挥发诱导自组装法制备结构有序的有机-无机纳米复合材料*

挥发诱导自组装方法（EISA）可以用来模拟自然界中的有机-无机杂化材料的纳米有序结构的形成过程。这是一种新兴的、有效的合成结构有序纳米复合材料的方法,其具有快速、简便、高效的特点。本文就挥发诱导自组装方法的原理及利用该方法制备结构有序的有机-无机纳米复合材料(MSC材料)的机理、有关影响MSC材料有序结构形成的因素作了详细探讨,并对利用EISA方法制备MSC材料的研究和发展前景进行了展望。     

帽状锌纳米结构的制备及其表面等离子体共振特性

利用真空热蒸发法在二氧化硅纳米粒子单层膜上沉积锌薄膜制备了帽状锌纳米结构. 采用透射电镜(TEM)、扫描电镜(SEM)、X射线衍射(XRD)和紫外-可见吸收光谱(UV-Vis)对样品的形貌、结构和光学特性进行了表征和研究. SEM照片表明所得到的复合纳米粒子为不完全包裹的帽状结构, 且其表面较粗糙. XRD分析结果显示在二氧化硅纳米粒子上沉积的锌膜呈多晶六角密堆结构. 吸收光谱研究表明, 帽状锌纳米结构在570～760 nm范围内具有明显的由纵向双极子表面等离子体共振引起的吸收峰, 且随着锌帽层厚度的增加或二氧化硅内核粒径的增大, 该吸收峰逐渐红移; 当内核粒径增大到500 nm时, 帽状锌纳米结构在412 nm附近还出现了一个四极子共振峰.     

原位复合法制备层状结构的壳聚糖/羟基磷灰石纳米材料

用原位复合法制备了高性能的壳聚糖/羟基磷灰石(CS/HA)纳米复合材料.用预先沉积的壳聚糖膜将含有羟基磷灰石前驱体的壳聚糖溶液与凝固液隔离,同时控制壳聚糖沉积与羟基磷灰石前驱体转化为羟基磷灰石的过程,使其缓慢且有序地进行.当pH值改变时,质子化的壳聚糖分子链在负电层诱导下有序沉积并形成层状结构与羟基磷灰石原位生成CS/HA,并实现二者分子级复合.XRD和TEM测试证实原位生成的磷酸盐是羟基磷灰石,且其颗粒长约为100nm,宽30～50nm.SEM结果表明,用原位复合法制备的材料具有层状结构,CS/HA(质量比100/5)纳米复合材料弯曲强度高达86MPa,比松质骨的高3～4倍,相当于密质骨的1/2,有望用于可承重部位的组织修复材料.     

一维ZnO纳米棒阵列的水热合成

以锌片为衬底,用硝酸锌和氨水为原材料,在90 ℃时由水热法合成了有序生长的ZnO纳米棒阵列。 纳米棒长度为500～800 nm,直径约为100 nm,SEM图片显示该纳米棒顶部截面是六边形。 XRD谱表明,ZnO纳米棒为六方纤锌矿结构。 考察了制备温度、时间和物料比对合成的材料形貌和结构的影响。     

介孔二氧化硅空心纳米蠕虫的制备

用L-苯丙氨酸衍生物的自组装体作为模板,四甲基氢氧化铵为催化剂,经溶胶-凝胶过程,制备出蠕虫状介孔二氧化硅纳米空心结构材料.表征结果显示,该二氧化硅的长度约为100～150nm,直径约30～50nm.介孔孔道平行于壳的表面,孔径为3.8nm.     

双孔道管状有序介孔炭对维生素B12的吸附缓释性能

通过纳米铸型法,以硅基介孔分子筛SBA-15为模板,糠醇为碳源,草酸作为聚合催化剂合成了具有双孔道管状有序介孔炭CMK-5.利用粉末X射线衍射(XRD)、扫描电子显微镜(SEM)和氮气物理吸附法等对其结构进行了表征.结果表明合成的CMK-5具有有序结构,比表面积和孔容积分别高达1856 m2·g-1和2.10 cm3·g-1,在3.1和5.5nm具有集中的双孔分布.由于独特的双孔道结构特点,CMK-5在120 min内快速吸附维生素B12至平衡,吸附量高达943 mg·g-1,远高于商用活性炭.CMK-5吸附维生素B12后可以直接用于缓释,动态缓释浓度维持在～9 mg·L-1,适用于维生素B12分子在人体内的缓释.     

高度有序ZnO-SnO_2异质外延枝状纳米结构的制备及其光催化性质研究

采用一种简单的热蒸发法制备了高度有序的ZnO-SnO2异质外延枝状纳米结构。制备过程分两步进行:首先,在氧化铝片基底上制备SnO2纳米线;然后,以此SnO2纳米线为模板在其上生长ZnO纳米线。用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)等手段对产物的形貌、结构进行了表征。XRD表征结果证实第一步和第二步生长的产物分别为SnO2和ZnO。SEM观察结果表明,第一步热蒸发得到直径约100nm、长度达几十微米的SnO2纳米线,第二步热蒸发后得到以第一步SnO2纳米线为主干、沿四个方向有序排列的枝状ZnO纳米结构。TEM观察结果表明,ZnO枝状纳米线沿[001]方向由SnO2纳米线(-101)晶面外延生长。所制备的枝状纳米结构由于具有巨大的比表面积,且外延异质结可以促进电荷的分离和快速转移,因此非常适合于光催化应用。该ZnO-SnO2异质外延枝状纳米结构用于光催化降解甲基橙,表现出优异的性能。     

三元荆棘状Zn1-xCdxO纳米结构及其光致发光特性

以锌粉(Zn)、镉粉(Cd)为源材料, 金(Au)做催化剂, 采用热蒸发法, 在硅(Si)衬底上制备出掺Cd摩尔分数为6.7%的三元荆棘状Zn1-xCdxO单晶纳米结构. 荆棘状纳米结构样品的主干直径均一, 约为100 nm. 主干两侧刺的直径和长度分别约为10和100 nm. 由于Cd替位原子对ZnO带隙的调节作用, 样品的近带边(NBE)紫外(UV)发射从3.37 eV红移到3.13 eV. 结果表明, 氧气(O2)分压是形成荆棘状Zn1-xCdxO纳米结构的重要条件.     

同轴静电纺丝技术制备Y_2O_3:Eu~(3+)@SiO_2豆角状纳米电缆与表征

采用同轴静电纺丝技术,以氧化钇、氧化铕、正硅酸乙酯(C8H20O4Si)、无水乙醇、PVP和DMF为原料,成功制备出大量的Y2O3:Eu3+@SiO2豆角状纳米电缆.用TG-DTA,XRD,SEM,TEM和荧光光谱等分析技术对样品进行了系统地表征.结果表明,得到的产物为Y2O3:Eu3+@SiO2豆角状纳米电缆,以无定型SiO2为壳层,晶态Y2O3:Eu3+球为芯,电缆直径约为200nm,内部球平均直径约150nm,壳层厚度约为25nm,电缆长度300μm.纳米电缆内部为球状结构,沿着纤维长度方向有序排列,形貌均一.Y2O3:Eu3+@SiO2豆角状纳米电缆在246nm紫外光激发下,发射出Eu3+离子特征的波长为614nm的明亮红光.对其形成机理进行了初步讨论.     

三元荆棘状Zn1-xCdxO纳米结构及其光致发光特性

以锌粉(zn)、镉粉(cd)为源材料,金(Au)做催化剂,采用热蒸发法,在硅(si)衬底上制备出掺Cd摩尔分数为6.7%的三元荆棘状Zn1-xCdxO单晶纳米结构.荆棘状纳米结构样品的主干直径均一,约为100 nm.主干两侧刺的直径和长度分别约为10和100 nm.由于Cd替位原子对ZnO带隙的调节作用,样品的近带边(NBE)紫外(UV)发射从3.37 ev红移到3.13 eV.结果表明,氧气(O2)分压是形成荆棘状Zn1-xCdxO纳米结构的重要条件.     

Tuning the orientation of an antigen by adsorption onto nanostriped templates

We investigate the adsorption of a globular protein (P.69 pertactin, also known as antigen 69k) on protein-repellent hydrophilic substrates bearing regularly spaced hydrophobic nanostripes, for stripe widths comprised between 20 and 160 nm. Protein adsorption is shown to be remarkably well-controlled by the templating substrates, with a near-to-perfect reproduction of stripes by the protein monolayer down to 20 nm width, except for a 5-10 nm broadening. However, whereas the ellipsoidal protein forms a dense monolayer with random orientation of its long axis for large stripe widths, it adsorbs in a predominantly side-on (flat-on) orientation for stripe widths below 50 nm, due to the easier reorientation (interfacial relaxation) of the proteins adsorbed at the edges of the stripes, which experience a decreased lateral interaction. These results show that protein confinement in regions of a size similar to their dimensions can be used to tune their orientation, which may be of interest for applications in high-density sensor devices.     

Nanoscale patterning in mixed fluorocarbon-hydrocarbon phospholipid bilayers

A growing body of literature suggests that fluorocarbons can direct self-assembly within hydrocarbon environments. We report here the fabrication and characterization of supported lipid bilayers (SLBs) composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a synthetic, fluorocarbon-functionalized analogue, 1. AFM investigation of these model membranes reveals an intricate, composition-dependent domain structure consisting of approximately 50 nm stripes interspersed between approximately 1 microm sized domains. Although DSC of 1 showed a phase transition near room temperature, DSC of DPPC:1 mixtures exhibited complex phase behavior suggesting domain segregation. Finally, temperature-dependent AFM of DPPC:1 bilayers shows that, while the stripe structures can be melted above the Tm of 1, the stripes and domains result from immiscibility of the hydrocarbon and fluorocarbon lipid gel phases. Fluorination appears to be a promising strategy for chemical self-assembly in two dimensions. In particular, because no modification is made to the lipid headgroups, it may be useful for nanopatterning biologically relevant ligands on bilayers in vitro or in living cells.     

The incommensurately modulated structures of the perovskites NaCeMnWO6 and NaPrMnWO6

The structures of the doubly ordered perovskites NaCeMnWO(6) and NaPrMnWO(6), with rock salt ordering of the Mn(2+) and W(6+)B-site cations and layered ordering of the Na(+) and (Ce(3+)/Pr(3+)) A-site cations, have been studied by transmission electron microscopy, electron diffraction, neutron and synchrotron X-ray powder diffraction. Both compounds possess incommensurately modulated crystal structures. In NaCeMnWO(6) the modulation vector (with reference to the ideal ABX(3) perovskite subcell) is q ≈ 0.067a* (～58.7 ?) and in NaPrMnWO(6)q ≈ 0.046a* (～85.3 ?). In both compounds the superstructures are primarily the two-dimensional chessboard type, although some crystals of NaCeMnWO(6) were found with one-dimensional stripes. In some crystals of NaPrMnWO(6) there is a coexistence of chessboards and stripes. Modeling of neutron diffraction data shows that octahedral tilting plays an important role in the structural modulation.     

Self-assembly of virus particles on flat surfaces via controlled evaporation

Dynamic self-assembly of nonvolatile solutes via controlled solvent evaporation has been exploited as a simple route to create a variety of hierarchically assembled structures. In this work, two glass slides were used to form a confined space in which a solution of a rodlike nanoparticle, tobacco mosaic virus (TMV), was evaporated to create large-scale stripe patterns. The height and width of the stripes are dependent on the TMV concentration. The large-scale-patterned surfaces can be applied to control surface hydrophobicity and direct the growth of bone marrow stromal cells. We systematically studied the effects of stripe width and height on surface hydrophobicity using optical microscopy, atomic force microscopy, and contact angle measurements. This technique offers a facile approach to form 2D patterns on a large surface from a wide range of proteins as well as other biomacromolecules.     

Shear-induced assembly of graphene oxide particles into stripes near surface

We report the shear-induced assembly of graphene oxide (GO) particles into periodic stripe-like patterns near the surface. These stripe-like patterns, which have an average periodic length of 100–250 μm, are aligned in a wavy manner along the normal to the flow direction. The self-assembled GO structures are investigated at different depths using three different analysis methods, namely, reflective microscopy observations of the photonic-crystalline GO dispersion, polarized optical microscopy, and fluorescence confocal laser scanning microscopy. The surface microstructures observed in reflection mode are different from the shear-induced band structures formed in bulk thermotropic liquid crystals and liquid crystal polymers, in terms of the shape and scale of the stripes. Further, there is also a difference in terms of the dependence of the stripe width on the shear rate. The observations suggest that the stripes are formed because of a competition between the stable surface-field-induced planar alignment of the GO particles near the surface and their relatively unstable shear-induced vertical alignment in the bulk. The findings of this study should advance our understanding of GO assembly under shear stress. Further, the proposed method is a novel one for inducing the assembly of GO particles into microstructures shaped as thread-like stripes.     

Locking of Turing patterns in the chlorine dioxide-iodine-malonic acid reaction with one-dimensional spatial periodic forcing

We use the photosensitive chlorine dioxide-iodine-malonic acid reaction-diffusion system to study wavenumber locking of Turing patterns with spatial periodic forcing. Wavenumber-locked stripe patterns are the typical resonant structures that labyrinthine patterns exhibit in response to one-dimensional forcing by illumination when images of stripes are projected on a working medium. Our experimental results reveal that segmented oblique, hexagonal and rectangular patterns can also be obtained. However, these two-dimensional resonant structures only develop in a relatively narrow range of forcing parameters, where the unforced stripe pattern is in close proximity to the domain of hexagonal patterns. Numerical simulations based on a model that incorporates the forcing by illumination using an additive term reproduce well the experimental observations. These findings confirm that additive one-dimensional forcing can generate a two-dimensional resonant response. However, such a response is considerably less robust than the effect of multiplicative forcing.     

Geometry-dependent stripe rearrangement processes induced by strain on preordered microwrinkle patterns

A preordered microwrinkle pattern on a metal-capped surface of a soft elastomer is employed to elucidate the elementary buckling phenomenon during strain-induced stripe rearrangement processes. The preordered one-dimensional stripe tends to align perpendicular to the direction of strain reversibly when lateral compressive strain is applied on the substrate at some angle phi with respect to the stripe orientation. For any value of strain, the film surface can be decomposed in domains containing stripes with two different orientations, namely the original and applied strain orientations. As strain is increased, the domains of the second type of stripes progressively grow and invade the whole surface. Interestingly, the domain shapes during growth are composed of parallelogram units that simply depend on phi and stripe wavelength. Moreover, domain growth proceeds in characteristic directions depending on the shape of the domain unit.     

Grid pattern of nanothick microgel network

A novel grid pattern of two kinds of nanothick microgels was developed by alternate patterning using photolithography. At first, 100-microm-wide nanothick PAAm microgel stripes were grafted on a polystyrene surface by UV irradiation of the photoreactive azidobenzoyl-derivatized polyallylamine-coated surface through a photomask with 100-microm-wide stripes. Then, a second set of 100-microm-wide nanothick PAAc microgel stripes were grafted across the PAAm-grated polystyrene surface by UV irradiation of the photoreactive azidophenyl-derivatized poly(acrylic acid)-coated surface through a photomask placed perpendicularly to the first set of PAAm microgel stripes. The PAAc microgel stripe pattern was formed over the PAAm microgel stripe pattern. The cross angle of the two microgel stripes could be controlled by adjusting the position of the photomask when the second microgel pattern was prepared. Swelling and shrinking of the microgels were investigated by scanning probe microscopy (SPM) in an aqueous solution. SPM observation indicated that the thickness of the gel network was 100 to 500 nm. The regions containing PAAm, PAAc, and the PAAc-PAAm overlapping microgels showed different swelling and shrinking properties when the pH was changed. The PAAm microgel swelled at low pH and shrank at high pH whereas the PAAc microgel swelled at high pH and shrank at low pH. However, the PAAc-PAAm overlapping microgel did not change as significantly as did the two microgels, indicating that the swelling and shrinking of the two gels was partially offset. The pH-induced structural change was repeatedly reversible. The novel grid pattern of nanothick microgels will find applications in various fields such as smart actuators, artificial muscles, sensors, and drug delivery systems as well as in tissue engineering and so forth.     

Colloidal liquid crystal type assemblies of spheroidal polystyrene core/polyglycidol‐rich shell particles (P[S/PGL]) formed at the liquid‐silicon‐air interface by a directed dewetting process

A method for the preparation of stripe‐like monolayers of microspheroids is described. The particles were obtained from polystyrene core/polyglycidol‐rich shell microspheres by stretching poly (vinyl alcohol) films that contain embedded particles. The stretching was performed under controlled conditions at temperatures above the T_g of the films and particles. The elongated films were dissolved in water, and the microspheroids were subsequently removed and purified from the poly (vinyl alcohol). The aspect ratio (AR) of the particles, which denotes the ratio of the lengths of the longer to shorter particle axes, was determined by the film elongation. The AR values were in the range of 2.9‐7.7. Spheroidal particles with various ARs were deposited onto silicon wafers from an ethanol (EtOH) suspension. The particle concentration and volume of the suspension were the same in each experiment. Evaporation of the EtOH yielded stripes of spherical particles packed into nematic‐type colloidal crystals and assembled into monolayers. The orientation of the stripes after ethanol evaporation was perpendicular to the triphasic (silicon‐ethanol‐air) interface along the silicon substrate. The adsorbed stripes on the wafers were characterized in terms of their interstripe distance (ID), stripe width, and crystal domain size. Nematic‐type spheroid arrangements in the stripes were the dominant structure, which enabled denser packing of the particles into colloidal crystals than that allowed by the smectic‐type arrangements. Furthermore, the number of spheroids adsorbed per surface unit of the silicon wafers was similar for all ARs, but the width and frequency of the spheroid stripes adsorbed on the wafers were different.     

CdSe Nanoplatelets: Living Polymers

Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self‐assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face‐to‐face self‐assembly of CdSe nanoplatelets into micron‐long polymer‐like threads made of up to ～1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re‐dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1‐dimensional structures are flexible and feature a “living polymer” character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends.