How to model the interaction of charged Janus particles

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Abstract

We analyse the interaction of charged Janus spheres including screening effects. The explicit interaction is mapped via a least square method on a variable number \(n\) of systematically generated tensors that reflect the angular dependence of the potential. For \(n = 2\) we show that the interaction is equivalent to a model previously described by Erdmann, Kr\"oger and Hess. Interestingly, this mapping is not able to capture the subtleties of the interaction for small screening lengths. Rather, a larger number of tensors has to be used. We find that the characteristics of the Janus type interaction plays an important role for the aggregation behaviour. We obtained cluster structures up to the size of \(13\) particles for \(n = 2\) and \(36\) and screening lengths \(\kappa^{-1} = 0.1\) and \(1.0\) via Monte Carlo simulations. The influence of the screening length is analysed and the structures are compared to results for an explicit electrostatic potential and for multipole-expanded DLVO. In conclusion we find that a dipole-like potential with a correction term, like the EKH or dipole DLVO approximations, cannot reproduce experimental cluster structures and a higher order expansion is needed to correctly express the properties of the electrostatic potential.

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Replica Monte Carlo Simulation of Spin-Glasses

Robert H Swendsen, Jian-Sheng Wang (1986)

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Directed self-assembly of a colloidal kagome lattice.

Qian Qian Chen, Sung Bae, Steve Granick (2011)

A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering and the design of porous materials, this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties, but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal-in this case a colloidal kagome lattice-through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres. This open network is of interest for several theoretical reasons. With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks.