(227k) Microfluidic Fabrication of Endoskeletal Droplets

Microfluidic fabrication of endoskeletal droplets

Tamas A. Prileszky
and Eric M. Furst

Department of Chemical and Biomolecular Engineering, University of
Delaware, Newark, DE 19716, United States

Microfluidic devices can produce emulsion
droplets rapidly and uniformly. The characteristic low flow rates and pressures
intrinsic to the small length scales that microfluidics utilize lend the
devices to producing Newtonian emulsions. However, there is interest in
developing oil-in-water emulsions where the dispersed oil phase has a significant
yield stress, termed endoskeletal droplets.¹

Endoskeletal droplets draw their name from an internal
scaffold comprising a percolating network of petrolatum crystallites with a
sufficiently high yield stress to resist the surface tension force that drives
Newtonian emulsions to the spherical morphology. Resisting surface tension
allows the droplets to maintain anisotropic shapes, enhancing their efficiency
as delivery vehicles because of the corresponding decrease in transport length
scales and increase in surface-area-to-volume ratios. Moreover, the yield
stress of the internal network can be changed in situ, permitting dynamic shape changes in response to changes in
environmental conditions.

We investigate a microfluidic system for continuously
generating endoskeletal droplets by incorporating droplet generation, heating,
and cooling regions into a single device. The devices are tuned to ensure that
droplets are generated at high temperatures as Newtonian fluids, then cooled until the internal network crystallizes,
resulting in the yield stress droplets of interest. In addition, the geometry
of the microfluidic channels imparts the droplets with three dimensions of
anisotropy after ejection from the device, greatly enhancing surface-area-to-volume
ratio.

Figure 1: Endoskeletal
droplets ejected from a microfluidic device.

1.    
Caggioni, M., Bayles, A. V,
Lenis, J., Furst, E. M. & Spicer, P. T. Interfacial stability and shape
change of anisotropic endoskeleton droplets. Soft Matter 10,
7647–52 (2014).