Structure-Wettability Influence

In this chapter, the development of a mesoscopic modeling formalism is presented in order to gain fundamental insight into the structure-wettability influence on the underlying liquid water transport and interfacial dynamics in the PEFC CL and GDL. 

A major difficulty is the proper selection of foam-forming surfactants for the challenging environments involved in petroleum reservoir applications, since many characteristics are thought to be necessary for performance, including good tolerance of the foam to interaction with crude oil in porous media [66, 102]. Here, the physical situation is even more complex than for bulk foams due to influences of pore structure, wettability and oil saturation. For both bulk foams and foams in porous media, oil-sensitive foams are usually less stable as increasing amounts of emulsified oil are contacted (bulk tests) or in the presence... 

Porous inkjet papers are in general created from colloidal dispersions. The eventual random packing of the colloid particles in the coated and dried film creates an open porous structure. It is this open structure that gives photographic-quality inkjet paper its apparently dr/ quality as it comes off the printer. Both the pore structure and pore wettability control the liquid invasion of the coated layer and therefore the final destination of dyes. Dispersion and stability of the colloidal system may require dispersant chemistries specific to the particle and solution composition. In many colloidal systems particle-particle interactions lead to flocculation which in turn leads to an increase in viscosity of the system. The viscosity directly influences the coating process, through the inverse relation between viscosity and maximum coating speed. 

The increasing demand for synthetic biomaterials, especially polymers, is mainly due to their availability in a wide variety of chemical compositions and physical properties, their ease of fabrication into complex shapes and structures, and their easily tailored surface chemistries. Although the physical and mechanical performance of most synthetic biomaterials can meet or even exceed that of natural tissue (see Table 5.15), they are often rejected by a number of adverse effects, including the promotion of thrombosis, inflammation, and infection. As described in Section 5.5, biocompatibility is believed to be strongly influenced, if not dictated, by a layer of host proteins and cells spontaneously adsorbed to the surfaces upon their implantation. Thus, surface properties of biomaterials, such as chemistry, wettability, domain structure, and morphology, play an important role in the success of their applications. 

These surface modifications were performed in "pure" micro-wave (2.45 GHz, "single-mode") or in combined microwave/ radio frequency (2.45 GHz/13.56 MHz, "dual-frequency") plasma. Important systematic changes of the surface composition, wettability, and adhesion of thin metal films were observed for different substrate bias values, and for the different gases. The modified surface-chemical structure is correlated with contact angle hysteresis of water drops this helps to identify which surface characteristics are connected with the wettability heterogeneity and with adhesive bonding properties, and how they are influenced by plasma-surface interactions. 

The second factor is related to the surface chemical structures on active carbons, in particular, with their ability to oxidize easily and form the oxide adsorption centers such as hydroxyl, carbonyl or carboxyl groups. As a result the energetics and wettability of the surface changes that influences essentially on the adsorption isotherm and hysteresis. The difference between adsorption-desorption isotherms for oxidized and reduced adsorbents is clearly demonstrated in Fig. 6.2. 

Chemical heterogeneity of a surface is an important property affecting adhesion, adsorption, wettability, biocompatibility, printability and lubrication behavior of a surface. It seriously affects gas and liquid adsorption capacity of a substrate and also the extent of a catalysis reaction. As an example, the partial oxidation of carbon black surfaces has an important, influence on their adsorptive behavior. In a chemically heterogeneous catalyst, the composition and the chemical (valence) state of the surface atoms or molecules are very important, and such a catalyst may only have the power to catalyze a specific chemical reaction if the heterogeneity of its surface structure can be controlled and reproduced during the synthesis. Thus in many instances, it is necessary to determine the chemical... 

Bau and Torrance [128] use a different relative permeability-saturation relation and arrive at a slightly different relation. Jones et al. [129] use a similar treatment and find a relationship for qc, that gives values lower than those predicted by Eq. 9.130 by a factor of approximately 2. It should be noted that these predictions of qCI are estimations and that the effects of wettability, solid matrix structure (all of these studies consider spherical particles only), and surface tension (all of which influence the phase distributions) are included only through the... 

The wettability of various wood fibres was studied in [173], including bleached and unbleached, and alkyl ketene dimer sized and non-sized fibres. An improvement of the wettability with an increase of the surfactant concentration, except nonionics, was observed for all types of fibres. It has been noted in [174] that the electrokinetic potential of fibres determines considerably the efficiency of their washing and dying. Alkali mercerisation of cotton influences not only the fine structure, morphology and conformation of cellulose molecules, but also the negative electrokinetic potential of the cotton fibres. Based on this, the selection of mercerisation conditions due to changes in the NaOH concentration will allow to... 

The degree of silanization and thereby the water wettability is controlled by the exposure time, the amount of silane used, and importantly the concentration of water. Water has a big influence on the mechanism of the silane monolayer formation and structural properties. In the absence of water submonolayers with only one siloxane bond binding can be formed. Water promotes the hydrolysis of the remaining SiCl groups on the initial immobilized silane layer enabling another silanization reaction yielding enhanced silane density. However excess water leads to uncontrolled silane... 

The reactant transport shall not be obstructed by the ccmdensation of water in the flow channels as well as by flcxxling of the GDL pore structure. Shape and wettability of the flow channel walls and the GDL have a significant influence to the probability of water accumulation and chaimel clogging. 

The chemical composition of the surface influences the interaction (hydrophilic or hydrophobic), and the wettability (soluble, hydrophilic or hydrophobic), as well as the chemical stability. The chemical composition of the powder is a result of its technical processing, or, if non-processed, its biological structure. 

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