A long single polymer can be viewed as a nanoscale porous material that can in principle block the passage of relatively large biomacromolecules or cells in a confined geometry. We propose that, by manipulating tethered polymer molecules using electrostatic or flow fields within micro- or nanofluidic flow devices, we can create new nanometer-scale mechanical control elements for fluidics, among which we will describe a switch and a valve.

We apply Brownian dynamics/finite element simulations to explore the working parameter space of these elements (electric field strength, polymer chain length, and characteristic length of the geometry). Chain position bistability was observed when the system is operated within certain parameter region, which indicates that there are double wells separated by a barrier in the free energy landscape. The potential of mean force calculation based on position histogram is consistent with this conjecture. Kramers' theory of barrier crossing is employed to study the transition dynamics between the two free energy wells. We will also discuss the free energy barrier dependence on the working parameters using a simple model.