Magnetic monolith

In collaboration with the University of Wageningen, magnetic resonance imaging (MRI) was used to visualize the film flow in the monoliths [15], As shown in Fig. 8.8, liquid (water) was fed onto a complete piece of monolith from which four channels then were prolonged for measurement. In Fig. 8.9, the liquid is represented as light areas in the corners of the four channels. Clearly, the channel walls are not uniformly irrigated. In the corners, the gas-liquid interface is shaped like an arc, whereas between the pockets, only a thin liquid film remains ( 70 pm). This retraction of the film into the corners can be attributed to the high surface tension of the liquid used (water). Additionally, the liquid pockets of one channel have different sizes, and this leads to channel scale maldistribution. 

Magnetic resonance imaging permitted direct observation of the liquid hold-up in monolith channels in a noninvasive manner. As shown in Fig. 8.14, the film thickness - and therefore the wetting of the channel wall and the liquid hold-up -increase nonlinearly with the flow rate. This is in agreement with a hydrodynamic model, based on the Navier-Stokes equations for laminar flow and full-slip assumption at the gas-liquid interface. Even at superficial velocities of 4 cm s-1, the liquid occupies not more than 15 % of the free channel cross-sectional area. This relates to about 10 % of the total reactor volume. Van Baten, Ellenberger and Krishna [21] measured the liquid hold-up of katapak-S . Due to the capillary forces, the liquid almost completely fills the volume between the catalyst particles in the tea bags (about 20 % of the total reactor volume) even at liquid flow rates of 0.2 cm s-1 (Fig. 8.15). The formation of films and rivulets in the open channels of the structure cause the further slight increase of the hold-up. 

We have prepared monolith magnetic polymers as well as highly swollen magnetic polymer gels. It is worth distinguishing two kinds of filler-loaded samples ... 

MCM-41 silica monoliths and diluted magnetic semiconductors a promising union for fabricating nanosized quantum wires... 

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