Packings of uniform microspheres with ordered macropores fabricated by double templating

Highly uniform 3-D ordered macroporous spheres in regular arrays were produced by a double templating process. The first template of larger silica balls produced the polymer skeleton for guiding the shape and size of the self-assembled superstructure of smaller polymeric balls, which are introduced subsequently into the internal space of the skeleton. The second templating with inorganic precursors has created novel superstructured materials, which could open up significant opportunities in a variety of areas ranging from absorbents/catalysts to novel photonic crystals.     

Heterogeneity within order in crystals of a porous metal-organic framework

Generally, crystals of synthetic porous materials such as metal-organic frameworks (MOFs) are commonly made up from one kind of repeating pore structure which predominates the whole material. Surprisingly, little is known about how to introduce heterogeneously arranged pores within a crystal of homogeneous pores without losing the crystalline nature of the material. Here, we outline a strategy for producing crystals of MOF-5 in which a system of meso- and macropores either permeates the whole crystal to make sponge-like crystals or is entirely enclosed by a thick crystalline microporous MOF-5 sheath to make pomegranate-like crystals. These new forms of crystals represent a new class of materials in which micro-, meso-, and macroporosity are juxtaposed and are directly linked unique arrangements known to be useful in natural systems but heretofore unknown in synthetic crystals.     

Macroporous gels prepared at subzero temperatures as novel materials for chromatography of particulate-containing fluids and cell culture applications

Macroporous gels (MGs) with a broad variety of morphologies are prepared using the cryotropic gelation technique, i. e. gelation at subzero temperatures. These highly elastic hydrophilic materials can be produced from practically any gel-forming system with a broad range of porosity extending from elastic and porous gels with pore sizes up to 1.0 microm to elastic and sponge-like gels with pore sizes up to 100 microm. The versatility of the cryogelation technique is demonstrated by use of different chemical reactions (hydrogen bond formation, chemical cross-linking of polymers, free radical polymerization) mainly in an aqueous medium. Appropriate control over solvent crystallization (formation of solvent crystals) and rate of chemical reaction during the cryogelation allows the reproducible preparation of cryogels with tailored properties. Different approaches, such as chemical modification of reactive groups, grafting of the pore surface with an appropriate polymer, or direct copolymerization with functional monomers are used for control of the surface chemistry of MGs. Typically, MGs with pore sizes up to 1.0 microm are produced in the shape of beads and MGs with pore size up to 100 microm are prepared as monoliths, discs, and sheets. The difference in porous structure of MGs defines the main applications of these porous materials. Elastic beaded MGs are mostly used as carriers for cell and enzyme immobilization or for capture of low-molecular weight targets from particulate-containing fluids in expanded-bed mode. However, the elastic and sponge-like MG monoliths with interconnected pores measuring hundreds of mum have been successfully used as monolithic columns for chromatography of particulate-containing fluids (crude cell homogenates, viruses, whole cells, wastewater effluents) and as three-dimensional scaffolds for mammalian cell culture applications.     

Generalized fabrication of two-dimensional non-close-packed colloidal crystals

In this paper we report a generalized templating approach for fabricating wafer-scale, two-dimensional, non-close-packed (ncp) colloidal crystals. Polymer nanocomposites consisting of monolayer ncp colloidal crystals prepared by a spin-coating process are used as sacrificial templates. After removal of the colloidal silica templates, the voids in the polymer matrix are infiltrated with other materials. By plasma-etching the polymer matrix, wafer-scale ncp colloidal crystals from a variety of functional materials can be made. This technique is scalable and compatible with standard microfabrication. Two-component colloidal arrays with complex micropatterns can also be fabricated by combining microfabrication with this templating approach. Normal-incidence reflectivity spectra of replicated titania ncp arrays agree well with theoretical prediction using Scalar Wave Approximation.     

Control of prolonged drug release and compression properties of ibuprofen microspheres with acrylic polymer, eudragit RS, by changing their intraparticle porosity [corrected]

Prolonged-release spherical micro-matrices of ibuprofen with Eudragit RS were prepared using a novel emulsion-solvent diffusion method. Those particles were termed "microspheres" due to their characteristic sponge-like texture and unique dissolution and compression properties unlike conventional microcapsules or microspheres. The internal porosity of microspheres could be easily controlled by changing the concentration of the drug and the polymer in the emulsion droplet (ethanol). With lower concentration of ibuprofen in the ethanol, the resultant microspheres had a higher porosity, about 50%. The drug release rate from the microspheres was interpreted by the Higuchi model of spherical matrices, which depended only on their internal porosity of the microspheres when size distribution and drug content were the same. The tortuosities in the microspheres were found to be almost constant (3-4) irrespective of porosity, suggesting the same internal texture. Microsphere compressibility was much improved over the physical mixture of the drug and polymer owing to the plastic deformation of their sponge-like structure. The more porous microspheres produced stronger tablets [corrected].     

Breath Figure Arrays: Unconventional Fabrications,Functionalizations, and Applications

A breath figure (BF) is the water droplet array that forms when moisture comes in contact with a cold substrate. This water droplet array has been widely utilized in the past two decades as a versatile soft template for the fabrication of polymeric porous films. Accordingly, the ordered pores on the polymer films formed with such a method are named a breath figure array (BFA).The BF templating technique is undergoing rapid development. Several unconventional BF processes have been established to prepare porous films with unique morphologies or primary materials, and various newly developed functionalization techniques have significantly improved the performance of polymeric films with BFA, leading to novel applications, including templates, biosensors, and separation membranes. These recent achievements will be described in this Minireview.     

聚合物单晶生长的三维相场模拟研究

利用元胞自动机方法与相场模型的结合建立新型三维模拟相场模型.同时,为模拟真实的、三维的高分子结晶的过程,采用元胞自动机方法离散方程,且元胞几何形状的选取符合真实聚合物晶格扩散方式的物理规律,以及新建立的相场模型套用间规聚丙烯的实验参数.利用该模型模拟了多种三维立方体或者薄层的晶体形貌及其相互之间的演化过程,包括正方形、长方形、菱形、六边形、多层单晶等.通过模拟结果与真实形貌作对比来证明所建立的相场模型真实可靠性.     

谈谈聚合物的结晶形态问题

向读者引介了聚合物球晶的三维立体电镜照片，并介绍了高分子科学近年来的新研究成果－尺寸已达厘米量级的聚合物宏观单晶体和只由一根大分子链结晶而成的高分子单链单晶的特殊形态。     

Tailored polymer-supported templates in dynamic combinatorial libraries: simultaneous selection, amplification and isolation of synthetic receptors

The thermodynamically controlled synthesis and isolation of macrocyclic receptors from dynamic combinatorial libraries has been achieved in a single step using a polymer-supported template. The templates were cinchona alkaloids which show interesting enantio- and diastereoselective molecular recognition events in libraries based on pseudo-dipeptide building blocks. The synthetic routes used to derivatise the alkaloids and attach them to polymer supports minimised any influence of the tethering linkage on the templating activity. Systematic studies have been carried out to probe how the polymer morphology and the template loading affect the selectivity and isolation yield of the macrocyclic receptors. Molecular recognition between solid-phase bound templates and selected receptors also enabled their affinity-type chromatographic separation.     

Unique crystal morphologies of glycine grown from octanoic acid-in-water emulsions

We have obtained both porous and dendritic, intricate morphology crystals of beta-glycine by the novel and simple method of emulsion droplet adhesion and encapsulation. By using octanoic acid emulsified with nonionic surfactants, the adhesion of the emulsion droplets can be so strong that, remarkably, crystal growth often proceeds around the droplets, leading to their inclusion within the single crystals. Consequently, porous single crystals can be produced with the pore diameters ( approximately 10-25 mum) corresponding to the emulsion droplet sizes. Highly intricate, dendritic morphologies for glycine were obtained by increasing the surfactant concentration in the emulsions to 50%. In this case, partial droplet encapsulation results in crystal dendrites growing on either side of adsorbed droplets, with the complex morphologies developing due to the high density of dendritic branches that can occur. These intricate morphologies are in stark contrast to the facetted crystals that normally develop at these low supersaturations in the absence of octanoic acid droplets. This study demonstrates that complex architectures can be attained by using simple emulsion systems and tuning the degree of droplet adhesion.     

Modification of the morphology of P(S-b-EO) templated thin TiO2 films by swelling with PS homopolymer

For the controlled modification of sol-gel-templated polymer nanocomposites, which are transferred to a nanostructured, crystalline TiO2 phase by a calcination process, the addition of a single homopolymer was investigated. For the preparation, the homopolymer polystyrene (PS) is added in different amounts to the diblock copolymer P(S-b-EO) acting as a templating agent. The homopolymer/diblock copolymer blend system is combined with sol-gel chemistry to provide and attach the TiO2 nanoparticles to the diblock copolymer. So-called good-poor solvent-pair-induced phase separation leads to the formation of nanostructures by film preparation via spin coating. The fabricated morphologies are studied as a function of added homopolymer before and after calcination with atomic force microscopy, field emission scanning electron microscopy, and grazing incidence small-angle X-ray scattering. The observed behavior is discussed in the framework of controlling the block copolymer morphologies by the addition of homopolymers. At small homopolymer concentrations, the increase in homopolymer concentration changes the structure size, whereas at high homopolymer concentrations, a change in morphology is triggered. Thus, the behavior of a pure polymer system is transferred to a more complex hybrid system.     

在“高聚物的结构与性能”课程中讲透高聚物的特点

通过对高分子链的柔性、聚合物独有的熵弹性、显著的粘弹性、特有的描述链段运动的WLF方程,可能实现的大尺寸取向和小尺寸解取向、银纹、单链凝聚态、折叠链片晶和伸直链晶体、分子量的多分散性、高分子溶液特性和高聚物熔体的弹性行为等的讨论,希望能突出“高聚物的结构与性能”课程中高聚物的特点。     

活性聚苯乙烯膜诱导碳酸钙异相成核结晶

0引言生物矿物材料(如骨、牙齿、贝壳等)的优异性能[1]使得无机材料的仿生合成(又称有机模板合成)成为近年来研究的热点之一[2]。该合成技术的优点是,通过有机物分子与无机离子的相互作用,能够在温和的条件下合成出具有多级结构、特殊形貌和优异性能的有机/无机复合材料。CaCO3     

Biomineralization‐Inspired Preparation of Zinc Hydroxide Carbonate/Polymer Hybrids and Their Conversion into Zinc Oxide Thin‐Film Photocatalysts

The development of ZnO thin films has been achieved through the conversion of zinc hydroxide carbonate thin‐film crystals. Crystallization of this compound is induced by a biomineralization‐inspired method with polymer‐stabilized amorphous precursors. The crystals grow radially on polymer matrices, leading to the formation of zinc hydroxide carbonate/polymer thin‐film hybrids that fully cover the substrate. These hybrids are converted into ZnO and retain their thin‐film morphologies. The resultant ZnO thin films exhibit a preferential crystallographic orientation that is attributed to the alignment of zinc hydroxide carbonate crystals before conversion. In addition, a photocatalytic function of the ZnO thin films has been demonstrated by analyzing the oxidation reaction of 2‐propanol. The biomineralization‐inspired approach reported herein is a promising way to develop ZnO materials with controlled morphologies and structures for photocatalytic applications.     

Amyloid-mediated synthesis of giant, fluorescent, gold single crystals and their hybrid sandwiched composites driven by liquid crystalline interactions

We report for the first time on the templating effect of β-lactoglobulin amyloid-like fibrils to synthesize gold single crystals of several decades of μm in dimensions. The gold single crystals were produced by reducing an aqueous solution of chloroauric acid by β-lactoglobulin amyloid protein fibrils. Atomic force microscopy, conventional and scanning transmission electron microscopy, electron diffraction and optical microscopy techniques were combined to characterize the structure of the gold crystals. The single-crystalline features of these macroscopic gold crystals are witnessed by their distinctive hexagonal and triangular shape and are confirmed by selected area electron diffraction (SAED). UV-vis absorption spectrum, recorded after a reaction time of 6h at the heating temperature of 55°C showed a surface plasmon resonance peak at 540 nm. With the increase of reaction time to 24h, the absorption spectrum peaks shift to a very broad and higher wavelength region extending up to near infrared region. Remarkably, these single crystalline gold crystals show auto fluorescence when illuminated to UV lamp. Further increase in β-lactoglobulin amyloid fibrils concentration above the isotropic-nematic transition, drives the formation of gold single crystals microplates stacking together and self-assembling into new hierarchical, layered protein-gold hybrid composites.     

DNA-templated assemblies of nickel hexacyanoferrate crystals

We report here the synthesis of nickel hexacyanoferrate (NiHCF) crystals using calf thymus DNA (CT-DNA) as a template. The double-stranded CT-DNA has been used as a template to self-assemble NiHCF crystals and to produce aggregates having different morphologies at different temperatures. The guided self-assembly behavior of DNA was studied at different temperatures by scanning electron microscopy. The cube-shaped crystals of NiHCF with an average diameter of 400 nm are observed along the DNA framework at room temperature; however, at higher temperatures, the morphology of NiHCF changed from open tubular to dendrimer. The intermediate temperatures show long chains (up to many micrometers) and spherical structures of NiHCF crystals. The micrometer long DNA template plays a key role in the formation of extended arrays of NiHCF crystals, suggesting that the templating action is retained even at the higher temperatures.     

Calcium oxalate crystals in tomato and tobacco plants: morphology and in vitro interactions of crystal-associated macromolecules

Plants form calcium oxalate crystals with unique morphologies under well-controlled conditions. We studied the morphology of single calcium oxalate monohydrate (whewellite) crystals extracted from tomato and tobacco leaves. These crystals have a pseudotetrahedral shape. We identified the (101), (101) or (102), (110), and (hk0) faces as stable faces. The morphology is chiral with unique handedness. We also show that calcium oxalate monohydrate crystals isolated from tomato, tobacco, and bougainvillea leaves contain macromolecules rich in Gly, Glx, and Ser. Crystal-associated macromolecules extracted from tomato and tobacco influence the morphology of calcium oxalate monohydrate crystals grown in vitro, promoting preferential development of the [120] faces. Furthermore, crystal-associated macromolecules from tobacco promote nucleation of calcium oxalate monohydrate crystals, whereas model polypeptides do not have any significant effect on nucleation. These results imply an active role of the crystal-associated macromolecules in the formation of pseudotetrahedral shapes in vitro, and these properties may in part be responsible for the unique chiral morphology of the natural pyramidal-shaped crystals.     

Selective crystallization of calcium salts by poly(acrylate)-grafted chitosan

The biopolymer chitosan was chemically modified by grafting polyacrylamide or polyacrylic acid in a homogeneous aqueous phase using potassium persulfate (KPS) as redox initiator system in the presence of N,N-methylene-bis-acrylamide as a crosslinking agent. The influence of the grafted chitosan on calcium salts crystallization in vitro was studied using the sitting-drop method. By using polyacrylamide grafted chitosan as substrate, rosette-like CaSO4 crystals were observed. This was originated by the presence of sulfate coming from the initiator KPS. By comparing crystallization on pure chitosan and on grafted chitosan, a dramatic influence of the grafted polymer on the crystalline habit of both salts was observed. Substrates prepared by combining sulfate with chitosan or sulfate with polyacrylamide did not produce similar CaSO4 morphologies. Moreover, small spheres or donut-shaped CaCO3 crystals on polyacrylic acid grafted chitosan were generated. The particular morphology of CaCO3 crystals depends also on other synthetic parameters such as the molecular weight of the chitosan sample and the KPS concentration.     

Incorporating polymers within a single-crystal: From heterogeneous structure to multiple functions

Single-crystals, commonly considered as homogeneous solids, are able to be internally interfaced abnormally with guest polymers, which can be found in the biominerals where single-crystals incorporate surrounding biomacromolecules to reinforce their mechanical properties. This unique feature combining heterogeneous structure and long-range atomic ordering have attracted abundant investigations of reproducing their synthetic analogs to expand the potential application scope. Here, we summarize the recent progresses in the synthetic single-crystal composites, where polymer guests are incorporated inside single-crystals to generate heterogeneous structures without interruption to the long-range ordering of crystal hosts. First, the uniform and patterned encapsulations inside the various single-crystals are concluded in the sequence of isolated and continuous polymer-based guests. In addition, the mechanisms are classified chemically and physically, and the corresponding controlled factors that govern the incorporation processes are discussed. Most importantly, typical attempts on the applications of these heterogeneous single crystals are introduced, including mechanical reinforcement, bandgap engineering, catalyst, self-healing, controlled release, and optoelectronic devices. We aim at stressing on the current and potential applications benefited from the unique structural properties of the polymer incorporated single-crystals, and accordingly propose the perspectives to accelerate the path from the structural analysis toward prosperous functions.     

Investigation of polymer-protected noble metal nanoparticles by transmission electron microscopy: control of particle morphology and shape

 Noble metal nanoparticles were prepared by the in situ reduction of the respective metal salt precursors in the presence of various protective polymers. Transmission electron microscopy (TEM) has been used to determine the particle shapes and morphologies. These are strongly influenced by the reduction methods and conditions chosen, but the choice of the protective polymer is equally important for controlling the particle morphologies and for the stabilization of the colloids. A whole spectrum of nanoparticle morphologies and shapes was obtained, ranging from nanoagglomerates which are nevertheless well-defined and well-stabilized to nanosized single crystals with triangular shape. Received: 2 February 1998 Accepted: 29 May 1998