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

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

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

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, 1519-1536 Velocity profile of emulsion-filled channel at different pressure differences Soft Matter, 2010,6, 2668-2678 M van Hecke, J. Phys.: Condens. Matter (2010) What can we learn about glassy systems from the jamming transition?

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

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

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)

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

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

One Hour Time Lapse Flow Velocityx as a Function of Time

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

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

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

Outlook & Acknowledgements 14 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.