Hydrophilic pore network

In low RH conditions, the cathode MPL can force flow through the membrane into the anode by capillary pressure forces, reducing dryout and increasing performance. The backflow of water would occur primarily through the hydrophilic pore network in the catalyst layer, since complete pore saturation in the catalyst layer would result in nearly total performance loss, and high saturation in the hydrophobic pores of the CL would likely... 

PTFE is used as an organic binder to link the catalyst particles and to produce a multifunctional electrode. For G D Es, hydrophobic and hydrophilic pore systems are required. For porous catalysts, for example, the Raney nickel catalyst, hydrophilic materials allow the penetration of the electrolyte into the electrode and the transport of the ions between the reaction zones the hydrophobic pore system - outside the catalyst - is required for the transport of gases to the reaction zones. In addition, to provide mechanical stability, the PTFE in the electrodes forms a hydrophobic pore network. 

The restricted access principle is based on the concept of diffusion-based exclusion of matrix components and allows peptides, which are able to access the internal surface of the particle, to interact with a functionalized surface (Figure 9.2). The diffusion barrier can be accomplished in two ways (i) the porous adsorbent particles have a topochemically different surface functionalization between the outer particle surface and the internal surface. The diffusion barrier is then determined by an entropy controlled size exclusion mechanism of the particle depending on the pore size of adsorbent (Pinkerton, 1991) and (ii) the diffusion barrier is accomplished by a dense hydrophilic polymer layer with a given network size over the essentially functionalized surface. In other words, the diffusion barrier is moved as a layer to the interfacial... 

An interesting result with respect to applications obtained with the IPN hydrogels is that these are two- phase systems (two glass transition temperatures), with the hydrophilic domains behaving essentially like the pure hydrophilic component.6,7,9 Thus, the two basic functions of these IPN hydrogels with respect to applications, namely hydrophilicity and mechanical stability, are separately taken over by the two IPN components, the hydrophilic and hydrophobic domains, respectively. Figure 1 shows TSDC and DMA results for the water content dependence of the a relaxation (dynamic glass transition) of PHEA in sequential IPNS prepared from PHEA and poly(ethyl methacrylate) (PEMA) as the hydrophobic component.9 In these IPNs a porous PEMA network was prepared first, and PHEA was then polymerized in the pores. In addition to the... 

Much more attention has been given to zeolites. Zeolites are crystalline microporous materials whose structure is based on a three-dimensional tetrahedral network of AlO and SiO (the Al/Si ratio can be varied from 1 to 0). The excess negative charges carried by AIO4 units are compensated by cations (Na, H+) which ensure the high hydrophilicity of the aluminated zeolites. The crystallinity of zeolites ensures also a very precise pore size. Typically, the size of zeolite pores ranges from 3 to 8 A, and the inner diameter of the interior spaces from 5 to 13 A. 

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