Temperature-Tuned Faceting and Shape Changes in Liquid Alkane Droplets

Shani Guttman, Zvi Sapir, Benjamin M. Ocko, Moshe Deutsch, Eli Sloutskin

Research output: Contribution to journalArticlepeer-review

36 Scopus citations

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 languageEnglish
Pages (from-to)1305-1314
Number of pages10
JournalLangmuir
Volume33
Issue number5
DOIs
StatePublished - 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.

FundersFunder number
University of Grenoble-Alpes
U.S. Department of Energy
Basic Energy SciencesDESC0012704
American Chemical Society Petroleum Research Fund
University of California, Los Angeles
University of Chicago

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