Microstructural construction

Fig. 4.12. (a) 2D quasi-equilibrium proton-driven spin-diffusion spectrum at 295 K of amorphous, atactic polystyrene C-enriched at the aromatic carbon Ci. The mixing time was set to 10 s. Within this time frame, a completely disordered environment is sampled (see Fig. 4.8(c)). (b) Rate-constants for r.f.-driven spin-diffusion obtained from mixing times smaller than 4 ms from the same compound, (c) Structure of a microstructure, constructed by Rapold et al. [71] to describe amorphous atactic polystyrene. The rate constants in (b) can be well explained by a set of such microstructures. From the microstructures, in turn, the weighted distributions p( 8)/sin /3 can be extracted. The result is given in (d). (Figure adapted from Refs. [30, 70]). 

Compared with laboratory fixed-bed reactors or conventional extruded monoliths, such a microstructured monolith is smaller in characteristic dimensions, lower in pressure loss by optimized fluid guiding and constructed from the catalytic material solely [3]. The latter aspect also leads to enhanced heat distribution within the micro channels, giving more uniform temperature profiles. 

In order to understand monolithic supports and the effects of polymerization parameters, a brief description of the general construction of a monolith in terms of microstructure, backbone and relevant abbreviations is given in Fig. 8.1 [63, 64]. As can be deduced therefrom, monoliths consist of interconnected microstrac-ture-forming microglobules, which are characterized by a certain diameter dp) and microporosity (gp). In addition, the monolith is characterized by an inter-microglobule void volume sfj, which is mainly responsible for the backpressure at a certain flow rate. The sum of gp and g directly translates into the total porosity gf. 

A phase diagram constructed from experiments on a series of poly(styrene)-poly(isoprene) (PS-PI) diblocks is presented in Fig. 2.2 (Khand-pur et al. 1995) and this will be used as a guide for the various microstructures. In order to determine a phase diagram experimentally, a variety of methods are... 

In Chap. 8 we have constructed the renormalization group, starting from bare perturbation theory for the discrete chain model. This expansion involves nonuniversal microstructure corrections which we will now absorb into renormalization factors, introduced via a redefinition of the interaction constant and the chain length, According to Eq. (11.1) we write... 

Detailed description of a porous microstructure is an essential prerequisite for unveiling the influence of pore morphology on the underlying two-phase behavior. This can be achieved either by 3-D volume imaging or by constructing a digital microstructure based on stochastic reconstruction models. Non-invasive techniques, such as X-ray micro-tomography, are the popular methods for 3-D... 

Similarly, the capillary pressure - saturation relations for the reconstructed GDL structures can be constructed from the two-phase LB drainage simulations. The capillary pressure response for reconstructed non-woven GDL microstructures was also evaluated using a full morphology (FM) approach, detailed in our recent work.33 Briefly, the FM model relies on morphological decomposition of the 3-D digital image of the reconstructed GDL to... 

Using the 2-D saturation maps from the two-phase LB simulation, shown in Fig. 14, the effective ECA can be evaluated and correlated according to Eq. (26). Based on several liquid water saturation levels, the catalytic surface coverage factor for the CL microstructure is estimated and the following correlation can be constructed, which can be used as valuable input to macroscopic two-phase fuel cell models.27,62... 

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