Electroacoustic characterization of trimmed hairy nanocelluloses

A cellulose-derived nano-toolbox has been developed via the chemical nano-trimming of electrosterically stabilized nanocrystalline celluloses (ENCCs). ENCC is a member of the class of hairy nanocellulose (HNC). The objective of this study is to determine the properties of chemically trimmed HNCs in order to establish whether or not they overcome the surface chemistry and size restrictions of conventional nanocelluloses. The newly "so-called crew-cut ENCCs" emerged by this approach address many technological and environmental challenges in colloidal systems, i.e., drug delivery, anti-scaling and self-assembly. Despite the importance of the crew-cut species, little is known about the systematic changes and the underlying mechanisms of the trimming of their hairs (the chains protruding from both ends of the cylindrical core).

To quantify the effect of the hair trimming on the charge density as well as the kinetics of this process, the carboxylic acid content is determined by conductometric titration as a function of time and reaction conditions. We use electro-acoustic spectroscopy to elucidate the differences in colloidal properties of various crew-cut ENCCs. We focus on the interplay between the time of the acid-catalyzed hydrolysis reaction and tunable parameters, such as size and surface electric charge of ENCC, as well as their microrheological behavior.

We show that a range of hairy ENCCs with various sizes and charge densities is easily obtained by taking advantages of the preferential hydrolysis of the amorphous chains protruding from both ends of the nanocrystals. The trimming mediated by a HCl-catalyzed hydrolysis is initially very fast, but slows down subsequently. The formation of crew-cut species with a smaller particle size and zeta potential was electro-acoustically verified by increasing the reaction time. The longitudinal viscosities of the trimmed ENCC suspensions also decreased with prolonging the reaction time. This research shows how manipulating HNCs enables both scientists and technologists to access a collection of nanocrystals with desired colloidal properties, based on the most abundant biopolymer in the world.