空心球合成

Polymer-Controlled Crystallizati Superstructures By Shao-Feng Chen, Jian-Hua Zhu, Jun Jiang 1. Introduction Recently, the synthesis of complex superstructures by organiza- tion of building blocks acrossmultiple scales to form a wide range of ‘‘mesocrystals’’ has attracted a great deal of attention.[1] The traditional methods of colloid chemistry have proved to be capable of controlling the sizes and polymorphs of inorganic materials by changing reaction parameters, such as temperature, pH, supersaturation, solvent, and simple inorganic ions.[2] In contrast, biological systems are very effective at controlling crystal growth, as demonstrated in discoveries on mollusk shells, sea urchins, coccoliths, nacre, and others.[3] Proteins and polysaccharides with complicated patterns of various functional groups in biological tissues are believed to play a crucial role in the formation of such complex forms.[4] Many unusual hierarchical structures of inorganic materials with high complexity and structural specialties can be artificially world, exhibiting non properties.[11] Investi the ordered hierarch understand the essen materials with physic As a similar substanc aragonite phase. The in biomineralization In this Research N in polymer-controlle superstructures. New polymer-controlled cr selective adsorption o mesoscale transform matrix or a substr combination with a suitable solution medium. in Aqueous soscale lymers in agent to locks into R E S E A R C H N E W S www.advmat.de www.MaterialsViews.com Hefei National Laboratory for Physical Sciences at the Microscale lo en d ni a en a bi str so ve iv or inorganic–organic hybrid materials with structural complexity, structural specialties, and improved functionalities. 540 DOI: 10.1002/adma.200901964 Superstructures The most useful function of hydrophilic block copo controlling crystal growth is their use as a directing induce coded self-assembly of nanoscale building b Department of Chemistry University of Science and Technology of China Hefei, Anhui 230026 (P. R. China) E-mail: shyu@ustc.edu.cn created by biomimetic mineralization, using such polymers as 2. Polymer-Controlled Crystallization Media: Selective Adsorption and Me Transformation to Highly Ordered [*] Prof. S.-H. Yu, S.-F. Chen, J.-H. Zhu, J. Jiang, G.-B. Cai Division of Nanomaterials and Chemistry Shu-Hong Yu* The origin of complex superstructures of biomaterials in bio and the amazing self-assembly mechanisms of their emerg attracted a great deal of attention recently. Mimicking nature, hydrophilic polymers with different functionalities and orga matrices have been designed for the morphogenesis of inorg this Research News, emerging new strategies for morphog trolled crystal growth of minerals, that is, selective adsorption transformation for highly ordered superstructures, the com synthetic hydrophilic polymer with an insoluble matrix, a sub solution interface, and controlled crystallization in a mixed highlighted. It is shown that these new strategies can be e extended to morphogenesis and controlled crystallization of d � 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim calcite is the most stable phase of the three crystalline anhydrous phases of CaCO3, and vaterite is less stable than aragonite. CaCO3 co-deposited with organic molecules from the organisms is one typical biomineral occurring in nature. It is widespread in the equilibrium shapes[3,4] and distinct physical gation of how nanoparticles assemble into ical structures of biominerals is helpful to ce of crystal growth and to produce artificial al properties similar to those of biominerals. e, BaCO3 is thermodynamically stable in the use of these two minerals as model systems studies is a hot subject.[12,13] ews, we will discuss the latest developments d crystallization of novel unique mineral emerging methodologies in the field of ystallization will be highlighted, such as the f a designed artificial functional polymer in ation, its synergistic effect with an insoluble ate, or the air/water interface, and its additives.[5–7] The polymers used include synthetic double-hydrophilic block copoly- mers (DHBCs), low-mass electrolytes, and triblock copolymers, which are widely used in biomimetic mineralization.[8] If the pattern of functional groups is designed to match some special crystal faces of one material, the functional block can selectively adsorb on them to hinder the growth of the crystal and affect its final morphology, then directing the mesoscale self-assembly of nanometer-scale building blocks into hierarchical superstructures.[5,7,9,10] From the viewpoint of thermodynamics, gical systems ce have iverse kinds of c insoluble nic crystals. In esis and con- nd mesoscale nation of a ate, or the air/ lvent are n further erse inorganic on of Unique Mineral , Guo-Bin Cai, and Adv. Mater. 2010, 22, 540–545 R E S E A R C H N E W S www.MaterialsViews.com www.advmat.de are many uncer- s noteworthy that nctional groups, ogy of inorganic most fascinating mation of helical ribbons, mainly supramolecular ono- or polypep- has been occa- echanism in the lical micrometer uced in alkaline nate helical form reported that a and silica leads to r structures that nd that further along the rim of rphs’’, including lf-assembly is to al surfaces; thus strongly bind free calcium ions in the process of mineralization, which alters the crystallization mechanism from ionic growth to mesoscale assembly.[12g] The negative polyelectrolyte PSS tends to adsorb on the positive (001) face of calcite. This adsorption leads to the formation of a long-term dipole along the c-axis of the whole crystal, which drives the dipolar arrangement of PSS-capped nanoparticles into superstructures. In the presence of PSS-co-MA (poly(4-styrenesulfonate)-co-(maleic acid)), the platonic calcite crystals with pseudododecahedral and pseudooctahedral shapes consist of nanoparticles and polymer incorporated in the voids in the microcrystal.[22] A continuous evolution of the crystallization mechanism from polycrystalline to mesocrystalline and then to single crystalline in the presence of poly(ethylene oxide)-b- poly(sodium 4-styrenesulfonate) (PEO22-PNaStS49) was investi- gated, based on aggregation of nonoriented larger nanoparticles, to oriented smaller nanoparticles, and then to classical Oswald-ripening ion-to-ion growth.[23] A thin layer of polymer on the fine crystallites of polycrystalline crystals (2.2 nm) and mesocrystals (3.7 nm) was observed, which can be further proved by thermogravimetric analysis (TGA). Recently, a rigid DHBC, poly(ethylene glycol)-b-poly(1,4,7, 10,13,16-hexaazacyclooctadecane ethylene imine) (PEG-b- hexacyclen), has been used as an excellent crystal modifier to synthesize triangular Au nanoplates by selective adsorption of the functional group of the polymer on the (111) face of Au.[24] In the ole no h en es. sio BaCO3 units (Figs. 1a,c). [21] BaCO3 fibers with a diameter of 200–500 nm and lengths as long as some millimeters are assembled from brick-like elongated nanocrystals with 200 nm length and 30 nm diameter (Fig. 1b). It is interesting that the polymer itself does not form helices in the solution with or without barium ions, thus, the formation of helices must be a result of the interaction between barium carbonate nanoblocks and the polymer. This architectonic arrangement via coded self-assembly relies on two processes. First, the adsorption of the stiff DHBC onto the favorable (110) faces results in a staggered arrangement that is controlled along the aggregation direction of the first three parti- cles. Second, a particle approaching an aggregate in the perpendicular direction is presented with favorable and unfavorable adsorption sites, leading to a twist in the par- ticle aggregate. The overlay of these two processes leads to helix formation (Fig. 1d). A nonclassical crystallization is realized in a simple polyelectrolyte-controlled mineraliza- tion also. Polystyrene sulphonate (PSS) can Figure 1. a) Them of helical BaCO3 na image showing the vacuum, not repres of the relevant fac duced with permis macroscopic superstructures, although there tainties in the complicated assembly process. It i functional group patterns, and the types of fu have a significant influence on the morphol crystals.[5,7,14–16] Helical and spiral architectures are the morphology that has chirality. Currently, the for structures, including nanofibers, tubes, and relies on the direct templating effect of nanoribbons, screw dislocations, chiral acidic m tides, and chiral gelators.[17] Micrometer-sized helical calcium carbonate sionally observed formed by an ambiguous m presence of chiral/achiral polyaspartate.[18] He filaments of silica-barium carbonate were prod sodium silicate solution, while strontium carbo grew in silica gel.[19] Recently, it has been chemically coupled coprecipitation of carbonate fibrillation of the growing front and to lamina experience curling at their growing rim, a propagation of these curls in a surflike way the laminae results in the formation of ‘‘biomo helicoids.[20] An effective way to encode nanoparticle se selectively adsorb additives onto specific cryst ‘‘programmed’’ self-assembly of nanoparticles occurs. We have demonstrated that the selective adsorption of a racemic phospho- nated DHBC (poly(ethylene glycol)-b- [(2-[4-dihydroxyphosphoryl]-2-oxabutyl) acrylate ethyl ester] (PEG-b-DHPOBAEE)) onto the (110) faces of BaCO3 leads to the formation of BaCO3 helices by programmed self- assembly of the elongated orthorhombic Adv. Mater. 2010, 22, 540–545 � 2010 WILEY-VCH Verlag Gm cular formula of PEG-b-DHPOBAEE, which acts as a template for formation particle superstructures. b)Magnified scanning electronmicroscopy (SEM) elical structure. c) The primary nanocrystalline witherite building block in ting the observed face areas in solution but just illustrating the orientation d) Proposed formation mechanism of the helical superstructure. Repro- n from [21]. Copyright 2005, Nature Publishing Group. bH & Co. KGaA, Weinheim 541 R E S E A R C H N E W S www.advmat.de www.MaterialsViews.com vaterite microspheres can be produced under control of the artificial DHBC PEG(m)-b-pGlu(n) in N,N-dimethylformamide 542 case of mineralizing CaCO3 crystals, so-called pancake structures were fabricated with a shape similar to the layered structure of nacre in Haliotis rufescens, as shown in Figures 2a,b.[12d] Layered crystals with different morphology and surface structures, even disk-like crystals, can be obtained by altering the reaction parameters in the system. This study suggested that the morphology of the crystal is influenced not only by epitaxial match between the polymer and crystal faces, but also by particle stabilization, crystallization time, time for polymer rearrange- ment, and surface ion density. In another case, polycrystalline round discs of CaCO3 consisting of nanocrystals capped by poly(ethylene gly- col)-b-poly(ethylene imine)-poly(acetic acid)-C17H35 (PEG-b- PEIPA-C17) can form microrings by dissolution of nanocrystal- lites at the center of the discs (Fig. 2c).[13b] At the initial nucleation stage, the primary hybrid polymer-capped CaCO3 nanocrystallites in the central part have a relatively high concentration of included multiple chelating ethylenediamine tetraacetic acid (EDTA) moieties, and then the outer area of the discs is of lower polymer concentration. With increasing aging time, the higher polymer concentration around the primary nanoparticles results in dissolution of inorganic nanobuilding blocks from the inside to the outside, leading to formation of the microrings.[13b] Figure 2. a) The structure of PEG-b-hexacyclen. b) A typical SEM image of pancake-like self-stacked CaCO3 obtained after two weeks gas diffusion reaction in the presence of 1 g L�1 PEG-b-hexacyclen, starting pH 4, [Ca2þ]¼ 10mM. Reproduced with permission from [12d]. Copyright 2005, Wiley-VCH. c) A typical SEM image of microrings of CaCO3. Reproduced with permission from [13b]. Copyright 2006, ACS. � 2010 WILEY-VCH Verlag Gm (DMF)/water mixed solvent with a suitable volume ratio by taking advantage of the synergic effects of the block copolymer and a selectivelymixed solvent (Figs. 3a,b).[34] The property of themixed solvent has been found to play a key pole in controlling the growth, polymorphism, and shape of CaCO3 mineral. [33] Further study indicated that uniform ellipsoidal-like particles with multiple thorns stretching out along different directions on the surface can be obtained at 14� 2 8C in DMF (Fig. 3c), which are quite different from those spherical structures formed in aqueous solution.[35] In addition, aragonite CaCO3 crystals with hierarchical tubular superstructures were obtained in DMFunder suitable conditions at the lower temperature of 4� 2 8C, and many small aragonite nanorods were observed grown on the surface of large microtubes (Fig. 3d). As the solvent quality for the polymer worsens in the mixed solvent, mineralization in a mixed solvent can result in externally triggered polymer aggregation, which will provide a new additional experimental variable for controlling the morphology. In addition, because the solubility product of a mineral is simultaneously changed in a mixed solvent system, interesting cooperative morphogenesis scenarios may be achieved. 4. Polymer-Controlled Crystallization on an Interface: Growth of Unique Superstructures Recent progress has demonstrated that the combination of polymer-controlled crystallization with a suitable interface, such as an insoluble hard substrate or an air/water interface, makes it possible to access a variety of unique mineral superstructures. The polymer PEG-b-DHPOBAEE with a different molecular weight has also been used for mineralization of BaCO3 to spontaneously form a concentric-circle Belousov–Zhabotinsky pattern made of BaCO3 nanorods in solution on a glass substrate.[36] The experimental evidence indicates that the formation of the Ba–polymer complex precursor plays a key role in the autocatalytic precipitation reaction occurring in a reaction–diffusion system, resulting in the spontaneous forma- tion of micrometer-sized periodic rings of nanocrystalline BaCO3 grown on the substrate in an aqueous solution.[35] The distance 3. Polymer-Controlled Crystallization in a Mixed Solvent: A New Way Toward Hierarchical Superstructures Mineralization reactions in nonaqueous solution, such as simple ethanol, isopropyl alcohol, and diethylene glycol, have been rarely studied.[25–27] In recent years, several research groups have occasionally focused on the use of different solvent media to control the crystal growth of CaCO3 and other com- pounds.[2b,28–31] CaCO3 nanoparticle aggregates, including elongated or spherical morphologies, can be formed in a water/alcohol solvent with various solvent compositions.[26] Even though vaterite microspheres can be crystallized in water solution using starburst dendrimers[32] and poly(ethylene glycol)-b-poly(L-glutamic acid) (PEG(m)-b-pGlu(n))[33] as crystal growth modifier, the vaterite spheres obtained are not uniform. Recently, we have demonstrated that highly monodisperse bH & Co. KGaA, Weinheim Adv. Mater. 2010, 22, 540–545 R E S E A R C H N E W S www.MaterialsViews.com www.advmat.de A continuous l (ACC) with 5 nm of Haliotis laevig bundle’’ are clea mesocrystals in n small building blo of ACC-PAA (poly process. The film ticles to achieve d on polymer-direct the polymer adsor thin film; the pat particular crystal f carbonate and thu It is well know organisms is gene molecules at the s Figure 3. a,b) SEM images of highly monodisperse vaterite CaCO3 micro- spheres mineralized in the presence of 1 g L�1 PEG(110)-b-pGlu(6) for 7 days at room temperature. The volume ratio of ethanol/water is 1/1.4. CaCl2 solution (0.6mL, 0.1 M) was added to mixed solution (6mL). between adjacent rings is almost constant (ca. 5mm), as shown in Figure 4a. The numerical simulations using a Bru¨sselator model for the reaction–diffusion equations qualitatively fit the observed oscillating precipitation reaction well (Fig. 4a). This amazing pattern formation underlines that it is possible to form a spontaneously self-organized pattern in solution by a mesoscale transformation process, which is similar to the patterns observed in a variety of physical, chemical, and natural systems. Reproduced from [34]. Copyright 2006, Wiley-VCH. c) SEM image of ellipsoid-like CaCO3 crystals obtained in the presence of 1 g L �1 PEG-b-pGlu after crystallization for 7 days at 14� 2 8C. [CaCl2]¼ 10mM. d) Complex prickly superstructures prepared in the presence of 1 g L�1 PEG-b-pGlu and [Ca2þ]¼ 20mM at 4� 2 8C for 7 days. Reproduced from [35]. Copyright 2008, ACS. Figure 4. a) SEM image of the concentric circle pattern of BaCO3 crystals [polymer]¼ 1 g L�1, [Ba2þ]¼ 10mM, starting pH 5.5. Reproduced from [36] Wiley-VCH. b) Square microcontact printing areas with BaCO3 nanofibers s Reproduced from [44]. Copyright 2009, RSC. Adv. Mater. 2010, 22, 540–545 � 2010 WILEY-VCH Verlag Gm study simulates the process by using an insoluble polymer matrix as the crystallization site and a soluble polymer as a stabilizer for chelating metal ions in solution. ACC was observed to first deposit on the hydroxylated PMMA (poly(methyl methacrylate)) film and then crystallize in the form of polycrystalline films, with the interplay of soluble PAA.[40] Metal carbonates (Ca, Ba, Sr) formed on a PVA (poly(vinyl alcohol)) film in the presence of soluble PAA have been shown to have a three-dimensional (3D) relief structure.[41] Periodic concentric circles were formed by oriented needle-like calcite nanocrystallites, the distance between two neighboring circles being about 10mm and the height of the circle about 5mm. Furthermore, the BaCO3 and SrCO3 needle- like crystals can periodically grow further on the CaCO3 circles. [40] Combining the method described in this section with the layer-by-layer technique, a nacre-like structure of alternating organic and inorganic layers can be fabricated.[42] One CaCO3 mineral layer is deposited on the diazo-resin/PAA film, and then the organic film is cast on the mineral layer again. Organic– inorganic layered structures can be easily achieved by repeating this process several times.[41] Generally, poly(aspartic acid) or PAA (poly(acrylic acid)) is used to induce the formation of the polymer-induced liquid precursor (PILP), in which the polymer is thought to sequester and concentrate the calcium ions and delay the crystal nucleation.[18] For example, nacre-type laminated CaCO3 thin film can be produced by heating a mixture of PAA and ACC.[43] A general route for fabrica- tion of patterned carbonates has been reported, which combines the advantages of the micro- contact printing technique and a PILP.[44] Square and linear patterns were stamped by microcontact printing with octadecyltrichloro- silanon (OTS). A tiny amount of PAA was introduced into the aqueous solution to take up metal ions for formation of a typical PILP. Calcite and BaCO3 (Fig. 4b) fibers stand on the special, OTS-printed, square areas. Based on the same idea, double-stranded and cylindrical helical BaCO3 nanofibers lay on the OTS film in the presence of a phosphonated block copolymer (Fig. 5).[45] The double-stranded helical fibers consist of two single helical grown for 1 day. . Copyright 2006, tanding on them. bH & Co. KGaA, Wein ayer of stable amorphous calcium carbonate thickness covering aragonite platelets in nacre ata and a DHBC-directed aragonite ‘‘sheaf r evidence of widespread distribution of ature and how to organize mesocrysals from cks.[12f,37] A free-standing transparent thin film (acrylic acid)) was synthesized by a spin-coating can adsorb organic dyes and metal nanopar- ifferent optical properties.[38] In another