Swelling of individual cellulose nanofibrils in water, role of crystallinity: an AFM study

Abstract

Atomic force microscopy (AFM) can be used to quantitatively study nanomaterials in different media, e.g. vacuum, air, or submerged in a liquid. A technique was developed to study swelling of individual cellulose nanofibrils (CNFs) using AFM. As a case study, CNFs with different degrees of crystallinity (DoC) were examined for swellability going from dry to wet (submerged in de-ionized water). Swelling was found to depend on DoC, but no significant correlation between fibril diameter and swellability was seen. Upon introduction of de-ionized water high DoC samples (65±2%) were found to have a diameter increase of 34% on average, whereas low DoC (44±2%) were found to have a diameter increase of 44% on average. A tested control, consisting of platinum nanowires on silisium, did not swell.