for general use. A long capillary and small upper reservoir result in a small kinetic eneigy correction the large diameter of the lower reservoir minimizes head errors. Because the upper and lower bulbs lie on the same vertical axis, variations in the head are minimal even if the viscometer is used in positions that are not perfectly vertical. A reverse-flow Cannon-Fenske viscometer is used for opaque liquids. In this type of viscometer the liquid flows upward past the timing marks, rather than downward as in the normal direct-flow instrument. Thus the position of the meniscus is not obscured by the film of liquid on the glass wall. 

A volumetric flask is calibrated to contain a particular volume of solution at 20°C when the bottom of the meniscus is adjusted to the center of the mark on the neck of the flask (Figure 2-9, Table 2-3). Most flasks bear the label TC 20°C, which means to contain at 20°C. (Pipets and burets are calibrated to deliver, TD, their indicated volume.) The temperature of the container is relevant because both liquid and glass expand when heated. 

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