Link to the University of Pittsburgh Homepage
Link to the University Library System Homepage Link to the Contact Us Form

Mini-/Micro-Scale Free Surface Propulsion

Yuan, Junqi (2015) Mini-/Micro-Scale Free Surface Propulsion. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

Primary Text

Download (5MB)


This work reports theoretical studies and experimental proofs of the propulsion of mini-/micro-scale floating objects that propel on air-liquid interface by using two different principles. The devices are extremely simple and do not include any moving parts.

The first principle takes advantage of three-phase contact line oscillation that is activated by AC electrowetting on dielectric (EWOD) to propel the floating object. The capillary wave that is generated by the free surface oscillation is visualized by using the Free-Surface Synthetic Schlieren (FS-SS) method. A 3-D flow field sketch is constructed based on the flow visualizations and PIV measurements. The flow field and trajectories of seeded particles suggest that Stokes drift is the responsible mechanism for the propulsion. The propulsion speed of the floating object highly depends on the amplitude, frequency, and shape of the EWOD signal. These phenomena are also explained by the measured oscillation amplitudes and Stokes drift relations. Additionally, it is shown that a wider EWOD electrode generates a faster propelling speed. Finally, with stacked planar receiver coils and an amplitude modulated signal, a wirelessly powered AC EWOD propulsion is realized.

The second principle of floating object propulsion is the Cheerios effect, which is also generally known as lateral capillary force. Four common physical configurations (interactions between two infinite vertical walls, two vertical circular cylinders, two spheres, and a sphere and a vertical wall) are reviewed. Through theoretical analysis, it has been revealed that not the wettability of the surface but the slope angle of the object is the most important parameter for the Cheerios effect. A general rule for this effect is that the lateral capillary force is attractive if the slope angles of the interacting objects have the same sign, otherwise the force is repulsive. In addition to the surface wettability, the size and the density of floating spheres are also important for the slope angle. Active control of the Cheerios effect is achieved by implementing EWOD and dielectrowetting methods to adjust the surface wettability. By sequentially activating micro-fabricated EWOD/dielectrowetting electrodes, linear translations of floating objects in the small scale channel are accomplished. A continuous rotational motion of the floating rod is achieved in a circular container by the EWOD method.


Social Networking:
Share |


Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Yuan, Junqijunqi.yuan@gmail.com0000-0002-9142-1315
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairCho, Sung Kwonskcho@pitt.eduSKCHO
Committee MemberChyu, Minkingmkchyu@pitt.eduMKCHYU
Committee MemberSchaefer, Lauralas149@pitt.eduLAS149
Committee MemberChun, Youngjaeyjchun@pitt.eduYJCHUN
Date: 9 June 2015
Date Type: Publication
Defense Date: 29 January 2015
Approval Date: 9 June 2015
Submission Date: 6 March 2015
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 122
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Mechanical Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Free surface, Propulsion, Electrowetting, Dielectrowetting, Surface tension, Cheerios effect
Date Deposited: 09 Jun 2015 15:22
Last Modified: 15 Nov 2016 14:26


Monthly Views for the past 3 years

Plum Analytics

Actions (login required)

View Item View Item