Fabrication of colloidal crystals with tubular-like packings

Methods are reported for the fabrication of colloidal crystal wires with tubular packings. Both free and silica-encased wires have been prepared. Porous silicon membranes are infiltrated with silica spheres, treated with silane, and annealed. After removal of the silicon template, short annealing times were found to result in colloidal crystal wires with varied packing geometries, while repeated annealing cycles produced a thin translucent silica sheath around the wires. Packing in the wires varies with the channel diameter of the Si membrane. The channels used in this study typically produce colloidal crystal wires with six strands, though wires with four to seven strands have been observed. Both chiral and achiral packings are also possible.     

功能型聚合物光子晶体的制备及应用

光子晶体因其特殊的光调控性能,在各类高性能光学器件方面具有重要的应用前景.本文主要阐述了功能型聚合物光子晶体的制备方法及其在防护涂层、高效发光、高灵敏检测和高性能光信息存储等方面的应用.     

Fabrication of superparamagnetic macroporous Fe3O4 and its derivates using colloidal crystals as templates

In this paper, we reported the preparation of superparamagnetic macroporous Fe(3)O(4) and its derivates using organic colloidal crystal as templates and their catalytic activity for chemical vapor deposition. The poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) copolymer colloids were deposited in an orderly manner onto the silicon surface, together with the infiltration of the Fe(3)O(4) nanoparticles into the interspaces of the colloids. The formed hybrid colloidal crystal subsequently was immersed in tetrahydrofuran to remove the organic components fully to obtain a macroporous Fe(3)O(4) framework with three-dimensional porous structure. The macroporous Fe(3)O(4) exhibits superparamagnetism due to the magnetic coupling of Fe(3)O(4) nanoparticles in the structure. Macroporous Fe(2)O(3) and Fe materials were obtained based on oxidization and reduction of the macroporous Fe(3)O(4), respectively. It was demonstrated that the macroporous Fe(3)O(4) materials possess catalytic activity and can induce growth of carbon nanotubes.     

Fabrication of colloidal crystals with defined and complex structures via layer-by-layer transfer

A new and versatile way--using poly(dimethylsiloxane) (PDMS) sheets to layer-by-layer (LbL) transfer hexagonal-close-packed particle monolayers from preformed colloidal crystals and stack them on substrates-has been demonstrated to create colloidal crystals. This approach allows LbL control of the thickness of the resulting crystals and especially of the size and the packing structure of the particles in each layer. Furthermore, it also allows fabrication of binary colloidal crystals over large areas by deformation of the PDMS sheets during LbL transfer. Two new binary crystals-one composed of identically sized particles but in different densities and the other of a nonclose-packed monolayer of large particles and a close-packed monolayer of small particles-were created, which are hard grown by other colloidal crystallization techniques developed thus far.     

Fabrication of binary colloidal crystals and non-close-packed structures by a sequential self-assembly method

Binary colloidal films of polystyrene (PS) spheres and silica spheres were fabricated with a sequential growth method using differently sized colloidal particles. In particular, we demonstrate the structures formed by a silica monolayer growing on top of a PS monolayer and a silica multilayer growing on top of a PS monolayer. By removal of the bottom PS layers, non-close-packed hexagonal, pentagonal, and square silica arrays were obtained at the original silica/PS interface. The possible formation mechanism of the non-close-packed structure was discussed, which may be used to explain how 3D colloidal crystals grow on patterned substrates.     

Defects of colloidal crystals

Reasons for the appearance of defects of various types in crystalline colloidal structures formed during the self-organization of the ensembles of spherical nanoparticles are analyzed using lyosols of metal nanoparticles stabilized with polymers as examples. Quantitative characteristic of the degree of imperfection of colloidal crystals is proposed and the procedures for the minimization of the degree of imperfection are discussed. Order-disorder phase transitions of colloidal crystals are studied.     

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.     

Video microscopy of colloidal suspensions and colloidal crystals

Colloidal suspensions are simple model systems for the study of phase transitions. Video microscopy is capable of directly imaging the structure and dynamics of colloidal suspensions in different phases. Recent results related to crystallization, glasses, and 2D systems complement and extend previous theoretical and experimental studies. Moreover, new techniques allow the details of interactions between individual colloidal particles to be carefully measured. Understanding these details will be crucial for designing novel colloidal phases and new materials, and for manipulating colloidal suspensions for industrial uses.     

Spontaneous two-dimensional spherical colloidal structures

Two-dimensional spherical crystalline colloidal structures are formed at the interface between water and oil as the result of spontaneous emulsification and colloidal self-assembly. When water droplets are introduced in oil containing a lipophilic surfactant, smaller water droplets of uniform size are spontaneously produced at the spherical interface. Initially of submicrometer size, the small droplets at the interface self-assemble, forming ordered structures, and grow uniformly with time until they reach a size of a few micrometers, maintaining the crystalline structure.     

Tunable two-dimensional non-close-packed microwell arrays using colloidal crystals as templates

In this paper we demonstrate a facile and efficient way to fabricate poly(dimethylsiloxane) (PDMS) molds with hexagonal non-close-packed (ncp) arrangements of microwells by casting PDMS prepolymer onto two-dimensional (2D) ncp colloidal crystals. The templates of the 2D ncp colloidal crystals were fabricated via coupling lift-up soft lithography and solvent-swelling. We found that the depths of the microwells together with the lattice spacing can be adjusted by the sphere interstices and chemical composition of the 2D ncp colloidal crystals. The relationship of the surface character of the templates with the depths of the microwells can be explained by the wetting behavior of PDMS prepolymer on the rough surface. Contact angle measurements are consistent with the experimental results of the microwells in depth and agree well with the Cassie-Baxter theory. There are at least three advantages of the approach. First, the depth and distance of the microwells can be controlled. Second, PDMS molds can be easily peeled from the surfaces of the templates, which results in reusing the original templates to make new molds. Third, this method can be applied to other materials, such as photopolymerizable resin or thermosetting resin. The potential application of the microwells is as microlenses to make a pattern or as microvials in bioanalytical techniques.     

Fabrication of gradient colloidal topography

A rather simple but yet effective way to self-assemble polystyrene (PS) beads in gradient colloidal crystal topography is proposed. The PS bead concentration, solvent, and substrate have a big effect on the colloidal crystal topography. Whether the gradient-shaped crystals can form or not depends on the Bond number [Bo; the ratio of gravitational potential energy (G) to adhesive energy (E(a)), or gravitational to capillary forces]. When Bo < 1, that is, the capillary force dominates over the gravitational force, the liquid meniscus is stable. The gradient-shaped crystals can form. Otherwise, PS beads form a uniform multilayer structure.     

Electro-optic effects of colloidal crystals

Many kinds of electro-optic effects of colloidal crystals are observed and discussed on the basis of the fundamental properties of colloidal crystals themselves. Several electro-optic effects of colloidal crystals have been found by the authors mainly by use of light-scattering, reflection- and transmitted-light intensity measurements in an electric field, (a) waveform deformation, (b) phase-shift effects, (c) second-order harmonics generation, (d) self-resonance frequency generation (characteristic frequency and harmonic oscillation), (e) peak wavelength-shift effects and (f) waveform transformation. These electro-optic responses are explained successfully by the resonance-, visco-elastic- and structural relaxation-parameters of colloidal crystals.     

Microcontact printing of colloidal crystals

Patterned two-dimensional (2D) colloidal crystals have been transferred by a modified mucp technique that was based on the use of polymer film as "glue" to provide an efficient interaction between the microsphere "ink" and substrate. The versatility of this method has been demonstrated by the patterning of colloidal crystal on a nonplanar substrate and heterogeneously structured colloidal crystal film. The table of contents graphic shows an SEM image of the ordered parallel lines of 2D colloidal crystals on a polymer-coated glass tube with a 3.7 mm radius of curvature.     

Synthesis of submicrometer-sized titania spherical particles with a sol-gel method and their application to colloidal photonic crystals

A synthetic method for preparing submicrometer-sized titania particles is proposed, which is based on hydrolysis of titanium alkoxide with the use of a cosolvent and an amine catalyst for alkoxide hydrolysis. The preparation was performed with different amines of ammonia, methylamine (MA), and dimethylamine (DMA) in different solvents of ethanol/acetonitrile, ethanol/methanol, ethanol/acetone, ethanol/acetonitrile, and ethanol/formamide for 0.1-0.3 M water and 0.03 M titanium tetraisopropoxide (TTIP) at temperatures of 10-50 degrees C. The use of the ethanol/acetonitrile solvent with MA was required for preparing monodispersed, spherical particles. The number average of the titania particle sizes and their coefficient of variation were varied from 143 to 551 nm and from 5.7 to 20.6%, respectively, with reaction temperature and concentrations of water and MA. Colloidal crystals of titania particles fabricated with a sedimentation method revealed reflection peaks attributed to Bragg's diffraction. Annealing at 100-1000 degrees C led to shrinkage and crystallization of titania particles followed by an increase in the refractive index of titania particles.     

Madelung-like attractions in colloidal crystals

The Debye-Hückel (Derjaguin-Landau-Verwey-Overbeek) two-sphere interaction potential is discussed in relation to the dissociative electrical double layer (DEDL) theory. The DEDL theory provides new electrostatic models to investigate the origin of attractions in colloidal crystals. Three Maxwellian models of two, three, and four interacting spheres are suggested. It is estimated that at least four spheres are needed to obtain Madelung-like attractions that are brought about by co-ion exclusion.     

Array patterns of binary colloidal crystals

Binary colloidal crystals (BCCs) were prepared from two kinds of poly(styrene-methyl methacrylate-acrylic acid) colloids approximately 190 and approximately 380 nm in diameter by the codeposition method. A variety of array patterns of BCCs were observed and characterized by AFM and SEM. The significance of these colloidal arrays in crystallography has been discussed preliminarily.     

Self-assembly patterning of silica colloidal crystals

We developed a self-assembly process of silica particles to fabricate desired patterns of colloidal crystals having high feature edge acuity and high regularity. A micropattern of colloidal methanol prepared on a self-assembled monolayer in hexane was used as a mold for particle patterning, and slow dissolution of methanol into hexane caused shrinkage of molds to form micropatterns of close-packed SiO2 particle assemblies. This result is a step toward the realization ofnano/micro periodic structures for next-generation photonic devices by a self-assembly process.     

Simultaneous growths of gold colloidal crystals

Natural systems give the route to design periodic arrangements with mesoscopic architecture using individual nanocrystals as building blocks forming colloidal crystals or supracrystals. The collective properties of such supracrystals are one of the main driving forces in materials research for the 21st century with potential applications in electronics or biomedical environments. Here we describe two simultaneous supracrystal growth processes from gold nanocrystal suspension, taking place in solution and at the air-liquid interface. Furthermore, the growth processes involve the crystallinity selection of nanocrystals and induce marked changes in the supracrystal mechanical properties.