We previously showed that long-lived nanoemulsions, seeming initially vesicular, might be prepared simply by diluting and cooling (quenching) warm microemulsions with n-hexadecane with precooled water. In this paper, we confirm that these systems are vesicular dispersions when fresh, and they can be made with similar structures and compositional dependence using alkanes with chain lengths ranging from octane to hexadecane. The nanostructures of fresh nanoemulsions are imaged with cryogenic transmission electron microscopy (cryo-TEM). We confirm that water-continuous microemulsions give simple dispersions of vesicles (sometimes unilamellar), typically less than 100 nm in diameter; these systems can avoid separation for over 2 months. Selected samples were also prepared using halogenated alkanes to create additional contrast in the cryo-TEM, allowing us to confirm that the oil is located in the observed vesicular structures.
Bibliographical noteFunding Information:
We acknowledge funding from the Nanostructural Materials and Processes program, of the Industrial Partnership for Research in Interfacial and Materials Engineering (IPRIME) at the University of Minnesota, for this research, including Eric Morrison's Industrial Fellowship. Part of this research (cryo-TEM methodology) was made possible in part by a grant supporting the Center for Molecular Engineering of Dispersant System from The Gulf of Mexico Research Initiative. Some of the materials were provided by Ecolab. Parts of this work were carried out in the College of Science and Engineering Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network (www.mrfn.org) via the MRSEC program. We thank Dr. Jinping Dong and Dr. Wei Zhang for their assistance in learning to perform the confocal Raman microscopy and cryo-TEM. We are grateful for helpful initiation of the questions leading to this work from our colleague and mentor, the late H. Ted Davis.
© 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society
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- confocal Raman microscopy
- phase change emulsification