Abstract
We study theoretically and by means of molecular dynamics (MD) simulations the generation of mechanical force by grafted polyelectrolytes in an external electric field, which favors its adsorption on the grafting plane. The force arises in deformable bodies linked to the free end of the chain. Varying the field, one controls the length of the nonadsorbed part of the chain and hence the deformation of the target body, i.e., the arising force too. We consider target bodies with a linear force-deformation relation and with a Hertzian one. While the first relation models a coiled Gaussian chain, the second one describes the force response of a squeezed colloidal particle. The theoretical dependences of generated force and compression of the target body on an applied field agree very well with the results of MD simulations. The analyzed phenomenon may play an important role in future nanomachinery, e.g., it may be used to design nanovices to fix nanosized objects.
Highlights
Due to its obvious importance for applications, the response of polyelectrolytes to external electric fields has been of high scientific interest for the past few decades
We analyzed the generation of a mechanical force by an external electric field, applied to a grafted polyelectrolyte that is linked to a deformable target body
We developed a theory of this phenomenon and performed molecular dynamics (MD) simulations
Summary
Due to its obvious importance for applications, the response of polyelectrolytes to external electric fields has been of high scientific interest for the past few decades (see, e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]). If the polyelectrolyte is exposed to an external electric field that favors adsorption at the grafting plane, its conformation will be determined by both the field and the restoring force exerted by the deformed target body on the chain (see Fig. 1). We analyze a model of a polyelectrolyte chain grafted to a plane, linked by its free end to a deformable target body and exposed to an external electric field. Counterions having the same charge sign as the grafting plane are repelled, leaving the chain unscreened see (see Fig. 1) This feature is dominating if the specific volume per chain is not small and the electric field is not weak. The simpler problem of the conformation of a grafted polyelectrolyte exposed to a constant force in an electric field has been explored theoretically and numerically in a previous study [12].
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