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When oil-in-water emulsions are confined in a quasi two-dimensional space, the oil droplets easily deform upon contact. At a critical area fraction, the characteristic of the system should change from a composition dominated by circular disks to one composed of disks deformed to varying degrees. We observe in a static system of toluene droplets in water that an increase in area fraction corresponds with an increase in average droplet deformation. Further, an increase in average droplet deformity corresponds with an increase in the heterogeneity of deformity within a given sample.
Recent studies of granular materials find spatially heterogeneous force distributions among contacting particles (Figure 1.) As a critical area fraction of particles is approached, such regions of high stress become more pronounced. This projects aims to establish a correlation between macroscopic granular (solid-in-gas) and microscopic emulsion (liquid-in-liquid) systems (Figure 2.) Demonstrating that these two systems are comparable in the static state suggests other potential correlations between their structural and dynamical properties. Additionally, this project is a foundation for future studies of dynamics in emulsions.
-Toluene in water emulsions [1] (Figure 3)
-Clean glass with 5:1:1 H2O:NH4OH:H2O2 [2]
-Squeeze glass and coverslip in vise,
then glue in place
-Flow emulsion into chamber (Figure 4,)
then glue shut
-Image with bright field microscopy
Experimental Difficulties
Possible explanations:
-Dirty slides
5:1:1 H20:NH4OH:H2O reduced strange deformation
-Depletion effect
excess surfactant could cause particles to stick together
-Spatial changes in t
-As in granular systems, regions of stress appear to increase as area fraction increases (see Figure 6), but chamber imperfections and the depletion effect cause unwanted deformation (see Figure 9,) which confuses the results.
-We observe spatially heterogeneous forces within emulsions (see Figure 8 and Figure 7d) but do not yet find chains of stressed particles as in the granular systems shown in Figure 1.
This work is supported by the Howard Hughes Medical Institute under Grant No. 52005873 and the Petroleum Research Fund administered by the American Chemical Society under Grant No. 47970-AC9. We thank Cara Hageman, Kazem Edmond, and Kenneth Desmond for support and guidance.
-J. Uglestad and P.C. Mork. Adv. Colloid & Interface Sci. 13, 101-140 (1980)
-J.J. Cras, et. al. Biosensors and Bioelectronics. 14, 683-688 (1999).
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