Tunable colors and conductivity by electroless growth of Cu/Cu 2 O particles on sol-gel modified cellulose
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arch Institute for Textile Chemistry and Textile Physics, University of Innsbruck, 6850 Dornbirn, Austria Department of Physical Chemistry, University of Innsbruck, 6020 Innsbruck, Austria † Present address: Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, 53359 Rheinbach, Germany 2
© The Author(s) 2020 Received: 4 March 2020 / Revised: 27 May 2020 / Accepted: 29 May 2020
ABSTRACT Development of colored surfaces by formation of nano-structured aggregates is a widely used strategy in nature to color lightweight structures (e.g. butterflies) without the use of dye pigments. The deposition of nanoscale particles mimics nature in it’s approach coloring surfaces. This work presents sol-gel modification of cellulose surfaces used to form a template for growth of Cu/Cu2O core–shell particles with defined size-distributions. Besides improving the adhesion of the deposited particulate material, the sol-gel matrix serves as a template for the control of particle sizes of the Cu/Cu2O structures, and as a consequence of particle size variation the surface color is tunable. As an example, red color was achieved with an average particle size of 35 nm, and shifts gradually to blue appearance when particles have grown to 80 nm on the sol-gel modified fabric. The copper concentration on representative fabrics is kept low to avoid modifying the textile characteristics and were all in the range of 150–170 mg per g of cellulose material. As a result of copper deposition on the surface of the material, the cellulose fabric also became electrically conductive. Remarkably, the electrical conductivity was found to be dependent on the average particle sizes of the deposits and thus related to the change in observed color. The generation of color by growth of nano-sized particles on sol-gel templates provides a highly promising approach to stain surfaces by physical effects without use of synthetic colorants, which opens a new strategy to improve environmental profile of coloration.
KEYWORDS electroless copper deposition, sol-gel support, thin film, structural coloration, tunable sheet resistance, LSPR
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Introduction
Structurally induced coloration is a phenomenon that is often associated with naturally occurring nanoscale structures, which lead to colorful appearances of some types of aquatic animals, birds and insects [1–3]. However, this is also a valuable resource to achieve brilliant colors and color effects by structureengineering or other nano-technological approaches. Structural coloration appears due to light interferences with nano-sized elements and structure, and is described by optical theories including (a) multilayer interference, (b) thin-film interference, (c) Mie scattering, (d) photonic crystals or (e) localized surface plasmon resonance [4]. In contrast, pigment-based coloration is due to absorption of incident light in a specific wavelength range, which is true for most conventional dyes [5]. Investigations on naturally occurring structural coloration effects show that various repetiti
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