Wan Yanglu, Lu Wei, Jiao Yang, Li Fulong, Zhan Mingfang, Wang Zichen, Sun Zheng
School of Innovation and Entrepreneurship, Wuchang University of Technology, Wuhan 430200, China.
Hubei Engineering Research Center for BDS-Cloud High-Precision Deformation Monitoring, Wuhan 430223, China.
Nanomaterials (Basel). 2025 Sep 19;15(18):1447. doi: 10.3390/nano15181447.
The effect of molecule-surface interaction strength on water becomes pronounced when pore size shrinks to the nanoscale, leading to the spatially varying viscosity and water slip phenomena that break the theoretical basis of the classic Lucas-Washburn (L-W) equation for the spontaneous imbibition of water. With the purpose of fulfilling the knowledge gap, the viscosity of nanoconfined water is investigated in relation to surface contact angle, a critical parameter manifesting microscopic molecule-surface interaction strength. Then, the water slip length at the nanoscale is determined in accordance with the mechanical balance of the first-layer water molecules, which enlarges gradually with increasing contact angle, indicating a weaker surface-molecule interaction. After that, a novel model for the spontaneous imbibition of nanoconfined water incorporating spatially inhomogeneous water viscosity and water slip is developed for the first time, demonstrating that the conventional model yields overestimations of 16.7-103.2%. Hydrodynamics affected by pore geometry are considered as well. The results indicate the following: (a) Enhanced viscosity resulting from the nanopore surface action reduces the water imbibition distance, the absolute magnitude of which could be 3 times greater than the positive impact of water slip. (b) With increasing pore size, the impact of water slip declines much faster than the enhanced viscosity, leading to the ratio of the nanoconfined water imbibition distance to the result of the L-W equation dropping rapidly at first and then approaching unity. (c) Water imbibition performance in slit nanopores is superior to that in nanoscale capillaries, stemming from the fact that the effective water viscosity in nano-capillaries is greater than that in slit nanopores by 5.1-22.1%, suggesting stronger hydrodynamic resistance. This research is able to provide an accurate prediction of spontaneous imbibition of nanoconfined water with microscopic mechanisms well captured, sharing broad application potential in hydraulic fracturing water analysis and water-flooding-enhanced oil/gas recovery.
当孔径缩小到纳米尺度时，分子与表面相互作用强度对水的影响变得显著，导致空间变化的粘度和水滑移现象，这打破了经典卢卡斯 - 沃什伯恩（L - W）方程中关于水自发吸入的理论基础。为了填补知识空白，研究了纳米受限水的粘度与表面接触角的关系，表面接触角是体现微观分子与表面相互作用强度的关键参数。然后，根据第一层水分子的力学平衡确定了纳米尺度下的水滑移长度，该长度随着接触角的增大而逐渐增大，表明表面 - 分子相互作用较弱。此后，首次建立了一个包含空间非均匀水粘度和水滑移的纳米受限水自发吸入新模型，结果表明传统模型的预测高估了16.7 - 103.2%。同时也考虑了孔隙几何形状对流体动力学的影响。结果表明：（a）纳米孔表面作用导致的粘度增强会减小水的吸入距离，其绝对值可能比水滑移的正向影响大3倍。（b）随着孔径的增加，水滑移的影响比粘度增强下降得快得多，导致纳米受限水吸入距离与L - W方程结果的比值先迅速下降，然后趋近于1。（c）狭缝纳米孔中的水吸入性能优于纳米尺度毛细管中的水吸入性能，原因是纳米毛细管中的有效水粘度比狭缝纳米孔中的大5.1 - 22.1%，这表明流体动力学阻力更强。本研究能够准确预测纳米受限水的自发吸入，并很好地捕捉微观机制，在水力压裂水分析和注水强化油/气采收方面具有广泛的应用潜力。
