Superstructure formation

Thus, we see that the digestive ripening process leads to highly monodispersed nanoparticles that can come together to form ordered superstructures similar to atoms or molecules that form crystals from a supersaturated solution. Then if the superstructure formation can indeed be related to atomic/molecular crystallization, it should also be possible to make these supercrystals more soluble in the solvent with a change of temperature. Indeed, the optical spectra of the three colloids prepared by the different thiols discussed above exhibit only the gold plasmon band at 80 °C suggesting the solubilization of these superlattices at the elevated temperatures [49]. 

We have already mentioned that depending on composition, semicrystalline triblock copolymers can show some conflict between microphase separation and superstructure formation. In fact, one of the controversial aspects is the question whether block copolymers can or cannot exhibit spherulites. This is a relevant question because spherulitic structures greatly affect the ultimate mechanical properties, and the boundaries between adjacent spherulites are often weak points in mechanical performance. Kim et al. [125] studied the competition between crystallization within microphase-separated regions and reorganization into supermolecu-lar spherulites in semicrystalline PS-b-PB-b-PCL triblock copolymers. These authors found that the formation of spherulites is strongly affected by the thickness of the specimen in such a way that thin films crystallize into... 

Scheme 3.8 Proposed (Au55)M superstructure formation in the presence of dendrimer excess.

In CoOP above 300 K the compound exists in the Cccm space group, but with characteristic diffuse X-ray lines indicative of the Peierls modulation and no evidence of superstructure formation. Below 300 K a superstructure develops as shown by the appearance of satellite reflections on the X-ray diffraction photographs. At 280 K a phase transition to the Pccn space group occurs and associated with this are changes in the satellite pattern.78 74 Superstructure development which is commensurate with the Peierls modulation is completed about 250 K. 

The electrical conductivity of CoOP as a function of temperature is shown in Figure 6. Above room temperature the compound exhibits metallic behaviour but coincidental with the development of the superstructure the conductivity falls rapidly with decreasing temperature. Below 250 K CoOp behaves as a semiconductor with an activation energy of meV.74 The conduction has been shown to be frequency dependent below 250 K.75 Thermopower studies have also clearly demonstrated the changeover from metallic behaviour above 300 K. to semiconductor behaviour below 250 K.72 The behaviour of ZnOP is very similar to that of CoOp, with the phase transition from the Cccm to Pccn space group occurring at 278 K. Superstructure formation is complete by about 260 K.77... 

Q. Sun, M.-C. Park, and Y. Deng, Dendritic superstructure formation of polyanihne prepared using a water-soluble polyelectrolyte copolymer as the support matrix. Mater. Lett., 61, 3052-3055 (2007). 

Gom] Superstructure formation by neutron dififtaction Along section Ni3Fe-Ni2Cr... 

Binary clathrates AgSn44 (A = Rb, Cs) provide an interesting example of a superstructure formation due to the ordering of vacancies within the clathrate framework [49, 70]. As it was pointed out earlier tin clathrates often exhibit vacancies in the framework for the electron precise composition, e.g. (A+),(4/7-Sn°)3g(3h-Sn-) gD2. Two vacancies in the four-bonded framework... 

Figure 20 A triblock copolymer (a) with two outer hydrophilic blocks that can self-assemble into mixed micelles (b), partly demixed or multicompartment micelles (c), or completely demixed, biphasic Janus micelles (d). The amphiphilicity on triggering the hydrophilic to hydrophobic transition may result in superstructure formation. (Reproduced from Ref. 49. American Chemical Society, 2010.)...

The PrMneSng, NdMneSn and SmMneSne are isotypic with HoFegSne. A new superstructure formation has been found in an X-ray diffraction study of a DyFeeSn single crystal by Oleksyn et al. (1995). The crystal structure is characterized by SG Cmmm with a=37.343, =21.560 and c=8.912 A. This structure may be described as a three-dimensionally commensurate modulated structure as well. 

Oleksyn, O.Ya., L.G. Akselrud and H. Boehm, 1995, New superstructure formation at DyFe Sn composition, in 6th Int. Conf. on Crystal Chemistry of Intermetal lie Compounds, Ukraine, Lviv, 1995 (Lviv State University, Lviv) p. 87. 

In addition to the above reported superstructure formation under control of block copolymers, the DHBCs can also be used to fine-tune the nanostructure details of other inorganic nanocrystals. Very thin one-dimensional and two-dimensional CdW04 nanocrystals with controlled aspect ratios were conveniently fabricated at ambient temperature or by hydrothermal ripening under control of DHBCs [304]. Simple temperature changes could be applied to tune the particle morphologies between plates and rods. 

Equal positions for all of the atoms Ordered substitution (superstructure formation) SmjGej —> CejSCjSi CeNij— CejCOgSi, etc. 

Molecular opto-electronic assemblies, which consist of a functionalized gold electrode with a photo-isomerizable redox-activated monolayer, enables amperometric transduction of the photonic information recorded by the interface. On-off operation of superstructure formation of hermaphroditic cyclodextrin derivatives is brought about by disturbing the monomer/dimer equilibrium of -azobenzene structures by photoisomerization. When the structures have the Z-form, the dimer dissociates. The thermal Z— isomerization can be enhanced by heating in favor of the dimer formation (Figure 89.8). ... 

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