Facile fabrication of polymer-dispersed liquid crystal films via nucleophile-initiated thiol-ene click reaction

Nucleophile-initiated thiol-ene click reaction was employed to prepare polymer-dispersed liquid crystal (PDLC) films initiated by 4-dimethylaminopyridine (DMAP). The PDLC films were prepared in different temperature. It is found that the reaction temperature has a big influence on the electro-optical properties of PDLC films and 60°C is the optimal temperature to fabricate PDLC film which has high ON state transmittance (T_on) and low OFF state transmittance (T_off). UV-Visible spectrophotometer, scanning electron microscopy and polarised optical microscope were employed to explore the obtained PDLC films. Nucleophile-initiated thiol-ene click reaction, without UV-light, probably provides a new pathway to prepare PDLC films.     

Correlative studies on the fabrication of poly(styrene-methyl-methacrylate-acrylic acid) colloidal crystal films

This research describes a one-step procedure for monodispersed poly(styrene-methyl-methacrylate-acrylic acid colloidal spheres [P(St-MMA-AA)] via soap-seeded emulsion polymerization. The effects ofreaction conditions such as temperature, stirring speed, initiation concentration, e.t.c. were examined. The results obtained showed that the spheres average particle diameter decreased with increase in initiator concentration, the reaction temperature and stirring speed and increased with an increase in monomer concentrations. The particles show stable mechanical properties within the transition and heating temperatures of 111.9?°C and 388?°C respectively. Zeta-potential values ranging from ?31.8?mV to ?36.5?mV which is indicative of stable dispersion of colloidal particles were obtained for all the prepared latexes. The assembled colloidal latex had periodic structures with mainly hexagonal three-dimensional structures with multi-facet arrangements. The latex also shows spherical shape of monodispersed core-shell particles.     

Facile fabrication of photonic MOF films through stepwise deposition on a colloid crystal substrate

Based on stepwise deposition of MOF films on a colloid crystal substrate, a strategy for fabricating photonic MOF films was developed. We found that the integration of a photonic structure endows MOF materials with unique optical properties, which can be used as a general and effective transduction scheme for a convenient study of the host-guest chemistry of MOFs.     

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.     

Facile fabrication of free-standing colloidal-crystal films by interfacial self-assembly

This paper reports a rapid and facile method of preparing free-standing colloidal crystals from monodisperse charged polystyrene (PS) microspheres. Mixed solvents (ethanol/water) were used as the dispersion medium in the self-assembly process of colloidal crystals. By a simple "floating self-assembly" method, PS microspheres floated on the surface of liquid and self-assembled into large area of three-dimensional (3D) ordered colloidal crystals within 15 min. Then epichlorohydrin was added in as a cross-linking agent to strengthen the colloidal-crystal film. After cross-linking reactions between the microspheres, the obtained colloidal-crystal film was free-standing and could be easily transferred to other substrates. Using tetrabutyl titanate as a titania precursor, 3D porous TiO(2) materials with rodlike skeletal structure were fabricated from the prepared free-standing colloidal crystal. This work provides a facile method to fabricate free-standing colloidal-crystal film, which can be used as an ideal template for the preparation of porous materials.     

Direct-write fabrication of colloidal photonic crystal microarrays by ink-jet printing

An array of the colloidal photonic crystals was directly fabricated using an ink-jet printing. The colloidal ink droplets containing the monodispersed polystyrene latex particles were selectively deposited on a hydrophobic surface. Solvent evaporation from each ink droplet leads to a formation of microdome-shaped colloidal assembles of close-packed structures. Microspectroscopic analysis has confirmed that the individual assembly serves as a photonic crystal and its optical properties can be correlated with the microstructural features. Unlike other techniques of patterned growth of colloidal photonic crystal, the substrate does not need to be patterned first and no template is needed in the direct writing by the ink-jet printing. Using our strategy, we have rapidly produced the colloidal photonic crystal microarrays composed of different-sized spheres addressably patterned on the same substrate.     

Growth dynamics of self-assembled colloidal crystal thin films

A theoretical and experimental analysis of the growth dynamics of colloidal crystal films deposited by evaporation induced self-assembly is herein presented. We derive an expression for the film growth velocity from which we obtain an equation that describes the evolution of the forming crystal thickness with time. Its validity is confirmed by comparison to the experimental profiles of a large number of films grown under different conditions. We find that, on top of the already reported linear increase in film width over long distances in the growth direction, periodic variations of the friction force at the meniscus give rise to short-range thickness fluctuations that are the main source of spatial inhomogeneities observed in these lattices. The key parameters that determine the period and the intensity of these fluctuations are identified.     

Inward-growing self-assembly of colloidal crystal films on horizontal substrates

Colloidal crystal films have been fabricated on solid substrates with a horizontal deposition method. Scanning electron microscope images showed that the colloidal crystal films exhibit ordered face-centered cubic structures in large domains. Optical measurements demonstrated the presence of photonic band gap along the crystallographic [111] direction. The fabrication method described in this paper allows one to rapidly fabricate colloidal crystal films of different thicknesses, which can be controlled by varying colloidal suspension concentration or volume. In addition, the method also works well for growing colloidal crystal films on a hydrophilic solid substrate with a rough surface. Furthermore, the fabrication of colloidal crystal heterostructures has been demonstrated. An inward-growing mechanism responsible for self-assembly of colloidal spheres on horizontal substrates has been proposed to interpret the observed experimental results.     

Large-domain colloidal crystal films fabricated using a fluidic cell

The growth of colloidal crystal films from a dispersion of monodispersed silica spheres using a simple cell with one opening was investigated. Colloidal crystal films with large domain sizes were successfully fabricated almost over the cell (approximately 10 cm2) without applying any external force at room temperature. During the drying process, three distinct conditions were observed, in each of which the films exhibited different optical properties. Films with high transmittance were formed in the first stage. Upon further solvent evaporation, the films entered a medium transmittance state via an extremely low transmittance state. Angle-resolved reflection spectroscopy, which was used to analyze the three conditions, revealed that close-packed arrays with water-filled spaces between were formed in the first stage. One-directional flow was generated in the cell because water evaporation occurred only at the opening. The flow caused the spheres to be arranged epitaxially, resulting in a large domain size.     

Rapid fabrication of large-area colloidal crystal monolayers by a vortical surface method

We have developed a simple approach for rapidly fabricating large-scale colloidal crystal arrays on substrates. Latex particles were first assembled into a close-packed monolayer on a vortical water surface; the monolayer was then transferred onto substrates by a withdrawer. Such an assembly method is conceptually similar to the Langmuir-Blodgett (L-B) methods for film deposition but does not require an L-B trough. The samples exhibit a large-scale periodic feature based on optical microscopy and scanning electron microscopy observations and diffract the laser beam, acting as crystals. This newly developed technique is timesaving, widely accessible, and applicable to large particles (up to 2 microm). It promises to be useful in nanofabrication.     

Growth of mesoporous materials within colloidal crystal films by spin-coating

A combination of colloidal crystal planarization, stabilization, and novel infiltration techniques is used to build a bimodal porous silica film showing order at both the micron and the nanometer length scale. An infiltration method based on the spin-coating of the mesophase precursor onto a three-dimensional polystyrene colloidal crystal film allows a nanometer control tuning of the filling fraction of the mesoporous phase while preserving the optical quality of the template. These materials combine a high specific surface arising from the nanopores with increased mass transport and photonic crystal properties provided by the order of the macropores. Optical Bragg diffraction from these type of hierarchically ordered oxides is observed, allowing performing of optical monitoring of the different processes involved in the formation of the bimodal silica structure.     

Facile method for fabrication of nanocomposite films with an ordered porous surface

This paper presents a novel and facile method for the fabrication of nanocomposite films with ordered porous surface structures. In this approach, a water-borne poly(styrene-co-butyl acrylate-co-acrylic acid)/silica nanocomposite dispersion was synthesized in situ by surfactant-free emulsion polymerization by using 3-allyloxy-2-hydroxy-1-propanesulfonate as a polymerizable surfactant. When this dispersion was dried to form a film at a certain temperature, an ordered porous structure could be directly obtained on the surface of the nanocomposite film. SEM, TEM, and AFM were employed to observe the morphology, and XPS and particle analyzer were used to analyze the surface composition of the ordered porous nanocomposite film and the particle size, respectively.     

Facile fabrication of poly(p-phenylene ethynylene)/colloidal silica composite for nucleic acid detection

Fabrication, characterization, and application of poly(phenylene ethynylene) (PPE)/silica composite particles are described. PPE is a class of conjugated polymers, which has been used for various sensory materials. However, its hydrophobic nature makes its application difficult in the aqueous phase, especially for biological substance detection. In this report, we utilized non-aqueous soluble PPE, 15 nm of colloidal silica particles, and aminosilane to fabricate a biosensory platform. The resulting composite showed high aqueous compatibility, large surface area, high quantum efficiency, and versatile chemical modification including oligonucleotide coupling. By monitoring the fluorescence quenching of PPE, we could detect a quencher-labeled target oligonucleotide specifically. Stern-Volmer (SV) analysis showed different accessibility of fluorophores (PPE) to a quencher labeled target oligonucleotide. The accessibility of fluorophores and SV constant are determined to be 0.54 and 4.2 x 10(7)M(-1), respectively, from a modified SV plot. This method will broaden the capability of conjugated polymers for the sensitive detection of biological substances.     

Facile fabrication of superhydrophobic surface from micro/nanostructure metal alkanethiolate based films

A series of superhydrophobic surfaces with micro/nanostructure have been successfully achieved by a simple process via the reaction between metal (such as Cd and Zn) salts and alkanethiolates.     

Facile fabrication of porous NiO films for lithium-ion batteries with high reversibility and rate capability

We report the high-rate capability and good cyclability of three-dimension nanoporous NiO films as the anodes of lithium-ion batteries. The NiO films are fabricated by immersing foam nickel substrates in an 80 °C aqueous solution containing ammonia and potassium peroxydisulfate, and subsequent heat treatment at 500 °C. At a rate of 1.0 C, the film electrodes maintain a capacity of 560 mAh g⁻¹ as well as capacity retention of 97% after 100 discharge/charge cycles. When the current density is increased to 14C, 42% of the capacity can be retained. Owing to the ease of large-scale fabrication and superior electrochemical performance, these NiO films will be promising anodes for high-energy-density lithium-ion batteries.     

Generalized fabrication of two-dimensional non-close-packed colloidal crystals

In this paper we report a generalized templating approach for fabricating wafer-scale, two-dimensional, non-close-packed (ncp) colloidal crystals. Polymer nanocomposites consisting of monolayer ncp colloidal crystals prepared by a spin-coating process are used as sacrificial templates. After removal of the colloidal silica templates, the voids in the polymer matrix are infiltrated with other materials. By plasma-etching the polymer matrix, wafer-scale ncp colloidal crystals from a variety of functional materials can be made. This technique is scalable and compatible with standard microfabrication. Two-component colloidal arrays with complex micropatterns can also be fabricated by combining microfabrication with this templating approach. Normal-incidence reflectivity spectra of replicated titania ncp arrays agree well with theoretical prediction using Scalar Wave Approximation.     

Facile fabrication of monodisperse polymer hollow spheres

This article reports the facile synthesis of monodisperse polymer hollow spheres by seeded emulsion polymerization without additional treatment. In this method, P(St-MMA-MAA) copolymer latex particles were first prepared by emulsifier-free emulsion polymerization and then used as seeds to carry out emulsion polymerization of methyl methacrylate (MMA), divinyl benzene (DVB), and 2-hydroxyethyl methacrylate (HEMA) with potassium persulfate (KPS) as initiator at 80 degrees C. The void of hollow spheres was readily adjusted by changing the monomer/seed weight ratio, and it could be enlarged while the diameters of hollow spheres changed little after etching by dimethyl formamide (DMF). The effects of synthetic parameters including the monomer composition and the properties of seeds on the morphology of hollow spheres were investigated in detail. On the basis of the experimental results, it seemed reasonable to conclude that the formation of hollow spheres was due to the "dissolution" of seeds in monomers and phase separation between the constituent polymers. As a thermodynamic factor, sodium dodecyl sulfate (SDS) would allow the preparation of solid particles depending on its level.     

Facile fabrication of nanoporous gold film electrodes

A novel one-step method has been developed for the fabrication of a three-dimensional (3D) nanoporous gold film (NPGF). The NPGF can be facilely made within 1 min from a pure gold substrate by applying a step potential just into the initial transition region of gold in an HCl medium. The pore formation and structural evolution have been revealed by scanning electron microscope, and the processes involve electrodissolution, disproportion, and deposition. The as-prepared 3D NPGF electrode has a large surface area and exhibits high catalytic activity in the electrooxidation of glucose. The NPGF electrode also shows excellent performance toward the electrooxidation of formic acid after being decorated with a tiny amount of Pt by electrodeposition.     

Facile fabrication of magnetic single-crystalline ceria nanobelts

The magnetic single-crystalline CeO₂ nanobelts were successfully prepared on Cu substrates by electrochemical deposition. The surface morphologies of CeO₂ can be well controlled by changing the additives and current densities of electrodeposition. Experimental results suggest that NH₄NO₃ plays a key role in the formation of CeO₂ nanobelts. The magnetic properties are clearly observed for the obtained CeO₂ nanobelts. The magnetizations of CeO₂ nanobelts increase with temperature decreasing. It is believed that this electrochemical synthetic route can be used to prepare other rare earth oxide nanobelts.