孔径梯度变化的聚苯乙烯多孔薄膜的制备

 为了对聚合物多孔材料的微观孔结构进行控制,利用垂直沉积技术,制备了蛋白石结构和多层异质结构的SiO₂胶体晶体,并通过模板导向前驱物填充手段,获得了反蛋白石结构和孔径梯度变化的聚苯乙烯多孔薄膜。扫描电镜分析表明,聚苯乙烯多孔结构精确复制了原始模板的反结构。光学透射谱显示,填充聚苯乙烯后复合蛋白石光子禁带位置相对原始模板发生红移,除去模板后,光子禁带位置发生蓝移。根据布拉格衍射方程,计算出胶体晶体模板空隙的填充分数。     

Polarization-dependent suppression of Bragg reflections in light reflection from photonic crystals

This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ? _c , at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ? _c , which depends on the geometric parameters and dielectric constants of the spatially periodic structure.     

Analysis of the imperfection of opal-like photonic crystals synthesized on conducting substrates

The type and degree of imperfection for opal-like photonic crystals on conducting substrates have been investigated using synchrotron small-angle X-ray scattering with a microradian resolution. It has been demonstrated that self-assembly of poly(styrene) spheres by the vertical deposition method leads to the formation of a face-centered cubic structure on a mica/Au substrate and a random hexagonal close packing on a glass substrate with the In₂O₃(SnO₂) conducting coating.     

Dynamic templating role of polynaphtalene sulphonate in the formation of silver nanocrystals in aqueous solution

We have used time resolved small angle X-ray scattering (SAXS) for investigating the early stages of the formation of crystalline colloidal Ag particles by AgNO₃ reduction with ascorbic acid in an aqueous acidic solution of a polynaphthalene sulphonate polymer (Daxad). In order to exploit the polymer role in silver crystallization, the measurements have been performed at different polymer concentrations. Data analysis suggests that the nucleation and growth of primary particles of about 20 nm in diameter, occurring in a surface-fractal arrangement of the dynamic polymeric template, is assisted by the development of long range spatial correlations. These correlations could be a sign of polymer-induced liquid fluctuations as intermediate precursors of Ag crystallization.     

Formation of two-dimensional ordered magnetic nanolattices in opal structures

A method of forming a two-dimensional ordered superlattice of magnetic nanoparticles in close-packed opal structures of silica (SiO₂) spheres has been developed. Nickel nanopowder with an average particle size of about 70 nm is used as a source of magnetic particles. Atomic-force and magnetic-force microscopy studies show that all magnetic particles are located in the interstices of the opal lattice, while the magnetization vectors of neighboring nickel particles can have different magnitudes and directions.     

BaSO4 nanorods produced in polymer-modified bicontinuous microemulsions

The influence of the water soluble polymer poly(ethylene glycol) (PEG) on structure formation in the quasiternary system sodium dodecylsulfate (SDS)/pentanol-xylene/water was checked by means of conductometry, rheology, and micro differential calorimetry. The polymer induces the formation of an isotropic phase channel between the o/w and w/o microemulsion. The transition from the normal as well as from the inverse micellar to the bicontinuous phase range can be detected by conductometry, rheology as well as micro-DSC. As a result of polymer–surfactant interactions, the spontaneous curvature of the surfactant film is changed and a sponge phase is formed. The bicontinuous phase is characterized by a moderate shear viscosity, a Newtonian flow behaviour, and the disappearence of interphasal water in the heating curve of the micro-DSC. When the polymer-modified bicontinuous phase is used as a template phase for the nanoparticle formation, spherical BaSO₄ nanoparticles were formed. During the following solvent evaporation process the primarily formed spherical nanoparticles aggregate to nanorods and triangular structures due to the non-restriction of the bicontinuous template phase in longitudinal direction.     

Ordered structures in a nonideal dusty glow-discharge plasma

The formation of ordered structures of charged macroparticles in a constant-current neon glow-discharge plasma is investigated. Experiments were performed with two types of particles: thin-walled glass spheres 50–63 μm in diameter and particles of Al₂O₃, 3–5 μm in diameter. Formation of quasicrystalline structures is observed in the standing strata and in an artificially created double electric layer. The formation of extended filamentary structures of macroparticles in the absence of visible stratification of the positive column has been observed for the first time. The influence of the discharge parameters on the formation of the ordered structures and their melting is examined. The form of the interaction potential between the charged macroparticles is considered, as well as changes in the conditions for maintaining the discharge in the presence of high concentrations of dust particles. Zh. éksp. Teor. Fiz. 112, 2030–2044 (December 1997)     

Colloidal particles of silicon dioxide for the formation of opal-like structures

The conditions of synthesis of silicon dioxide particles with a high degree of monodispersity have been investigated. The particles have been synthesized using both the hydrolysis of tetraethoxysilane in the presence of L-arginine and a combination of this technique with the traditional Stöber method. It has been shown that the use of SiO₂ particles synthesized by the heterogeneous hydrolysis of tetraethoxysilane in the presence of the amino acid for their further growth according to the Stöber method makes it possible to obtain particles 100 nm and more in size with a narrow size distribution (the deviation of the diameter is less than 3%), a nearly perfect spherical shape, and a smooth surface.     

Self-assembly of CuS nanoparticles to solid,hollow, spherical and tubular structures in a simple aqueous-phase reaction

We report fabrication of CuS particles with solid, hollow, spherical and tubular structures in a simple aqueous system under microwave irradiation, employing CuSO₄ and Na₂S₂O₃ as the starting materials without assistance of any surfactant or template. Energy-dispersive X-ray analysis and an X-ray powder diffraction pattern proved that the product is hexagonal CuS phase. The morphologies of the product were observed by scanning electron microscopy and transmission electron microscopy. Some factors affecting the morphologies of the product are discussed. PACS 81.05.Hd; 81.07.Bc; 81.16.Be; 81.16.Dn; 81.20.Ka     

Photonic crystals for the visible spectrum by holographic lithography

We describe a general and flexible technique for the fabrication of three-dimensional photonic crystals that is particularly well adapted to the production of structures with the sub-micron periodicity required for applications in the visible optical spectrum. Three-dimensional microstructure is generated by using a four-beam laser interference pattern to expose a thick layer of photoresist. Exposed areas are rendered insoluble; unexposed areas are dissolved away leaving a three-dimensional photonic crystal formed of cross-linked polymer with air-filled voids. The polymeric structure may be used as a template for the production of photonic crystals with higher refractive index contrast. Photonic crystals made of polymer and of TiO₂ have been characterized by scanning electron microscopy and by optical diffraction measurements.     

Mesoporous silica-coated superparamagnetic particles prepared by pseudomorphic transformation and their application in purification of plasmid DNA

Abstract  

Mesoporous silica-coated superparamagnetic particles were prepared via pseudomorphic transformation of pre-made amorphous silica-coated Fe₃O₄–polymer composite particles using n-cetyltrimethylammonium bromide (CTAB) and 1,3,5-trimethyl benzene (MES) as template. The mesoporous particles presented almost the same size, shape, and magnetic property as the original amorphous particles but an ordered mesoporous shell with wormhole-like pore structure. The pore size of the shells increased from 2.4 to 3.1 and 4.2 nm as the molar ratio of MES/CTAB increased from 0 to 1.0 and 1.5. DNA extraction experiments showed the mesoporous particles were qualified for purification of plasmid DNA from bacterial lysate.     

Growth of magnetic materials and structures on Si(0 0 1) substrates using Co2Si as a template layer

We report in this paper the use of Co₂Si silicide as a template layer for the integration of magnetic materials and structures on silicon substrate. By undertaking Co deposition on silicon at a temperature of about 300 °C, we show that it is possible to obtain a smooth and epitaxial Co₂Si layer, which can act as a template layer preventing the reaction between Co and other transition metals with silicon. Two examples of over-growth of magnetic materials and structures on this template layer will be presented: growth of ferromagnetic Co layers and of magnetic tunnel junctions (Co(Fe)/AlO_x/NiFe).     

Optical properties of two-dimensional inverse photonic structures upon disordering of their unit cell

Transmission frequency spectra of two-dimensional inverse photonic structures constituting a hexagonal packing of cylindrical pores in a non-absorbing matrix have been calculated using the Riccati equation. The dependence of the spectral width of the structure opacity band on the degree of a positional disorder of pores in their unit cell has been investigated for the case where the magnitude of the wave vector of electromagnetic radiation in a matrix is on the order of the pore size.     

Enhancing fluorescence of tricolor fluorescent powders by silica inverse opals

Silica inverse opal photonic crystals (PCs) were fabricated by using a sacrificial polymer template method, and were characterized by scanning electron microscopy and reflection spectra. The fluorescence of tricolor fluorescent powders has been enhanced obviously by silica inverse opals as the emission wavelengths of the tricolor fluorescent powders are in the range of stop bands of the inverse opal PCs, which demonstrates that the PCs will be efficient and selective reflection mirrors. A promising application of the strategy would be in novel effective lighting devices. PACS 42.70.Qs; 78.55.-m; 78.55.Mb; 78.68.+m; 78.67.-n An erratum to this article can be found at     

Cu_2O particles with ordered pores via electrochemical deposition method

Cu2O particles cube with ordered pores are electrodeposited by using colloidal crystal template method. The shape of Cu2O cube particle is partly determined by its growing habit. Therefore, Cu2O cube particles with ordered pores are fabricated instead of three dimensional inverse opal structures.     

Optical and photoluminescent properties of plasma polymer films used in electroluminescent display structures

The optical and photoluminescent properties of plasma polymer layers synthesized from hexamethyldisiloxane are examined. The value of the polymer layer transparence is in the limits from 55% at 400 nm to 88% at 800 nm. Photoluminescence is stimulated by using the spectral line λ=365 nm emitted by a Hg spectral lamp.The organosilicon plasma polymers are included as protective and capsulating layers in electroluminescent (EL) structures. The structure obtained is characterized by a significant increase in emission brightness, compared to inorganic protective layers. For EL structures with a chalcogenide protective layer the increase is more than 6 times and for structures with heterogeneous matrix on the base of TiO₂ it is more than 20 times. As a stable covering the organosilicon plasma polymer increases the lifetime of the EL structures too.     

Memory effects in field-effect transistor structures based on composite films of polyepoxypropylcarbazole with gold nanoparticles

The memory effects in field-effect transistor structures with an active layer based on composite films of a semiconductor polymer, i.e., the carbazole derivative and gold nanoparticles, manifesting themselves in the hysteresis of the transient characteristics of the transistor have been studied. It has been shown that the observed effects are associated with the features of transport in the polymer-gold nanoparticle structure, where the gold particles serve as a medium of charge carrier collection (accumulation). The data writeerase mechanism based on conductivity modulation of the working channel of the field-effect transistor by the gate voltage have been discussed.     

Formation of a bioactive material for selective laser sintering from a mixture of powdered polylactide and nano-hydroxyapatite in supercritical carbon dioxide

Supercritical carbon dioxide (SC-CO₂) is used to prepare bioactive composites from powdered polylactide and nanosized hydroxyapatite for surface-selective laser sintering of three-dimensional tissue engineering structures. The mixture of powdered polylactide and nanosized hydroxyapatite and cannot be directly laser-sinter because of the impossibility of forming continuous filaments from sintered polymer particles. The use of composite particles for sintering formed in SC-CO₂ medium makes it possible to eliminate this shortcoming and to form continuous structures. Analysis of the composition and mechanical tests of such structures showed that the sintered composite obtained is fairly uniform, without destruction centers, capable of withstanding the same mechanical loads as the pure polymer, and therefore, suitable for use in tissue scaffold engineering.     

Lamellar versus isotropic structures in dilute phases of fluid membranes

In recent years, considerable attention has been focused on dilute phases of fluid membranes in surfactant systems. At the present time, the structure of two different phases have been well characterized. The lamellar phase (L_α) shows long range smectic order and consists of a regular stack of parallel bilayers. At high dilution, its long range order has been shown to be stabilized by the steric interaction between adjacent undulating membranes. The other phase (L₃) is isotropic and shows no long range positional order. Scattering patterns and transport properties strongly suggest that its structure consists of a randomly multiconnected bilayer separating two equivalent subvolumes of solvent. We here discuss the relative stability of these two structures in connection with the elastic properties of the amphiphilic membrane. A general scaling law for the free energy of the L₃ phase as function of the degree of dilution is proposed and is checked against experimental measurements of some of its static and dynamic physical properties.     

Imprinting by hot embossing in polymer substrates using a template of silica glass surface-structured by the ablation of LIBWE method

Laser-induced backside wet etching (LIBWE) of silica glass plates was performed to fabricate an imprinting template for hot embossing in polymer substrates such as polystyrene and silicone resin. Well-defined inverse surface-micropatterns of gratings and grid arrays on the substrates were produced by the hot embossing using a surface-structured silica glass as the template. These results indicate that the LIBWE method allows us to generate robust glass molding tools that exhibit the inverse shapes of the intended microstructures. PACS 52.38.Mf; 68.47.Mn; 81.05.Kf; 81.05.Lg; 83.50.Uv