Dispersive Ability of Carboxylated Cellulose Nanofibrils for Aqueous Monolayer Montmorillonite Dispersion:Influence of Na+ and Ca2+ Concentrations

Carboxylated cellulose nanofibrils(CNFs)have emerged as effective green dispersants for monolayer montmorillonite(MMT)dispersions.However,their dispersion capability is sensitive to the metal ion concentration in aqueous solutions.Hence,this study investigated the effects of Na+and Ca2+concentrations on the dispersive ability of carboxylated CNFs for monolayer MMTs in water.Quartz crystal microbalance with dissipation monitoring(QCM-D)and atomic force microscopy(AFM)were utilized to explore the interfacial interactions between the carboxylated CNFs and monolayer MMTs under different Na+and Ca2+concentrations.When the concentration of Na+reached 0.1 mmol/L,the adhesion mass of carboxylated CNFs on MMT-coated wafer peaked at 24.47 mg/m2,higher than control sample(carboxylated CNF-dispersed monolayer MMT dispersion without metal ions,16.03 mg/m2).Moreover,the electrostatic shielding effect promoted a better dispersion of monolayer MMTs by carboxylated CNF dispersant.With a further increase in the Na+concentration,the surface charge of CNFs and MMTs would be reversed resulting from the improved electrostatic shielding effect,which weaken the dispersive ability of carboxylated CNFs.The addition of Ca2+reduced the dispersive ability of carboxylated CNFs for monolayer MMTs,because Ca2+required a lower concentration for the onset of charge reversal compared to Na+.This study provides interfacial scale insights into the influence of metal ion concentration on carboxylated CNF-dispersed monolayer MMT dispersions.It also provides a strategy to enhance the dispersive ability of carboxylated CNFs for monolayer MMTs.