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 ($$65\pm 2\%$$ 65 ± 2 % ) were found to have a diameter increase of 34% on average, whereas low DoC ($$44\pm 2\%$$ 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. Graphic abstract

Cellulose Nanocrystals Examined by Atomic Force Microscopy: Applications and Fundamentals

“…1 Swelling (as will be shown it is examined regularly with AFM) of individual fibers depends heavily on the degree of crystallinity that depending on sources will vary across cellulose byproducts here CNC and CNFs. For instance, in ref 45, after wetting the samples with DI water sample with a high degree of crystallinity (65%), the diameter increased on average by 34%; however samples with a degree of crystallinity of 44% swelled on average by 44%. As will be shown later, Onsager's theory can mark the transition point between isotropic to nematic phase separation in CNCs as calculated based on the aspect ratio; these changes in diameter upon swelling can heavily change the transition point, and therefore precise correlation between the degree of crystallinity and level of swelling shall be done for more precise forecasts.…”

Nanodancing with Moisture: Humidity‐Sensitive Bilayer Actuator Derived from Cellulose Nanofibrils and Reduced Graphene Oxide

“…[ 38 ] However, the partly amorphous CNF may display a larger intrinsic water uptake and expansion than highly crystalline nanocellulose materials such as cellulose nanocrystals (CNCs). [ 39 ] The adsorption of water onto the fibril surface can be tuned and controlled by, for example, the surface charge density of the fibrils; the more charged it is, the higher the water adsorption capacity is expected to be.…”

The influence of temperature on cellulose swelling at constant water density

“…An asymmetric ion distribution between the gel and bulk and cellulose-water interactions were considered the driving forces of surface water (ad)sorption. Ottesen et al quantized fibril liquid water swelling by atomic force microscopy, finding degrees of swelling around 30-40% 22 . Seemingly, these values are similar to amorphous cellulose liquid water swelling, e. g. 35% found by Esker et al 23 The principle difference between CNFs and CNCs, is crystallinity if one disregards surface charge-and type.…”