1. Droplet Dynamics of a Flowing Emulsion System in a Narrow Channel
Olivia Cypull, Nick Mirenda, Harry Hicock, John Crocker, Klebert Feitosa
Dept. Physics and Astronomy
James Madison University

2. Outline The Great Mystery of Soft Matter Our Emulsion System
Creating Flow and Experimental Methods
Observations
Future Work

3. One of the Great Mysteries of Condensed Matter
Glass transition is not well understood
‘Solid’ glass has very high viscosity, achieved with relatively small change in temperature or pressure
Viscosity vs. Temperature for Different Glasses
Super-cooled liquid /amorphous solid

4. What can we learn about glassy systems from the jamming transition?
Jamming Systems
Emulsion, foams, pastes, granular systems - also amorphous solids
Jam after a critical load, temperature or volume fraction is reached
Jamming can be induced in flowing materials by the application of shear stress.
Soft Matter, 2014,10,
Velocity profile of emulsion-filled channel at different pressure differences
Soft Matter, 2010,6,
M van Hecke, J. Phys.: Condens. Matter (2010)
What can we learn about glassy systems from the jamming transition?

5. The Emulsion System
Polar and non-polar solutions are index-matched at room temperature for an optically clear emulsion that can be viewed through the confocal microscope.
Polar Phase (30% volume)
52.5% Water
44.2% Glycerol
3.5% P105 surfactant
w/ 2 μmL of 55 mM Fluorescein disodium dye per 15 mL of solution
Polar Phase (Light background, 30% volume):
52.5% Water, 44.2% glycerol, 3.5% P105 (Surfactant), w/w
2 μmL of 55mM Fluorescein disodium dye
Non-Polar Phase (black spheres, 70% volume):
Silicon oil
arrows
Non-polar Phase (70% volume)
Silicon oil

6. Stability of Emulsion
No significant change in size distribution over time period of experiment
Radius Histogram of Fresh Emulsion
Radius Histogram of Emulsion after 12 Days

7. Making Channels
Near top (3350 μm)- 338 μm wide
Middle
(3150 μm)-
384 μm wide
- Note v shape and rough edges
Cross section view
Bottom
(2960 μm)- 570 μm wide
A laser printer was used to etch a narrow channels approximately 0.5 mm wide, 5 cm long and 0.4 mm deep into pieces of 2 mm thick plastic (PMMA)

8. Creating Flow
Flow was achieved by lightly plunging a syringe filled with emulsion through tubing into the channel
The pressure difference in the syringe created is high enough the emulsion moving a longer period of time, but low enough for the emulsion to be moving at speed observable under the confocal microscope
syringe
tubing
clamp
plastic stand
Experimental apparatus
yellow/green- emulsion
Channel Edge
Scale bar, less words
channel x y
100 μm
Time lapse of emulsion Photos were taken ~0.5 seconds between frames
Principle of Confocal Microscope

9. Measuring Flow Velocity
Individual Droplet Flow
Generate a binary image and assign Euclidian distance to nearest ‘background’ voxel
Creates landscape with the peaks corresponding to droplet centers and the height corresponding to the radii
Track droplets from frame to frame using program
Bulk Flow
Generate a binary image
Divide image into slices based on distance from the channel edge
Shift each 1 pixel at a time and subtracted from the previous image until a minimum value (best fit) is found
Frame 1209
Distanced moved between frames (1 sec)
Frame 1210

10. One Hour Time Lapse
Flow Velocityx as a Function of Time

11. Analysis of Shorter Time Lapse
Mean Square Droplet Speed as a Function of Time

12. Analysis of Non-Affine Motion
Mean Square of Droplet Speedy as a Function of Distance from Channel Edge
Droplet Velocityy as a Function of Radii Size

13. Summary
Soft materials experience a jamming transition similar to the glass transition
We created optically clear emulsion system near jamming transition and made it flow through a tiny channel to investigate the effects of confinement on flow
We found that
Flow velocity parallel to the channel edge is independent of distance from channel edge
Flow decreases linearly, then fluctuates
Droplets closer to the edge have more nonaffine motion
Smaller droplets have more nonaffine motion; they tend to be pushed around by larger droplets

14. Outlook & Acknowledgements14
Interests for the future:
Better control over flow rate
Analysis at different flow velocities and depths
Studying nonaffine droplet motion
Capturing droplet flow in 3 dimensions
We gratefully acknowledge support from the Research Corporation for Science Advancement, The National Science Foundation, and James Madison University.