Effects of organic ligands, electrostatic and magnetic interactions in formation of colloidal and interfacial inorganic nanostructures

This paper discusses effects of organic ligands, electrostatic and magnetic interactions involved in morphological control of chemically synthesized inorganic nanostructures including colloid and planar systems. The special attention was concentrated on noble metal (gold and palladium) nanoparticles and nanostructures formed at the gas-liquid interface. The analysis of experimental data showed that electrostatic and ligand-related interactions influence very strongly on the metal nanostructure morphology. The hydrophobicity of ligand, charge and binding affinity to inorganic phase are important factors influencing the morphology of inorganic nanostructures formed in a layer at the gas/liquid interface by the interfacial synthesis method. The important point of this method is the quasi two-dimensional character of reaction area and possibilities to realize ultimately thin and anisotropic dynamic monomolecular reaction system with two-dimensional diffusion and interactions of precursors, intermediates and ligands resulting in planar growth and organization of inorganic nanoparticles and nanostructures in the plain of Langmuir monolayer. The morphology of resulting inorganic nanostructures can be controlled efficiently by variations of growth conditions via changes in state and composition of interfacial planar reaction media with the same precursor, and by variations of composition of adjacent bulk phases. The extreme anisotropy and heterogeneity of two-dimensional interfacial reaction system allows creating conditions when growing inorganic particles floating on the aqueous phase surface interact selectively with hydrophobic water-insoluble ligands in interfacial monolayer or with hydrophilic bulk-phase ligands, or at the same time with ligands of different nature present in monolayer and in aqueous phase. The spatial anisotropy of interfacial reaction system and non-homogeneity of ligand binding to inorganic phase gives possibilities for growth of integrated anisotropic nanostructures with unique morphologies, in particularly those characterized by very high surface/volume ratio, high effective perimeter, and labyrinth-like structure. In a case of magnetic nanoparticles dispersed in colloids specific magnetic dipolar interactions can result in formation of chains, rings and more complex nanoparticulate structures or separated highly anisotropic nanoparticles. Theoretical considerations indicate to the importance of system dimensionality in relation to the energy balance which determines specific features of structure organization in planar charged metallic and magnetic nanostructures. For example, a requirement of Coulomb energy minimum, the possibility of free electron redistribution and strengthened attractive interactions between particles in metallic nanostructures can explain formation of very branchy systems with extremely high "effective perimeter". The obtained experimental and literature data show that system dimensionality, organic ligand nature along with electrostatic and magnetic interactions are most important factors of morphological control of chemically synthesized inorganic nanomaterials. The understanding and appropriate exploitation of these factors can be useful for further developments of efficient nanofabrication techniques based on colloidal and interfacial synthetic methods.     

Langmuir膜及LB膜中的金属参与

本文主要介绍了金属离子与Langmuir膜及LB膜相互作用中静电、配位等作用方式及其对膜相态和分子二维排列的影响。在此基础上探讨了Langmuir膜对金属离子的识别与传感。以Langmuir膜和LB膜为二维模板诱导无机盐定向生长作为金属/单分子膜结合的重要应用在文中也进行了讨论。通过举例展示了金属离子参与的Langmuir膜和LB膜催化有机反应的特点。最后对金属参与的Langmuir膜和LB膜在功能化和器件化等方面的研究也作了论述， 并通过介绍金属螯合类脂分子的Langmuir膜在蛋白质等生物大分子界面定向聚集研究中的应用表明了金属参与的Langmuir膜及LB 膜在生命科学研究中的意义。全文贯穿了金属结合调节Langmuir膜和LB膜组装结构以及通过金属结合导入功能基团进行有序组装的思想。     

Structure of organized organic mono- and multi-layer films

A review is presented of some interesting structural properties of monomolecular layers at the air/water interface (Langmuir films) and of organized multilayer structures of organic molecules (Langmuir-Blodgett films). In particular multilayer films of bipolar lipids from archaebacteria and of proteins are considered, together with single-electron junction quantum effects in parallel, special emphasis is given to some recently developed experimental techniques based on X-ray scattering. supramolecular assemblies consisting of multilayers containing nanoparticles.     

Computer simulation of the microstructure of a nanoparticle monolayer formed under interfacial compression

The uniaxial compression of a monolayer of nanosized monodisperse spherical particles adsorbed at a planar interface is simulated using the Brownian dynamics technique. Initially, the particles spread at the interface form crystalline loosely interconnected clusters. As the interface is compressed, the gaps between the clusters are removed and a close-packed monolayer is formed. At this stage, the structure of the interface consists of two-dimensional crystalline grains separated by defect boundaries. Further interfacial compression induces desorption of nanoparticles at these boundaries and creates striplike patterns of a secondary adsorbed layer. The structural features observed show remarkable agreement with recent experimental studies of the compression of gold nanoparticles in a Langmuir trough.     

Formation of silver nanoparticles at the air-water interface mediated by a monolayer of functionalized hyperbranched molecules

Nanofibrillar micellar structures formed by the amphiphilic hyperbranched molecules within a Langmuir monolayer were utilized as matter for silver nanoparticle formation from the ion-containing water subphase. We observed that silver nanoparticles were formed within the multifunctional amphiphilic hyperbranched molecules. The diameter of nanoparticles varied from 2-4 nm and was controlled by the core dimensions and the interfibrillar free surface area. Furthermore, upon addition of potassium nitrate to the subphase, the Langmuir monolayer templated the nanoparticles' formation along the nanofibrillar structures. The suggested mechanism of nanoparticle formation involves the oxidation of primary amino groups by silver catalysis facilitated by "caging" of silver ions within surface areas dominated by multibranched cores. This system provides an example of a one-step process in which hyperbranched molecules with outer alkyl tails and compressed amine-hydroxyl cores mediated the formation of stable nanoparticles placed along/among/beneath the nanofibrillar micelles.     

芳香席夫碱衍生物在有序分子膜中的相行为与二维-三维形变

研究了芳香席夫碱的设计合成、界面相行为以及与铜离子的配位过程,并与离位合成的铜复合物的界面组装行为进行了对比.利用表面压-面积等温线、紫外光谱、红外光谱、原子力显微镜等一系列实验方法来详细表征组装膜.结果表明,席夫碱配体与铜复合物均可在气液界面上形成稳定的有序组装膜,并可以转移到固体基片上构筑多层膜.进而,席夫碱配体在纯水界面上表现出奇特的相变.在相变点前后,二维的平膜变化成了三维的纤维状组装结构.然而,对于铜离子亚相上的组装过程却没有出现较大的变化.两者之间明显的差异可归因于在气液界面超分子组装过程中的分子构型以及疏水性能的不同引起的.目前的工作为制备和调控有序组装膜提供了有益探索.     

Control of CaCO3 crystallization by demixing of monolayers

In this paper we describe how to template a demixed monolayer into a spatially patterned inorganic replica. For this purpose a new amphiphilic monomer was synthesized which can be polymerized both in solution and in the monolayer of a Langmuir-Blodgett (LB) trough. Since it inhibits the crystallization of CaCO3, it can be used--in combination with stearic acid (nucleation-promotor)--to control CaCO3 crystals formed under the monolayer. Investigations of the two-component monolayer (Langmuir isotherms and AFM measurements of transferred films) show--in the biphasic region--demixing in solid analogue stearic acid domains and the liquid analogue phase of the monomer. Crystallization of CaCO3 starts under the stearic acid domains whose size varies from less than 100 nm to several tens of micrometers. The addition of poly(acrylic acid) into the subphase hinders the three-dimensional growth of CaCO3 crystals from the monolayer into the solution. Thus, it becomes possible to transfer the pattern of the demixed domains into an inorganic replica of CaCO3.     

Interfacial assembly and host-guest interaction of anthracene-conjugated L-glutamate dendron with cyclodextrin at the air/water interface

The interfacial assembly of photo-induced dimerization of atypical anthracene-containing amphiphilic dendron and host-guest interaction with γ-cyclodextrin has been investigated.It has been proved that even without long alkyl chain the amphiphilic dendron could still form stable Langmuir monolayer at the air/water interface.Through the host-guest interaction,γ-cyclodextrin can be used to encapsulate two headgroups of amphiphilic dendron in the antiparallel direction.However,the formed host-guest complex was sensitive to the surface pressure.Slight compression of surface pressure led amphiphilic dendron to reassemble into nanofibers through the strong π-π stacking between headgroups.On the other hand,under in sitv irradiation,the amphiphilic dendron was stabilized in the cavity of γ-cyclodextrin through headgroup dimerization and the host-guest complex further irregularly aggregated to nanoparticles.Meanwhile,γ-cyclodextrin,as a silencer,blocked the supramolecular chirality transfer.Our conclusion was demonstrated through UV/vis,FT-IR,CD spectrum and AFM images,respectively.     

Langmuir–Blodgett Monolayers and Films of Alkylated Tetraazacrowns Containing Metal Ions and Nanoparticles

The behavior of individual 1,7-dicetyltetraaza-12-crown-4 and its mixture with 1,4,7,10-tetracetyltetraaza-12-crown-4 in the Langmuir monolayers at the subphases containing Cu(II) ions or colloidal gold particles is studied. Based on the compression isotherms, the complexing ability of these amphiphilic cyclenes in a monolayer at the surface of aqueous dilute solutions of copper salt is established. It was shown that the fraction of complexes in a monolayer is proportional to the copper ion concentration in the subphase. Using surface balance, atomic force microscopy, and electron microscopy methods, it was revealed that the monolayer of dicetylcyclene at the surface of gold hydrosol binds nanoparticles from the subphase; the number of particles bound by the monolayer is proportional to their content in the hydrosol. The Langmuir–Blodgett films (LBF) of dicetylcyclene are prepared; their ability to bind copper ions from solution was disclosed by quartz crystal microbalance. The LBFs of dicetylcyclene containing gold nanoparticles in each layer are assembled.     

Synthesis and assembly of gold nanoparticles in organized molecular films of gemini amphiphiles

Generation and assembly of gold nanostructures were investigated in the organized molecular films of a series of gemini amphiphiles. The chloroauric acid, dissolved in the aqueous subphase, was incorporated into the monolayers of the gemini amphiphiles containing ethyleneamine spacers through an interfacial assembly. The in situ formed complex monolayers were transferred onto solid substrates, and gold nanoparticles were generated in the film by a chemical or photochemical reduction. Discrete gold nanoparticles with an absorption maximum at 550 nm were generated in the films by photoirradiation, while different gold nanostructures were obtained by chemical reduction. Depending on the chemical reductant, various shape and assembly of gold nanostructures were obtained. When reduced by hydroquinone, a tree-branched assembly of the nanoparticles was obtained and the film showed a broad band centered at around 900 nm. When NaBH 4 was applied, crooked nanowires or assembly of nanoparticles were obtained, depending on concentration, and the film showed absorption at 569 or 600 nm. Furthermore, by combining the photochemical and chemical reduction methods, i.e., the chloroaurate ion-incorporated film was initially irradiated with UV light and then subjected to chemical reduction, the optical absorption of the formed gold nanostructures can be regulated.     

Electrochemical synthesis of SnO2 films containing three-dimensionally organized uniform mesopores via interfacial surfactant templating

SnO2 films containing organized mesopores and nanocrystalline frameworks with easily removable surfactant templates were produced electrochemically using interfacial amphiphilic assemblies formed on the working electrode as a template.     

Langmuir monolayers as unique physical models

Physico-chemical processes at air/liquid interfaces are of paramount importance in nature. The Langmuir technique offers the possibility of forming a well-defined monolayer of amphiphilic molecules under study at the air/liquid interface, with a unique control of the area per molecule and other experimental conditions. Despite being a traditional technique in Colloid and Interface science, there is an ever growing interest in Langmuir studies. Herein, recent developing fields of research currently taking advantage of the Langmuir technique are reviewed, comprising the interfacial structure of: water, biomolecules and inorganic/organic hybrids. The good state of the Langmuir technique at present and the foreseeable increase of its usage are discussed.     

Preparation of microscopic and planar oil-water interfaces that are decorated with prescribed densities of insoluble amphiphiles

Langmuir monolayers (monolayers of insoluble molecules formed at the surface of water), and associated Langmuir-Blodgett/Schaefer monolayers prepared by transfer of Langmuir films to the surfaces of solids, are widely used in studies aimed at understanding the physicochemical properties of biological and synthetic molecules at interfaces. In this article, we report a general and facile procedure that permits transfer of Langmuir monolayers from the surface of water onto microscopic and planar interfaces between oil and aqueous phases. In these experiments, a metallic grid supported on a hydrophobic solid is used to form oil films with thicknesses of 20 mum and interfacial areas of 280 mum x 280 mum. Passage of the supported oil films through a Langmuir monolayer is shown to lead to quantitative transfer of insoluble amphiphiles onto the oil-water interfaces. The amphiphile-decorated oil-water interfaces hosted within the metallic grids (i) are approximately planar, (ii) are sufficiently robust mechanically so as to permit further characterization of the interfaces outside of the Langmuir trough, (iii) can be prepared with prescribed and well-defined densities of amphiphiles, and (iv) require only approximately 200 nL of oil to prepare. The utility of this method is illustrated for the case of the liquid crystalline oil 4-pentyl-4'-cyanobiphenyl (5CB). Transfer of monolayers of either dilauroyl- or dipalmitoylphosphatidylcholine (DLPC and DPPC, respectively) to the nematic 5CB-aqueous interface is demonstrated by epifluorescence imaging of fluorescently labeled lipid and polarized light imaging of the orientational order within the thin film of nematic 5CB. Interfaces prepared in this manner are used to reveal key differences between the density-dependent phase properties of DLPC and DPPC monolayers formed at air-water as compared to that of nematic 5CB-aqueous interfaces. The methodology described in this article should be broadly useful in advancing studies of the interfacial behavior of synthetic and biological molecules at liquid-liquid interfaces.     

Synthesis of amphiphilic V-type silica nanogels and study of their self-assembling at the air–water interface

The methods for the synthesis of silica nanogels and a modifying agent, as well as related amphiphilic V-type silica nanogels are presented. Self-assembly of the synthesized amphi philic nanogels during the formation of Langmuir monolayers at the air–water interface is considered. Aggregate structures were revealed to form during ordering of the silica V-type nanogels at the air–water interface after collapse of the Langmuir monolayer. For the low-molecular-weight fraction of the silica nanogels, the aggregates do not completely decompose upon the expansion of the Langmuir layer since are formed by mutually penetrating macromolecules. For the highmolecular- weight fraction, they are reversibly formed and decompose in consecutive compression– expansion cycles, which is characteristic of Langmuir layers of nanoparticles.     

Synthesis of ultrathin polymer films by self assembly

Recent progresses in the self assembly of ultrathin polymer films are described. Bilayer membranes of polymeric hydrogen-bond networks are formed in water. Two-dimensional networks of organic and inorganic polymers are formed in cast films of synthetic bilayer membranes to give stable multilayer films upon removal of the matrices. The monolayer at the air-water interface constitutes suitable templates for 2D polymer networks, and it may be either removed or part of the 2D film. Successive adsorption of polycations and polyanions under carefully controlled conditions produces layered polyion complexes in the stepwise manner. Various polymer chains are epitaxially adsorbed onto graphite. All these results indicate that molecularly defined 2D polymer structures are readily available.     

Langmuir films of (alpha-amino) phosphorus amphiphiles on various ion-containing subphases

Monolayers of amphiphilic (alpha-amino)phosphonocarboxylic and (alpha-amino)phosphonic acids have been formed by adsorption at the air/water interface. The influence of both the ionic strength and the pH of the subphase on the stability and compactness of the monolayers have been studied. The stability and the compactness of the Langmuir films are enhanced by introduction of metallic ions such as Ca(2+) or Mg(2+) in the subphases. These effects are more pronounced with Ca(2+). These metal ions can form dimeric complexes with the phosphorus moieties of the surfactant polar heads and therefore bring the amphiphiles closer. For the less hydrophobic derivative, complexation with Ca(2+) or Mg(2+) is required to ensure the formation of a stable monomolecular film. For both phosphonocarboxylic and phosphonic compounds, models have been proposed to represent the complexation phenomenon at the air/water interface.     

Preparation and characterisation of monolayers and Langmuir–Blodgett films of liquid crystal mixed with cubic silsesquioxanes

Polyhedral oligomeric silesquioxanes (POSS) with eight polyether substituents were mixed with the liquid crystal (LC) 4-octyloxy-4′-cyanobiphenyl and spread at the air/water interface. The surface pressure-area and surface potential-area isotherms were recorded for different weight ratios of both components. The obtained results showed that POSS molecules had beneficial influence on LC monolayer improving its stability and rigidity. Moreover, it was found that some LC–POSS mixtures collapse reversibly and form multilayer films on the top of LC monolayer. On the other hand, interfacial dilatational and shear rheology indicated decrease of elasticity of the films after mixing. Brewster angle microscopy revealed multilayer structure of the condensed film and formation of net-like structures in the expanded film. These films were successfully transferred on solid substrates using the Langmuir–Blodgett technique. The scanning electron microscopy images confirmed the film deposition and formation of networks by POSS–LC mixtures. These findings may be useful in the fabrication of electronic devices based on LCs.     

聚合物Langmuir—Blodgett膜研究进展

聚合物LB膜可用两种方法制备,一种是两亲单体成膜再进行聚合反应,另一种为直接从两亲聚合物在亚相表面铺展成膜并转移。本文综合聚合物LB膜的研究状况,包括两亲聚合物和非两亲聚合物,对聚合物LB膜的成膜特点,结构和性能作了描述,并简要介绍了聚合物LB膜的应用前景。     

Microstructure formation and property of chitosan-poly(acrylic acid) nanoparticles prepared by macromolecular complex

We report here a study on the microstructure formation process of polymeric nanoparticles based on polyelectrolyte complexes. When polyanion poly(acrylic acid) (PAA) was dropped into polycation chitosan (CS) solution, CS-PAA nanoparticles with diverse microstructure would be formed under different experimental conditions. The microstructure of CS-PAA nanoparticles changed from solid spherical nanoparticles to core-shell separative ones and turned back to solid spherical ones with the variation of preparation conditions. The influence of molecular weight of CS and PAA, shell cross-linking, dropping temperature on the size, stability and morphology of CS-PAA nanoparticles were also studied. The nanoparticle size was affected by the molecular weight of CS and PAA, the ratio of amino group to carboxyl group (na/nc) and the incubation temperature as well. The shell-cross-linking provides a means to stabilize these nanoparticles. These nanoparticles can encapsulate plasmid DNA very well, which makes them have great potential in gene delivery.