Morphogenesis of polyoxometalate cluster-based materials to microtubular network architectures

Pressed pellets of polyoxometalate (POM)-based materials are shown to undergo morphogenesis to produce microtubular network architectures without the need for a large single crystal precursor. The compression of the POM material into a pellet lowers the solubility sufficiently to allow tube initiation and growth from POMs that would otherwise be too soluble in their native crystalline state, thus yielding hollow, highly controllable, tubes of diameter 10-100 μm.     

Mesocrystals: inorganic superstructures made by highly parallel crystallization and controlled alignment

Controlled self-organization of nanoparticles can lead to new materials. The colloidal crystallization of non-spherical nanocrystals is a reaction channel in many crystallization reactions. With additives, self-organization can be stopped at an intermediary step-a mesocrystal-in which the primary units can still be identified. Mesocrystals were observed for various systems as kinetically metastable species or as intermediates in a crystallization reaction leading to single crystals with typical defects and inclusions. The control forces and mechanism of mesocrystal formation are largely unknown, but several mesocrystal properties are known. Mesocrystals are exiting examples of nonclassical crystallization, which does not proceed through ion-by-ion attachment, but by a modular nanobuilding-block route. This path makes crystallization more independent of ion products or molecular solubility, it occurs without pH or osmotic pressure changes, and opens new strategies for crystal morphogenesis.     

Replicated Banded Spherulite: Microscopic Lamellar-assembly of Poly(L-lactic acid) Crystals in the Poly(oxymethylene) Crystal Framework

The morphologies of poly(L-lactic acid) (PLLA) spherulites,when crystallized within the pre-existed poly(oxymethylene)(POM) crystal frameworks,have been investigated.PLLA/POM blend is a melt-miscible crystalline/crystalline blend system.Owing to the lower melting point but much faster crystallization rate than PLLA,POM crystallized first upon cooling from the melt state and then melted first during the subsequent heating process in this blend system.Lamellar assembly of PLLA crystals within the pre-existed POM spherulitic frameworks was directly observed with the polarized light microscopy by selectively melting the POM frameworks.The investigation indicated that PLLA crystals fully replicated the spherulitic morphology and optical birefringence of the POM crystal frameworks,which was independent of Tc.On the other hand,POM could also duplicate the pre-existed PLLA morphologies.The result obtained provides us a possibility to design the lamellar assembly and crystal structures of polymer crystals in miscible crystalline/crystalline polymer blends.     

Controlled growth for synthesizing a compact mordenite membrane

Controlling the growth of zeolite crystals on a porous alumina support is essential for preparing a compact zeolite membarne. First, mordenite seed crystals applied on a nonporous -alumina disk were grown and morphological change of mordenite crystals were observed in the course of growth. Then, mordenite membranes were synthesized on a porous -alumina tube under the same conditions employed in the study using the alumina disks. We found that seed crystal growth was widely controllable by changing water content in reaction solution, which resulted in better control of the morphology of mordenite crystals for synthesizing a thin compact mordenite membrane. Separation properties for mordenite membranes were studied in water–hydrogen binary system at 473 K with 10 kPa of water partial pressure, where no capillary condensation was expected in non-zeolitic pores. Separation factor for a mordenite membrane with a few defects was poor; however, a defect-free mordenite membrane prepared under a suitable condition highly separated steam from hydrogen.     

Influence de la complexation sur le transfert des cations en osmose inverse

The influence of complexation by different ligands on the transfer of metallic cations in reverse osmosis has been studied by using membranes composed of aromatic polyamides. In spite of the large volume increase of the diffusing solute, the addition of a complexant can significantly improve the transfer of metallic cations through a reverse osmosis membrane. The most important factor in the improvement of the transfer is the solubility in the membrane of the complexes created. This solubility is linked to the possibility of creating hydrogen bonds between the membrane and the complex. Moreover, the addition of substances which strongly solvate both the membrane and the solute leads to an improvement of transfer which increases considerably with the increasing pressure. These results suggest the possibility of separating metal cations by specific complexation.     

化学气相输运法(CVT)制备微米级的喇叭管状ZnO晶体

氧化锌为直接带隙宽禁带半导体材料,由于其优良的光电性能,预计在未来光电信息领域有着巨大的应用前景,引起了广泛的研究兴趣.     

Redox-induced solid-solid phase transformation of TCNQ microcrystals into semiconducting Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures: a combined voltammetric, spectroscopic, and microscopic study

The facile solid-solid phase transformation of TCNQ microcrystals into semiconducting and magnetic Ni[TCNQ]2(H2O)2 nanowire (flowerlike) architectures is achieved by reduction of TCNQ-modified electrodes in the presence of Ni2+(aq)-containing electrolytes. Voltammetric probing revealed that the chemically reversible TCNQ/Ni[TCNQ]2(H2O)2 conversion process is essentially independent of electrode material and the identity of nickel counteranion but is significantly dependent on scan rate, Ni2+(aq) electrolyte concentration, and the method of solid TCNQ immobilization (drop casting or mechanical attachment). Data analyzed from cyclic voltammetric and double-potential step chronoamperometric experiments are consistent with formation of the Ni[TCNQ]2(H2O)2 complex via a rate-determining nucleation/growth process that involves incorporation of Ni2+(aq) ions into the reduced TCNQ crystal lattice at the triple phase TCNQ|electrode|electrolyte interface. The reoxidation process, which includes the conversion of solid Ni[TCNQ]2(H2O)2 back to TCNQ0 crystals, is also controlled by nucleation/growth kinetics. The overall redox process associated with this chemically reversible solid-solid transformation, therefore, is described by the equation: TCNQ0(S) + 2e- + Ni2+(aq)+ 2 H2O <==> {Ni[TCNQ]2(H2O)2}(S). SEM monitoring of the changes that accompany the TCNQ/Ni[TCNQ]2(H2O)2 transformation revealed that the morphology and crystal size of electrochemically generated Ni[TCNQ]2(H2O)2 are substantially different from those of parent TCNQ crystals. Importantly, the morphology of Ni[TCNQ]2(H2O)2 can be selectively manipulated to produce either 1-D/2-D nanowires or 3-D flowerlike architectures via careful control over the experimental parameters used to accomplish the solid-solid phase interconversion process.     

Nanoscale polyoxometalate‐based inorganic/organic hybrids

The latest advances in the area of polyoxometalate (POM)‐based inorganic/organic hybrid materials prepared by self‐assembly, covalent modification, and supramolecular interactions are presented. This Review is composed of five sections and documents the effect of organic cations on the formation of novel POMs, surfactant encapsulated POM‐based hybrids, polymeric POM/organic hybrid materials, POMs‐containing ionic crystals, and covalently functionalized POMs. In addition to their role in the charge‐balancing, of anionic POMs, the crucial role of organic cations in the formation and functionalization of POM‐based hybrid materials is discussed. DOI 10.1002/tcr.201100002     

Thermal growth of organic supramolecular crystals with screw dislocations

We report here a simple pathway to thermally assemble acene-based molecules into large crystals without modification of their chemical structures. Differential scanning calorimetry was used to characterize properly thermal events occurring during successive heating and cooling processes. More interestingly, observations by means of polarized light microscopy (POM) revealed that a spontaneous formation of screw dislocations within crystals during the isothermal treatment triggered a structural reorganization by forming large and well-defined spiral architectures. After this reorganization, new crystals showed an excellent ordering in both vertical and horizontal directions. Due to the richness in pi-electrons of acene-based molecules, we expect this work of importance to organic electronics, especially in the design of new molecular building blocks and investigation of their assembly into sophisticated supramolecular structures.     

Particle nucleation and growth models

This review concentrates on the progress of modeling the nucleation process of particles by the balanced nucleation-growth (BNG) process. The BNG model will be compared with other models that try to predict material nucleation. Compared to other models, the BNG model allows quantifying the nucleation rate, maximum growth rate, and supersaturation during the nucleation period as a function of nucleation efficiency and maximum growth rate of the crystals. From this model, equations are derived that correlate the number of stable crystals formed with molar addition rate of reactants, solubility of the crystals, and temperature. The BNG model predicts the experimental result that many crystallization processes result in a limited number of crystals followed by growth. The model also predicts that factors like diffusion and kinetically controlled growth process, Ostwald ripening agents and growth restrainers control the crystal number. Equations are given for each of the variables that agree with experiments. The BNG model predicts the conditions for renucleation (formation of new crystals during precipitation). It leads to new equations for the prediction of crystal number and crystal size during controlled continuous precipitation in the continuous stirred tank reactor (CSTR) as a function of precipitation conditions.     

Morphological evolution of inorganic crystal into zigzag and helical architectures with an exquisite association of polymer: a novel approach for morphological complexity

The morphology of potassium sulfate (K(2)SO(4)) crystals grown in a viscous polymer solution of poly(acrylic acid) (PAA) was remarkably changed from the tilted columnar assembly into zigzag and helical architectures with increasing PAA concentration. The habit modification of orthorhombic K(2)SO(4) with adsorption of PAA molecules on a specified crystal face fundamentally led to the formation of tilted unit crystals. Concurrently with the habit modification, a diffusion-limited condition controlling the assembly of tilted units was achieved in the presence of PAA molecules in the matrix. Various complex morphologies, including zigzag and helical assembly, emerged through the formation of twinned crystals with the variation of the diffusion condition. Understanding the morphogenesis observed in this report would provide a novel approach for sophisticated crystal design by using an exquisite association of organic and inorganic materials.     

Synthesis of small crystal polycrystalline mordenite membrane

Mordenite membrane was prepared on -Al₂O₃ tube by in situ hydrothermal synthesis with tetraethylammonium bromide (TEABr) as template agent. By the application of aging process of the parent solution, the size of mordenite crystals could be remarkably reduced from 20–30 (without aging) to 4–5 μm. The small crystal mordenite membrane had higher performance of pure gas permeation than big crystal mordenite membrane. The ideal selectivity of H₂/N₂ was 9.80, much higher than 3.82 of big crystals mordenite membrane. The membrane displayed high water-permselective performance in pervaporation (PV) test toward water/organic liquid mixtures. The highest separation factors achieved toward water/methanol, water/ethanol, water/n-propanol and water/i-propanol were 2600 (X_W=50%, T=323 K), 5500 (X_W=50%, T=343 K), 6000 (X_W=15%, T=343 K) and 6800 (X_W=50%, T=343 K), respectively.     

Vertically Oriented Microporous Membranes Prepared by Bidirectional Freezing

Polystyrene membranes with precisely controlled and vertically oriented pores are fabricated by a bidirectional freezing process. In this process, the influence of polymer in growth of diphenyl sulfone (DPS) crystals has been demonstrated by XRD and simulated by DFT based on the interaction between DPS crystal faces and polystyrene (PS). The influence of temperature gradient on membrane structures is also elucidated. Compared to the original membrane and modified traditional membranes, modified PS membranes with vertically oriented pores show large and stable fluxes in the processes of multiple oil and water separation.     

Epitaxial crystallization of polyoxymethylene on NaCl single crystal in dilute solution

The epitaxial crystallization of polyoxymethylene (POM) is observed from 0.01% cyclohexanol solution on the (001) cleavage face of NaCl. High-resolution electron microscopy reveals that the crystals are definitely triangular, rather than rectangular prisms, although the crystals have previously been interpreted as “edge-on” arrangements of lamellar crystals. An electron diffraction pattern obtained from films, which were piled up with a maximum of nine sheets per grid, shows that plane spacing of the epitaxial crystals is 3.87 Å and almost the same as the \[ \left\{ {10\bar 10} \right\} \] spacing (3.86 Å) of hexagonal single crystal of POM: the axes of POM fold chains in the crystals are parallel to the (001) plane. A possible mechanism for the epitaxial crystallization of POM is proposed.     

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

Polyoxometalates (POMs) are molecular metal‐oxide anions applied in energy conversion and storage, manipulation of biomolecules, catalysis, as well as materials design and assembly. Although often overlooked, the interplay of intrinsically anionic POMs with organic and inorganic cations is crucial to control POM self‐assembly, stabilization, solubility, and function. Beyond simple alkali metals and ammonium, chemically diverse cations including dendrimers, polyvalent metals, metal complexes, amphiphiles, and alkaloids allow tailoring properties for known applications, and those yet to be discovered. This review provides an overview of fundamental POM–cation interactions in solution, the resulting solid‐state compounds, and behavior and properties that emerge from these POM–cation interactions. We will explore how application‐inspired research has exploited cation‐controlled design to discover new POM materials, which in turn has led to the quest for fundamental understanding of POM–cation interactions.     

Tunable Surface Wrinkling by a Bio-Inspired Polyamine Anion Coacervation Process that Mediates the Assembly of Polyoxometalate Nanoclusters

A bio-inspired method is used to render controlled wrinkling surface patterns on supramolecular architectures assembled from polyoxometalate (POM) clusters. It involves a polyamine-multivalent anion interaction generating positively charged coacervates, which while dictating the assembly of POM into spherical structures further facilitate an interesting surface morphogenesis with wrinkling patterns. This spontaneous surface wrinkling depends on the type of multivalent anion and the pH. As the polyamine-anion interaction becomes stronger, the wrinkles turn denser with lesser depth, which eventually undergoes post-buckling to engender a complex surface pattern. Interestingly, the order of influence exerted by different anions on the morphology follows the Hofmeister series. Moreover, the mild synthesis conditions keep the functional POM units dispersed in the sphere with a structural transformability to their lacunary form.     

Stereospecific morphogenesis of aspartic acid helical crystals through molecular recognition

Helical morphologies were generated from aspartic acid (Asp) crystals in agar gel matrix. The morphogenesis stereospecifically proceeded in the helical crystal growth: D- and L-Asp provided left- and right-handed structures, respectively. The backbone of the helical morphology was twisted twins of tilted unit crystals, as was the case with inorganic helical crystals. The molecular recognition between the Asp crystals and agar matrix molecules resulted in the stereospecific morphogenesis. The chirality in Asp and agar molecules, the enantiomorph of unit crystals, and the resultant macroscopic helix were exquisitely associated with each other.     

Epitaxial crystallization of polyoxymethylene during cationic polymerization of trioxane

Epitaxial crystallization of polyoxymethylene (POM) during cationic polymerization of trioxane in ethane dichloride was studied. Nascent POM crystals grew epitaxially on the surface of drawn, high-molecular-weight POM and on the (001) surface of KCl single crystals. Half-hexagonal crystals several thousand angstroms in thickness were formed on these substrates. No discrete diffraction maximum could be observed in small-angle x-ray scattering patterns, but diffuse streaks were present on both the equator and the meridian of the pattern. These diffuse streaks are due to inhomogeneities in the nascent crystals. It is proposed that the crystals contain voids due to occlusion of reactive chain ends in the crystal. The optical diffraction pattern from a model made up of rectangles agreed qualitatively with the actual x-ray pattern.     

RNA catalysis in model protocell vesicles

We are engaged in a long-term effort to synthesize chemical systems capable of Darwinian evolution, based on the encapsulation of self-replicating nucleic acids in self-replicating membrane vesicles. Here, we address the issue of the compatibility of these two replicating systems. Fatty acids form vesicles that are able to grow and divide, but vesicles composed solely of fatty acids are incompatible with the folding and activity of most ribozymes, because low concentrations of divalent cations (e.g., Mg(2+)) cause fatty acids to precipitate. Furthermore, vesicles that grow and divide must be permeable to the cations and substrates required for internal metabolism. We used a mixture of myristoleic acid and its glycerol monoester to construct vesicles that were Mg(2+)-tolerant and found that Mg(2+) cations can permeate the membrane and equilibrate within a few minutes. In vesicles encapsulating a hammerhead ribozyme, the addition of external Mg(2+) led to the activation and self-cleavage of the ribozyme molecules. Vesicles composed of these amphiphiles grew spontaneously through osmotically driven competition between vesicles, and further modification of the membrane composition allowed growth following mixed micelle addition. Our results show that membranes made from simple amphiphiles can form vesicles that are stable enough to retain encapsulated RNAs in the presence of divalent cations, yet dynamic enough to grow spontaneously and allow the passage of Mg(2+) and mononucleotides without specific macromolecular transporters. This combination of stability and dynamics is critical for building model protocells in the laboratory and may have been important for early cellular evolution.     

Tunable Surface Wrinkling by a Bio‐Inspired Polyamine Anion Coacervation Process that Mediates the Assembly of Polyoxometalate Nanoclusters

A bio‐inspired method is used to render controlled wrinkling surface patterns on supramolecular architectures assembled from polyoxometalate (POM) clusters. It involves a polyamine‐multivalent anion interaction generating positively charged coacervates, which while dictating the assembly of POM into spherical structures further facilitate an interesting surface morphogenesis with wrinkling patterns. This spontaneous surface wrinkling depends on the type of multivalent anion and the pH. As the polyamine‐anion interaction becomes stronger, the wrinkles turn denser with lesser depth, which eventually undergoes post‐buckling to engender a complex surface pattern. Interestingly, the order of influence exerted by different anions on the morphology follows the Hofmeister series. Moreover, the mild synthesis conditions keep the functional POM units dispersed in the sphere with a structural transformability to their lacunary form.