Early regimes of water capillary flow in slit silica nanochannels

Abstract

Molecular dynamics simulations are conducted to investigate the initial stages of spontaneous imbibition of water in slit silica nanochannels surrounded by air. An analysis is performed for the effects of nanoscopic confinement, initial conditions of liquid uptake and air pressurization on the dynamics of capillary filling. The results indicate that the nanoscale imbibition process is divided into three main flow regimes: an initial regime where the capillary force is balanced only by the inertial drag and characterized by a constant velocity and a plug flow profile. In this regime, the meniscus formation process plays a central role in the imbibition rate. Thereafter, a transitional regime takes place, in which, the force balance has significant contributions from both inertia and viscous friction. Subsequently, a regime wherein viscous forces dominate the capillary force balance is attained. Flow velocity profiles identify the passage from an inviscid flow to a developing Poiseuille flow. Gas density profiles ahead of the capillary front indicate a transient accumulation of air on the advancing meniscus. Furthermore, slower capillary filling rates computed for higher air pressures reveal a significant retarding effect of the gas displaced by the advancing meniscus.

Effect of Nanoparticles on Spontaneous Imbibition of Water into Ultraconfined Reservoir Capillary by Molecular Dynamics Simulation

“…Figure 4a and Figure 4b show the relations between displacement l and time t for fluids with hydrophobic and hydrophilic nanoparticles, respectively. In Figure 4a, displacement l for water increases with time and obeys the relationship of t scaling in time, similar to previous simulation studies and the theoretical relationship [10,52]. When nanoparticles are added into the fluid, all the displacement curves are also qualitatively parabolic and obey t scaling in time.…”

“…Imbibition in porous media is ubiquitous and has numerous applications in many natural and industrial processes, such as groundwater remediation, oil recovery, and nanofluidic devices [1][2][3][4][5][6][7]. For the imbibition phenomena, capillary action is the main transport mechanism for the spontaneous process, which results in the diffusing motion of fluid into porous solids or the capillary [8][9][10][11]. It is proven that the liquid's behavior can be described by the Lucas-Washburn equation [12][13][14].…”

Anomalous capillary filling and wettability reversal in nanochannels

“…In view of its importance for many applications, this phenomenon has been thoroughly investigated for more than an century [4][5][6]. Yet it still raises many questions, as a growing number of situations of interest now concerns capillary effects arising in nanometric to subnanometric channels [3,[7][8][9][10][11][12][13][14]. This is associated with the fast development of nanofluidics [15] and the renewed activities around membranes and nanoporous media arising from water resources or energy problematics.…”

Nanoscale Capillary Flows in Alumina: Testing the Limits of Classical Theory

“…The maximum flow rates occur at the beginning of the test and decrease with time. Time dependent effects have been previously observed only over short times for filling of silica [38][39][40][41][42][43][44] and silicon capillaries 15,40,45,46 . The measurements of Figure 3 are for the highest flow rates and the time dependences are discussed further in the Supporting Information.…”