Temperature-Dependent Underoil Wettability of Cellulose Nanocrystals and Their Biobased Modifications

Surface wettability is crucial in applications ranging from biomaterials to coatings. This study investigates the wettability of cellulose nanocrystals (CNCs) modified with biobased agents, methyl cellulose (MC), ethyl cellulose (EC), and tannic acid (TA), in alkane solvents. Contact angles were measured in a temperature-controlled setup with water droplets placed on surfaces immersed in heptane or hexadecane. MC-modified CNCs showed superhydrophilic behavior, while EC addition imparted hydrophobicity. On the other hand, TA-coated CNCs and unmodified CNCs remained in the hydrophilic region. The pure modifiers were generally more hydrophobic than their CNC-bound forms, likely due to interfacial conformation. Temperature increase led to more hydrophobic surfaces overall. Wettability kinetics revealed that MC-coated CNCs spread water faster than MC alone due to a precursor water layer. These materials show promise for selective sorption: CNC@MC as water sorbents in oil and CNC@EC aerogels as reversible oil sorbents in water. This work enhances our understanding of CNC surface tuning for functional surfaces and environmental remediation.