(484h) Interrelationship Between Cellulose Nanocrystal Phase Behavior and Assembly into Anisotropic Ordered Films

This study is focused on exploring the potential of using cellulose nanocrystals (CNCs) as an alternative substrate for microdevice and other film applications. It is our hypothesis that CNC dispersions can be processed into films with tailored mechanical, optical and electrical properties suitable for micromachining to produce MEMS and other microdevices. In order to test this hypothesis it is imperative to understand its liquid crystal (LC) phase behavior and self-assembly. We report the dimensions, surface chemistry and self-assembly cellulose nanocrystals with acetate groups (CNC-AA) produced from cotton sources using acetic acid hydrolysis. An optimized synthesis procedure has been conducted to remove persisting agglomerates of CNC-AA at lower concentration level and produce rod-shaped particle 193 ± 66 nm in length, 30 ± 8 nm in width and 9 ± 3 nm in height.  A thermodynamic and colloidal interaction energy modeling approach involving molecular interaction between the solvent and CNC was used to explain CNC-AA aqueous suspension phase behavior.  CNC-AA show markedly different microstructures than the cholesterogenic liquid crystals formed from the more commonly studied CNC produced by sulfuric acid hydrolysis (CNC-SA).  Polydomain structures for both CNC-AA and CNC-SA maintain orientation in their dried films, which provides a way to characterize their micro scale assembly pattern with atomic force microscopy.  Confinement effects on CNC ordering and agglomeration were also observed. Intriguingly, mixtures of CNCs with different surface functionalities show thread like textures (under polarized light microscopy) that may be indicative of nematic liquid crystal formation. The effects of the relative surface chemistry ratios and total CNC concentration on the microstructure are reported. CNCs film processing is also conducted here by correlating shearing conditions with CNC orientation order and film surface uniformity.