Aleksandr V. Yakovlev

Inkjet Color Printing by Interference Nanostructures.

Color printing technology is developing rapidly; in less than 40 years, it moved from dot matrix printers with an ink-soaked cloth ribbon to 3D printers used to make three-dimensional color objects. Nevertheless, what remained unchanged over this time is the fact that in each case, dye inks (CMYK or RGB color schemes) were exclusively used for coloring, which inevitably limits the technological possibilities and color reproduction. As a next step in printing color images and storing information, we propose the technology of producing optical nanostructures. In this paper, we report use of inkjet technology to create colored interference layers with high accuracy without the need for high-temperature fixing. This was made possible due to using titania-based colloidal ink yielding monolithic coatings with a high refractive index (2.00 ± 0.08 over the entire visible range) when naturally dried. By controlling the film thickness by using inkjet deposition, we produced images based on controlled interference and implementing color printing with one ink. The lack of dyes in the proposed method has good environmental prospects, because applied systems based on a crystalline anatase sol are nontoxic and biologically inert. The paper explains in detail the principle of producing interference images by the classical inkjet method and shows the advantages of this technique in depositing coatings with uniform thickness, which are required for large-scale interference color imaging even on unprepared polymer films. This article demonstrates the possibility of inkjet printing of nanostructures with a precision in thickness of up to 50 nm, we believe that the proposed approach will be the groundwork for developing interference color printing approach and allow to implement new methods of forming optical nano-objects by widely available techniques.

Reversible sol–gel–sol medium for enzymatic optical biosensors

In this paper we for the first time report a reversible sol-gel-sol approach to obtain optical enzymatic biosensors with improved enzyme stability and good sensitivity by using desktop inkjet printing. The developed technique is based on the bio-inorganic inks allowing for a sol-gel-sol transition of the inorganic matrix: from liquid ink to a solid alumina matrix with entrapped enzymes and a subsequent color response due to the enzymatic reaction upon the resuspension of the matrix. This approach improves the stability of the enzymes entrapped in the porous inorganic matrix, and at the same time maintains a high sensitivity of the biomolecules, whose facile release is ensured by the gel-sol transition. Rheological parameters of the developed bio-inorganic ink are highly adjustable making it suitable for the deposition on different surfaces by inkjet printing. The potential and utility of this approach is demonstrated by a successful production of optical biosensors for glucose and uric acid.

UV-curable hybrid organic–inorganic composite inks with a high refractive index for printing interference images and holograms

Herein we report a new, facile and inexpensive methodology for obtaining highly refractive polymers suitable for inkjet printing using hexacoordinated titanium complexes (THC) and a UV-curable lacquer based on triethylene glycol dimethacrylate (TGD) that is a cheap and non-toxic monomer that can be rapidly polymerized under UV irradiation under ambient conditions. The resulting polymeric materials are characterized by a refractive index (RI) of about 1.85 in the solid state and have rheological properties suitable for inkjet printing applications. The polymeric materials can be printed onto solid supports resulting in surface structures giving rise to interference images and masking of rainbow holograms illustrating thus the prospective practical applications of the described approach.

Inkjet printing of TiO2/AlOOH heterostructures for the formation of interference color images with high optical visibility.

This paper describes a practical approach for the fabrication of highly visible interference color images using sol-gel ink technique and a common desktop inkjet printer. We show the potential of titania-boehmite inks for the production of optical heterostructures on various surfaces, which after drying on air produce optical solid layers with low and high refractive index. The optical properties of the surface heterostructures were adjusted following the principles of antireflection coating resulting in the enhancement of the interference color optical visibility of the prints by as much as 32%. Finally, the presented technique was optimized following the insights into the mechanisms of the drop-surface interactions and the drop-on-surface coalescence to make it suitable for the production of even thickness coatings suitable for printing at a large scale. We propose that the technology described herein is a promising new green and sustainable approach for color printing.

Inkjet printing of transparent sol-gel computer generated holograms

In this paper we report for the first time a method for the production of transparent computer generated holograms by desktop inkjet printing. Here we demonstrate a methodology suitable for the development of a practical approach towards fabrication of diffraction patterns using a desktop inkjet printer and nonocrystalline sol-gel ink. In particular, the reported inkjet printing method can be used to generate transparent diffraction structures on supports such as those widely applied in security technologies. Transparent highly refractive layers were deposited with a high precision via a wet-to-dry printing method based on the sol-gel transition phenomenon. With this approach we were able to print a diffraction pattern by TiO2 xerogel, with which a transparent computer generated hologram was created. We argue that this new technology can form the foundation for a new generation of commercial protective coating technologies applied by industrial inkjet printing.

Inkjet printing of specular holograms based on a coffee-ring effect concave structure

Inkjet printing is a promising direction for materials application and structuring. The proposed method for creating specular holograms on a variety of surface materials is based on creating a three-dimensional surface microstructure by controllable ink deposition. The foundation of the proposed approach is precise control of the applied ink containing titania nanoparticles with a high refractive index. This allows one to achieve a densely packed concave structure through the coffee-ring effect. Surface specular glints on the concave surface of the printed structure underlie the principle of this type of holography. The printed samples have high visibility and easy application and reproduction. Besides this, the retaining of high transparency and structure be applied to traditional print images or text. The presented method allows us to prove that inkjet printing is not only a method for layer-by-layer application of materials but also a method for creating complex three-dimensional functional optical structures. The proposed approach has direct applications in industry and can be used for additional holographic protection, along with showing researchers a different point of view on the inkjet printing method in general.