Filling of charged cylindrical capillaries.
We provide an analytical model to describe the filling dynamics of horizontal cylindrical capillaries having charged walls. The presence of surface charge leads to two distinct effects: It leads to a retarding electrical force on the liquid column and also causes a reduced viscous drag force because of decreased velocity gradients at the wall. Both these effects essentially stem from the spontaneous formation of an electric double layer (EDL) and the resulting streaming potential caused by the net capillary-flow-driven advection of ionic species within the EDL. Our results demonstrate that filling of charged capillaries also exhibits the well-known linear and Washburn regimes witnessed for uncharged capillaries, although the filling rate is always lower than that of the uncharged capillary. We attribute this to a competitive success of the lowering of the driving forces (because of electroviscous effects), in comparison to the effect of weaker drag forces. We further reveal that the time at which the transition between the linear and the Washburn regime occurs may become significantly altered with the introduction of surface charges, thereby altering the resultant capillary dynamics in a rather intricate manner.
Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA.
Siddhartha
S
Das
Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G8.
Sourayon
S
Chanda
BIOS, The Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
J C T
JC
Eijkel
Transducers Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
N R
NR
Tas
Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur-721302, India.
Suman
S
Chakraborty
Department of Mechanical Engineering, Lassonde School of Engineering, York University, Toronto, Ontario, Canada M3J1P3.
Sushanta K
SK
Mitra
D000388:Air; D004583:Electrons; D007477:Ions; D008962:Models, Theoretical; D009038:Motion; D009994:Osmolar Concentration; D013499:Surface Properties; D014783:Viscosity
D007477:Ions