Dynamics and collapse of two-dimensional colloidal lattices

One interesting aspect of colloidal particles is the formation of colloidal crystals at the 2D and 3D levels. Here we report the dynamics and collapse of colloidal lattices at liquid-liquid interfaces using Pickering emulsions as an experimental template. The colloidal particles oscillate around their equilibrium positions. The short-time diffusion constant (<10 s) of single particles increases with increasing lattice spacing; the oil-phase viscosity has an effect on diffusion only at large interparticle distances. Strikingly, we observe that the equilibrium structure can be disturbed when increasing the output laser intensity in a confocal laser scanning microscope, which leads to the collapse of colloidal lattices in the presence of small laser powers.     

General bottom-up construction of spherical particles by pulsed laser irradiation of colloidal nanoparticles: a case study on CuO

The development of a general method to fabricate spherical semiconductor and metal particles advances their promising electrical, optical, magnetic, plasmonic, thermoelectric, and optoelectric applications. Herein, by using CuO as an example, we systematically demonstrate a general bottom-up laser processing technique for the synthesis of submicrometer semiconductor and metal colloidal spheres, in which the unique selective pulsed heating assures the formation of spherical particles. Importantly, we can easily control the size and phase of resultant colloidal spheres by simply tuning the input laser fluence. The heating-melting-fusion mechanism is proposed to be responsible for the size evolution of the spherical particles. We have systematically investigated the influence of experimental parameters, including laser fluence, laser wavelength, laser irradiation time, dispersing liquid, and starting material concentration on the formation of colloidal spheres. We believe that this facile laser irradiation approach represents a major step not only for the fabrication of colloidal spheres but also in the practical application of laser processing for micro- and nanomaterial synthesis.     

Shape-Shifting Patchy Particles

A facile method to synthesize shape-shifting patchy particles on the colloidal scale is described. The design is based on the solvent-induced shifting of the patch shape between concave and convex features. The initial concave patchy particles were synthesized in a water suspension by a swelling-induced buckling process. Upon exposure to different solvents, the patches were tuned reversibly to be either concave or convex. These particles can be assembled into chained, branched, zigzag, and cyclic colloidal superstructures in a highly site-specific manner by surface–liquid capillary bridging. The biphasic nature of the particles also enables site-selective surface functionalization.     

双亲性离子液体功能化复合胶体颗粒的合成与催化性能

采用硅烷偶联剂4-氯苄基三氯硅烷对二氧化硅颗粒表面进行改性, 制得表面接枝氯苄基的亲油二氧化硅颗粒. 在亲油二氧化硅颗粒表面继续接枝亲水性的十二烷基咪唑, 即可制得含有离子液体基团的双亲性二氧化硅颗粒. 通过静电吸附氯铂酸和硼氢化钠还原, 可在两亲性二氧化硅颗粒表面负载铂纳米颗粒, 从而得到双亲性二氧化硅颗粒催化剂. 用扫描电镜、 透射电镜、 X射线衍射和红外光谱等对所得样品进行表征, 并以苯甲醇氧化反应为研究对象对催化剂性能进行评价, 结果显示, 使用此催化剂可使苯甲酸的产率达到90%.     

Covalently Immobilized Colloidal Metal Particles as Selective Catalysts for Olefin Hydrogenation

Abstract

Homogeneous colloidal dispersions of ultrafine noble metal particles have been prepared by the reduction of the corresponding metal ions in the presence of protective polymers. These colloidal metal particles show effective and selective catalyses in hydrogenation of olefins’. However, separation of these homogeneous catalysts from reaction mixtures for the repeated use is difficult. Thus, immobilization of these colloidal metal particles to supports is required. This paper reports immobilization of colloidal rhodium particles onto polymer support by use of covalent bonding between the protective polymer and the support. Activities and selectivities of the resultant immobilized catalysts for hydrogenation of olefins are shown.     

Shape‐Shifting Patchy Particles

A facile method to synthesize shape‐shifting patchy particles on the colloidal scale is described. The design is based on the solvent‐induced shifting of the patch shape between concave and convex features. The initial concave patchy particles were synthesized in a water suspension by a swelling‐induced buckling process. Upon exposure to different solvents, the patches were tuned reversibly to be either concave or convex. These particles can be assembled into chained, branched, zigzag, and cyclic colloidal superstructures in a highly site‐specific manner by surface–liquid capillary bridging. The biphasic nature of the particles also enables site‐selective surface functionalization.     

Stability in Colloidal Mixtures Containing Particles with a Large Disparity in Size

An experimental approach, based on turbidity measurements, is proposed for studies of the stability in colloidal mixtures containing particles with large disparity in size. The main advantage of this approach is that it permits investigations even under conditions of comparable particle number concentrations of the two colloidal populations. Binary mixtures containing a poly(vinyl acetate) (PVAc) latex and a Ludox AS-40 silica sol were investigated. The silica particles were much smaller than the latex ones. The experimental stability factors were compared with the theoretical values computed on the basis of the Kihira-Ryde-Matijevic model (J. Chem. Soc., Faraday Trans. 88(16), 2379 (1992)) for interaction between spherical particles with unevenly distributed surface charges. All the experimental results support the idea that, even when both sols are negatively charged, the small silica particles are adsorbed onto the latex surface. Under these conditions, the heteroaggregates, which are composed of PVAc cores surrounded with silica particles, can be modeled as PVAc particles having "modified" surface characteristics (i.e., average Stern potential and varying extents of the surface charge segregation). Copyright 2001 Academic Press.     

具有疏水核/亲水壳的双亲胶体粒子的制备

制备了具有疏水性聚苯乙烯核/亲水性聚丙烯酰胺壳的双亲粒子.疏水核通过超浓乳液聚合制备,亲水壳层通过过氧化羟基异丙苯和硫酸亚铁的界面引发制备.控制条件可得到网孔(半包覆)、褶皱(全包覆)两种形态的壳层.壳层孔的存在使得核层聚合物能够与外界接触.粒子的双亲性通过吸水吸油率进行表征.     

以胶体粒子为模板制备核壳纳米复合粒子

核壳纳米复合粒子具有许多不同于单组分胶体粒子的独特的光、电、磁、催化等物理与化学性质,是构筑新型功能复合材料的重要组元,在光子带隙材料、微波吸收材料、电磁流变液、催化剂和生物等领域有重要应用.本文从控制核壳复合粒子的微观结构及壳层均匀性与厚度的角度,详细评述了目前以胶体粒子为模板制备粒径从纳米到微米尺度的核壳复合粒子的方法.指出利用胶体粒子模板表面与壳层物质或其前驱物间的特殊相互作用(包括静电和化学相互作用),是完善现有制备方法和发展新方法来制备具有设定组成、结构和性能的核壳复合粒子的关键,同时也是将来的粒子表面纳米工程和获取有序的、先进纳米复合材料的主要方向。     

Adhesion of Colloidal ZnO Particles on ZnS-Type Phosphor Surfaces

Chemical and physical aspects of the adhesion of colloidal ZnO particles (d(50)=81 nm) on the surface of ZnS-type phosphors have been studied. Here, the green-emitting phosphor ZnS:Cu,Al,Cu (d(50)=5.0 μm) applied in TV screens was chosen as model compound. The ZnS material was pretreated in various ways (H(2)O, HCl, H(2)O(2)) and reacted thereafter with a suspension containing colloidal ZnO particles. Analytical investigations (SEM, ESCA) have shown that the adhesion of colloidal ZnO particles is strongly affected by the degree of hydrolysis of the ZnS surface. Electroacoustic investigations (ESA) prove that both types of surfaces, hydrolyzed ZnS as well as colloidal ZnO, are positively charged. Even so, adhesion of ZnO particles is encouraged very much under these conditions, indicating that secondary attractive forces (electrostatic interaction, chemical bonding) determine the amount of colloidal ZnO adhered on a ZnS-type phosphor. Copyright 2000 Academic Press.     

Size Effect of Colloidal Selenium Particles on the Inhibition of LPS‐Induced Nitric Oxide Production

We have studied the size‐dependent inhibition capabilities of colloidal selenium (Se) particles on lipopolysaccharide (LPS)‐induced nitric oxide (NO) production in RAW 264.7 cells. Four particle sizes of the nano‐Se, ranging from 45 ? 220 nm in diameter, were examined. All of them, unlike their bulk material, show clear capabilities of inhibition and a trend dependent on the particles size. The inhibition becomes more potent as the particle size increases. It indicates that pursuing the reduction of colloidal sizes into nanoscale is not favoured in this biological system.     

Optical differential mobility analyzer for micron size colloidal particles: theoretical approach

A loosely focused light beam is very useful for separating colloidal particles. For micron size colloidal particles suspended in a fluid and irradiated with a laser beam perpendicular to the direction of fluid flow, particles have a retention distance determined by their size and composition, the flow rate of fluid, and characteristics of the laser. An optical differential mobility analyzer for separating colloidal particles using a loosely focused beam is proposed theoretically and the concept of optical mobility is introduced. For the proposed optical differential mobility analyzer, particle trajectories and retention behavior are discussed and a transfer function described by operational parameters is derived. The possibility of separating particles of various sizes and different chemical compositions is discussed. It is proposed that the analyzer can be integrated into a microfluidic lab-on-a-chip system suitable for separating colloidal particles and biological cells at a very high resolution.     

Preparation of Nanosized Metallic Particles in Polyaniline

The preparation of nanosized gold and palladium particles in polyaniline has been carried out via the reduction of AuCl(3) or Pd(NO(3))(2) by polyaniline in either aqueous media or N-methylpyrrolidinone (NMP). When the reduction of AuCl(3) was carried out in NMP solutions of polyaniline, the Au particles were on the order of 20 nm. The reduction of AuCl(3) or Pd(NO(3))(2) by polyaniline in the powder form in aqueous media resulted in the accumulation of the elemental Au or Pd on the surface of the polyaniline particles. Subsequent dissolution of the polyaniline in NMP resulted in metal particles of about 50 to 200 nm being dispersed in the NMP solution of polyaniline. The rate of metal salt reduction and the size of the metal particles were found to be strongly dependent on the medium used, the initial ratio of metal ions to polyaniline, and the reaction time. The polyaniline-metal particle systems were characterized using X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy, and FTIR spectroscopy. Scanning and transmission electron microscopy and laser light scattering were used to determine the size of the metal particles in polyaniline. Copyright 2001 Academic Press.     

Cationic Spherical Polyelectrolyte Brushes as Nanoreactors for the Generation of Gold Particles

Summary: If long polyelectrolyte chains are attached densely to colloidal latex particles, a spherical polyelectrolyte brush results. These spherical polyelectrolytes are dispersed in water and carry a high charge. We demonstrate that these systems can be used to immobilize ions of heavy metals, such as gold, as counter‐ions. Reduction of these ions leads to metallic nanoparticles. In this way the brush layer attached to the surface of the particles becomes a “nanoreactor” that may be used for chemical conversions of the metal ions. We show that the reduction of AuClequation/tex2gif-stack-1.gif ions within these nanoreactors leads to well‐defined and rather monodisperse gold nanoparticles that are attached to the surface of the core. A stable dispersion of polymeric core particles with attached nanoparticles results. All results reported here suggest that chemical reactions of ions immobilized in spherical polyelectrolyte brushes provide a new route to composite particles of inorganic and organic materials.

Transmission electron micrograph of gold particles on a core‐shell system.     

Formation and dynamics of capillary-flow-induced colloidal rings

We have directly observed the ring formation of colloidal particles of 1 μm diameter at the contact lines of air, water, and oil using a laser scanning confocal microscope. Colloidal rings form and grow through the transport of particles induced by capillary flow due to water evaporation. In addition, we observe the sudden "jump in" of particles into the ring and the "depletion" of particles in the ring. Particle-tracking experiment shows that the particles within the ring exhibit 1D-like motion along the circular ring geometry, and the pair correlation function of the ring configuration suggests an equilibrium interparticle distance of approximately 2.8 μm. It is also found that the structure and formation speed of the colloidal rings can be controlled by accelerating water evaporation by the addition of methanol as a cosolvent.     

PET/PC共混体系的酯交换反应对其高压结晶行为的影响

利用转矩流变仪、DSC、SEM及WAXD等表征手段研究了PET/PC共混体系的酯交换反应对其高压结晶行为的影响.SEM观察表明,PET和PC熔混时的酯交换反应有利于PET/PC体系在高压结晶时生成厚度较大的伸直链晶体,且可以促进其高压下酯交换反应的发生.楔形伸直链晶体和弯曲伸直链晶体的存在证明链滑移扩散和酯交换反应两种机制对体系中聚酯伸直链晶体的增厚有贡献.拟合分峰法和War-ren-Averbach傅里叶分析法的计算结果表明,随PET/PC体系熔混时酯交换反应程度的增加,高压结晶共混物的结晶度降低,PET的平均微晶尺寸增大,点阵畸变平均值则减小,而微晶尺寸分布变宽.提出了在共聚物组分都具备结晶能力时,结晶诱导化学反应和化学反应诱导结晶两种过程在一定条件下可同时发生的观点.     

Evaporation‐Driven Self‐Assembly of Colloidal Silica Dispersion: New Insights on Janus Particles

The evaporation driven self‐assembly of novel colloidal silica Janus particles was evaluated by scanning electron microscopy in comparison to unfunctionalized silica particles. The cyclodextrin‐ and azobenzene‐modified compound was obtained utilizing Pickering emulsion approach, in which the particles were immobilized on solidified wax droplets and subsequently functionalized. Silica particles were modified with 3‐aminopropyl trimethoxysilane and afterward reacted with tosyl‐β‐CD or phenylazo(benzoic acid), respectively. Mesoscopic structures of the colloidal dispersions, as dried films from aqueous solution, have been investigated by scanning electron microscopy and dynamic light scattering. Interestingly, it has been observed that the Janus particles show a significantly different evaporation‐induced assembly than the unmodified particles.     

含盐胶体液滴的蒸发图案形成机理

研究了聚四氟乙烯(PTFE)胶粒与NaCl混合液滴的蒸发过程及其图案形成机理. 结果表明, PTFE颗粒对接触线具有强烈的钉扎作用, 胶体液滴蒸发伴有显著的“咖啡环”效应. 由于液滴中心液相区表面张力法向分力的作用, 使得凝胶区存在辐射状应力, 进而产生从液滴边缘向中心的辐射状裂纹, 裂纹数量随胶粒的体积分数增大而减少. NaCl与PTFE胶粒的混合液滴出现了复杂多样的蒸发图案. 盐的加入抑制了向外的毛细补偿流, 从而有利于获得宏观上厚度均匀的沉积膜. NaCl与PTFE胶粒耦合形成了凹凸不平的枝晶状形貌, 这可能是释放蒸发应力的结果.     

An Enthalpic Analysis on the Aggregation of Colloidal Particles Studied by Microcalorimetry

There are different theories concerning the stability of colloidal suspensions. Most of them arise from the well-known DLVO theory which relates colloidal stability to intermolecular forces between particles. Experimental corroboration of these theories has been obtained mainly by using different optical techniques that analyze changes in the optical properties of the solution while particles aggregate. However, no attention has been paid to studying the aggregation process thermodynamically. This is why we have focussed on studying the heat released during the agglutination of polystyrene particles. The enthalpy change in this aggregation process was detected by using a highly sensitive and modern technique called isothermal titration calorimetry. In addition, some results about repeptization, that is, reversibility in the aggregation process, are also shown. Copyright 2001 Academic Press.     

A Microfluidic Approach to Chemically Driven Assembly of Colloidal Particles at Gas–Liquid Interfaces

Bubbling up : Dissolution of CO₂ bubbles in a suspension of colloidal particles chemically induces the assembly of particles on the surface of shrunken bubbles, and thus yields rapid continuous formation of a colloidal armor. This approach maintains the high colloidal stability of particles in bulk, has increased productivity, and allows the formation of bubbles with precisely controlled dimensions.