title: Viscoelastic effects on electrokinetic particle focusing in a constricted microchannel.
abstract: Focusing suspended particles in a fluid into a single file is often necessary prior to continuous-flow detection, analysis, and separation. Electrokinetic particle focusing has been demonstrated in constricted microchannels by the use of the constriction-induced dielectrophoresis. However, previous studies on this subject have been limited to Newtonian fluids only. We report in this paper an experimental investigation of the viscoelastic effects on electrokinetic particle focusing in non-Newtonian polyethylene oxide solutions through a constricted microchannel. The width of the focused particle stream is found NOT to decrease with the increase in DC electric field, which is different from that in Newtonian fluids. Moreover, particle aggregations are observed at relatively high electric fields to first form inside the constriction. They can then either move forward and exit the constriction in an explosive mode or roll back to the constriction entrance for further accumulations. These unexpected phenomena are distinct from the findings in our earlier paper [Lu et al., Biomicrofluidics 8, 021802 (2014)], where particles are observed to oscillate inside the constriction and not to pass through until a chain of sufficient length is formed. They are speculated to be a consequence of the fluid viscoelasticity effects.
authors.affiliation: Department of Mechanical Engineering, Clemson University , Clemson, South Carolina 29634-0921, USA.
authors.forename: Xinyu
authors.initials: X
authors.lastname: Lu
authors.affiliation: Department of Mechanical Engineering, Clemson University , Clemson, South Carolina 29634-0921, USA.
authors.forename: John
authors.initials: J
authors.lastname: DuBose
authors.affiliation: School of Mechanical Engineering, Yeungnam University , Gyongsan 712-719, South Korea.
authors.forename: Sang Woo
authors.initials: SW
authors.lastname: Joo
authors.affiliation: Institute of Micro/Nanotechnology, Old University , Norfolk, Virginia 23529, USA.
authors.forename: Shizhi
authors.initials: S
authors.lastname: Qian
authors.affiliation: Department of Mechanical Engineering, Clemson University , Clemson, South Carolina 29634-0921, USA.
authors.forename: Xiangchun
authors.identifier: 0000-0003-0158-4186
authors.initials: X
authors.lastname: Xuan