Contact angle Washburn method

Gurau et al. [194] proposed a method to estimate the internal contact angle to water by combining the Washburn technique with the Owens-Wendt... 

The applied pressure is related to the desired pore size via the Washburn Equation [1] which implies a cylindrical pore shape assumption. Mercury porosimetry is widely applied for catalyst characterization in both QC and research applications for several reasons including rapid reproducible analysis, a wide pore size range ( 2 nm to >100 / m, depending on the pressure range of the instrument), and the ability to obtain specific surface area and pore size distribution information from the same measurement. Accuracy of the method suffers from several factors including contact angle and surface tension uncertainty, pore shape effects, and sample compression. However, the largest discrepancy between a mercury porosimetry-derived pore size distribution (PSD) and the actual PSD usually... 

Contact angles on finely divided solids are more difficult to measure, but are often more desired and more important than those on large solid surfaces. One method of obtaining such contact angles is to pack the powder into a glass tube and measure the rate of penetration of the liquid into it (Brail, 1974). The distance of penetration l in time t of a liquid of surface tension yM and viscosity T is given by the modified Washburn equation (Washburn, 1921) ... 

The wettability of the PE powders was evaluated in terms of contact angle using the Washburn method [7] with benzyl alcohol and ethylene glycol. Each contact angle value corresponds to the mean value of three measurements. The accuracy of the results is 3°. 

To improve the current models, the contact angles in the interior of PTL samples have been calculated via sorption experiments (Gurau et al., 2006 Gurau and Mann Jr., 2010 Parry et al., 2010) that were based on modified versions of the Washburn method (Washburn, 1921). 

The Washburn constant can be obtained from measurements with liquids of known properties and contact angles. The unknown contact angle with a different liquid can be determined by subsequent measurements using the calculated Cyf which is assumed to depend on the porous topology only. This method provides average values, but does not consider local interactions. 

Another characterization method that can be included with those based on the Laplace equation is mereury intrusion porosimetry. The method (also proposed by Washburn [101]) was developed by Ritter and Drake [52] and was applied for the first time to the characterization of membrane filters by Honold and Skau [102]. It has been shown to be a reliable method for the characterization of pore size distributions, pore strueture, and speeific surface areas. Here, a Hg-air interface appears inside each pore. Thus, Eq. (4) is also followed. However, in this case, Hg does not wet practically any kind of sample (the corresponding contact angles ranging from 112° to 150°) [52, 101]. 

The method for measuring the contact angle relies on the test fluids penetrating the porous sample, which can be expressed by the theory of Washburn [15] ... 

The influence of surfactant concentration and the accompanying surface tensions are shown in Figure 5 for a nonionic surfactant solution being applied to severely hydrophobic packed beds. With decreasing surface tension, the imbibition rate progressively increased. A Zisman plot of the contact angle data obtained from the Washburn initial slope method showed a linear relationship with a similar slope to the planar hydrophobic surface described above, although systematically shifted to lower surface tensions. 

Hard particles, of a diameter of 1 fim or more, when spread into flat layers will form a surface that is too rough for accurate contact angle measurement by the sessile (advancing) drop method (Chaudhury, 1984). However, by using a packed column of such particles, capillary rise velocity measurements of a liquid in that column can also yield the contact angle of that liquid with respect to the particles surface. This wicking approach can also be used for contact angle measurement of porous bodies, strands of fibers, etc. In these cases one uses the Washburn equation (Ku et al., 1985 Adamson, 1990) ... 

Section 3.7, the gas adsorption method breaks down for practical reasons. Since the angle of contact of mercury with solids is 140° (see later), and therefore more than 90°, an excess pressure Ap is required to force liquid mercury into the pores of a soh d. The idea of using mercury intrusion to measure pore size appears to have been first suggested by Washburn who put forward the basic equation... 

---