Infiltration Dynamics in Flexible Nanochannels

Capillary forces at the liquid interface can become dominant in microscale and nanoscale systems, often rivaling or even exceeding the elastic resistance of solid materials. Phenomena illustrating this effect include coalescence of wet hair and the collapse of microscale lithographic patterns, demonstrating how capillary forces can significantly deform solid geometries. The early-time elastocapillary behavior in nanoscale systems remains a strikingly overlooked research gap. While fluid-structure interactions are well understood at larger scales, the initial transient dynamics at the nanoscale, where elastic and capillary forces interact, have received very limited attention. This study investigates liquid infiltration into nanochannels and examines the influence of capillary forces on flexible channel walls. Molecular dynamics (MD) simulations are employed, using water as the infiltrating liquid inside graphene channels. From the simulation data, key parameters such as infiltration length and instantaneous channel width are calculated. The behavior of liquid infiltration in nanochannels with fixed and flexible walls is compared. The simulations analyze the interaction between channel deformation and infiltration, highlighting the contribution of capillary and elastic forces. The study also examines the role of wall wettability, wall elastic stiffness, and channel width in influencing infiltration dynamics and wall bending. While theoretical models for liquid infiltration in fixed microchannels are well established, the current work extends this understanding to flexible nanochannels. A new model is developed based on the Euler-Bernoulli beam theory to relate the channel width and infiltration length. Furthermore, a modified Lucas-Washburn equation, incorporating Molecular Kinetic Theory, is used to predict the liquid meniscus infiltration profile. This combined theoretical approach effectively captures both the wall deformation and the liquid progression. This study highlights the importance of capillary-elastic interactions in technologies such as self-assembled nanostructures and soft robotics, enabling improved performance of next-generation micro/nanoscale systems.