Self-assembly of nano-ellipsoids into ordered structures via vertical deposition

Abstract

The self-assembly of anisotropic particles into two or three dimensional ordered arrays has diverse applications in several areas of science and engineering. In this article, we report the formation of a multi-layer film of nano-sized ellipsoids with long-range orientation and positional order through an evaporation driven vertical deposition technique. Using nano-sized ellipsoids of tunable surface charge, we show that electrostatic interactions can be exploited to control the arrangement of ellipsoids in the film. The pH of the aqueous suspensions used for vertical deposition is adjusted such that the surface charge and hence the electro-static interactions can be controlled. We show that the interplay between various Derjaguin and Landau, Verwey and Overbeek (DLVO) interactions can be effectively controlled to fabricate films with a random arrangement of particles as well as to create particulate films with threedimensional ordering of ellipsoids. When the particles are weakly charged, the nano-ellipsoids in the film are randomly oriented giving an amorphous particulate film. However, when the particles are highly charged, the nano-ellipsoids in the film are oriented with major axis parallel to each other and ordered in three dimensions. These particulate film are observed to have parallel cracks across the entire width of the film. The major axis of the particle is found to be parallel to the crack direction and therefore, the direction of crack formation can be exploited to indicate the nature of particle ordering. † Electronic supplementary information (ESI) available: Document contains measurement of zeta potential of hematite particle as a function pH, results of peeling experiment that demonstrate self-assembly of particles across the cross section of the lm and DLVO potential calculations. See

Monte Carlo simulation of evaporation-driven self-assembly in suspensions of colloidal rods

“…The phenomenon of EDSA and the ordering of anisotropic particles have been experimentally investigated [13]. The EDSA of hematite nano-ellipsoids with an aspect ratio 2 and 5 tunable surface charge has been studied [14]. Orientational self-organization of particles has been observed for highly repulsive particle-particle interactions.…”

Role of particle shape anisotropy on crack formation in drying of colloidal suspension

“…Interestingly these dried colloidal films very often accompany spatially periodic cracks which can be of different morphologies 1 . Different evaporation techniques such as sessile drop evaporation 5 6 7 , drying under confinement 8 9 , vertical deposition 10 11 12 13 , etc, have been used to tailor and achieve different types of particulate films. Moreover, different model systems have been studied to understand the crack nucleation and their propagation during drying 8 14 15 16 .…”

Hybrid magnetic iron oxide nanoparticles with tunable field-directed self-assembly

“…However, for uncoated particles the diffraction peak along the field direction is very clear, which indicates that all the particles are aligned along this direction. 46 The peak corresponds to a repeat distance of 215.8 nm, which is significantly larger than the value expected from the length of the particles along this direction for the coated ones. This is because of the fact that the silica coating partly screens out the dipolar interactions, allowing the particles to form a more compact structures in the presence of the coating.…”