Swelling of individual cellulose nanofibrils in water, role of crystallinity: an AFM study
Vegar Ottesen, Kristin Syverud
Abstract
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 ( $$65\pm 2\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>65</mml:mn> <mml:mo>±</mml:mo> <mml:mn>2</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> ) were found to have a diameter increase of 34% on average, whereas low DoC ( $$44\pm 2\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>44</mml:mn> <mml:mo>±</mml:mo> <mml:mn>2</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> ) were found to have a diameter increase of 44% on average. A tested control, consisting of platinum nanowires on silisium, did not swell. Graphic abstract