Wetting Phenomena and Multiphase Flow in Nanoscale Channels(3/3)

Wetting phenomena and fluid flow in nanoscale channels exhibit physical behavior not observed inlarger structures. Because of interactions between the fluid molecules and the confining walls, nonuniformfluid density profiles in the vicinity of the channel walls are formed. A shift in the equilibrium propertiesand a modification of the transport properties is therefore resulted. While macroscopic confined flows canbe described by classical Navier–Stokes hydrodynamic theory, it must be generalized to allow for local,position dependent transport coefficients, once the confinement approaches molecular dimensions. Inaddition, the characteristic length associated with hydrodynamic slip becomes comparable to the system size.To resolve the aforementioned issues, the nonlocal linear hydrodynamic constitutive model or Navierboundary condition with the slip length has been employed. It has been suggested that the slip length relatesto the fluid-solid interaction (interfacial tension or wettability). In two-component systems such as binaryliquid mixtures and solutions, fluid-wall interactions lead to segregation or the formation of wetting layersin which the structure of the fluid differs from its bulk properties. Therefore, the wettability influencesmultiphase flows in nano-channels as well.In this project, continuum theories and molecular simulations such as Surface Evovler and DissipativeParticle Dynamics will be performed to explore nanoscale wetting and flows, including planar Poiseuilleflow and Couette flow. In addition, two-phase immiscible flows will be simulated in order to understand thecharacteristics of plugs in nanochannels and the influences of wettability. Two scenarios can be identified bywhether the confined wall is wetted by the fluid forming plugs or not. Because of the difficulties associatedwith direct nanoscale observations of hydrodynamic slip and multiphase flows, macroscopic experimentsassociated with contact line motion will be conducted to understand the influence of hydrodynamic slip(nanoscale) on the behavior of wetting and fluid flow. For example, the motion of a drop in asuperhydrophobic tube or in a superhydrophilic one will be observed and the slip profile of the movingcontact line will be analyzed.Both theoretical and experimental approaches will be employed in this three-year project. In the 1st year,contact line motion will be studied, including compression and stretching of a liquid bridge and drop motionin a superhydrophobic tube. In the 2nd year, hydrodynamic slip and flows of two immiscible liquids inpartial-wetting and non-wetting nanochannels will be investigated. In the 3rd year, liquid-gas flows andplugs in nanochannels will be explored. Our final goals are to understand transport phenomena in nanoscale,which are useful for microscale separations.