Steve Kelley

Ultrathin film coatings of aligned cellulose nanocrystals from a convective-shear assembly system and their surface mechanical properties

Ultrathin films of aligned cellulose nanocrystals (CNCs) were deposited on solid supports by using convective and shear forces. Compared to previous systems involving high electric or magnetic fields to control the orientation of these rod-like natural nanoparticles, the proposed process of alignment was very simple, inexpensive and with potential for scale up. The effect of concentration of CNC in aqueous suspensions, type of solid support, relative humidity and rates of withdrawal of the deposition plate were determined by using atomic force microscopy (AFM) and ellipsometry. The degree of orientation was quantified from the number density of CNCs in leading angles by using image analyses. Also, the contribution of shear and capillary forces on alignment parallel and normal to the withdrawal direction was elucidated. The best alignment of CNCs in the withdrawal direction, favored by shear effects, was achieved with gold and silica supports with a pre-adsorbed cationic polyelectrolyte layer and at a CNC suspension concentration above 2.5% (w/w), below the critical concentration for chiral nematic phase separation. Compared to the bare solid support, nanoindentation of the obtained coatings of ultrathin films of oriented CNCs provided enhanced surface mechanical strength and wear resistance. A transverse Youngs modulus, hardness and coefficient of friction of 8.3 ± 0.9 GPa, 0.38 ± 0.03 GPa and 0.51 ± 0.23 GPa, respectively, were measured. Notably, the transverse Youngs modulus was found to be in agreement with reported values predicted by molecular modeling and measured for single CNCs by using atomic force microscopy.

Distribution of wood polymers within the cell wall of transgenic aspen imaged by Raman microscopy

Abstract Little is known about the effect of genetic modification on the chemical composition and structure of wood, which could have a significant effect on reactivity during chemical and enzymatic processing. In this study, information was collected by confocal Raman microscopy (CRM) on the spatial distribution of lignin and polysaccharides in the cell wall of young transgenic aspen with reduced lignin content, increased syringyl/guaiacyl (S/G) ratio, and simultaneously reduced lignin content and increased S/G ratio. CRM revealed that the lignin content of the cell wall and compound middle lamella was reduced by the genetic modification. A higher volume of water was also found in the cell wall of transgenic aspen compared with wild-type aspen, indicating an increase in the hydrophilicity of the cell wall.