Hydroplasticity of Nanocrystal Films Induced by Mesopore Change

Hydroplastification offers an eco-friendly route to plasticize hydrophilic polymers by enhancing chain mobility, yet it remains ineffective for rigid crystalline nanomaterials. Here, we report a novel plasticity mechanism governed by mesopores acting as structural free volume between rigid hydrophilic nanocrystals, cellulose nanocrystals (CNCs). During the mechanosorptive vapor training process to change the mesopores, the plasticity arises from a dynamic competition between external tensile stress and internal capillary forces. We establish a semiquantitative constitutive relationship revealing that the network’s wet-state yield strength is critically regulated by the aspect ratio and surface chemistry of the nanocrystals. Specifically, the weak acidity of carboxyl groups ( p K a ∼ 3.2 ) combined with high aspect ratios creates a defect-dominated soft skeleton; here, the internal Laplace pressure ( ∼ 2 6 MPa ) exceeds the yield strength, driving the splitting of bottlelike mesopores into smaller domains until a geometric locking limit defined by the nanocrystal diameter is reached. In contrast, strong electrostatic repulsion from sulfonates ( p K a ∼ 1.0 ) or spatial jamming in short nanorods results in rigid networks that resist this capillary-driven densification. This novel hydroplastification mechanism by capitalizing on mesopores with competing capillary force, opposing network stress, and external stress enables shaping CNC films into stable geometries, rather than lattice disruption. Moreover, such findings extend hydroplasticity concepts to rigid matter, establishing mesopore engineering as a physical pathway to regulate the plasticity of crystalline nanomaterials.