磁性液体中非磁性小球与磁性纳米颗粒的相互作用及磁组装

利用磁性液体与聚苯乙烯小球溶液混合得到的复合磁性液体, 研究了聚苯乙烯小球和磁性纳米颗粒在外加磁场作用下的动力学过程. 实验结果表明, 当外加磁场的方向平行于样品平面时, 聚苯乙烯小球在沿着磁场的方向上表现出相互吸引而形成链状结构, 其动力学过程可分为聚苯乙烯小球被反磁化产生相互吸引而形成短链的快过程以及短链间相互吸引形成长链的慢过程; 当外加磁场的方向垂直于样品平面时, 相邻聚苯乙烯小球表现出排斥的相互作用而形成短程有序的二维结构, 当磁场强度增加到一定的阈值时, 聚苯乙烯小球和磁性纳米颗粒形成的团簇会产生相互吸引而组装成复合式的花瓣结构. 关键词： 磁性液体 磁组装 非磁性颗粒     

抗磁性物质磁悬浮可行性分析及实现

从理论和实验上说明石墨、铜等抗磁性的"非磁"物质在磁场中也受到磁场的作用力.实验中尝试了各种不同类型的永磁体序列,并利用4块一组的永磁铁序列产生梯度场,使磁铁表面上方产生可供抗磁性物质悬浮的稳定区域,成功实现了石墨的悬浮.此外,还利用顺磁性溶液及电磁铁实现了氧化铝和硅的悬浮.     

Effect of solvent evaporation on the self‐assembly of poly(3‐hexylthiophene‐2,5‐diyl) and on the film morphology during electrospray deposition

A high‐voltage rectangular pulse was applied to the electro‐spray deposition (ESD) to control the evaporation‐induced self‐assembly of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). Two groups of P3HT thin films were deposited by a series of high‐voltage rectangular pulses. Compared with the ESD driven by a constant voltage, the pulse‐driven ESD enables to probe the effect of solvent evaporation on the self‐assembly of P3HT molecules. The droplet size and the evaporation of residual solvent in the droplet determine the film morphology. Ultraviolet–visible absorption spectroscopy was used to identify the ordering of P3HT molecules in the films. The self‐assembly of P3HT molecules took place during the solvent evaporation which can be controlled by a combination of the pulse amplitude and the pulse interval. With an appropriate combination of the amplitude and the interval, the ESD produced a P3HT thin film with high chain ordering.

     

A three‐dimensional surface‐enhanced Raman scattering substrate: Au nanoparticle supramolecular self‐assembly in anodic aluminum oxide template

A three‐dimensional surface‐enhanced Raman scattering (SERS) substrate via the self‐assembly of properly sized Au nanoparticles in anodic aluminum oxide templates was designed and prepared. Au nanoparticles first underwent hydrophobic surface modification. Then, the hydrophobic Au nanoparticles self‐assembled, aggregated and formed many hot spots in the anodic aluminum oxide templates through a supramolecular interaction. We chose thiophenol as a probe molecule to evaluate the SERS enhancement ability of this three‐dimensional substrate. The enhancement factor was calculated to be 4.6 × 10⁶ under the radiation of a 785‐nm laser. By further comparing SERS signals from different points on the same substrate, we confirmed that this substrate possessed good reproducibility and could be applied for SERS detection. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering sensing on black silicon

Reactive ion etching was used to fabricate black‐Si over the entire surface area of 4‐inch Si wafers. After 20 min of the plasma treatment, surface reflection well below 2% was achieved over the 300–1000 nm spectral range. The spikes of the black‐Si substrates were coated by gold, resulting in an island film for surface‐enhanced Raman scattering (SERS) sensing. A detection limit of 1 × 10^?6 M (at count rate > 10² s^?1 . mW^?1) was achieved for rhodamine 6G in aqueous solution when drop cast onto a ～ 100‐nm‐thick Au coating. The sensitivity increases for thicker coatings. A mixed mobile‐on‐immobile platform for SERS sensing is introduced by using dog‐bone Au nanoparticles on the Au/black‐Si substrate. The SERS intensity shows a non‐linear dependence on the solid angle (numerical aperture of excitation/collection optics) for a thick gold coating that exhibits a 10 times higher enhancement. This shows promise for augmented sensitivity in SERS applications.     

Supramolecular assemblies of azobenzene‐β‐cyclodextrin dimers and azobenzene modified polycaprolactones

Click chemistry is employed to couple two β‐cyclodextrins at both ends of azobenzene moiety yielding dumbbell‐shaped amphiphiles (AZO‐β‐CD dimer) constructed by rigid aromatic building blocks as “body”, and hydrophilic cyclodextrins as “head” with almost quantitative yield and purity. Bulk aggregates formed by the self‐assembly of the supraamphiphiles through π–π stacking and hydrophobic effect are observed. Meanwhile, the rationally designed polyesters, named as AZO‐PCL with controllable molecular weights and low polydispersities, are successfully synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of p‐aminoazobenzene as initiator. In the aqueous phase, very stable spherical particles are formed by host–guest interactions between AZO‐β‐CD and AZO‐PCLs; the spherical aggregates inherit the photo‐responsiveness of azobenzene. The detailed aggregation and disaggregation behaviors are fully investigated by TEM, SEM, NMR, 2D NOESY, IR, UV and XRD measurements. Compared to the previous works, our newly developed system can be fabricated with more readily manners, avoiding tedious synthetic process; the reversible and dynamic nature of the non‐covalent interactions also can be modulated alternatively by UV or visible light. Thus, such dumbbell‐shaped supra‐amphiphiles are of great potential applications in the controlled delivery systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Correlation‐induced magnetic order and magnetic phenomena in transition‐metal δ‐doped cubic ZnO

The properties of transition‐metal (V, Cr, Mn, Fe, Co, Ni) δ‐doped ZnO are reported based on ab‐initio electronic structure calculations where the on‐site electronic correlations are included using the Hubbard parameters. The calculated electronic and magnetic properties are considerably altered with respect to usual band‐structure calculations. Most of the studied systems are found to be either half‐metals or ferromagnetic/antiferromagnetic semiconductors and thus can be employed in a variety of spintronic applications as spin‐filter materials.

     

Vibrational spectroscopy of self‐assembling aromatic peptide derivates

Peptides can assemble to supramolecular structures, of which fibers are of special biochemical and medical relevance. We employed Raman and infrared spectroscopy to elucidate the chemical integrity of fibers built from peptides and peptide derivates that contain the aromatic side groups fluorenyl and phenyl. Because the observed spectra compare very well with simulation results of the respective single molecules in vacuum, we were able to assign all observed vibrations. We found the main differences between solid phase and single molecule for O‐H and N‐H stretching and bending vibrations, owing to hydrogen bonding in solids. The fluorenyl and phenyl residues cause π‐stacking of the molecules, which barely manifests in the spectra, but clearly in the structures. Whereas hydrogen bonds provide the principal stability of the fiber backbone, aromatic π‐stacking supports the assembly to fibers, especially when electrospinning assists the molecular alignment. Copyright © 2012 John Wiley & Sons, Ltd.     

Immobilization of galactose oxidase on self‐assembled monolayers of thiols on Au and Ag surfaces

Galactose oxidase (GalOD) was immobilized on self‐assembled monolayers of thiols on silver and gold surfaces using trans‐stilbene (4,4′‐diisothiocyanate)‐2,2′disulphonic acid (DIDS) as the bridging compound. DIDS is the symmetrical bifunctional reagent that reacted with the amine moiety of the thiol and with primary amino groups of enzyme. The Raman measurement revealed that onto cysteamine‐modified silver and gold electrodes, bands corresponding to the galactose oxidase (about 694, 1076, 1274 cm^—1 on Au and 762, 1058, 1274 cm^–1 on Ag ) appeared and clearly demonstrated its immobilization onto Au and Ag surfaces. Simultaneously, we have also observed changes in the ratio of trans–gauche conformers of adsorbed cysteamine molecules. Layers revealing high content of trans conformer are transformed into layers composed mainly of cysteamine molecule in gauche conformation after galactose oxidase adsorption. These observations deliver a strong support for enzyme immobilization on cysteamine‐modified gold and silver surfaces. The surface plasmon resonance experiment gave a surface coverage of ~8.4 × 10⁷ g/cm² for gold electrode modified cysteamine using DIDS chemistry and 1.1 × 10⁷ g/cm² for the cysteamine only modified gold substrate and demonstrated that galactose oxidase layers immobilized with DIDS coupling reagent are quite stable and cannot be easily removed from the surface by treatment with a buffer solution. The surface plasmon resonance results indicated that in this method, a multilayer of galactose oxidase have been immobilized. Our new method of covalent attachment of enzymes seems to be quite promising as a new way of manufacturing biosensors. Copyright © 2012 John Wiley & Sons, Ltd.     

Self‐assembly of p‐tert‐butyl thiacalix[4]arenes and metal cations into nanoscale three‐dimensional particles

The shape of supramolecular aggregates based on stereoisomers of p‐tert‐butyl thiacalix[4]arenes functionalized with secondary, tertiary amide and hydrazide groups at the lower rim in cone, partial cone and 1,3‐alternate conformations with several metal cations were investigated by atomic force microscopy. The examined p‐tert‐butyl thiacalix[4]arenes form host–guest complexes; dimers, spherics ellipsoids and elongated nanoscale particles depending on the conformation of macrocycles, the nature of the binding centers and the nature of the metal cation. Only associates formed by p‐tert‐butyl thiacalix[4]arenes with morpholide groups at the lower rim in cone conformation with silver cations exhibited a higher antimicrobial activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Self‐Organization of Anisotropic and Binary Colloids in Thermo‐Switchable 1D Microconfinement

Anisotropic and binary colloids self‐assemble into a variety of novel supracolloidal structures within the thermo‐switchable confinement of molecular microtubes, achieving structuring at multiple length scales and dimensionalities. The multistage self‐assembly strategy involving hard colloidal particles and a soft supramolecular template is generic for colloids with different geometries and materials as well as their binary mixtures. The colloidal architectures can be controlled by colloid shape, size, and concentration. Colloidal cubes align in chains with face‐to‐face arrangement, whereas rod‐like colloids predominantly self‐organize in end‐to‐end configurations with their long axis parallel with the long axis of the microtubes. The 1D microconfinement imposed on binary mixtures of anisotropic and isotropic colloids further increases the diversity of colloid‐in‐tube structures. In cube–sphere mixtures, cubes may act as additional confiners, locking in colloidal sphere chains, while a “colloidal Morse code” is generated where rods and spheres alternate in the case of rod–sphere mixtures. The versatile confined colloidal superstructures including their thermoresponsive assembly and disassembly are relevant for the development of stimulus–responsive materials where controlled release and encapsulation are desired.     

Phosphonated Polyethylenimine‐Coated Nanoparticles: Size‐ and Zeta‐Potential‐Adjustable Nanomaterials

Novel partially phosphonated polyethylenimine polymers are developed in order to control the modification of nanoparticle (NP) surfaces. This polymer is built by an accessible one‐step process. The numerous phosphonate functions assume both a strong covalent anchoring on metal oxide NPs and a modulation of electric charges, while amino groups are associated with dispersion preservation and subsequent biofunctionalization. The zwitterionic nanomaterials obtained display a good stability toward pH and ionic strength. According to the selected percentage of phosphonation and the polymer size, zeta potential, and diameter of the particles are controlled.     

Tunable magnetic anisotropy of CoFe2O4 nanopillar arrays released from BiFeO3 matrix

We deposited epitaxial BiFeO₃–CoFe₂O₄ (BFO–CFO) self‐assembled thin films on (001) SrTiO₃ (STO) substrates. We find that a combined annealing and etching process could remove the BFO matrix, thereby resulting in free‐standing CFO nanopillar arrays. Scanning electron and atomic force microscopies showed well separated CFO nanopillars, which were very similar to the original CFO ones in the self‐assembled structure. Finally, comparison of the magnetic hysteresis loops before and after removal of the BFO matrix showed a significant decrease of the coercive field and a dramatic decrease in the strain dominated magnetic anisotropy. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐Assembly of Spherical or Rod‐Shaped Magnetic Nanocrystals onto Curved Substrates Governed by the Radius of Curvature

The way the assembly of colloidal nanostructures into heterostructures takes place substantially affects their physicochemical properties and performance. The layer‐by‐layer self‐assembly has shown in this regard a huge ability to drive nanomaterials onto curved substrates. Hindering the clustering to improve the distribution and allocation of nanoparticles on these assemblies can be partially controlled by geometric frustration, herein demonstrated driving magnetic nanocrystals with different morphology onto spherical substrates of tuned curvature.     

Self‐assembly of a [2]pseudorotaxane complex by the threading of a nitrobenzimidazol‐based guest on dibenzo‐24‐crown ether host

A new derivative of the previously reported 1,2‐bis(benzimidazol‐2‐yl)ethane motif, cation [1H₂]²⁺, was synthesized under microwave irradiation and fully characterized by solution NMR, high‐resolution mass spectrometry, cyclic voltammetry and X‐ray crystallography. This cation presents a linear geometry and incorporates nitro substituents as electrochemical handles. In solution, cation [1H₂]²⁺, is capable of threading the cavity of dibenzo‐24‐crown‐8 ether host (DB24C8) giving rise to a [2]pseudorotaxane complex [1H₂?DB24C8]²⁺, regardless of the counterion, [CF₃SO₃]^? or [CF₃COO] ^?. The interpenetrated structure of [1H₂?DB24C8]²⁺ was proven by solution NMR and X‐ray crystallography. This host–guest complex is held together by several non‐covalent interactions, such as hydrogen bonding and ion‐dipole. An electrochemical study of [1H₂]²⁺ in the presence of variable amounts of DB24C8 was performed; due to the irreversible redox behavior of cation [1H₂]²⁺, it was not possible to electrochemically control the association/dissociation process with DB24C8. Copyright © 2014 John Wiley & Sons, Ltd.     

Multiscale electromagnetic SERS enhancement on self‐assembled micropatterned gold nanoparticle films

In this work, we demonstrate a cascaded, multiplicative electromagnetic enhancement effect in surface‐enhanced Raman scattering (SERS) on periodically micropatterned films made of colloidal gold nanoparticles, prepared by a self‐assembly approach, without implying lithography procedures. The multiplicative enhancement effect is obtained by combining surface plasmon near‐field enhancement due to nanoscale features with far‐field photonic coupling by periodic microscale features. The effect is observed for both internal Raman reporters (molecules attached to the Au colloids before their assembly) and external Raman probes (molecules adsorbed on the samples after film assembly). The ability of the patterned films for far‐field light coupling is supported by reflectivity spectra, which present minima/maxima in the visible spectral range. Finite‐difference time‐domain computer simulations of the electric field distribution also support this interpretation. The fabricated dual‐scale SERS substrates exhibit a good spot‐to‐spot reproducibility and time stability, as proved by the SERS response over a time scale longer than 1 month. The experimental demonstration of this cascaded electromagnetic enhancement effect contributes to a better understanding of SERS and can affect future design of SERS substrates. Moreover, such dual‐scale colloidal films prepared by convective self‐assembly can be of general interest for the broader field of nanoparticle‐based devices. Copyright © 2014 John Wiley & Sons, Ltd.     

Raman imaging and stress quantification in self‐assembled graphene oxide fiber ‘Latin Letters’

To probe the intrinsic stress distribution in terms of spatial Raman shift (ω) and change in the phonon linewidth (Γ), here we analyze self‐assembled graphene oxide fibers (GOF) ‘Latin letters’ by confocal Raman spectroscopy. The self‐assembly of GOF ‘Latin letters’ has been explained through surface tension, π–π stacking, van der Waals interaction at the air–water interface and by systematic time‐dependent investigation using field emission scanning electron microscopy analysis. Intrinsic residual stress due to structural joints and bending is playing a distinct role affecting the E_2g mode (G band) at and away from the physical interface of GOF segments with broadening of phonon linewidth, indicating prominent phonon softening. Linescan across an interface of the GOF ‘letters’ reveals Raman shift to lower wavenumber in all cases but more so in ‘Z’ fiber exhibiting a broader region. Furthermore, intrinsic stress homogeneity is observed for ‘G’ fiber distributed throughout its curvature with negligible shift corresponding to E_2g mode vibration. This article demonstrates the significance of morphology in stress distribution across the self‐assembled and ‘smart‐integrable’ GOF ‘Latin letters’. Copyright © 2016 John Wiley & Sons, Ltd.