Natural anisotropic building-blocks such as cellulose nanocrystals (CNCs) have attracted considerable attention due to their biodegradability and nanometer-size. In this work the colloidal behavior of CNCs, obtained from sulfuric acid hydrolysis of microcrystalline cellulose, has been studied in presence of salts of different valences. The influence on the colloidal stability and nature of aggregates has been investigated for monovalent salts (LiCl, NaCl, KCl, CsCl), divalent salts (CaCl₂ and MgCl₂), and a trivalent salt (AlCl₃), both experimentally by means of turbidity and small angle X-ray scattering (SAXS) measurements, as well as by Monte Carlo simulations using a simple coarse-grained model. For the entire salt series, a critical aggregation concentration (CAC) could be determined by turbidity measurements, as a result of the reduction of effective Coulomb repulsions due to the presence of sulfate groups on the CNC surface. The CACs also followed the Schulze–Hardy law, i.e. the critical aggregation concentration decreased with increasing counterion valence. For the monovalent ions, the CACs followed the trend Li⁺ > Na⁺ > K⁺ > Cs⁺, which could be rationalized in terms of matching affinities between the cation and the sulfate groups present at the surface of CNCs. From the SAXS measurements it was shown that the density of the aggregates increased with increasing salt concentration and ion valence. In addition, these findings were rationalized by means of simulation, which showed a good correlation with experimental data. The combination of the experimental techniques and the simulations offered insight into interaction-aggregation relationship of CNC suspensions, which is of importance for their structural design applications.

Polyethyleneimine (PEI) is a common polymer used in many industrial applications and in research, especially in surface chemistry. It is available in a wide range of molecular weights and different degrees of branching. It is classified as linear or branched and sometimes the term hyperbranched is also used. This description, however, is quite rough, which limits the possibility to correlate the structure of the PEI to its properties. The aim of this study is to provide analytical tools to characterize the polymer at a level of detail not normally provided by the supplier of PEI. To this end, five commercially available polyethyleneimines were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and nuclear magnetic resonance spectroscopy to gain insight into the structure and the functional groups present in the polymers. Quantitative ¹³C NMR analysis turned out to be particularly useful, revealing the degree of branching of the polymer based on the ratio of primary, secondary, and tertiary amino groups.