Card-house structure

In terms of structure, the FF association leads to the build-up of successively larger stacks of partides called oriented aggregates, or tactoids [321-323], The EE and EF assodations produce floes and can lead to voluminous, three-dimensional assemblages, often described as card-house structures. Figure 1.7 provides an illustration of these modes of interaction. Descriptions of the details surrounding the transitions from one structure to another are given by van Olphen [1],... 

Beyond some critical concentration in solid, aggregation of tactoids occurs undoubtedly. The critical concentration depends, obviously, on many factors, but at the present time we are not aware of any experimental studies on this matter, nor on the factors controlling the critical concentration. This further aggregation process yields larger objects with complicated texture and porous structure. Upon drying thick pastes, some kind of cards house structure has been reported (3). However, irregular stacks composed of tactoids with face to face aggregation have been commonly observed (9). 

In a poor solvent (cyclohexane), the clay lamella packages form aggregates due to adhesion of the secondary particles (a card house structure is formed). Furthermore, the value of dt is very close to the thickness of the silicate layer plus the cross sections of two alkyl chains. It follows that in a poor solvent, the alkyl chains are laying flat on the surface and no swelling takes place. In that case, the interstitial sites are not available for reactants and reaction proceeds on the external surface sites. 

Sodium silicates are also used to provide the fluid with a yield stress large enough to hold the particles at high water content. The mechanism is completely different from that of bentonite platelets that, having opposite charges on the faces and on the edges, gel the fluid by forming card house structures. Here, sodium silicate reacts with lime or calcium chloride to form a calcium silicate gel. It is this gel that provides the yield stress required to hold the particles. 

In the past, many groups have tried to encapsulate clay platelets inside latex particles. This encapsulation poses some extra challenges because of the tendency of the clay platelets to form stacks and card-house structures. Most of the attempts resulted in the so-called armored latex particles, i.e. clay platelets in the surface of the latex. Recently, natural and synthetic clays were successfully encapsulated. The anisotropy of the clay resulted in non-spherical latex particles (Figs. 5 and 6), either peanut-shaped [63] or flat [64]. Clay platelets also turned out to be good stabilizing agents for inverse Pickering emulsion polymerizations [65]. 

Drying is also a critical parameter in the preparation of PILCs. Slow drying (or air-drying) allows the clay layers to settle down in an ordered, parallel way (face-to-face stacking). This favors the microporosity and crystallinity of the final PILC. Fast techniques, like freeze-drying, fix the random orientation of pillared clay plates or aggregates to form a card-house structure. This structure also exists for the laponite clay. PILCs dried in this way exhibit a larger meso-porosity, but are less crystalline. 

When the lateral dimensions of the clay layers are small (< 0.05 pm) and the layer morphology is lath-like, the flocculation of smectite clays by polyoxycations can lead to delaminated aggregates [45, 61]. Under these conditions, the previously discussed card-house structure has been proposed for delaminated clays. It differs dramatically from the well-ordered F-to-F lamellar structures formed by pillared clays when the layer size is large (< 2 pm) and pancake-like in morphology. Schematic drawings of the pillared and delaminated clay... 

The sedimentation volume of the heterocoagulated sediment of a 8.0% w/v MN slurry and 0.1% w/v latex was 22 cm at pH 5.5. This was decreased to 13 cm when the pH was increased to 10 and in the presence of 350 ppm calcium chloride. This clearly shows that the more open card-house structure of EF association results in a much larger sedimentation volume of the floes than the card-pack structure of FF asociation brought about by high electrol3de concentration (111. This is well correlated with a decrease in floe size of the sediment with increase in pH at any particular concentration of calcium chloride as shown in Fig 3. 

Continuous structure. Aggregates Floes. Card-house... 

Choy etal. [197] attempted to fabricate a house-of-cards (HOC) structured Ti02 nanohybrid to overcome the disadvantage of both nanoparticle-derived and mesoporous Ti02 films. This structure offers salient features for dye-sensitized nanocrystalline Ti02 solar cell. 

The large deformability as shown in Figure 21.2, one of the main features of rubber, can be discussed in the category of continuum mechanics, which itself is complete theoretical framework. However, in the textbooks on rubber, we have to explain this feature with molecular theory. This would be the statistical mechanics of network structure where we encounter another serious pitfall and this is what we are concerned with in this chapter the assumption of affine deformation. The assumption is the core idea that appeared both in Gaussian network that treats infinitesimal deformation and in Mooney-Rivlin equation that treats large deformation. The microscopic deformation of a single polymer chain must be proportional to the macroscopic rubber deformation. However, the assumption is merely hypothesis and there is no experimental support. In summary, the theory of rubbery materials is built like a two-storied house of cards, without any experimental evidence on a single polymer chain entropic elasticity and affine deformation. 

By achieving random dispersion of the Kaolin in the sodium silicate solution prior to formation of the silica-alumina gel, it was possible to disperse the clay crystals. They condensed somewhat perpendicular to each other and were bound together by silica-alumina gel. I therefore speculated that spray drying, during which the gel system contracts, might create a dual structure. An analogy would be a house built of cards (Kaolin), cemented together with silica-alumina gel. 

A good state of dispersion of the organoclay has been found in the CR matrix. The exfoliated structure can be directly observed from the of the OMMT-filled CR composite (left-hand image in Fig. 30). It is noticed from this micrograph that all silicate layers are exfoliated and distributed very nicely throughout the whole rubber matrix. It is also observed that some of the exfoliated clay platelets form a house of cards structure (right-hand image in Fig. 30). 

Phenomenon (iii) is responsible for so-called house of cards structure with very large irregular mesopores. 

In dilute suspensions clays tend to form gels. The classical model is the house of cards structure of kaolinite in which the face-to-edge association leads to an open 3-D structure (van Olphen, 1965). In the case of smectite-water systems it now seems more likely that the microstructure is mainly controlled by the face-to-face interactions (Van Damme et al., 1985). 

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