Transition Kinetics of Self-Assembled Supramolecular Dodecagonal Quasicrystal and Frank–Kasper σ Phases in ABn Dendron-Like Giant Molecules
Xueyan FengGengxin LiuDong GuoKening LangWei ZhangJiahao HuangZebin SuYiwen LiMingjun HuangTao LiStephen Z. D. Cheng
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Abstract:
A series of noncrystalline ABn dendron-like giant molecules DPOSS-MPOSSn (n = 2-6, DPOSS: hydrophilic polyhedral oligomeric silsesquioxane (POSS) cage; MPOSS: hydrophobic POSS cage) were synthesized. These samples present a thermodynamically stable phase formation sequence from the hexagonal cylinder phase (plane group of P6mm), to the Frank-Kasper (F-K) A15 phase (space group of Pm3̅n), and further to the F-K σ phase (space group of P42/mnm), with increasing the number of MPOSS in a single molecule (n, from 2 to 6). Moreover, for DPOSS-MPOSS5 and DPOSS-MPOSS6, an intriguing dodecagonal quasicrystal (DQC) structure has been identified and revealed as a kinetic favorable metastable phase at lower temperatures, while the thermodynamically stable phase is the σ phase. The detailed investigation of the transition kinetics between the DQC and σ phase in these samples makes it possible to identify how the self-assembly directs the phase transition in terms of molecular and supramolecular aspects.Keywords:
Silsesquioxane
Metastability
The electronic properties of polyhedral oligomeric silsesquioxanes (POSS) have recently been subjected to study. Although theoretical calculations have predicted that POSS can work as an acceptor for π-conjugated organic units, an effective reaction to incorporate aryl groups into a POSS backbone remains to be established. In this work, Rh-catalyzed direct arylation has been developed. Heptaisobutyl-POSS with a Si-H group was reacted with various aryl halides to form aryl-substitued POSSs.
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The dendritic (or dendrimer) effect is observed when a functional group behaves differently when it is alone or linked to a dendrimer; its properties can even vary depending on the generation of the dendrimers. The dendritic effect can be observed with any type of dendrimer, and for any type of property, even if it has been most generally tracked in catalysis and biology, and to a lesser extent in the field of materials. This review is mainly oriented towards the various types of dendritic effects observed with polyphosphorhydrazone dendrimers, even if many examples obtained with other types of dendrimers are given.
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Quasicrystals are metallic alloys that exhibit atomic scale order, but not periodic order. Atomic scale properties of these materials are different from single crystalline material, for example, extraordinary mechanical properties, electrical and thermal transport properties, and electronic structure. This book presents topical research in the study of quasicrystals, including vacancies in quasicrystals; the formation of quasicrystals in bulk metallic glasses and their effects on mechanical behavior; the electrical transport observed in Al-Pd-Mn quasicrystals; logarithmic periodicity in quasicrystals; and positron annihilation studies of quasicrystals.
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Abstract A set of new titanium‐silsesquioxane epoxidation catalysts was discovered by exploring the hydrolytic condensation of a series of trichlorosilanes in highly polar solvents by means of high‐speed experimentation techniques. The most promising silsesquioxane leads were prepared on a conventional laboratory scale and fully characterised. The lead generated by the hydrolytic condensation of t BuSiCl 3 in DMSO consisted of a set of incompletely condensed silsesquioxane structures, whereas that obtained from the hydrolytic condensation of t BuSiCl 3 in water consisted of a single silsesquioxane structure, t Bu 2 Si 2 O(OH) 4 . This is the first reported example of the use of this silsesquioxane as a precursor for active Ti catalysts. The Ti complexes prepared with t Bu 2 Si 2 O(OH) 4 were supported on silica to produce active heterogeneous epoxidation catalysts.
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The structure and propertyt of polyhedral oligomeric silsesquioxane are reviewed.A few methods to synthesize polyhedral oligomeric silsesquioxane and the applications in the polymer of polyhedral oligomeric silsesquioxane are discussed.The developments of polyhedral oligomeric silsesquioxane aftertime are expatiated.
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Divergent synthesis methods have been used to prepare 2nd generation dendrimers based on polyhedral silsesquioxane cores with up to 72 terminal groups at their surface. Repetitive hydrosilation/allylation of vinyl-functionalised polyhedral silsesquioxanes produce chlorosilyl- and allyl-derivatised dendrimers respectively. Hydroboration/oxidation of the allyl-functionalised dendrimers produces alcohol (hydroxy) terminated dendrimers. Energy minimisation and molecular dynamics techniques have been used to model the architectures of the dendrimers. The results show the dendrimers are relatively spherical, globular molecules, with a large proportion of the terminal hydroxy groups located in a shell at the exterior of the dendrimer. As the number of terminal groups on the dendrimers increases the number of the dendrimer branches that back fold towards the core of the dendrimer also increases.
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Hydrosilylation
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Hybrid material
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Polyhedral oligomeric silsesquioxane(POSS) based hybrid materials have excellent properties and comprehensive applications for the molecule hybrid system based on the chemical bonding.The structure and property as well as synthesis of POSS monomers and their derivatives were described in this review.The potential applications of POSS-polymers were also introduced.At the same time,the existing problem of the study on hybrid POSS-polymers system in our country was discussed.
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Abstract A stable one-dimensional quasicrystal has been found in slowly cooled Al75Pd15Fe10. The one-dimensional quasicrystal can be derived from a two-dimensional decagonal quasicrystal by introducing a finite linear phason strain. The melting temperature of the one-dimensional quasicrystal was measured to be lower than that of the two-dimensional decagonal quasicrystal.
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