Nanostructured biopolymers as sustainable dispersants of aqueous carbon nanofibers inks

Abstract

Nanostructured biopolymers (NBs) have enhanced properties with respect to their bulk counterparts, due to their smaller size. The main type of NBs are cellulose nanocrystals (CNCs), which are needle-shaped crystals of cellulose with lengths ranging from 100 to 500 nm and diameters around 10 nm. They may be present in different cellulose allomorphs, among which types I and II are the most common.1 Another example of NBs are chitin nanocrystals (ChNCs), being also of similar size and shape as CNCs.2 On the other hand, carbon nanofibers (CNFs), produced by chemical vapor deposition (CVD), and with structures similar to multiwall carbon nanotubes, exhibit interesting transport properties that make them valuable for electronic applications.3 It is for this latter reason that the objective of this study was to disperse commercial as-received CNFs by using NBs as sustainable surfactants to produce aqueous conductive inks. In a first step, various aqueous colloidal dispersions of CNFs and NBs (CNCs, ChNCs) were prepared using ultrasounds as dispersion inducers. Afterwards, centrifugation was used to separate the non-dispersed CNF agglomerates from the final ink (Figure 1). Finally, and as a proof-of-concept, an optimized CNFs/NBs dispersion (namely, ink) was used to prepare films of controlled thicknesses on glass substrates by spray coating. Here, the relationship between the thickness and the surface resistivity (Rsh) was monitored. The results gathered here aim at contributing to the development of more sustainable conductive inks for the fabrication of electronic wearable devices.