Dipolar colloids in apolar media: Direct microscopy of two-dimensional suspensions

Erez Janai, Avner P. Cohen, Alexander V. Butenko, Andrew B. Schofield, Moty Schultz, Eli Sloutskin

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Spherical colloids, in an absence of external fields, are commonly assumed to interact solely through rotationally-invariant potentials, u(r). While the presence of permanent dipoles in aqueous suspensions has been previously suggested by some experiments, the rotational degrees of freedom of spherical colloids are typically neglected. We prove, by direct experiments, the presence of permanent dipoles in commonly used spherical poly(methyl methacrylate) (PMMA) colloids, suspended in an apolar organic medium. We study, by a combination of direct confocal microscopy, computer simulations, and theory, the structure and other thermodynamical properties of organic suspensions of colloidal spheres, confined to a two-dimensional (2D) monolayer. Our studies reveal the effects of the dipolar interactions on the structure and the osmotic pressure of these fluids. These observations have far-reaching consequences for the fundamental colloidal science, opening new directions in self-assembly of complex colloidal clusters.

Original languageEnglish
Article number28578
JournalScientific Reports
StatePublished - 27 Jun 2016

Bibliographical note

Funding Information:
We are grateful to Peter J. Lu for sharing his PLuTARC codes, to Dov Fridman for technical assistance, and thank Antonio Scala for sharing the HardBrown event-driven Brownian dynamics codes. We thank A. V. Tkachenko, Y. Rabin and D. Osmanovic for fruitful discussions. The Kahn foundation and the Israel Science Foundation (No. 1668/10) have generously funded some of the equipment used in this project. This research is supported by Israel Science Foundation 85/10. A.B.S. is partially funded by the UK Engineering and Physical Sciences Research Council grant EP/J007404/1.


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