The aim of the project is to develop original, environmentally friendly, nano-structured surfaces and coatings with fabricated optical functionality to control colors when reflecting light. The surfaces and coatings will be made from cost-effective natural materials such as cellulose or clay, which enables environmentally friendly colored surfaces with improved energy efficiency, and thus can provide innovative technology for design or architecture. The project is coordinated from the Norwegian University of Science and Technology (NTNU) in Trondheim, and the partners representing various disciplines and industrial areas are: In Norway: Department of Energy Technology (IFE) in Kjeller, SME Giamag Technologies, a large industrial company Borregaard AS and design and the architectural firm Snøhetta Oslo AS. From Portugal, the partners are: NOVA.id:FCT and Instituto Superior Tecnico (IST-ID), both in Lisbon.
In the period 2017-18, the project focused mainly on making structurally colored films based on nanocellulose and nano-clay. It is known that cellulose nanocrystals (CNCs) present iridescence and selective reflection of left circular polarized (LCP) light. It is also well known that water suspensions of clay nanoplates can form a nematic liquid crystalline phases. In the project, we have mixed different amounts of cellulose nano-rods with clay nematic liquid crystalline suspensions. Above a certain critical concentration of cellulose, the suspensions are iridescent with a left-twisted nanostructure. Solid films were made from the solutions. We have shown that not only iridescent films can be produced, but also that selective reflection of the LCP light channel is preserved. The colors reflected by the films can vary from blue to red, depending on the amount of CNC. This demonstrates that the nanoscale chirality is transformed into photonic solid films made from water suspended CNCs / clay suspensions. The suspensions and the fixed films are characterized using various techniques such as SEM, AFM and POM.
During 2019-20, the work from 2017-18 was expanded, and in addition, the project began to use other cellulose nanocrystal (CNC) rods derived from various cotton base sources (cellulose microcrystalline (Avicel® Ph 101) and filter paper), and especially also from Exilva cellulose from Borregaard. Cellulose nanostars were isolated from the industrial samples using a set of reactions with different experimental hydrolysis conditions (acid concentration and reaction time). A set of techniques was used to characterize the original industrial sample and the materials produced (FTIR, XRD, SEM, AFM, Elemental Analysis, TG / DSC). This work yielded colored structural films from aqueous solutions. Various cellulose systems that can generate structural colors were investigated, not only systems that reflect in the visible area, but also structural white materials formed from nanometric fibers randomly distributed.
Liquid crystals bounded between different geometries and under the influence of external fields were also examined to better understand the liquid crystalline CNC system underlying the structural colors.
Other photonic structures derived from CNCs / clay water suspensions were prepared and the suspensions with different solids ratios were characterized by optical microscopy, AFM, SEM, DSC and TGA. Promising photonic stable water suspensions, encapsulated between two flat glass surfaces, were prepared from 2% by weight of sodium fluorohectorite (NaFh) by CNC.
The following reference gives an example of a concrete collaboration result from the project: "Photonic Composite Materials from Cellulose Nanorods and Clay Nanolayers", Ana C. Trindade, Miguel Carreto, Geir Helgesen, Kenneth D. Knudsen, Florian Puchtler, Josef Breu, Susete Fernandes, Maria Helena Godinho, Jon Otto Fossum, EUROPEAN PHYSICAL JOURNAL SPECIAL TOPICS 229, 2741?2755 (2020)
The project aimed to develop protocols for proposals for upscale industrial production that structurally colored films based on CNCs and composites of CNCs and clays. This work was started, but not completed during the project period due to the Covid-19 situation. Further work on this will be continued in 2021.
Main objectives achieved included development of environmentally friendly routes for nanostructured materials used in structural coloration and reflection, and in the tailoring of nano-structured materials for responsive surfaces and coatings, for design and architecture. The surfaces and coatings were fabricated from cost effective natural materials.
The originality of the work performed comprised:
- Preparation and characterization of thin films from thermotropic, lyotropic and functionalized cellulose derivatives.
- Preparation of micro- and nano cellulose-based anisotropic systems
- Raise and solve physical-chemistry questions, at the fundamental level, related to the comprehension of patterns which develop in liquid crystals and cellulose-based liquid crystalline solutions, and the chirality inversion observed in cellulosic systems, at different length scales.
The systems prepared were studied in solution and as casted solid films.
The aim of the project is to develop original, environmentally friendly, nano-structured surfaces and coatings with engineered optical functionality for coloration and reflection of light. The surfaces and coatings will be fabricated from cost effective natural materials like cellulose, and will allow for environmentally friendly energy control and improved energy efficiency, thus providing innovative technology for future delsign or architecture, beyond the lifetime of the project. The project is coordinated from the Norwegian University of Science and Technology (NTNU) in Trondheim Norway, and the partners representing the various academic and industrial areas are: In Norway: Institute for Energy Technology (IFE) in Kjeller, the SME Giamag Technologies, the large industrial company Borregaard AS, and the design and architectural firm Snøhetta Oslo AS. From Portugal the partners are: NOVA.id:FCT and Instituto Superior Tecnico ? IST-ID, both in Lisbon.