Abstract
Recent extensive studies reveal that surfactant-stabilized spherical alkane emulsion droplets spontaneously adopt polyhedral shapes upon cooling below a temperature Td while remaining liquid. Further cooling induces the growth of tails and spontaneous droplet splitting. Two mechanisms were offered to account for these intriguing effects. One assigns the effects to the formation of an intradroplet frame of tubules consisting of crystalline rotator phases with cylindrically curved lattice planes. The second assigns the sphere-to-polyhedron transition to the buckling of defects in a crystalline interfacial monolayer, known to form in these systems at some Ts > Td. The buckling reduces the extensional energy of the crystalline monolayer’s defects, unavoidably formed when wrapping a spherical droplet by a hexagonally packed interfacial monolayer. The tail growth, shape changes, and droplet splitting were assigned to the decrease and vanishing of surface tension, γ. Here we present temperature-dependent γ(T), optical microscopy measurements, and interfacial entropy determinations for several alkane/surfactant combinations. We demonstrate the advantages and accuracy of the in situ γ(T) measurements made simultaneously with the microscopy measurements on the same droplet. The in situ and coinciding ex situ Wilhelmy plate γ(T) measurements confirm the low interfacial tension, ≲0.1 mN/m, observed at Td. Our results provide strong quantitative support validating the crystalline monolayer buckling mechanism.
Original language | English |
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Pages (from-to) | 1305-1314 |
Number of pages | 10 |
Journal | Langmuir |
Volume | 33 |
Issue number | 5 |
DOIs | |
State | Published - 7 Feb 2017 |
Bibliographical note
Publisher Copyright:© 2017 American Chemical Society.
Funding
We thank C. Quilliet (University of Grenoble-Alpes), T. A. Witten (University of Chicago), and R. Bruinsma (UCLA) for illuminating discussions. We are grateful to M. Weitman and M. Schultz (Bar-Ilan University) for technical assistance and thank the Donors of the American Chemical Society Petroleum Research Fund (E.S. and M.D.) and the U.S. Department of Energy, Office of Basic Energy Sciences, under contract no. DESC0012704 (B.M.O), for support.
Funders | Funder number |
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University of Grenoble-Alpes | |
U.S. Department of Energy | |
Basic Energy Sciences | DESC0012704 |
American Chemical Society Petroleum Research Fund | |
University of California, Los Angeles | |
University of Chicago |