Event Type:
MSE Grad Presentation
Date:
Talk Title:
3D Printed Cellulose Nanocrystals-based Photonic Films with Periodic Circular Dichroism and Infra-Red Reflectance
Location:
MoSE Room 3201A

Committee

• Prof. Vladimir Tsukruk – School of Engineering (advisor)
• Prof. Meisha Shofner – School of Engineering
• Prof. Wenshan Cai – School of Engineering

Abstract

Daylight management has an increasing importance due to ongoing efforts to reduce energy consumption. Current commercially available absorption-based technologies affect the visible range of the spectrum and near-infrared (NIR) reflecting materials, including chiral nematic liquid crystals, are achieved by crosslinking stabilization of synthetic organic mesogens. It is of interest to develop a material that has good visible transmittance, limits NIR interior irradiation, and is based on abundant and renewable sources manufactured via an accessible method. Additionally, there is a growing demand for materials with engineered circular dichroism for various applications sensitive to circularly polarized light. In this work, two distinct cases of top-down structured photonic films were investigated. First, twisted helical cellulose nanocrystal (CNC) films with dual chiroptical NIR reflectance properties are produced via a facile blade coating 3D printing method. The films show both left and right-handed (LH, RH) chiroptical reflectance/transmittance properties, as opposed to natural homochiral CNC films. It is demonstrated that by manipulation of the process parameters of discrete twisted helical organization– twisting angle and anisotropic block thickness – distinct circular dichroism patterns and transmittance could be achieved. It is further shown the produced films could be treated as a hybrid between two extremes – a 1D photonic crystal and a traditional chiral film, exhibiting respectively reflectance and circular dichroism peaks, to yield a pre-programmed material with dual chiroptical properties as well as an achiral film with NIR reflectance. Second, a 1D Photonic crystal with vivid structural coloration based on alternating CNC and MXene (MX) phases was produced and studied. The films show strong optical properties with only 4 bilayer repetitions with an overall film thickness around 1 um. Partial transparency and pronounced reflectance in the visible range was observed. Different coloration is achieved by changing the period step resulting in blue to orange films. The 1D photonic crystals with a conductive MX phase hold the potential for electrochromics, and the 2D nature of the MX flakes open possibilities for tuning the reflective and emissive properties for advanced radiative cooling and filtration applications.