Abstract
Sol–gel monoliths based on SiO2, TiO2 and ZrO2 with holographic colourful diffraction on their surfaces were obtained via a sol–gel synthesis and soft lithography combined method. The production was carried out without any additional equipment at near room temperature and atmospheric pressure. The accurately replicated wavy structure with nanoscale size of material particles yields holographic effect and its visibility strongly depends on refractive index (RI) of materials. Addition of multi-walled carbon nanotubes (MWCNTs) in systems increases their RI and lends absorbing properties due to extremely high light absorption constant. Further prospective and intriguing applications based on the most successful samples, MWCNTs-doped titania, were investigated as reversible optical humidity sensor. Owing to such property as reversible resuspension of TiO2 nanoparticles while interacting with water, it was proved that holographic xerogels can repeatedly act as humidity sensors. Materials which can be applied as humidity sensors in dependence on holographic response were discovered for the first time.
Highlights
Nowadays, materials with structured periodic micron-scale surfaces or superstructures are widely used both in industry and science
We show here—using optical and structural measurements—that sol–gel matrices with high refractive index (RI) can be applied for soft lithography of holographic colourful diffraction at atmospheric conditions and that after entrapment within multi-walled carbon nanotubes (MWCNTs), they quite significantly enhance the visibility of the diffraction colour, making it much brighter
In the idea we propose in this work, qualitative detection of air humidity is achieved by change of effective refractive index (RI) because of water absorption and change in diffraction grating’s geometry along all three linear dimensions
Summary
Materials with structured periodic micron-scale surfaces or superstructures are widely used both in industry and science These are applied as holographic materials [1,2], distributed feedback resonators [3], diffraction gratings [4], guides of stem cells growth [5] and others. These structured materials can be prepared by the soft lithography route, which was chosen in this study because of simplicity of its technology, absence of additional equipment and low cost of production.
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