Interactions between cellulose nanocrystals and conventional/gemini surfactants

Research on the interaction between surfactants and cellulose nanocrystals (CNC) has mainly focused on the interaction between CNC and conventional surfactants, and there are no reported studies on the interaction between CNC and gemini surfactants. The interactions between CNC and conventional surfactant (tetradecyltrimethylammonium bromide, termed as TTAB), asymmetric gemini surfactant ([C₁₄H₂₉(CH₃)₂N⁺(CH₂)₆N⁺(CH₃)₂C₆H₁₃]Br (14-6-6)) or symmetric gemini surfactant ([C₁₄H₂₉(CH₃)₂N⁺(CH₂)₆N⁺(CH₃)₂C₁₄H₂₉]Br₂ (14-6-14)) were examined. With increasing surfactant concentration, interaction of TTAB/CNC was described by three regions, i.e. electrostatic interaction, CNC induced micellization and dilution of free micelles. However, in the case of gemini surfactant/CNC, four binding regimes were observed, i.e. cooperative adsorption, CNC induced micellization, formation and dilution of free micelles. The behavior of 14-6-6/CNC was similar to 14-6-14/CNC where CNC promoted the partition of gemini surfactant to the air-water interface at high surfactant concentration, while it was inhibited at low surfactant concentration. At low CNC concentration, micellization induced by CNC and aggregation of surfactant/CNC complexes were absent. pH had a minimal impact on the binding process at low CNC concentration, but it affected the binding at higher CNC concentration. Additionally, the presence of electrolytes influenced the micellization process induced by CNC by reducing the electrostatic interactions.