Cellulose Nanocrystal (CNC) Synthesis: An AFM Study

Cellulose nanocrystals (CNCs) are charged nanoparticles with a high aspect ratio derived from the most common biological polymer, cellulose. Acid hydrolysis is one of the most common methods for CNC production. Whatman #1 filter paper was hydrolyzed by sulfuric acid and characterized by AFM in this research to examine the morphology and size distribution of CNCs. One drop of CNC suspension was air-dried on microscope cover glass to be analyzed by AFM with non-contact mode. The CNC dimensions were determined by measuring individual and isolated particles (n=88) via Nanosurf Easyscan2 software. The measurement data was analyzed by Excel statistically. Synthesized CNCs were ellipsoidal with the length, height, and aspect ratio of 219.87 ± 42.12, 6.25 ± 2.27, and 41.17 ± 21.70 nm, respectively. Although the length and height of the produced CNCs were in acceptable range, but the width of CNCs was an overestimation and it was not reliable, mostly due to AFM tip broadening effect. Particle size measurement of CNCs is a challenging process because of their rapid aggregation and rod shape. Although hydrolysis parameters are influential on the final shape and size of CNCs, but it is necessary to optimize and maximize the quality of sample preparation and AFM adjustment to obtain the size of CNCs with the most accuracy and reliability. The CNC dimensions were determined by AFM are slightly different in the literature but height (thickness) is the most reliable one based on this experiment. Further studies are required to standardize CNC size measurement by AFM.