Patent Application
20090205410
1. Field of the Invention
This invention relates to an apparatus for measuring surface tension.
2. Description of the Related Art
When a tube, which is relatively narrow and long, is inserted into a beaker filled with a liquid, it can be found that the height of the liquid in the tube is higher than that in the beaker. The phenomenon is caused by surface tension between the liquid and air. Surface tension enables a liquid to maintain a minimum surface area so that energy of the surface of the liquid is minimized and the liquid surface is maintained at a stable state.
Since a conventional apparatus for measuring surface tension is somewhat complicated and difficult to operate, there is a need in the art to provide an apparatus for measuring surface tension, that is simple and easy to operate.
According to this invention, an apparatus for measuring surface tension includes: a U-shaped communicating tube having a base section that defines a horizontal line, and first and second sections that extend from the base section, that are opposite to each other, and that respectively have first and second top open ends distal from the base section; and a capillary connected to and extending from the second top open end of the second section of the U-shaped communicating tubes in fluid communication with the U-shaped communicating tuber and having a top open end. The U-shaped communicating tube has a diameter greater than that of the capillary such that the U-shaped communicating tube does not exhibit capillary property when a liquid is filled therein. The first top open end of the first section of the U-shaped communicating tube has a height relative to the horizontal line that is greater than that of the top open end of the capillary such that the height difference therebetween is greater than that between the liquid level at the first section of the U-shaped communicating tube and a liquid drop formed on the top open end of the capillary.
Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment of this invention, with reference to the accompanying drawings, in which:
a,
3
b, and 3c are schematic sectional views illustrating consecutive steps for measuring surface tension using the preferred embodiment of the apparatus according to this invention.
Referring to
Preferably, the first section 12 of the U-shaped communicating tube 1 has a lower portion 122 and an upper portion 123. The upper portion 123 has a connecting segment 1231 that is detachably connected to the lower portion 122, and a free segment 1232 that is enlarged in cross-section from the connecting segment 1231. As shown in
The apparatus further includes an elastic plug 3 that is sealingly and detachably fitted into the second top open end 131 of the second section 13 of the U-shaped communicating tube 1. The capillary 2 extends sealingly through the elastic plug 3 and into the second section 13.
It should be noted that, in the preferred embodiment of this invention, although the capillary 2 and the U-shaped communicating tube 1 are two separate parts, they can be integrally formed, and thus, the elastic plug 3 can be dispensed with. Furthermore, as shown in
It should be noted that the capillary 2 can be made from any material suitable for this invention. However, since fluoropolymeric resin has minimum adsorption with respect to a liquid, the capillary 2 is preferably made from polytetrafluoroethylene so as to prevent the adsorption of the liquid at an inner surface and the top open end 22 of the capillary 2.
The measurement of surface tension using the apparatus of this invention will now be described in detail hereinbelow.
First of all, it is well known that surface tension (T) can be obtained using the following formula.
T=ρghr/2
Specifically, in this invention, ρ is specific weight of the liquid; g is the acceleration due to gravity; h is height difference between the liquid levels at the upper portion 123 of the first section 12 and the top open end 22 of the capillary 2 (the height of the liquid drop 16 formed on the top open end 22 of the capillary 2 can be disregarded); and r is an inner radius of the capillary 2.
As shown in
The height difference (h) can be measured using a laser level meter. In addition, in order to easily determine the height of the liquid in the upper portion 123 of the first section 12, the upper portion 123 is preferably transparent.
In addition, the applicant conducted a series of tests to determine the influence of the length of the capillary 2 on measurement of surface tension. As shown in Table 1, the height differences (h) in groups (A) and (B) are identical. In group (C), i.e., the length of the capillary is 200 mm, the height difference (h) is increased by 0.8 mm as compared with groups (A) and (B). With respect to the height difference (h) attributed to the surface tension (i.e., 60 mm), the influence of 0.8 mm on the measurement of surface tension is small. Therefore, the length of the capillary 2 has little influence on surface tension measurement.
In addition, as described above, the free segment 1232 preferably has an inner diameter not less than 36 mm. By choosing the inner diameter of the free segment 1232 to be not less than 36 mm, the capillary phenomenon of the free segment 1232 can be greatly decreased (see Table 2). As shown in Table 2, in groups (E) to (J) where the inner diameter of the free segment 1232 ranges from 5.0 to 26.0 mm, the height difference (h) thus measured is relatively high as compared with groups (A) to (D) where the inner diameter of the free segment 1232 is not less than 36 mm.
In order to prove the apparatus of this invention, several liquids (e.g. pure water, glycerol, olive oil, and alcohol) are used for testing the accuracy of the apparatus in measuring surface tension. The tests are measured at 20° C. As shown in Table 3, the value of surface tension measured using the apparatus of this invention is very close to the standard surface tension (obtained from the published information on the internet) for each test liquid. (ok)
With the apparatus of this invention, surface tension can be easily obtained by measuring the height difference (h) between the liquid levels at the upper portion 123 of the first section 12 and the top open end 22 of the capillary 2. The apparatus of this invention provides an easy and quick measurement for surface tension. In addition, the apparatus has a simple structure and is easy to store and transport.
While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements.
