Igor M. Kulic, Miodrag L. Kulic
When two polarizable objects interact in spatially randomly fluctuating fields, we speak of Van der Waals-like forces. But what happens if the random excitation becomes spatially coherent? We show that such a spatially coherent fluctuation interaction (scFI) displays remarkable physical features distinguishing it from its sister, the incoherent fluctuation interaction (icFI). In particular, we investigate how scFI gives rise to complex, hierarchically structured, self-assembled materials, in contrast to the usual phase-separated droplets generated by icFI. We discuss a recent example of scFI, implemented with superparamagnetic colloids in triaxial magnetic fields by Martin et al. and explore the main steps in the hierarchical formation process of coherent colloid self assemblies, from chains, through membranes, to large-scale foamy superstructures of the material. We predict that such coherent "dipolar doughs" exert positive pressure, can easily swell against gravity on cm-scales and we derive their equation of state.
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http://arxiv.org/abs/1304.5703
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