Cellulose nanocrystal structure in the presence of salts

Abstract

Aggregation and gelation of cellulose nanocrystals (CNCs) induced by magnesium chloride (MgCl2) are investigated as a function of CNC and MgCl2 concentrations. Transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) are employed to study the effect of ionic strength and CNC concentration on the extent of aggregation and structure of the CNC network. The location of CNC particles is traced with Fluorescent brightener 28 staining agent. The results show that the addition of different amounts of MgCl2 causes a cluster formation of CNCs with different fractal dimensions, confirmed by TEM. The fractal dimension of CNC clusters varied from approximately 1.56 ± 0.08 to 1.98 ± 0.01 as the MgCl2/CNC concentration ratio is increased from 0.17 to 0.42. We use the MgCl2/CNC concentration ratio as a global parameter to correlate the results of different measurements and imaging data, including TEM, zeta potential and CLSM. Furthermore, we conduct molecular dynamic simulations to quantitatively examine different CNC behavior in MgCl2 salt–CNC suspension. The results on the potential of mean force (PMF) indicate that the PMF of different ions concentration gravitates to zero where the distance between CNCs is increased from 3.1 nm to 3.5 nm. However, adding ions to the system changes the energy of the system and leads to a different behavior of CNC interactions.