Transportation issues alternative mechanisms

The diamines are isoelectronic with hydroquinone (an eiectron donor) while the diimines are isoelectronic with p-benzoquinone (an electron acceptor). It was recently proposed that this built-in redox couple, which is pH-sensitive, is the source of charge carriers in the form of semiquinone radical cations which are generated upon protonation of the quinonediimine, whose accepting power is expected to increase on protonation. A subsequent perusal of the literature indicates that a similar idea was proposed many years ago. A key issue yet to be resolved is whether electron transfer from diamine to diimine is an inter- or intramolecular process. An alternative mechanism of carrier generation which involves spin unpairing of diimines (creating a pair of radical cations) has recently been proposed." Carrier transport is believed to occur via intermolecular redox reactions between radical cations and diamine and/or diimine units. 

More recent approaches [42], based on studies with isolated leaf cuticles in vitro with a wide range of formulations, considered transport through the cuticle to be a three stage diffusion mechanism, namely absorption into the cuticle, diffusion through the cuticle and finally desoiption from the cuticle into the internal leaf cells. This experimental method used a constant cuticular area, constantly covered by a volume of spray solution, so variable spreading was not an issue. An alternate version of this approach uses droplets applied to cuticular membranes which is more realistic [43]. The modified Pick s equation used in these in vitro studies [41,42] has the following form ... 

Furthermore, in 2001, Ballard entered an alliance with Victrex to produce two new membrane alternatives. One membrane is based on sulfonated poly(arylether) ketone (a variant of PEEK) supplied by Victrex, which may be better suited to PEMFC fabrication applications. In March 2002, U.S. Patent 6,359,019 was issued to Ballard Power for a graft-polymeric membrane in which one or more trifluorovinylaromatic monomers are radiation graft polymerized to a preformed polymeric base. The strucmres of BAM membranes have been studied by way of small-angle neutron scattering (SANS) [97]. The study of the ionomer peak position suggests the existence of relatively small ionic domains compared to Nalion, despite large water content. Phase separation in the polymer matrix is possibly crucial for the membrane s mechanical and transport properties. 

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