Regular Article

The European Physical Journal E

, 35:24

First online:

Sample-to-sample torque fluctuations in a system of coaxial randomly charged surfaces

  • Ali NajiAffiliated withSchool of Physics, Institute for Research in Fundamental Sciences (IPM)Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge
  • , Jalal SarabadaniAffiliated withDepartment of Physics, University of Isfahan
  • , David S. DeanAffiliated withLaboratoire de Physique Théorique (IRSAMC), Université de Toulouse, UPS and CNRSUniversité de Bordeaux and CNRS, Laboratoire Ondes et Matière d’Aquitaine (LOMA), UMR 5798
  • , Rudolf PodgornikAffiliated withLaboratoire de Physique Théorique (IRSAMC), Université de Toulouse, UPS and CNRSDepartment of Theoretical Physics, J. Stefan InstituteDepartment of Physics, Faculty of Mathematics and Physics, University of Ljubljana

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Polarizable randomly charged dielectric objects have been recently shown to exhibit long-range lateral and normal interaction forces even when they are effectively net-neutral. These forces stem from an interplay between the quenched statistics of random charges and the induced dielectric image charges. This type of interaction has recently been evoked to interpret measurements of Casimir forces in vacuo, where a precise analysis of such disorder-induced effects appears to be necessary. Here we consider the torque acting on a randomly charged dielectric surface (or a sphere) mounted on a central axle next to another randomly charged surface and show that although the resultant mean torque is zero, its sample-to-sample fluctuation exhibits a long-range behavior with the separation distance between the juxtaposed surfaces and that, in particular, its root-mean-square value scales with the total area of the surfaces. Therefore, the disorder-induced torque between two randomly charged surfaces is expected to be much more pronounced than the disorder-induced lateral force and may provide an effective way to determine possible disorder effects in experiments, in a manner that is independent of the usual normal force measurement.


Soft Matter: Colloids and Nanoparticles