Sessile drop method, contact angle measurement

The most commonly used techniques for contact angle measurements are the sessile drop method and the Wil-helmy plate method. Results obtained from these two methods are in good agreement. 

One of the most common ways to characterize the hydrophobicity (or hydrophilicity) of a material is through measurement of the contact angle, which is the angle between the liquid-gas interface and the solid surface measured at the triple point at which all three phases interconnect. The two most popular techniques to measure contact angles for diffusion layers are the sessile drop method and the capillary rise method (or Wihelmy method) [9,192]. 

For the DMFC, Zhang et al. [127] used the sessile drop method to study the wettabilities of liquid methanol solutions on the surface of the anode DLs and MPLs. They were able to observe that the contact angles of the materials were the smallest with low PTFE content. In addition, the effect of Nafion ionomer content on the MPL (to increase hydrophilicity see Section 4.3.2) was also shown through the contact angle measurements (i.e., smaller contact angles compared to MPLs with PTFE). 

In addition to the sessile drop method which measures the contact angle directly, Neumann and Renzow (1969) have developed the Wilhelmy slide technique to measure it to 0.1° precision. As shown in Fig. 2.20, the meniscus at a partially immersed plate rises to a finite length, h, if the contact angle, 0, is finite. 6 is calculated from... 

The antistatic properties of the step 2 product were evaluated by preparing tapes of blends with polystyrene by extruding in a twin-screw extruder using a flat die at 200°C. The contact angle of the tapes was measured using the sessile drop method and water as the measuring liquid. Testing data not supplied by author. 

Some of the commonly used techniques for measuring contact angle [215, 216, 217] are the sessile drop method, captive bubble method and Wilhelmy plate method. These techniques have been extensively used and well documented for characterisation of modified PE surfaces [218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230] for various applications. Whitesides et al. [231 ] studied the wetting of flame-treated polyethylene film having ionisable organic acids and bases at the polymer-water interface. The effect of the size of substituted alkyl groups in amide and ester moieties on the surface hydrophilicity was also studied [232]. The biocompatibility of the polyethylene film surface modified with various water-soluble polymers was evaluated using the same technique [233]. The surface properties of hy-perbranched polymers have been very recently reported [234]. 

The sessile drop method, described in Section 3.2.3, can also be used for the determination of contact angle. A sessile drop is created as for surface tension measurement, but instead of measuring drop shape, the contact angle (0) is measured through the liquid phase (Figure 3.16). This can be done using a goniometer. 

Table II presents the results of some wettability measurements on adsorbed monolayers prepared from molten Compound D on pure, polished, clean, chromium surfaces after solvent treatment had been used to remove all surplus solidified acid. A series of successive solvent treatments was applied to each coated specimen (see first four columns of Table II) using liquids which have been shown to be good solvents for Compound in the bulk (9). These liquids were either absolute ethyl alcohol or benzene at or above 20°C., or n-hexane at or above 60°C. In the remaining columns are listed the average values of the slowly advancing contact angles measured by the drop-buildup method on from three to five different drops. Measurements were made on sessile drops of water, thiodiglycol, and methylene iodide. These three diagnostic liquids were chosen because of their high surface tensions (72.8, 54.0,...

RH and at 25°C. using the sessile drop method. Surface tensions were measured at 25°C. using the duNouy ring method. Unless otherwise noted in the text, the contact angles were reproducible to 2° and the critical surface tensions to 0.5 dynes/cm. 

Allain, C. Ausserre, D. Rondelez, F. A new method for contact angle measurements of sessile drops. J. Colloid Interface Sci. 1985,107 (1), 5-13. 

Sessile drop method is the most frequently used method (c.f. Section 6.2.4.1.). In the measurement at high temperatures the drop of the melt is lying on the solid base placed in a horizontal furnace tube. The contact angle is measured on photographs of the drop. 

Silny (1987) has carried out very detailed contact angle measurements of cryolite melts on graphite and the measurement of surface tension using the sessile drop method. He used the Leitz microscope for photographing the sessile drop and used a sophisticated computerized approach to calculate the contact angle and the surface tension from the shape of the drop. However, the results showed a dispersion of approximately 20%. 

Contact Angle Measurements, were obtained with a Drop Shape Analysis System DSA100 (Kriiss GmbH, Hamburg, Germany) using water and diiodomethane as test liquids. The contact angles were measured by the sessile drop method within two seconds. The surface tension y as well as the dispersive and polar components (yD and yp) were calculated based on the Owens-Wendt method [7],... 

Sessile Drop Method A method for determining surface or interfacial tension based on measuring the shape of a droplet at rest on the surface of a solid substrate (in liquid—liquid systems, the droplet may alternatively rest upside down, that is underneath a solid substrate). This technique may also be used to determine the contact angle and contact diameter of the droplet against the solid. 

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