Capillary-rise technique

The capillary rise technique is considered to be very useful for DL materials, especially if the angle is less than 90° and/or for measurements that are taken under different temperature conditions [192]. In this method, a sample material is immersed in a container filled with water and the meniscus height is measured with a microscope (see Figure 4.23). Contact angles between the water and DL are calculated using Equation 4.1 and by measuring the... 

Vernhet, A., Bellon-Fontaine, M. N., Brillouet, J.-M., Roesink, E., Moutounet, M. (1997). Wetting properties of microfiltration membrane determination by means of the capillary rise technique and incidence on the adsorption of wine polysaccharide and tannins. /. Membrane Sci. 128, 163-174. 

For practical reasons the capillary rise technique is rarely used for the measurement of interfacial (rather than surface) tensions large amounts of the two liquids are needed and there are suitable and convenient alternatives. An exception to this is the measurement of the Interfacial tension between mercury and (mostly) aqueous solutions at various potential differences applied across the liquid-liquid interface. Such measurements are done in a so-called Lippmann capillary electrometer, already described in the chapter on electric double layers (fig. 11.3.47). 

Some variants of the capillary rise method have been employed. In the differential capillary rise technique, two tubes of different diameters are used, and the difference in height between the two menisci is measured. In the inclined capillary rise scheme, the tube is inclined at a known angle so that the length Q of the tube occupied by the wetting fluid is greater than the height h of the rise in a vertical tube. This method is useful when the interfacial tension is low because under these conditions the vertical rise h is small and difficult to measure accurately. 

Adamson and Cast [6] have discussed corrections to the capillary-rise technique when the meniscus is not spherical as well as the experimental issues associated with the measurements. 

In Chapter 2 the capillary-rise technique for measuring yuv was described. A number of other techniques, which are based on the Laplace... 

Table 14.2 shows a comparison of measured contact angles using ADSA and capillary rise. It can be seen that the capillary rise technique is also able to produce contact angle data with high accuracy, and there is excellent agreement between the two techniques. 

The contact angle measurements with the capillary rise technique can be time-consuming, and hence automation of the measurements is desirable. Figure 14.18 shows a schematic of an automated capillary rise apparatus. In the automated capillary rise measurements, the cathetometer, which is used to measure the capillary rise, is replaced by a computer and a microscope on motorized positioning stages. Three computer-controlled motorized translational stages (Micro-control) are used to move a horizontally mounted microscope fitted with a video scanner (Cohu CCD) in three directions, i.e. X, y and z. The x-, y- and z-axis stages... 

Table 14.2. Comparison of measured contact angles, 0 (degree), using the capillary rise technique and ADSA-P for two solid surfaces, FC-721 and FEP. The error limits are 95% confidence limits...

The automated capillary rise technique has been employed to carry out various dynamic advancing and receding contact angle measurements (54) at different immersion speeds ranging from 0.008 to 0.9 mm/min. This technique has also been utilized to study both dynamic advancing and receding contact angles on dry, pre-wetted, and soaked fluorocarbon FC-722 (3M Inc.) surfaces (55). Such measurements reveal that the... 

Budziak, C. and Neumann, A. W., Automation of the capillary rise technique for measuring contact angles. Colloid Surf., 43, 279-293 (1990). 

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