Surface properties contact angle

The transport of liquid water through the GDL is not well understood at this point in time. Liquid water is transported by a pressure gradient between the catalyst layer and the gas chaimel, where it is removed from the cell. However, the buildup of the transportation paths depends on the local pore sizes and the surface properties (contact angle) of the GDL. Understanding has been gained in ex situ experiments by determining the liquid saturation as function of the capillary pressure [8,9]. 

Surface properties Contact angle measurements indicated enrichment of the siloxane containing copolymer at the surface (Table 3). Contact angles of water and methylene iodide on copolymer PTM02K-IP-B2 are values expected for a polyetherurethane, while contact angles of the same... 

Furthermore, titanium oxide thin films have been found to exhibit a unique and useful function (i.e., a superhydrophilic property). Usually, the contact angle of a water droplet on a surface is 50 -70° therefore, metal oxide surfaces become cloudy when water is dropped on them or if there is moisture in the atmosphere. However, under UV light irradiation of the titanium oxide surfaces, this contact angle of water droplets becomes smaller, even reaching zero (superhydrophil-icity), its extent depending on the UV irradiation time and irradiation intensity. Thus, under UV light irradiation, titanium oxide thin-film surfaces never become... 

Phenomena such as the ones described above are usually (and conveniently) described in terms of macroscopic properties such as surface tension, contact angle, and so on. This is what was done in Chapters 6 and 7. In the present chapter, we probe the molecular origin of van der Waals forces, go into some of the details of how they scale up in the case of macroscopic bodies, and illustrate their importance in molecular as well as macroscopic phenomena. 

Mercury porosimetry is performed nearly exclusively on automatic commercial instruments that differ mainly in the highest operative pressure, which determines the size of smallest attainable pores. The highest pressure is limited by the uncertainty about the validity of the Washburn equation, which forms the basis of data evaluation. In pores with sizes similar to the mercury atom the assumption that physical properties of liquid mercury (surface tension, contact angle) are equal to bulk properties is, probably, not fully substantiated. For this reason the up-to-date instruments work with pressures up to 2000 - 4000 atm, only. 

Spreading of drops on powder surface spreading Contact angle goniometer Contact angle Drop height or volume Spreading velocity References Kossen and Heertjes, Chem. Eng. Sd, 20, 593 (1965). Pan et al., Dynamic Properties of Interfaces and Association Structure, American Oil Chemists Society Press, 1995. 

In summary, this chapter presents the basic thermodynamic principles and the work of adhesion that quantitatively characterize surfaces of materials. Laboratory techniques for surface characterization have been described, which allow an understanding of the chemical and physical properties of material surfaces. Empirical equations have been described for calculating surface tension (energy) of solid polymeric surfaces using contact angle and other parameters. 

In summary, we have developed two techniques to impart superhydrophobic property to the surfaces of devices. In the first approach, oxygen plasma treatment was used to roughen the Teflon coating whose surface water contact angle could be tuned form 120° to 168° by varying the oxygen plasma treatment time. However, the application of the oxygen plasma process is limited to fluoropolymers. In the second approach, nanoimprint process was used to create nanostructures on the... 

Table 1 provides an overview of a small sampling of liquids of the relevant properties for a few common optofluidic liquids. Note that this represents a non-comprehensive list, other parameters of particular interest include fluid-fluid surface tension, fluid-solid surface energy, contact angle, fluid-solid electroosmotic mobility, compatibility with soft elastomers (or other materials of interest), and numerous others. 

Keywords fibre, surface, organosilane, titanate, zirconate, chrome complex, surface energy, contact angle, interface, mechanical properties, adhesion, maleic anhydride. 

In a recent case study (see Svendsen et al, 2007 and also Problem 6.1), in collaboration with a paint company, the adhesion of six different epoxies-silicon systems has been studied. These paints are used in marine coating systems. Some epoxies showed adhesion problems in practice while others did not. The purpose of the study was to understand the origin of these problems and whether adhesion could be described/ correlated to surface characteristics, e.g. surface tensions. An extensive experimental study has been carried out including both surface analysis (contact angle measurements on the six epoxies, surface tension of silicon at various temperatures, atomic force microscopy (AFM) studies of the epoxies), as well as measurements of bulk properties (pull-off adhesion tests and modulus of elasticity). Theoretical analysis included both estimation of Zisman s critical surface tensions and surface characterization using the van Oss-Good theory. 

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