Cubic topology

Several synthetic strategies to control the sizes of mesoporous nanoparticles have been reported. Lu[272] reported a rapid, aerosol-based process for synthesizing solid, well ordered spherical particles with stable pore mesostructures of hexagonal and cubic topology, as well as layered (vesicular) structures. This method relies on evaporation-induced interfacial self-assembly confined to spherical aerosol droplets. This simple, generalizable process can be modified for the formation of ordered mesostructured thin films. 

A large number of MOFs have been synthesized and reported by researchers to date. Isoreticular metal-organic frameworks (IRMOFs) denoted as IRMOF-zr ( = 1 through 7, 8, 10, 12, 14, and 16) are one of the most widely studied MOFs in the literature. These compounds possess cubic framework structures in which each member shares the same cubic topology [3, 21]. Figure 4 shows the structure of IRMOF-1 (MOF-5) as simplest member of IRMOF series. 

As mentioned above, uranium trioxide exists in six weU-defined modifications with colors ranging from yeUow to brick-red. Of these phases, the y-phase has been found to be the most stable, however, other phases, especially a and 3, are also frequently used and studied. The stmcture of the a-modification is based on sheets of hexagons, whereas the 3-, y-, and 8-modifications contain an infinite framework. AH of these topologies have been fliUy described (105,106). They are a-brown, hexagonal 3-orange, monoclinic y-yeUow, rhombic 5-red, cubic S-brick red, triclinic and Tj-rhombic. 

Mesostructured materials with adjustable porous networks have shown a considerable potential in heterogeneous catalysis, separation processes and novel applications in optics and electronics [1], The pore diameter (typically from 2 to 30 nm), the wall thickness and the network topology (2D hexagonal or 3D cubic symmetry) are the major parameters that will dictate the range of possible applications. Therefore, detailed information about the formation mechanism of these mesostructured phases is required to achieve a fine-tuning of the structural characteristics of the final porous samples. 

VTO, and that of the G structure (Ia3d symmetry, Fig. 4) index to /6 /8 /l4 VT6 V O V"22 /7A. Finally the measurements of the surface area inside the cubic cell can yield partial information about a topology of the structure. One can expect a small unit cell and the small surface area per side of... 

It is believed that the Gaussian bending modulus k controls the membrane topology. In particular, a negative value of this constant is needed for stable bilayers. A positive value will induce nonlamellar topologies, such as bicontinuous cubic phases. Therefore, it is believed that k is negative for membranes. 

MCM-50 consists of stacks of silica and surfactant layers. Obviously, no pores are formed upon removal of the surfactant layers. The silica layers contact each other resulting in a nonporous silica. It is noteworthy to mention that materials of M41S type were probably already synthesized by Sylvania Electric Products in 1971 [32], However, at that time the high ordering of the materials was not realized [33], M41S-type materials are synthesized under basic reaction conditions. Scientists from the University of Santa Barbara developed an alternative synthesis procedure under acidic conditions. They also used alkyltrimethyl ammonium as the surfactant. The porous silica materials obtained (e.g., hexagonal SBA-3 Santa BArbara [SBA]) had thicker pore walls but smaller pore diameters. Furthermore, they developed materials with novel pore topologies, e g., the cubic SBA-1 with spherical pores. 

Topology is cubic, with one independent T site. The structure of analcime has been determined and refined for a long time in the cubic space group [50], even if there is evidence of its non-cubic symmetry. 

---