Justin Brackenridge
Advisor: Prof. Vladimir V. Tsukruk

will propose a doctoral thesis entitled,

Hierarchical Nanostructures from Cellulose Nanocrystals for Optical and mechanical Functionality

On

Thursday, July 10 at 9:30 a.m.
Molecular Science and Engineering Building (MoSE) Room 3201A

and

Virtually via Zoom

Committee Members

Prof. Vladimir Tsukruk (Advisor), MSE

Prof. Natalie Stingelin, MSE

Prof. Shucong Li, MSE

Prof. Jerry Qi, ME

Dr. Dhriti Nepal, AFRL

Abstract

Bio-based materials have become a forefront of scientific research for their natural renewability, fundamental properties, and broad range of advanced applications. At the center of bio-based materials are polysaccharides, polymers made of long chains of carbohydrate molecules that can be broken down into smaller units often classified as chitin, cellulose, or other polysaccharide subgroups. Cellulose nanocrystals, short, needle-like chains of carbohydrates, are a commonly studied cellulose derivative and exhibit hierarchical helical ordering as a chiral nematic liquid crystal above critical concentrations. This complex, self-assembled architecture leads to unique optical phenomena such as structural coloration and birefringence induced polarization. Taking advantage of these material properties is of critical interest for advanced optical applications but current scientific knowledge lacks a fundamental understanding of structure-property relationships when helical architectures are modified into more complex biomimetic structures.

This work will investigate fundamental structure-property relationships for nature inspired hierarchical nanostructures from cellulose nanocrystals with a focus on optical and mechanical functionality. While CNCs are known to self-assemble into helical stacks with constant rotational angle between layers, known as single Bouligand structures, more complex hierarchical structures made of similar materials have been found in nature. A double Bouligand structure has been discovered in the scales of some fish species, providing mechanical integrity and crack suppression due to the incorporation of two intertwined helices, resulting in orthogonal bilayer ordering. This work aims to investigate these double Bouligand structures by creating shear-aligned CNC films with varying internal architectures. While this structure has been reproduced in previous studies, none have investigated mechanical properties on the nanoscale and optical functionality remains an untouched topic. By utilizing a bio-renewable polymer such as CNC, chiroptical properties of double Bouligand structures can be compared to the well-known single Bouligand structures found in nature. 

This work will provide an understanding of structure mechanisms for double Bouligand films with an advanced study on crack suppression and propagation, elastic recovery, and strain distribution throughout the structure that is an unrealized area of the scientific community. In addition, a study of the optical polarization mechanisms for these structures will provide fundamental knowledge on structure-property relationships for multifunctional CNC films.