CSM Microrobotics Research Poster
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Transcript of CSM Microrobotics Research Poster
Movement and propulsion of colloidal chains under an AC
electric field:
Formation and Motion Analysis of Colloidal Particle
Chains Under an AC Electric Field
Conclusion: Using a method that we developed to seal and heat a colloidal
solution, we were able to successfully form colloidal chains that were flexible, but
not durable. Additionally, we developed a mass production plate which allowed us
to produce exponentially more chains, and extract the solution. We also observed
partially correlated motion within chains when the entire chain acted under the
influence of Brownian motion.
William Trevillyan, Kelley Heatley, Dr. Ning Wu
Introduction: Research on formation and motion of colloidal particle chains
under an AC electric field is being conducted to develop micro-robotic technology
that can potentially be used in drug delivery, micro-surgery, and active sensors.
The final goal is to understand the formation of colloidal chain systems,
characterize them, and probe the fundamental mechanisms of chain propulsion
under AC electric fields.
A “Colloidal dispersion” consists of the solvent and the particles suspended in
the solvent. Colloidal particles range in size from a few nanometers to a few
micrometers. When present under a parallel electric or magnetic field, the particle
gains an induced-dipole similar to a bar magnet. Dipolar interactions between the
particles make them attract towards each other forming long chains in the
direction of the applied field. After chains have been formed, we can apply a
perpendicular AC electric field. An electro-hydrodynamic (EHD) Flow will be
induced surrounding the chain and possibly cause it to propel. This flow is caused
by the movement of cations and anions in the solution being attracted to the
oppositely charged electrodes. When there is an imbalanced EHD flow
surrounding a particle or chain, the fluid induces a force on the particle or chain
causing it to propel. When under the influence of this force, chains oscillate or
propel just like an Earth worm or a snake as seen in nature.
Future Work: We will run experiments regarding the formation of flexible,
durable chains in an electric or magnetic field while changing many variables: salt
concentration, PVP concentration, field strength, frequency, particle concentration,
and the process of cross-linking polymerizations. We will be modifying the mass
production plate procedure in hopes of reducing air bubbles in the sealed system.
Additionally, we will develop a mathematical model for the further understanding of
EHD flow affects on the chain behavior under AC electrical fields.
Figure 5: Capillary TubeTension is placed on the two
copper wires that line the walls of
the capillary tube. This is the first
of two systems for producing
colloidal chains under an AC
electric field.
References:“Inducing Propulsion of Colloidal Dimers by Breaking the Symmetry in Electrohydrodynamic Flow” F. Ma, X. Yang, H. Zhao, and
N. Wu, PRL 115, 208302 (2015) “Electric-field–induced Assembly and Propulsion of Chiral Colloidal Clusters” F. Ma, S. Wang, D.T. Wu, and N. Wu, PNAS 112,
6307-6312 (2015)
Acknowledgements:I would like to thank Dr. Ning Wu who has lent much insight, along with CSM’s
Department of Chemical and Biological Engineering and the
National Science Foundation for supporting my REU experience.
Figure 2: During FormationFigure 1: Before Formation
Figure 3: Heating UnitA heat gun heats the inside of the container. The large volume container maintains a consistent
temperature as hot air flows into the smaller container atop the microscope containing the
sealed capillary or the sealed mass production plate. Heating a solution of particles under the
influence of a field causes the physical bond between two particles to strengthen.
Figure 7: Magnetic Chain Formation SystemAn magnetic field is applied around seven different magnetic colloidal particle solutions as an air
gun cools the electromagnet.
EHD Flow Diagram:
E0e-iwt
+ + + ++ + + +
+++ +
---
-+ +++ +- - - - - -- - -
- - -- - -
--
+ + + + + ++ + +
-
--
+ + ++ + ++ + + - - - - - -- - -
100 μm ITO Glass
Slide
Chain Formation Under an AC Electric Field:Typical Experimental Condition:
Field Condition: 20Vpp (amplified 14x), 100kHz
Temperature: 70-80°C
Particle Solution: 2 wt% 4 µm Sulfonate-functionalized Polystyrene Particles
1 wt% Polyvinylpyrrolidone (Mw=1.3M) & Sodium Chloride (1mM)
Chain Formation Under a DC Magnetic Field:Typical Experimental Condition:
Field Condition: 300 Gauss
Temperature: 75°C
Particle Solution: 2.8 µm Epoxy Magnetic Particles
1 wt% Polyvinylpyrrolidone (Mw=1.3M) & Potassium Chloride (0.01M)
Figure 6: Mass Production PlateThis is the second system for producing colloidal chains
under an AC electric field. Two glass slides were sealed
together using nail polish after the colloid solution was
added. In between each of the glass slides lies a layer
of alternating electrodes. The picture on the right
shows air that was trapped beneath the electrode
leaking in to the main solution.
Characterization of Chains without Applied Field:
Bond angles are strongly correlated during chain propulsion.
Bond angles are weakly correlated.
Non-propulsive Five-bead Chain
Frame 1 Frame 31 Frame 61 Frame 91
Propulsive Four-bead Chain
Frame 8 Frame 33 Frame 54 Frame 77
Some bond angles are strongly correlated.
Brownian Motion of Six-bead Chain
Frame 1 Frame 21 Frame 41 Frame 61 Frame 81 Frame 100 Frame 121 Frame 141
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Figure 4: After
Formation