Effect\nof Surface Modification on Water Adsorption\nand Interfacial Mechanics of Cellulose Nanocrystals

Abstract

With increasing environmental concerns about petrochemical-based\nmaterials, the development\nof high-performance polymer nanocomposites with sustainable filler\nphases has attracted significant attention. Cellulose nanocrystals\n(CNCs) are promising nanocomposite reinforcing agents due to their\nexceptional mechanical properties, low weight, and bioavailability.\nHowever, there are still numerous obstacles that prevent these materials\nfrom achieving optimal performance, including high water adsorption,\npoor nanoparticle dispersion, and filler properties that vary in response\nto moisture. Surface modification is an effective method to mitigate\nthese shortcomings. We use computational approaches to obtain direct\ninsight into the water adsorption and interfacial mechanics of modified\nCNC surfaces. Atomistic grand-canonical Monte Carlo simulations demonstrate\nhow surface modification of sulfated Na-CNCs impacts water adsorption.\nWe find that methyl­(triphenyl)­phosphonium (MePh₃P⁺)-exchanged CNCs have lower water uptake than Na-CNCs, supporting\nexperimental dynamic vapor sorption measurements. The adsorbed water\nmolecules show orientational ordering when distributed around the\ncations. Steered molecular dynamics simulations quantify traction–separation\nbehavior of CNC–CNC interfaces. We find that exchanging sodium\nfor MePh₃P⁺ effectively changes the surface\nhydrophilicity, which in turn directly impacts interfacial adhesion\nand traction–separation behavior. Our analysis provides guidelines\nfor controlling moisture effects in cellulose nanocomposites and nanocellulose\nfilms through surface modifications.