Abstract
Recently there has been strong experimental and theoretical interest in studying the self-assembly and the phase behavior of patchy and Janus particles, which form colloidal suspensions. Although in this quest a variety of effective interactions have been proposed and used in order to achieve a directed assembly, the critical Casimir effect stands out as being particularly suitable in this respect because it provides both attractive and repulsive interactions as well as the potential of a sensitive temperature control of their strength. Specifically, we have calculated the critical Casimir force between a single Janus particle and a laterally homogeneous substrate as well as a substrate with a chemical step. We have used the Derjaguin approximation and compared it with results from full mean field theory. A modification of the Derjaguin approximation turns out to be generally reliable. Based on this approach we have derived the effective force and the effective potential between two Janus cylinders as well as between two Janus spheres.
Highlights
The critical Casimir effect has been predicted[1] as a classical analogue of the celebrated Casimir effect in quantum electrodynamics.[2]
An experimentally convenient realization of the critical Casimir effect is provided by binary liquid mixtures, for which the boundary conditions on the confining surfaces correspond to the adsorption preference for one of the components of the mixture
We investigate this link which is confirmed by the order parameter distribution to occur in the modified form within mean field theory (MFT)
Summary
The critical Casimir effect has been predicted[1] as a classical analogue of the celebrated Casimir effect in quantum electrodynamics.[2]. Interactions, e.g. due to surface charges[36,37] or critical fluctuations In this sense, the critical Casimir effect is a viable candidate to achieve a controlled self-assembly, as demonstrated experimentally by the trapping of homogeneous colloids adjacent to chemically patterned substrates,[38,39] in very good agreement with corresponding theoretical predictions.[39,40]. The Derjaguin approximation implies an intriguing link in the description between the presence of chemical steps on a striped surface and of the chemical step on a Janus particle We investigate this link which is confirmed by the order parameter distribution to occur in the modified form within mean field theory (MFT).
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