Modified reverse microemulsion synthesis for iron oxide/silica core–shell colloidal particles

Iron oxide/silica core–shell colloidal particles were prepared by basic reverse microemulsion (RM) method and two modified RM methods. By basic RM method, maximum particle size obtained was mere 40 nm. For building photonic crystals working in the visible range, the colloidal particles must be larger than 100 nm. Thus two modified RM methods were used. By alcohol modified RM method, short chain alcohols were used as co-surfactant. The particle size rose to near 100 nm, but the core–shell structure was comparatively poor. By emulsifier pair modified RM method, the particle size leapt to over 200 nm and a narrow growth window was found favorable to enhance the stability and rigidity of the surfactants layers. The core–shell mechanism was also discussed and a new four-step mechanism was proposed.     

Effect of Surfactants on the Formation,Morphology, and Surface Property of Synthesized SiO2 Nanoparticles

Abstract

This study investigated the effect of cationic, anionic (saturated and unsaturated), and nonionic surfactants on the formation, morphology, and surface properties of silica nanoparticles synthesized by the ammonium‐catalyzed hydrolysis of tetraethoxysilane in alcoholic media. Results indicate that at a relatively low surfactant concentration (1 × 10^?3–1 × 10^?6 M), cationic surfactants significantly affected the growth of silica particles as measured by dynamic light scattering and transmission electron microscopic analyses. In contrast, the anionic and nonionic surfactants showed relatively minor effects in the low concentration range. The magnitude of negative zeta potential was reduced for silica colloids that were synthesized in the presence of cationic surfactant because of charge neutralization. The presence of anionic surfactants only slightly increased the negative zeta potential while the nonionic surfactant showed no obvious effects. At high surfactant concentrations (>1 × 10^?3 M), cationic and anionic surfactants both induced colloid aggregation, while the nonionic surfactant showed no effect on particle size. Raman spectroscopic analysis suggests that molecules of cationic surfactants adsorb on silica surfaces via head groups, aided by favorable electrostatic attraction, while molecules of anionic and nonionic surfactants adsorb via their hydrophobic tails.     

Size-dependent interaction of silica nanoparticles with different surfactants in aqueous solution

The size-dependent interaction of anionic silica nanoparticles with ionic (anionic and cationic) and nonionic surfactants has been studied using small-angle neutron scattering (SANS). The surfactants used are anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethyl ammonium bromide (DTAB), and nonionic decaoxyethylene n-dodecylether (C(12)E(10)). The measurements have been carried out for three different sizes of silica nanoparticles (8, 16, and 26 nm) at fixed concentrations (1 wt % each) of nanoparticles and surfactants. It is found that irrespective of the size of the nanoparticles there is no significant interaction evolved between like-charged nanoparticles and the SDS micelles leading to any structural changes. However, the strong attraction of oppositely charged DTAB micelles with silica nanoparticles results in the aggregation of nanoparticles. The number of micelles mediating the nanoparticle aggregation increases with the size of the nanoparticle. The aggregates are characterized by fractal structure where the fractal dimension is found to be constant (D ≈ 2.3) independent of the size of the nanoparticles and consistent with diffusion-limited-aggregation-type fractal morphology in these systems. In the case of nonionic surfactant C(12)E(10), micelles interact with the individual silica nanoparticles. The number of adsorbed micelles per nanoparticle increases drastically whereas the percentage of adsorbed micelles on nanoparticles decreases with the increase in the size of the nanoparticles.     

Fabrication of photonic crystals with nigrosine-doped poly(MMA-co-DVB-co-MAA) particles

A convenient approach was developed to fabricate monodisperse nigrosine-doped poly(methyl methacrylate-co-divinylbenzene-co-methacrylic acid) nanoparticles with different cross-linkage by soap-free emulsion polymerization at boiling status and swelling process. The dye-doped nanoparticles were used for the fabrication of colloidal crystal films and beads. It was found that nigrosine dye in the nanoparticles can efficiently depress the light scattering inside the colloidal crystal films and eliminate the iridescent effect in the photonic beads. These results make the colloidal crystals useful in photonic paper, bioassay, and so on.     

Fabrication and characterization of core-shell photonic crystals via a dipping process

High-quality polystyrene (PS) colloidal photonic crystals in large area were fabricated in 24 h via a capillary-enhanced process. Then, the photonic crystals with core-shell structure were obtained by incorporating silica nanoparticles into the interstitial space of opal template via a dipping process. The filling ratio (V_silica) of interstitial space could be manipulated by dipping colloidal crystals into suspensions with different concentrations of silica nanoparticles, which in turn renders the obtained core-shell photonic crystals. The absorptive peak of opal without dipping process is at 445 nm as measured by UV–vis spectrometry. The filling ratios of 0.130, 0.167 and 0.253 can be calculated according to the modified Bragg's Law, which corresponds to the absorptive peaks for core-shell opals at 453, 463 and 469 nm obtained from suspensions with silica nanoparticles of 0.017, 0.122, and 0.244 wt%, respectively. Therefore, by using this dipping process, the characteristic absorption wavelength for photonic crystal will be varied easily, efficiently and cost effectively than that by traditional methods for constructing opal from monodispersed colloids of different diameters.     

金属Al薄膜基微池强制沉积胶体光子晶体的制备

强制沉积法是一种利用自组装原理快速沉积胶体晶体有序阵列的模板方法. 我们利用微机械刻划法加工金属Al薄膜, Al膜厚控制微粒粒径和聚醚砜膜厚控制层数, 成功地制备了用于强制沉积光子晶体的微池装置. 为了检验该微池装置的有效性, 我们分别测试了不同粒径(224, 245和283 nm)单分散聚苯乙烯微球的沉积效果, 并且对其中一种微球(283 nm)进行了不同温度的烘干处理, 检验了烘干温度对该样品表面形貌和光子带隙中心波长的影响. 实验结果表明, 该光子晶体呈面心立方结构, 内部晶格完整, 缺陷较少, 带隙中心波长的实验值与计算值符合得较好. 此外, 烘干处理可以使构成光子晶体的微球发生微观变化, 并导致光子带隙中心波长的蓝移.     

Structural and optical characterization of colloidal Se nanoparticles prepared via the acidic decomposition of sodium selenosulfate

Colloidal selenium nanoparticles (NPs) were synthesized via acidic decomposition of sodium selenosulfate. The effects of synthesis and post-synthesis treatment conditions on the size, structure and size distribution of the Se nanoparticles are discussed. It is shown that the decomposition of sodium selenosulfate with non-oxidative acids (e.g., HCl) in aqueous solutions of polymers (sodium polyphosphate, gelatin, polyvinyl alcohol, polyethyleneglycole) and surfactants (sodium dodecylsulfonate, cetylpyridinium chloride) results in the formation of amorphous 25–200 nm Se nanoparticles converting upon ageing at 90 °C into trigonal 150–250 nm Se nanocrystals. Optical properties (absorption and Raman spectra) of freshly prepared and aged Se nanoparticles both in colloidal solutions and in polymeric (polyvinyl alcohol) films are analyzed.     

Effects of liquid bridge between colloidal spheres and evaporation temperature on fabrication of colloidal multilayers

For the application of colloidal crystal films as "photonic band gap" materials, their domain size and thickness are significant. The substrate withdrawing speed, the colloidal suspension volume fraction, and the colloidal suspension temperature have been studied for the domain size and thickness controls of colloidal crystals in this study. Stable dispersions of monodispersed polystyrene spheres with a diameter of 245 nm were synthesized according to a general emulsion polymerization for colloidal crystal films. By experimental results and the theoretical relationship between the number of layers and other parameters, we could know that the water bridge between colloidal spheres (which is formed by capillary force) influences the number of colloidal crystal layers significantly.     

Effects of surfactants and electrolytes on adsorbed layers and particle stability

Adsorbed polymer and polyelectrolyte layers on colloidal silica nanoparticles have been studied in the presence of various salts and surfactants using photon correlation spectroscopy and solvent relaxation NMR. Poly(ethylene oxide) (PEO; molar mass 103.6 kg mol (-1)) adsorbed with a relatively high affinity and gave a layer thickness of 4.2 +/- 0.2 nm. While the nonionic surfactant used only increased this thickness slightly, anionic surfactants had a much greater effect, mainly due to repulsions between adsorbed aggregates, leading to expansion of the layer. A nonionic/anionic surfactant mixture was also tested and resulted in a larger increase in layer thickness than any of the individual surfactants. The dominant factor on addition of salt was generally the reduced solvency of PEO, which resulted in a further increase in the layer thickness but in some cases caused flocculation. This was not the case when the surfactant was sodium dodecylbenzenesulfonate; instead screening of the intermicellar repulsions possibly combined with surfactant-cation binding resulted in a reduction in the layer thickness. In comparison the affinity between silica and sodium polystyrenesulfonate was very weak. Anionic surfactants and salts did not noticeably increase the strength of adsorption, but instead encouraged flocculation. The situation was different with a nonionic surfactant, which was able to adsorb to silica itself and apparently facilitated a degree of polyelectrolyte adsorption as well.     

胶体光子晶体的平面介电常数缺陷

为引入特殊的光学性质,通常需要在三维光子晶体中人为可控地引入缺陷.通过改变局部结构单元的尺寸或介电常数,相应地引入给体或受体掺杂,带来不同的缺陷态.以前文献报道的向胶体光子晶体中引入缺陷,常会因为同时引入尺寸和介电常数掺杂,给掺杂性质的界定带来困难.本文中,我们结合对流自组装法和L-B膜法,在实心二氧化硅微球组成的三维光子晶体内引入尺寸相同的二氧化硅空心球(与实心球相比具有不同折光率)组成的单层平面缺陷,或者在空心球晶体内引入实心球缺陷层,构成实心-空心-实心或空心-实心-空心的三明治结构,在不破坏整体晶格的同时,在三维胶体光子晶体中引入单一的平面介电常数缺陷.     

Formation and drying of colloidal crystals using nanosized silica particles

Much interest has been generated in the fabrication of colloidal crystals from suspensions because of the promise of photonic band gap applications. However, since the case of small, nonsedimenting colloidal particles indeed remains rather rarely treated, spherical silica particles with diameters varying from 75 down to 20 nm have been used in the present work to fabricate colloidal crystals by drying the suspending liquid. Typical events that take place during the drying process of a particulate film, such as cracking, compaction and penetration of air into a porous network, have been evaluated using existing theories, and the maximum stress in the drying film could be approximated. Investigation on the dry film structure by scanning electron microscopy showed the arrangement of particles in a close-packed system. To interpret the formation of such crystals, the amplitudes of the interparticle and capillary forces have been estimated from existing models. The repulsive interparticle forces allow the particles to remain stable and thus rearrange up to fairly high particle concentration. These modeling results showed the dominance of the capillary contribution at the end of the drying process. Nitrogen adsorption/desorption measurements gave very coherent results regarding both pore volume and pore size of the dry particulate films when compared to the expected ordered packing arrangements.     

AHOT/异辛烷反胶束体系制备铁酸钴纳米粒子

分别以阴离子表面活性剂二(2-乙基己基)丁二酸酯磺酸钠(AOT)和新型表面活性剂二(2-乙基己基)羟基丁二酸酯磺酸钠(AHOT)与异辛烷/水构建的反胶束体系为微反应器,合成了CoFe2O4纳米粒子;利用TGA,XRD,TEM等手段对产物进行了表征;讨论了两种表面活性剂构建的反胶束体系对产物合成过程及纳米粒子形貌和尺寸的影响.     

Hybrids of colloidal silica and waterborne polyurethane

Waterborne polyurethane (WPU) was synthesized and followed by adding colloidal silica to prepare WPU-silica hybrids. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results revealed that the viscosity of these hybrid solutions increased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. The latter result was evidenced by SEM examination. The effect of interaction between silica particle and urethane polymer chains is more significant with increasing silica content. The prepared hybrid films show much better thermal stability and mechanical properties than pure WPU. The optical transparence did not linearly decrease with increasing the silica fraction in the hybrid thin film. At below 20% silica content, the film transparence decreased with increasing silica content; the converse is true at above 20% silica content. These results showed that the prepared hybrid films demonstrated tunable transparence with the silica fraction in the films.     

TiO2掺杂调控聚苯乙烯微球折射率及胶体光子晶体结构色

胶体光子晶体由于其可调变的结构色在绿色印刷、印染等领域备受关注,而其光子带隙的宽度和位置由光子晶体的晶格参数(晶面间距,通常受胶体微球尺寸影响)和介质的折射率决定。现有人工胶体光子晶体主要基于SiO_2和高分子(如聚苯乙烯(PS)等)微球的组装制备,由于胶体微球材质种类有限,折射率调控受限,因而目前调控胶体光子晶体结构色主要靠改变胶体微球的尺寸来实现。本文首先制备高折射率(2.6)的TiO_2纳米晶,在乳液聚合制备单分散的PS(折射率1.6)微球过程中,将所制备的TiO_2纳米晶掺杂于PS微球中,通过TiO_2的掺杂量有效调控胶体微球的折射率,进而实现胶体光子晶体的结构色调控。以多色胶体光子晶体微球的水溶液为墨水,采用彩色喷墨打印技术打印了电脑设计的光子晶体彩画。本文发展的光子晶体结构色调控新技术拓展了胶体光子晶体的应用。     

Dry etching of colloidal crystal films

Two types of non-close-packed colloidal crystal films were prepared by etching the films made of polystyrene nanospheres using a hyperthermal neutral beam of oxygen gas. Etching without sintering above glass transition temperature of the polymer particles resulted in the non-close-packed structure of the nanospheres, in which polystyrene nanospheres in different lattice planes touched each other due to the reduction in the size of the nanospheres that occurred during the etching process. In contrast, a different non-close-packed structure with inter-connecting networks between etched nanospheres was generated by annealing of the colloidal crystal and a subsequent etching process. The photonic bandgap could be tuned during this dry etching of colloidal photonic crystals. This connected open structure could be used as a template for a silica inverse opal by chemical vapor deposition. An alternative dry etching process, reactive ion etching, mainly affected the morphology of particles near the top surface, and only a slight change in the stop band position of the colloidal crystal film was observed.     

Inverse opal photonic crystal of chalcogenide glass by solution processing

Chalcogenide opal and inverse opal photonic crystals were successfully fabricated by low-cost and low-temperature solution-based process, which is well developed in polymer films processing. Highly ordered silica colloidal crystal films were successfully infilled with nano-colloidal solution of the high refractive index As(30)S(70) chalcogenide glass by using spin-coating method. The silica/As-S opal film was etched in HF acid to dissolve the silica opal template and fabricate the inverse opal As-S photonic crystal. Both, the infilled silica/As-S opal film (Δn ~ 0.84 near λ=770 nm) and the inverse opal As-S photonic structure (Δn ~ 1.26 near λ=660 nm) had significantly enhanced reflectivity values and wider photonic bandgaps in comparison with the silica opal film template (Δn ~ 0.434 near λ=600 nm). The key aspects of opal film preparation by spin-coating of nano-colloidal chalcogenide glass solution are discussed. The solution fabricated "inorganic polymer" opal and the inverse opal structures exceed photonic properties of silica or any organic polymer opal film. The fabricated photonic structures are proposed for designing novel flexible colloidal crystal laser devices, photonic waveguides and chemical sensors.     

Growth kinetics of sulfur nanoparticles in aqueous surfactant solutions

Sulfur is an important element has many practical applications when present as nanoparticles. Despite the practicable applications, limited studies are available in the literature related to synthesis of sulfur nanoparticles. Growth kinetics of colloidal sulfur particles synthesized from aqueous solutions using different surfactants have been studied here. The effects of different parameters such as reactant concentration, temperature, sonication, types of acids, types of surfactants, and even surfactant concentration are studied on the growth kinetics. Since the reaction rate is fast, particle growth depends on the parameters which affect diffusion of sulfur molecules. There is a linear relationship found among the reactant concentration and the particle coarsening rate constant. The growth kinetics was studied in the presence of different surfactants such as nonionic (poly(oxyethylene) p-tert-octylphenyl ether, TX-100), anionic (sodium dodecylbenzene sulfonate, SDBS), cationic (cetyltrimethyammonium bromide, CTAB) and results show the coarsening constant changes according to the following order: water>TX-100>SDBS>CTAB. The particle growth rate also depends on the surfactant concentration, coarsening rate constant decreases with the increase in surfactant concentration and become constant close to the critical micellar concentration (CMC). The coarsening rate constant also highly depends on the types of acid used as catalyst.     

Gelatine thin films as biomimetic surfaces for silica particles formation

The formation of silica nanostructures by several living organisms, such as diatoms or sponges, involves specific macromolecules that control the growth and the organization of silica nanoparticles. In order to investigate if a single molecular system could perform both particle size control and morphological template, gelatine thin films of various concentration and strength were prepared as biomimetic models and their reactivity towards sodium silicate aqueous solutions was studied. Simultaneous formation of silica particles in the nanometric and micrometric size range was observed. The former corresponds to colloids grown at the surface of the gelatine films and the latter to particles induced by gelatine chain brushes formed at the film/water interface. These results are in good agreement with well-known principles of biomineralization and suggest that multi-molecular systems, rather than single components, are responsible for biogenic silica nanostructure formation.     

油页岩灰渣提取硅酸钠制备纳米二氧化硅

以油页岩灰渣提取的硅酸钠为原料,采用溶胶-凝胶法并结合多种纳米粉体分散技术,制备了分散性好、粒径均一的纳米SiO2,其平均粒径约为10 nm。 制备过程中聚乙二醇（PEG）的加入能够有效的降低纳米SiO2的表面能,减少粒子的团聚, PEG的最佳浓度为3.0%;超声振荡的空化作用所释放出的巨大冲击波和微射流,能有效地击散纳米SiO2团聚体,其最佳超声时间为0.5 h;硅酸湿凝胶与正丁醇共沸蒸馏能有效脱除凝胶中的水,防止干燥过程中颗粒间硬团聚。     

Three-dimensional centimeter-sized colloidal silica crystals formed by addition of base

Three-dimensional (3D) centimeter-sized colloidal crystals can be spontaneously formed simply by dropping a NaOH solution (10 mM, approximately 10 microL) into an aqueous dispersion of dilute charged colloidal silica (particle diameter 110 nm, particle volume fraction phi = 0.023, 3-4 mL). The charge number of the silica particle increases with pH. Upon adding the NaOH solution, first, sub-millimeter-sized polycrystals are formed in the upper part of the sample due to charge-induced crystallization. The local phi value in the crystal region becomes nonuniform. The crystals with a high phi value accumulate at the bottom of the cell and then grow upward as columnar crystals. The crystal widths increase discontinuously with the growth, and in some cases, 3D centimeter-sized crystals are formed. The centimeter-sized crystals are also obtainable by the controlled diffusion of the base from its dilute reservoir. The present findings may prove valuable in the fabrication of large 3D single-crystalline photonic materials.