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.
Highlights
0 2 4 6 8 10 2 4 6 8 10 r/σ r/σ microscopy, allowing their positions to be detected in real motion, which is practically impossible with fluids of atoms and molecules[3,7]
The studies of colloids are by no means restricted to three-dimensional systems; colloids can readily be confined, through introduction of either solid[24,27] or liquid boundaries[28,29], to a 2D space, forming a very simple physical model of a Langmuir film (LF), where molecular degrees of freedom are constrained to two spatial dimensions[30]
We have studied 2D fluids of PMMA colloidal spheres in an organic solvent, a simple model of the fluid Langmuir films
Summary
0 2 4 6 8 10 2 4 6 8 10 r/σ r/σ microscopy, allowing their positions to be detected in real motion, which is practically impossible with fluids of atoms and molecules[3,7]. Recent computer simulations[23,25] of hard disks (HDs) suggest a phase transition from a fluid to an hexatic phase to occur when the area fraction of the disks reaches η ≈ 0.704; the corresponding number density is ρ = 0.896 σ−2, where σ is the particle diameter This transition, where the spatial correlations between the nearest-neighbor (NN) bond orientations become quasi-long-ranged, was demonstrated to be of the first-order, followed by a second-order transition at η ≈ 0.72 to a two-dimensional solid. These new theoretical results, following decades of fierce debates over the nature of phase transitions in HDs23, pose a whole range of new questions. In order to fill this gap, in present work we detect particle positions by a corrected particle location algorithm[19] and directly compare the experimental fluid structures with computer simulations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
