Monodisperse polystyrene (PS) spheres with controllable size have been synthesized by a straight forward and simple procedure. The as-synthesized PS spheres have a typical diameter ranging from ~180 nm to ~900 nm, where a reduced sphere size is obtained by increasing the polyvinylpyrrolidone (PVP)/styrene weight ratio. The PS spheres function as sacrificial templates for the fabrication of hollow silica nanospheres (HSNSs) for thermal insulation applications. By modifying the silica coating process, HSNSs with different surface roughness are obtained. All resulting HSNSs show typically a thermal conductivity of about 20 mW/(mK), indicating that the surface phonon scattering is probably not significant in these HSNS samples.

Thermal conductivity of TiO2 nanotubes prepared from a NaOH treatment of TiO2 particles with subsequent acid washing and annealing has been investigated. The obtained TiO2 nanotubes have a tetragonal anatase structure, and have a typical inner diameter of about 4-5 nm, wall thickness of about 2-3 nm, and length up to several hundred nanometers. TiO2 nanotubes show a significantly reduced thermal conductivity of about 0.40-0.84 W/(m·K) (average 0.62 W/(m.K)) at room temperature, as compared to about 8.5 W/(m·K) for the bulk TiO2 materials. The great suppression in thermal conductivity can be understood by means of increased phonon-boundary scattering and enhanced phonon confinement in TiO2 nanotubes with unique nanotubular morphology, small featured sizes, and large surface area (~258 m2/g). A theoretical analysis including the surface scattering and size confinement effects of phonon transport in TiO2 nanotubes is also reported, which results in an intrinsic thermal conductivity of 0.30-0.77 W/(m·K) (average 0.54 W/(m.K)) for individual TiO2 nanotubes with wall thickness of 2-3 nm, in harmony with the experimental values.

The application of manufactured nanomaterials provides not only advantages resulting from their unique properties but also disadvantages derived from the high energy use and CO2 burden related to their manufacture, operation, and disposal. It is therefore important to understand the trade-offs of process economics of nanomaterial production and their associated environmental footprints in order to strengthen the existing advantages while counteracting disadvantages. This work reports the synthesis, characterization, and life cycle assessment (LCA) of a new type of superinsulating materials, nano insulation materials (NIMs), which are made of hollow silica nanospheres (HSNSs) and have great flexibility in modifying their properties by tuning the corresponding structural parameters. The as-prepared HSNSs in this work have a typical inner pore diameter of about 150 nm and a shell thickness of about 10–15 nm and exhibit a reduced thermal conductivity of about 0.02 W/(m K) because of their size-dependent thermal conduction at the nanometer scale. The energy and raw material consumption related to the synthesis of HSNSs have been analyzed by the LCA method. The results indicate that the recycle of chemicals, up-scaling production, and use of environmentally friendly materials can greatly affect the process of environmental footprints. New synthesis routes for NIMs with improved thermal performance and energy and environmental features are also recommended on the basis of the LCA study.

Monodisperse hollow silica nanospheres have been prepared by using a polystyrene nanosphere template-assistant approach and their potential as antireflection (AR) coatings for window applications has been discussed. The as-prepared hollow silica nanospheres have a typical inner diameter of 200 nm and a shell thickness of 15–20 nm. The AR effect over the ultraviolet-visible-near infrared spectral region has been observed for the hollow silica nanospheres, with a minimized reflection of about 5.2 % at 500 nm, compared to 8.5 % of a plain float glass substrate. By modifying the structural features of the hollow silica nanospheres, their AR properties can be further enhanced.

Electrochromic (EC) materials that change their optical transmittance under an external electrical field may form the basis of “smart windows”, which are of great interest in forthcoming building technologies. Nanostructured EC materials or assemblies have revealed remarkable improvement on colouration efficiency and switching time due to their small featured sizes and large surface areas. Here, the recent progress of nanoelectrochromics is reviewed; the scientific and technical issues related to material preparation and device assembly for large-area and large-scale window applications are discussed.