(450c) Interfacial Energetics of Dynamically Reconfigurable Complex Emulsions

Vishnu Sresht¹, Lauren D. Zarzar²,
Ellen M. Sletten², Julia A. Kalow², Timothy M. Swager²,

Daniel Blankschtein¹

¹Department of Chemical Engineering,
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

²Department of Chemistry and Institute for
Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139, USA

Session: ENGINEERING
SCIENCES AND FUNDAMENTALS, 01C20 Anisotropic Particles: Synthesis, Characterization,
Modeling, Assembly, and Applications I

Emulsification is a powerful age-old technique for mixing and
dispersing immiscible components within a continuous liquid phase. 
Consequently, emulsions are central components of medicine, food, and
performance materials.  Complex emulsions, including multiple emulsions and
Janus droplets, are of increasing importance in pharmaceuticals and medical
diagnostics, in the fabrication of microparticles and capsules for food, in
chemical separations, for cosmetics, and for dynamic optics.  As complex
emulsion properties and functions are related to the droplet geometry and
composition, the development of rapid and facile fabrication approaches
allowing precise control over the droplets' physical and chemical
characteristics is critical.  Significant advances in the fabrication of
complex emulsions have been accomplished by a number of procedures, ranging
from large-scale less precise techniques that give compositional heterogeneity
using high-shear mixers and membranesto small-volume microfluidic
methods.  However, such approaches have yet to create droplet morphologies that
can be controllably altered after emulsification. Reconfigurable complex
liquids potentially have greatly expanded utility as dynamically tunable
materials. 

Using theories of interfacial energetics, we have modeled the
interplay between interfacial tensions during the one-step fabrication of
three- and four-phase complex emulsions displaying highly controllable and
reconfigurable morphologies. The fabrication makes use of the
temperature-sensitive miscibility of hydrocarbon, silicone, and fluorocarbon
liquids and is applied to both microfluidic and scalable batch production of
complex droplets.  We demonstrate that droplet geometries can be alternated
between encapsulated and Janus configurations via variations in interfacial
tensions as controlled with hydrocarbon and fluorinated surfactants including
stimuli-responsive and cleavable surfactants. Therefore, we have discovered a
generalizable strategy for the fabrication of multiphase emulsions with controllably
reconfigurable morphologies to create a diversity of responsive materials.