Sessile drop method contact angles

Table 12.1 Contact angle (sessile drop) and surface energy of several hydrophilic polymers (calculated by the Owens Wendt method).

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 can also be used for the determination of contact angle (Section 3.4). 

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. 

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. 

Langmuir and Schaeffer [II) used the specular reflection from a drop surface to measure the contact angle in a method that was later refined by Fort and Patterson [12]. A light source is pivoted about the three-phase line to observe the angle at which reflection from the drop surface just disappears. This is the contact angle, and it can usually be measured in this way to within I. The method has been used with sessile drops and with menisci on flat plates and inside tubes [7]. 

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. 

The most commonly used is the sessile drop method, and most of the available literature data are for smooth, macroscopic, solid surfaces. Some special problems arise when one is interested in the wettability of finely divided solids. The small size of the particles makes measurement difficult, but, more importantly, surface roughness and particle shape can have a significant effect on the contact angle. 

Three methods are usually used to calculate contact angle—Wilhelmy plate method, sessile drop method [33], and captive bubble method [34]. Sessile drop method is the most commonly used method for biomedical polymers. In this method, about 3 pi of a liquid droplet is placed on the polymer surface and images of the drop are acquired about 30 s of equilibration of the drop. Interface energy between the solid sample snrface and hqnid can also be calculated using the Young s eqnation ... 

The contact angle was measured on planed lamellas before bonding in order to determine the wettability of the wood surface with water and with the PF adhesive. The sessile drop method was used to measure the contact angle of a drop deposited... 

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