Drawing with Cellulose-Based Colourful Patterns

• Autor(a) principal: Bolinhas, Joana Varela
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/152398
• topic: HPC; structural colours; cholesteric liquid crystals; cellulose derivatives; cellulose- based system; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia dos Materiais

Cellulose based systems can have many applications, and some of them include the production of systems with structural colours. Structural colours occur due to the interaction of light with micro and nanostructures. It is present in nature; it can be seen in different patterns in animals and plants. Structural colouration can be obtained from biocompatible and ecological materials, those materials are good candidates for the replacement of fuel-based materials. Cellulose is a green material that can develop structural colours, when it is obtained from liquid crystalline (LC) phases. In this work an eco-friendly cholesteric liquid crystalline system was investigated. The system consists in a cellulose derivative (hydroxypropyl cellulose) mixed with water in the presence of acetic acid. The obtained solutions for a range of acetic acid concentrations showed vivid iridescent colours, that change in time due to mechanisms of diffusion and evaporation of water and acetic acid. A polar- izing optical microscope (POM) equipped with circularly polarizer was used to study the system. Pre- liminary rheological studies were performed using a cone and plate geometry to investigate the liquid crystalline solutions. Solid films obtained from the lyotropic phase by casting and shear casting tech- niques were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), circular dichroism (CD) and Fourier transform infrared spectroscopy (ATR-FTIR). Depending on the initial concentration of the LC solutions and the deposition conditions, the solid films show a “zigzag” tracery at the micro/nano scale along the cross-section, which was attributed to the LC elasticity associ- ated to the shear conditions and evaporation of the solvent. This work has relevant implications, not only for the understanding of cellulose-based structures that can also be found in nature, but for applications in sensors and optical devices, the obtained mate- rials are also good candidates to replace inorganic pigments in synthetic dyes.