聚苯乙烯微球在乙醇/水混合分散介质悬浮液气-液界面自组装:快速组装单层胶粒晶体

本文提出了一种组装单层聚苯乙烯(PS)胶粒晶体的方法。一定温度下,一定质量比乙醇和水(乙水比K)作为分散介质的悬浮液气-液界面处,可快速自组装出单层PS胶粒晶体。研究表明,悬浮液中的PS微球在对流的带动下到达气-液界面,在两个PS微球之间由弯液面产生的毛细管力推动下组装在一起,并形成组装核心。后续到达气-液界面的PS微球与组装核心持续组装,最终在悬浮液的气-液界面形成单层PS胶粒晶体。通过改变乙水比K,调整混合分散介质与到达气-液界面的PS微球之间的润湿性,进而改变组装推动力,最终实现单层PS晶体的组装。因此分散介质中的乙水比K是单层PS胶粒晶体形成的关键因素。PS微球的质量百分比浓度虽也可影响PS胶粒晶体薄膜的层数,但乙水比K15∶1时,单纯降低浓度无法得到单层PS胶粒晶体。组装温度仅对晶体的质量产生影响。     

Processing optimization and optical properties of 3-D photonic crystals

The synthesis optimization of three-dimensional photonic crystals (direct and inverse opals) is discussed in terms of the influence of processing parameters on the final optical quality. A colloidal/sol–gel route, starting with the self-organization of polystyrene microspheres into opal structures by convective self-assembly, followed by infiltration with a dielectric matrix precursor sol and heat treatment, has been followed. Several substrate hydrophilization methods have been tested and different substrates. Sol–gel infiltration of the opal template interstices with silica was achieved by dip-coating or micro-syringe application and it was followed by removal of the polymeric template. The concentration of the colloidal sol, containing polystyrene spheres of 235 or 460 nm in diameter, was optimized. The structural and optical properties of the opals and inverse opals have been studied by field emission scanning electron microscopy and optical reflectivity spectroscopy, in order to assess the relationship between their structure and the photonic properties obtained. By using borosilicate glass substrates hydrophilized with hydrochloric acid, colloidal photonic crystals of good quality have been obtained, with well ordered regions up to ～100 μm². By monitoring the effective refractive index change with relative humidity of the surrounding atmosphere, using spectroscopic ellipsometry with an environmental chamber, it was concluded that the present photonic crystals are suitable for humidity sensing applications.     

Microwave‐assistant route to hybrid semiconductor nanocrystals with quasi solution‐solid‐solid mechanism

A facile microwave‐assistant route was developed for the synthesis of hybrid nanocrystals. Colloidal hybrid nanocrystals, Ag₂S‐CdS, were prepared by using Ag₂S nanocrystals and cadmium diethyldithiocarbamate as raw materials under microwave irradiation. The fast ion conductor, Ag₂S nanocrystal, catalyzes the growth of CdS nano‐building blocks through a quasi solution‐solid‐solid mechanism. The ultraviolet‐visible absorption and photoluminescence spectra of the Ag₂S‐CdS hybrid nanocrystals were investigated. One of the main advantages for this synthesis is the efficiency of dramatically reducing overall processing time. This report provides a new route for the growth of semiconductor hybrid nanocrystals based on Ag₂S and may be extended to the preparation of other hybrid colloidal nanostructures.     

Effect of leaching concentration and time on the morphology of pores in porous glasses

Herein, porous glass was prepared by the acid leaching of phase-separated sodium borosilicate glass. The effects of hydrochloric acid (HCl) leaching concentrations varying from 0.1 to 3 M and of leaching times varying from 2 to 48 h on pore size and shape are reported here. The porous structure evolution was investigated through small angle X-rays scattering measurements and were compared to the classical nitrogen adsorption technique. We argue that the composition of these samples is not significantly modified with the acidic concentrations of the solution or with the leaching times tested. However, as expected a priori, we clearly show strong differences in porous structure. The investigation of different HCl leaching concentrations (from 0.1 to 3 M), with a small variation between each concentration, has enabled the observation of an interesting result. That is, we clearly show a non-linear effect of acidic concentration on the porous structure of these materials. At low acid concentrations, the specific area of these materials is relatively low. Increasing the HCl concentration to approximately 0.7 M leads to a strong increase in a specific BET area and total pore volume. However, further increasing of the acid concentration of the leaching solution leads to a decrease of both the specific surface area and the total pore volume. All of these results due to the presence of colloidal silica inside the pore structure can be explained by the well-known Zhdanov's model. These nanoparticles formed at an intermediate acid concentration seem to cluster when the acidity increases. The effect of the leaching time is less significant than the HCl concentration; however, this same assumption can be explained by the experimental results.     

乙酰丙酮对PMMA负载锐钛矿型TiO2薄膜及其光催化性能影响

以钛酸丁酯作为钛源,水为溶剂,乙酰丙酮(AcAcH)为表面修饰剂,采用微波水热辅助溶胶-凝胶法制备了纳米晶二氧化钛水溶液,利用提拉镀膜法在聚合物聚甲基丙烯酸甲酯(PMMA)基板上沉积得到了透明TiO2纳米晶薄膜.通过X射线衍射(XRD)、红外光谱(FTIR)、透射电子显微镜(TEM)、原子力显微镜(AFM)和紫外-可见光吸收光谱(UV-Vis)等对TiO2纳米颗粒和薄膜的晶相组成、表面形貌及光学性能进行表征.同时通过紫外光光催化降解罗丹明B研究了TiO2薄膜的光催化性能.结果表明:通过引入乙酰丙酮,可以得到高度分散、晶相为锐钛矿型的TiO2水溶胶,在PMMA基板上沉积得到的薄膜表面平整、致密,具有良好的透光率,经过180 min紫外光照射,对罗丹明B的降解率达到90;以上.     

Modification of the Langmuir–Schaefer method for fabrication of ordered protein films

A modification of the Langmuir–Schaefer method for the fabrication of high-quality protein films on a solid substrate was proposed and applied to lysozyme. The procedure relies on the use of a pre-prepared protein solution, the parameters of which correspond to crystallization conditions. A lysozyme Langmuir monolayer was shown to be formed with the involvement of complexes, namely, dimers and octamers of protein molecules that are present in such protein solutions. These complexes apparently retain the structure after spreading a protein solution onto an aqueous subphase in a Langmuir trough. The thickness of the film after the transfer of the monolayer, which was formed by the proposed procedure, onto a solid substrate corresponds to the diameter of the octamer and this film is dense, continuous, and uniform, as was demonstrated by several methods: X-ray reflectivity, total external reflection X-ray standing wave, and atomic force microscopy. A layer of chloride ions that formed under the Langmuir monolayer was found at the air–protein film interface. This fact confirms an important role of the precipitating agent (chloride ions) in all steps of the formation of lysozyme films.     

Epitaxy of CdS and PbS on Langmuir layers

The results of a structural study of CdS and PbS nanocrystals grown from solutions under a Langmuir monolayer of a fatty acid are presented, and the influence of the geometric and stereochemical factors on the mutual orientation of the monolayer and the nanocrystals grown are considered.     

化学气相沉积单层VIB族过渡金属硫化物的研究进展

2004年以来,石墨烯因其优异的光学、电学性质而被广泛地研究,但由于其零带隙的特性极大地限制了它的应用前景.单层的VIB族过渡金属硫化物(TMDs)拥有类似石墨烯的晶体结构及可控的能带结构,是一类理想的二维直接带隙半导体材料,不仅可用于探索如谷极化等一些基础和前沿的物理问题,也可以广泛应用于纳米器件、光电子学和光催化的研究.近年来,化学气相沉积(CVD)技术作为一种相较于传统化学合成或物理剥离更加有效的制备方法被引入此类材料的生长,能够合成出拥有大面积连续的、厚薄均匀和较高晶体质量的单层TMDs.基于此,重点介绍了利用CVD技术生长单层TMDs所取得的进展,讨论了各工艺条件(如反应温度、载流气体、衬底、前驱物与衬底之间的距离等)对单层TMDs的生长及性质的影响.最后,探讨了利用CVD技术实现调控单层TMDs的尺寸、覆盖度和层厚均匀性的途径和方法.     

Molecular Cooperation in Photo-Induced Electron Transfer in Monolayer Assemblies

Quenching of fluorescence due to electron transfer is observed in monolayer assemblies when electron donor D and electron acceptor A are either at the same interface or separated by one spacer monolayer. When the donor and acceptor monolayers are separated by two or more fatty acid interlayers no fluorescence quenching is detected.     

Phase separation in the solution of water glass and poly(vinyl alcohol)

Silica gel samples with macropores were prepared from solutions of silicate and poly(vinyl alcohol) (PVA), where macropores were formed by fixing a transitional structure of phase separation. Among the silica sources tested, tetraethoxysilane (TEOS), colloidal silica and water glass, only the system with water glass shows phase separation and forms macroporous silica gel. In the system with TEOS, ethanol formed during hydrolysis of TEOS becomes good solution and stabilizes the system not to induce phase separation. In the system with colloidal silica, dense structure of silica is probably not suitable for controlling phase separation and gelation. In the system with water glass, driving force of phase separation is considered to be a repulsive interaction between solvent molecules and PVA interacting with silica surface and the solution separates into a phase rich in solvent and that rich in silica and PVA. One of the features in the water glass-PVA system is insensitivity of macropore size against compositional change in the solution, i.e. macroporous morphology in the resultant silica gel hardly changes by changing the composition ratio in the solution. This would be an advantage in the preparation of well-defined macroporous silica from water glass, whose composition varies among the product lot number, because reproducibility in macroporous morphology is ensured regardless of the lot number of the water glass.     

Synthesis and optical properties of MPTMS-capped CdS quantum dots embedded in TiO2 thin films for photonic applications

CdS nanoparticles have been prepared via a colloidal route using 3-mercatopropyltrimethoxysilane as a capping agent. The stability of the particles in solution and embedded in TiO₂ matrices has been followed by optical absorption. Both the size and the size distribution of the particles are well controlled, thus allowing a tunable emission. Raman and photoluminescence spectroscopies have been used to characterize colloidal CdS, TiO₂:CdS solutions and thin films deposited on soda-lime slides. The Z-scan technique has been used to measure the non-linear refractive indices of the solutions and the non-linear absorption coefficients of the thin films.     

Colloidal structure and stabilization mechanism of aqueous solutions of unmodified fullerene C60

Despite the inability of fullerenes to be directly dissolved in water, there are methods for preparing stable dispersions of fullerenes in water without any particular modifications of the fullerene or addition of stabilizers. The colloidal properties of such systems prepared by replacing the solvent and structural changes in them during coagulation have been studied. The coagulation dynamics has been investigated by spectroscopy and small-angle neutron scattering. The results obtained confirm the colloidal nature of such systems. During coagulation, particles retain a large volume of water around them, an indication of interaction between fullerene and water during solution stabilization.     

Influence of Nature of Silica Source on Template‐Free Synthesis of ZSM‐5

Synthesis of ZSM‐5 from template‐free batches which preceded the preparation of template‐free ZSM‐5 layers on porous supports was studied to ascertain the effect of nature of silica source on the purity of template‐free ZSM‐5. Silicic acid and two colloidal silica sols were used as silica sources to prepare the template‐free batches with a molar composition of 6.5Na₂O:Al₂O₃:80SiO₂:3196H₂O. One of the colloidal silica sols contained methanol as stabilizer while the other did not. The product purity and rate of crystallization increased when colloidal silica sols were used as silica source, however, use of silicic acid led to low purity and slow crystallization rate. The methanol in the colloidal silica sol appeared to act as template to promote the crystallization and was occluded in the resultant ZSM‐5 pores. The dissolution of the meta‐stable ZSM‐5 phase and formation of quartz was observed regardless of the nature of the silica source in case of prolonging the crystallization time more than 90 h at 200°C.     

Solvent effects in the synthesis process of tin oxide

Water is the most frequently used solvent in the chemical synthesis of inorganic materials where hydrolysis and condensation are the main reactions. In this work, we synthesized tin oxide nanoparticles using ethanol or acetic acid as a solvent by the controlled precipitation method. The main physicochemical phenomena that take place during the synthesis process and the possible reactions that led to the formation of the particles in the solution are described. The ceramic powder obtained was characterized by X-ray diffraction (XRD), thermal analysis, infrared (IR) spectroscopy and transmission electron microscopy (TEM). Interestingly, Romarchite SnO was the main crystalline phase obtained when acetic acid was used as solvent.     

Effects of magnetic interparticle coupling on the blocking temperature of ferromagnetic nanoparticle arrays

In this work we report on the study of the magnetic properties of 2D arrays and 3D dispersions of colloidal iron oxide nanoparticles prepared by Langmuir–Blodgett technique and by dilution in paraffin wax solid solution, respectively. The influence of magnetic interparticle coupling on the superparamagnetic relaxation behavior was investigated by means of DC magnetization measurements. A quantitative analysis of the field dependence of the blocking temperature and the role of the interparticle coupling is presented. We explain our results using a phenomenological model based on the random anisotropy and micromagnetic theories that account for particle coupling effects in the superparamagnetic properties.     

Porous characteristics of carbon-coated silica gel beads prepared by liquid phase deposition of organic colloidal nanoparticles

Carbon-coated silica gel beads could be prepared by immersing porous silica gel beads in a resorcinol–formaldehyde (RF) aqueous solution and then following by drying and pyrolysis in nitrogen atmosphere. With the proposed method, deposition of colloidal nanoparticles formed during the sol–gel polycondensation of the RF solution was successfully prepared on the mesopores of the silica gel beads. Both size and concentration of the colloidal particles could be controlled by the gelation time and the mixing ratio (V_EtOH/V_RF) of the RF solution to ethanol. The porous characteristics of the prepared carbon-coated silica gel beads and the amounts of deposited carbon could be controlled by changing V_EtOH/V_RF. Without any significant decrease in mesoporosity, the maximal carbon contents of carbon-coated silica gel beads could be increased up to 18 wt% in the inner part and 53 wt% on the outer surface, respectively.     

Role of the surface layer of aqueous subphase in the self-organization mechanism of metal sulfide textures under a Langmuir monolayer

The structural self-organization mechanism of the axial textures of the metal sulfide nanocrystals from an aqueous subphase under a condensed Langmuir monolayer of fatty acid molecules, with allowance for the existence of a thin structured water surface layer on the aqueous subphase surface, is considered.     

Synthesis and characterization of germanium sulfide aerogels

The synthesis of germanium sulfide gels by thiolysis reactions of a non-aqueous solution of Ge(OEt)₄, followed by supercritical fluid extraction to create aerogels, is described. Analysis of the as-prepared GeS_x aerogels by powder X-ray diffraction (PXRD) and surface area analysis reveals an amorphous structure exhibiting very high surface areas, 755 m²/g, that rival those of the best SiO₂ aerogels when compared on a per mole basis. Transmission electron microscopy shows that the aerogel material is composed of a continuous network of GeS_x colloidal particles assembled in a three-dimensional architecture. A detailed comparison of GeS_x aerogels and their xerogel (bench-top dried) counterparts in terms of the influence of the synthetic methodology on morphology and surface area is reported. In the presence of adventitious moisture, the amorphous GeS_x is oxidized to a crystalline phase identified by X-ray photoelectron spectroscopy, Raman spectroscopy and PXRD cell refinement to be hexagonal GeO₂.     

Densification kinetics of porous colloidal P2O5-doped silica gels using constant heating rate measurements

Commercially available fumed colloidal silica was gelled in an aqueous solution containing PO₄H₃. Instantaneous gelation was obtained by adding several drops of HF (48 wt%). The objective of this paper was to study the gel-to-glass conversion of these colloidal gels using constant heating rate (CHR) experiments.

Gel densification was measured at temperatures ranging from 50 to 1550°C at different heating rates (1 to 10°C/min) using a dilatometer.

Shrinkage and shrinkage rate as a function of temperature were measured and CHR equations were used to derive information on the densification mechanisms.

The experimental results show that small additions of PO₄H₃ into pure silica dispersions give rise to gels which densify to high silica glass at much lower temperatures than pure colloidal silica gels. The bloating effects produced by pure colloidal silica gels at temperatures above 1280°C were also eliminated. For these P₂O₅-doped silica gels maximum shrinkage rates were found at temperatures between 1050 and 1150°C according to the heating rate used.

The CHR analysis showed that several different mechanisms seem to operate in a complex interdependence in the whole range of temperature studied. This CHR analysis was compared with those results obtained from isothermal shrinkage experiments in the range where viscous sintering is the predominant shrinkage-controlling mechanism (between 1000 and 1100°C).     

Assembling ultra-thick and crack-free colloidal crystals via an isothermal heating evaporation induced self-assembly method

Ultra-thick and crack-free colloidal crystals have many advantages in a number of existing and emerging applications. In this work, such systems are fabricated by a simple and reproducible method based on assembly of monodisperse silica particles by a crystalline layer assembly technique (CLAT). We find that high quality of colloidal crystals is obtained by using two simple processes: sintering of silica particles and thermal treatment of colloidal crystals. The crack-free colloidal crystal with a thickness of 100 μm is fabricated. The morphologies and microstructures of colloidal crystals are identified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The reflection spectra are measured by UV-VIS spectrum measurement. The reflection spectra of the colloidal crystal with different thicknesses are calculated by using multiple scattering methods. When the thickness of the colloidal crystal is smaller than 60 μm, the reflection spectra of experimental measurements agree very well with that of theoretical calculations.