title: Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions.
abstract: 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.
authors.affiliation: Physics Department and Institute for Nanotechnology &Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
authors.forename: Erez
authors.initials: E
authors.lastname: Janai
authors.affiliation: Physics Department and Institute for Nanotechnology &Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
authors.forename: Avner P
authors.initials: AP
authors.lastname: Cohen
authors.affiliation: Physics Department and Institute for Nanotechnology &Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Butenko
authors.affiliation: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Schofield
authors.affiliation: Physics Department and Institute for Nanotechnology &Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
authors.forename: Moty
authors.initials: M
authors.lastname: Schultz
authors.affiliation: Physics Department and Institute for Nanotechnology &Advanced Materials, Bar-Ilan University, Ramat-Gan 5290002, Israel.
authors.forename: Eli
authors.initials: E
authors.lastname: Sloutskin