Colloidal inks

Other efforts have also been made to modify the CL microstructure by controlling the agglomerate size in the catalyst ink. Uchida et al. [145] proposed a colloidal ink fabrication procedure using low-dielectric-constant solvents to generate a good network and a uniformity of perfluorinated... 

Although many areas of nanotechnology do not directly deal with colloidal dispersions (such as nanoelectronic devices [952]) other areas do, such as the use of colloidal ink dispersions in robocasting to build near-nanometre scale three-dimensional structures. The possible use of nanoemulsions for intravenous delivery and in medical diagnostics has already been mentioned in Sections 14.4 and 14.5. Some other application areas include ... 

Smay JE, Cesarano J, Lewis JA. (2002) Colloidal Inks for Directed Assembly of 3-D Periodic Structures. Langmuir 18 5429-5437. 

Hence a volmnetric three-dimensional region has to be provided for the reaction. The most common methods of applying the electrode layer on the electrolyte are plasma spraying, vapor deposition, solution coating and colloidal ink methods. 

The subject of the mechanisms and degree of polymer adsorption at interfaces is also discussed in more detail in Chapter 14. For now, suffice it to say that macromolecular additives to emulsion systems constitute a major pathway for attaining workable, long-lived practical emulsions. In fact, their use is essential to many important product types, not the least of which are food colloids, inks, pharmaceuticals, and the photographic industry. 

Colloidal inks containing 5-7 nm particles of gold and silver in an organic solvent, i.e., a-terpmeol, cf.. Figure 4.5, can be used to build electrically and mechanically functional metallic structures. After sintering at 300°C the resistivity of printed silver structures was found to about twice that of bulk silver (33). 

Suminagashi A technique of spreading colloidal ink on the surface of water and transferring the resulting patterns to a sheet of paper by laying it horizontally on the water. 

In this section, we discuss theoretical and computational studies that provide insights into structural correlations and dynamical behavior of species in CLs. Structural complexity is an inherent trait of CLs. Advanced fabrication aims to improve Pt utilization by enhancing the interfacial area of Pt with water in pores and with Nafion ionomer [12, 94—95], A practical way to achieve this is by mixing ionomer with dispersed Pt/C catalysts in the ink suspension prior to deposition to form a CL. The solubility of the ionomer depends upon the choice of a dispersion medium. This influences the microstructure and pore size distribution of the CL [95]. Self-organization of ionomer and carbon/Pt in the colloidal ink leads to the formation of phase-segregated agglomerated morphologies. 

Hviii tmliobit- ink Hvdiooliilic ink colloid ink Catalvsl ion iuliitioii itik Pi foil... 

Another example of tuning particle interactions to achieve desired material properties is in the work of Smay er al (2002a, 2002b) who fabricate mesoscopic structures via directed assembly of colloidal inks. The colloidal inks were concentrated gels with tailored viscoelastic properties so that the structmes were self supporting. 

An alternative method to conventional thin-film techniques is the colloidal method. Typically, the catalyst layers are applied as a solution. It is well known that Nafion forms a solution in solvents with dielectric constants greater than 10. When a solvent which has a dielectric constant of 5.01 is employed as the solvent, a colloid forms in lieu of a solution. Shin et al. (2002) suggested that in the conventional solution method the catalyst particles could be excessively covered with ionomer, which leads to under-utilization of platinum. In addition, it was proposed that in the colloidal method the ionomer colloid absorbs the catalyst particles and larger Pt/C agglomerates are formed. The colloidal method is known to cast a continuous network of ionomer that enhances proton transport. The thickness of a catalyst layer that Shin et al. (2002) formed by the colloidal ink was twice that of the 0.020 nun thick layer formed with solution ink, In addition, the size of Pt/C agglomerates increased from 550 to 736 nm with the introduction of the colloidal method. The colloidal method dramatically outperformed the solution method at high current densities in single cell experiments. 

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