Session: 03-03: Micro/Nanoscale Interfacial Transport Phenomena

Paper Number: 131972

131972 - A New Model for Capillary Imbibition With Asymmetric Wettability Walls 

Abstract: 

Capillary imbibition, such as plant roots taking up water, reservoir rocks absorbing brine, and tissue paper wiping stains, has long been an important subject in studying plant cells, seed germination, microfluidics, and heat transfer in micro/nanochannels. It refers to the capillary-driven invasion of wetting fluid to minimize the free energy of the multiphase system and is earliest modeled through the process that wetting liquid is spontaneously propelled by capillary pressure into regular geometry models. Recently, how to improve a more accurate physical model of capillary-driven flow processes has been a frontier topic. 

Wettability is critical to capillary imbibition in micro/nano scale. However, most of the previous studies on capillary imbibition have focused on channels with walls of homogeneous and symmetric wettability. The imbibition dynamics in channels with asymmetric wettability are not well understood. Meanwhile, the energy dissipation mechanism in capillary imbibition also remains to be elucidated.

The imbibition dynamics is controlled by energy dissipation mechanisms and influenced by asymmetric wettability in a nanochannel. In this work, theoretical analysis and molecular dynamics simulations are combined to investigate the energy dissipation mechanism of capillary imbibition in nanochannels. A new theoretical model is proposed for capillary imbibition while the imbibition dynamics are described by a combined model of the Lucas–Washburn equation and the Cox-Voinov law considering velocity-dependent contact angles. The energy conversion and dissipation during capillary imbibition is quantified, and the critical condition for the occurrence of capillary imbibition is obtained. The model is further extended to consider the effect of asymmetric wettability of the walls. The molecular dynamic simulation results show that the proposed model is more aligned to molecular dynamic simulation results which means it’s more accurate than the classical LW model. Moreover, results indicate that the reduction in surface energy during the capillary flow process is primarily dissipated through two mechanisms: solid-liquid friction near the three-phase contact line and viscous losses in the liquid. Additionally, when there is a significant difference in wettability between the walls on both sides of the nanochannel, partial energy loss due to fluctuations in the liquid-gas interface during the capillary flow process should also be considered. In the scenario where the walls on both sides of a nanochannel exhibit different hydrophilicities, the liquid-gas interface undergoes fluctuations. The greater the difference in hydrophilicity between the walls, the more pronounced the fluctuations become.

This new model has a wide range of applications, for example, in the development of novel materials and microfluidic chips, control of the transport of water molecules and ions in cement-based materials, and regulating the spontaneous imbibition of hydraulic fracturing fluids in shale reservoirs.

Presenting Author: Chenyue Zhu University of Nottingham

Presenting Author Biography: CHENYUE ZHU is a current year 3 PhD student of University of Nottingham. Her research focuses on spreading, flow and evaporation of liquid on micro/nano scale surfaces with molecular dynamic simulations.

Authors:

Chenyue Zhu University of Nottingham
Yuying Yan University of Nottingham
Mark Alston University of Nottinghan