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For the preparation of electrically conductive composites, various combinations of cellulose and conducting materials such as polymers, metals, metal oxides and carbon have been reported. The conductivity of these cellulose composites reported to date ranges from 10−6 to 103 S cm−1. Cellulose nanocrystals (CNCs) are excellent building blocks for the production of high added value coatings. The essential process steps for preparing such coatings, i.e. surface modification of CNCs dispersed in water and/or alcohol followed by application of the dispersion to substrate samples using dip coating, are low cost and easily scalable. Here, we present coatings consisting of Ag modified CNCs that form a percolated network upon solvent evaporation. After photonic sintering, the resulting coatings are electrically conductive with an unprecedented high conductivity of 2.9 × 104 S cm−1. Furthermore, we report the first colloidal synthesis that yields CNCs with a high degree of Ag coverage on the surface, which is a prerequisite for obtaining coatings with high electrical conductivity.

Antireflective coatings (ARCs) are applied to reduce surface reflections. We review coatings that reduce the reflection of the surface of the transparent substrates float glass, polyethylene terephthalate, poly(methyl methacrylate), and polycarbonate. Three main coating concepts exist to lower the reflection at the interface of a transparent substrate and air: multilayer interference coatings, graded index coatings, and quarter-wave coatings. We introduce and discuss these three concepts, and zoom in on porous quarter-wave coatings comprising colloidal particles. We extensively discuss the four routes for introducing porosity in quarter-wave coatings through the use of colloidal particles, which have the highest potential for application: (1) packing of dense nanospheres, (2) integration of voids through hollow nanospheres, (3) integration of voids through sacrificial particle templates, and (4) packing of nonspherical nanoparticles. Finally, we address the remaining challenges in the field of ARCs, and elaborate on potential strategies for future research in this area.

The use of cellulose nanocrystals (CNCs) in optical materials has been extensively studied. Key in most applications reported to date is the chiral nematic ordering of CNCs. Here, we demonstrate that random packing of silicated CNCs can also yield materials with interesting optical properties, i.e., highly porous, ultra-low refractive index coatings. Needle-shaped CNCs with an aspect ratio of 25 were extracted from Avicel, and subsequently covered with a silica layer. In one single dip coating step, highly porous coatings of CNC-silica core–shell particles were deposited on glass slides and silicon wafers. The lowest refractive index achieved was 1.03, which corresponds to a porosity of 94%; the thickness of these coatings ranged from 101 nm to 239 nm. The substrates, coated with a layer of CNC-silica core–shell particles, were heated to 450 °C for two hours. Cellulose was removed through pyrolysis, which resulted in porous coatings of sub-micron sized hollow silica rods. The porosity increase generated through pyrolysis of cellulose, however, was largely compensated by the decrease in packing porosity due to shrinkage of the coating.

Materials / Molecular Diversity Preservation International 6(9), 3710-3726 (2013). doi:10.3390/ma6093710, Published by MDPI, Basel

A reversible crosslinking mechanism enabling bonding and debonding of adhesives and coatings based on Diels-Alder chemistry is described. The Diels-Alder compounds form a covalently crosslinked network at low temperatures that break at elevated temperatures. As a result, the adhesive exhibits good solvent resistance, adhesion, and mechanical properties at temperatures of use, and additionally it can debond at elevated temperatures for optimal positioning, adjustments or total debonding. Upon cooling the covalent crosslinks are formed again and the properties of the original bond are re-obtained.The choice of crosslinker and binder material allows tailoring of the properties of the adhesive joint for different applications and processing conditions. At TNO, we have developed various Diels-Alder based binders for coatings and adhesives. This paper focuses on the design of a carrier adhesive for the semi-conductor industry. © 2010 Elsevier B.V. All rights reserved.

In this paper we present the use of Photonic Crystals as chemical sensors. These 2D nanostructured sensors were prepared by nano-imprint lithography during which a nanostructure is transferred from a nickel template into a responsive polymer, that is be specifically tuned to interact with the chemical compound that must be detected. By creating a Photonic Crystal in a responsive polymer, the sensitivity of such a sensor can be greatly enhanced with respect to nanophotonic sensors that are only functionalized by a surface treatment. We have shown the functionality of an imprinted sensor by exposing the nanostructures to various liquids and vapours and monitor the change in reflected signal. Depending on the interactions and refractive index contrasts, the maximum wavelength of the reflected light can decrease (when exposed to toluene) or increase (when exposed to acetone). © 2011 Published by Elsevier Ltd.

The success of nanomaterials in PV applications depends for a large part on their availability and procesability. Processes for large scale applications of these nanostructures are evaluated, with respect to antireflection and up/down conversion. © 2010 Optical Society of America.

Textured transparent conductors are widely used in thin-film silicon solar cells. They lower the reflectivity at interfaces between different layers in the cell and/or cause an increase in the path length of photons in the Si absorber layer, which both result in an increase in the number of absorbed photons and, consequently, an increase in short-circuit current density (Jsc) and cell efficiency. Through optical simulations, we recently obtained strong indications that texturing of the transparent conductor in copper indium gallium (di-)selenide (CIGS) solar cells is also optically advantageous. Here, we experimentally demonstrate that the Jsc and efficiency of CIGS solar cells with an absorber layer thickness (dCIGS) of 0.85 μm, 1.00 μm and 2.00 μm increase through application of a moth-eye textured resist with a refractive index that is sufficiently similar to AZO (nresist = 1.792 v s. nAZO = 1.913 at 633 nm) to avoid large optical losses at the resist-AZO interface. On average, Jsc increases by 7.2%, which matches the average reduction in reflection of 7.0%. The average relative increase in efficiency is slightly lower (6.0%). No trend towards a larger relative increase in Jsc with decreasing dCIGS was observed. Ergo, the increase in Jsc can be fully explained by the reduction in reflection, and we did not observe any increase in Jsc based on an increased photon path length.