Manipulating Polyelectrolyte Conformations In Solution and At Surface by AC-Electric Fields

Recently, we have studied the conformational dynamics of polyelectrolytes under AC-electric fields of varied AC-field frequency and strength. By using florescence correlation spectroscopy (FCS), we examine the structural dynamics of poly(2-vinyl pyridine) (P2VP) at a single molecular level in response to uniform AC-fields between two extended conducting plates, where no net force is imposed on P2VP chains. In stark contrast to an abrupt first-order coil-to-globule transition (CGT) by tuning solution pH, we surprisingly observe a gradual and hysteretic CGT of P2VP conformations within an optimum AC-frequency window and beyond a critical AC-field strength of molecular-weight dependence. The hysteresis is attributed to an asymmetric bistable energy landscape of a single hydrophobic polyelectrolyte chain, whose electrostatic barrier between coil and globule conformations can be reduced below thermal fluctuation energy by AC-field induced polarization due to counterion migration and condensation. Currently, we further explore the AC-field induced conformational dynamics of surface-tethered P2VP brush chains to thereby control surface hydrophobicity and morphology.