(337cw) ‘Structure- Processing- Property’ Relationship of Cellulose Nanocrystals for Optical and Sensing Applications

• 'Structure-Processing-Property' relationship of anisotropic nanomaterials
• Nanomaterial surface functionalization and characterization
• Photonic applications of nanomaterial films
• Microfabrication and nanomaterial-based sensor development
• Material processing and microstructure tunning for macro scale properties

Research Summary:

This research investigated the ‘structure-processing-property’ relationships of an anisotropic nanomaterial called cellulose nanocrystals (CNCs); the focus was on developing optical films and sensors. Sulfated CNCs are readily dispersed in water, which enables aqueous manufacturing of CNCs into functional materials. In addition, sulfated CNC dispersions form a lyotropic liquid crystal phase within a specific concentration range, leading to anisotropic mechanical and optical properties based on ordering. The first part of this research involved the impact of nanocrystal size on dispersion phase behavior, microstructure, and rheological properties. Sedimentation was used to separate polydisperse CNC dispersions in two fractions. The shorter nanocrystals (L = 170 ± 6 nm) stayed at the top, whereas the bottom fraction contained the larger (L = 290 ± 80 nm) CNCs. The phase transitions, dispersion microstructure, and rheological properties of the fractionated CNCs differed from the parent dispersions. Since CNCs can be used in 3D printing and as rheological modifiers, size fractionation can help to tune flow characteristics (viscosity, shear modulus) for these targeted applications. The acquired understanding of how size distributions affected dispersion properties was utilized to prepare optical films exhibiting chiral nematic ordering. Based on the pitch length and orientation of chiral helices, lights of different wavelengths were reflected from different domains of the films. These optical films have the potential to be used as a light filter and in optical encryption. The second part of this research focused on liquid phase processing and surface modification of CNCs for use in sensing applications. The hydrolytic stability of sheared CNC films was enhanced using 3-aminopropyltriethoxysilane (APTES) modification without altering most of the inherent mechanical properties. A molecularly imprinted polymer (MIP) was developed and used as a coating over CNC-APTES films to selectively detect carbofuran, a pesticide and water contaminant. A similar approach of CNC surface modification can be applied to other analytes, such as food allergens or antibiotic residues. The modified CNC has the potential to be utilized for micro-sized device fabrication to promote ‘ASSURED’ (affordable, sensitive, selective, user-friendly, rapid, equipment-free, and deliverable) sensing applications. In summary, this work provides fundamental insights into CNC dispersion phase behavior, microstructure, and self-assembly for use in macro-scale optical and sensing applications.