Negatively charged ions readily interact with the surface of positively charged pyridinium-grafted cellulose nanocrystals. In this work we investigated the thermodynamics of these interactions using isothermal titration calorimetry. We investigated the effect of the ionic charge, using carboxylate salts with different valence (1–4), and compared it with sodium sulfate as another delocalized ionic charge. Experiments performed using cellulose nanocrystals with three different degrees of substitution of pyridinium grafts showed that the number of ions adsorbed onto the surface of cellulose nanocrystals is directly linked to the number of grafted cationic functionalities. The adsorption of anions onto pyridinium-grafted nanocrystals was further found to be endothermic and driven by an increase in entropy upon adsorption of the anions due to the release of surface bound water. The association constant increased with the net …