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This paper describes a simple and convenient procedure based on the Tollens process for the preparation of silver nanoparticles with a relatively narrow distribution in size. The starting reagents were similar to those commonly used in the electroless deposition of silver. Only under appropriate conditions, mixing of these reagents was able to generate stable aqueous dispersions of silver colloids rather than thin films of silver deposited on the surfaces of objects immersed in the plating solution (including the interior surface of the container). We have demonstrated the capability and feasibility of this approach by forming silver nanoparticles with dimensions in the range of 20–50 nm. These silver nanoparticles could exist as very stable dispersions in water, or as submonolayer coating on microscale colloids. We have also explored the use of light scattering simulation to study the oxidation (by air) of these nanoparticles.

Supermolecular multilayers with high levels of compositional and structural complexities have been fabricated with an example that involves formation of stable host–guest complexes from bolaamphiphiles and cyclodextrins, followed by sequential build-up of multilayered films by these complexes in combination with anionic polystyrene sulfonate polymer chains.

A novel Fe3O4@SiO2/PEG acrylate photonic crystal humidity sensor has been fabricated by combining magnetic assembly and photo-polymerization. The sensor self-displays brilliant colors as the humidity changes. By optimizing the cross-linking level and the thickness of the polymer film, the reflection wavelength can shift 160 nm in several minutes, while its intensity is readable by the naked eye. The tested sensors demonstrate good reversibility and durability in cycling experiments. Such photonic crystal sensors may have great potential as energy efficient devices, as no electric power is required for their operation.

A convenient route for the preparation of thermochromic VO2 particles has been developed by combining solution-phase hydrolysis and a thermal reduction process. With this method, the particle size can be easily tuned from tens to hundreds of nanometres. The liquid dispersibility of these VO2 particles facilitates convenient observation and effective measurement of the temperature-dependent optical properties in the visible region. We observe a blue shift of the resonance peak of metal-phase VO2 particles with decreasing size. The size effect also exists in the phase transition behavior: smaller VO2 particles exhibit a wider hysteresis curve during the semiconductor-to-metal transition. We also demonstrate that the VO2 particles in the form of a colloidal dispersion can be easily incorporated into thin plastic thermochromic films that may be used as smart windows for energy management.

Magnetically responsive photonic crystal structures have been produced by self-assembling superparamagnetic colloidal particles under the balance of repulsive and attractive interactions. The optical properties can be tuned rapidly, widely, and reversibly in the entire visible spectrum. By taking advantage of many unique features of the field responsive systems, we demonstrate in this article some of their niche applications for various display purposes, including antifraud devices, rewritable photonic papers, and full colour high resolution printing systems.

Superparamagnetic Fe3O4/SiO2/TiO2 peapod-like nanostructures have been successfully synthesized by using Fe3O4/SiO2 core/shell particles as building blocks and TiO2 as the adhesive without the need of any hard or soft templates. The fabrication process involves chaining the Fe3O4/SiO2 cores during magnetic stirring and subsequent fixing of the chain structure during TiO2 coating. The number of Fe3O4/SiO2 cores arranged linearly in the chains could be effectively controlled by tuning the amount of titanium precursor or the magnetic stirring rate. The double layer coating of SiO2 and TiO2 enhances thermal and chemical stability of the nanopeapods, and the one-dimensional chain structure produces interesting properties that enable applications not possible with conventional magnetite materials. As a demonstration, we show here the use of these superparamagnetic peapod-like nanostructures for low-frequency optical modulation.

We report the self-assembly behavior and tunable plasmonic property of gold nanoparticles on the surface of mercapto-silica colloidal spheres. The mercapto-silica spheres provide a quasi two-dimensional surface for nanoparticle immobilization through the strong gold–thiol interactions, making it convenient to control the interparticle separation by varying both the length of the capping ligands and the molar ratio of gold nanoparticles to the supporting mercapto-silica microspheres. With the ability to fine tune the interparticle separation and consequently the strength of the electromagnetic coupling, we demonstrate a high degree of control over the plasmon resonance property of the resulting composite microspheres. The colloidal form of the assembled nanostructures promises broad applications in which tailored plasmonic property and solution dispersibility are required.

Magnetically responsive colloidal photonic crystals have been fabricated by using highly charged superparamagnetic Fe3O4 colloidal nanocrystal clusters (CNCs) as the building blocks. The colloids form chainlike structures with regular interparticle spacing of a few hundred nanometers along the external field so that the system strongly diffracts light. The diffraction wavelength can be tuned across the entire visible spectrum by simply changing the strength of the magnetic field. The fast and reversible response suggests great potential of these photonic materials in applications such as displays and sensors. Further modification of the Fe3O4 CNCs with silica coating allows the dispersion of the particles in nonaqueous solutions. The modified particles also self-assemble into ordered structures in alcohol solvents under an external magnetic field. Embedding droplets of such a colloidal solution in a polymer matrix produces solid composite materials with magnetically responsive optical properties.

This communication describes a simple route to Ag nanoplates by slowing the polyol reduction of silver nitrate with polyacrylamide (PAM). In addition to its role as a stabilizer for Ag colloids, the amino groups of PAM can form complexes with Ag+ ions in the solution to substantially reducing the reduction rate, leading to the formation of thin nanoplates.