Internal contact angle

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

V. Gurau, M. J. Bluemle, E. S. De Castro, et al. Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells. 1. Wettability (internal contact angle to water and surface energy of GDL fibers). Journal of Power Sources 160 (2006) 1156-1162. 

Since mercury has a contact angle with most solids of about 140°, it follows that its cosine is negative (i.e., it takes applied pressure to introduce mercury into a pore). In a mercury porosimeter, a solids sample is evacuated in a cell, mercury is then intruded, and the volume, V, is noted (it actually reads out), and the pressure, P, is then increased stepwise. In this fashion it is possible to deduce the pore volume of a particular radius [corresponding to P by Eq. (21)]. A pore size distribution will give the total internal pore area as well, which can be of importance in dissolution. 

Once the durability testing of the fuel cells is finalized, the internal components are then characterized. For diffusion layers, some of these characterization techniques include SEM to visualize surface changes, porosimetry measurements to analyze any changes in porosity within the DL and MPL, IGC (inverse gas chromatography) to identify relative humidity effects on the hydrophobic properties of the DLs, contact angle measurements to observe any changes in the hydrophobic/hydrophilic coatings of the DL, etc. [254,255]. 

It is believed that in the presence of dampproofing admixtures, the surfaces of the concrete, and the internal surfaces of the pores become coated with either a layer of molecules in the case of stearic acid and other fatty acids (Fig. 4.5b) or a layer of coalesced or separate particles of material in the case of waxes and bitumens, etc. (Fig. 4.5c). The end result in both cases is the production of hydrophobic surfaces exhibiting high contact angles to water, as shown in Fig. 4.6. 

When the contact angle is greater than 90°, cos0 is negative, and the liquid falls in the tube. This occurs with mercury in glass, as a general rule, and with water in tubes coated with paraffin wax internally. 

Powdered solids are very useful emulsifiers, and are frequently used, and it is found that emulsions of either the oil-in-water or the water-in-oil type can be stabilized by them. Here it has been shown (Chap. V, 21) that the liquid which forms the internal phase in the emulsion is the one which wets the solid least this is very easily understood in terms of the contact angle formed by the liquid interface with the solid surface, and the theory is easy. 

Apparatus. Contact angle measurements were made on a Model A-100 Rame-Hart version of the NRL Contact Angle Goniometer. Exposures were carried out in a forced-draft hood with the unfiltered radiation from a General Electric UA-3 medium-pressure mercury lamp. Spectra were recorded on a Perkin-Elmer Model 350 ultraviolet spectrophotometer, a Beckman IR-12 infrared spectrophotometer with a Wilks Model 7 internal reflectance attachment, and an Aminco-Bowman Spec-trofluorometer with a 1P28 photocell. 

Literature values of the contact angles for various liquids on four of the five polymers used in this work are given in Table I. These values may be compared with those for our unirradiated polymers. In the case of polystyrene, exhaustive methanol or n-heptane extraction followed by drying did not result in a change in contact angles, and residual extractant could not be observed by means of frustrated multiple internal reflectance (FMIR) spectra of the films. 

The crystallographically determined structure of 15 confirms the presence of a butterfly arrangement of iron atoms within which the boron atom resides in contact with all four metal atoms [Fe—B = 2.044(6), 2.047(6), 1.966(6), and 1.974(6) A] and 0.31 A above the Fe —Fe vector the internal dihedral angle of the Fe4 butterfly is 114.0°. These parameters are compared in Table II with those of related clusters. Compound 15 was first isolated as a product from the reaction of Fe2(CO)6B2H6 with Fe2(CO)9 (60), and evidence for increased iron-boron interaction is observed in a dramatic change in nB-NMR spectral shift (8) from S — 24.2 to +116.0. 

To have unreserved confidence in such 0 data it is advisable to measure several geometric and dimensional characteristics of the sessile drop and to test for their internal consistency. Thus the 0 values assumed by the left hand and right hand sides of the drop profile should be measured and compared for consistency. Additionally, it is prudent to measure the height of the drop apex, H, and the radius R of the substrate contact area. If the drop has the profile of a spherical cap then a value can be calculated for the contact angle, 0Caic. by substitution in... 

E. Assume that the water in the cell walls is in equilibrium with the internal cellular water. What are cos a and the contact angle at the ail-water interface for cylindrical cell wall pores 20 nm in diameter Assume that... 

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