Rectification of the ionic current through carbon nanotubes by electrostatic assembly of polyelectrolytes.

Rectification of the ionic current flowing through nanotubes embedded in a polymeric membrane is achieved by selective adsorption of polycations to the nanotubes' mouths. A one-dimensional model of ionic flux through a nanotube with charged entrance regions qualitatively describes current-voltage curves before and after polycation exposure; reversal potential measurements confirm that charge reversal takes place upon polycation adsorption. The inherent simply of this electrostatic approach makes it attractive in membrane and nanofluidic applications employing rectification.

Director dynamics in liquid-crystal physical gels.

Nematic liquid-crystal (LC) elastomers and gels have a rubbery polymer network coupled to the nematic director. While LC elastomers show a single, non-hydrodynamic relaxation mode, dynamic light-scattering studies of self-assembled liquid-crystal gels reveal orientational fluctuations that relax over a broad time scale. At short times, the relaxation dynamics exhibit hydrodynamic behavior.

Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent.

Rheological properties of triblock copolymers dissolved in a nematic liquid crystal (LC) solvent demonstrate that their microphase separated structure is heavily influenced by changes in LC order. Nematic gels were created by swelling a well-defined, high molecular weight ABA block copolymer with the small-molecule nematic LC solvent 4-pentyl-4'-cyanobiphenyl (5CB). The "B" midblock is a side-group liquid crystal polymer (SGLCP) designed to be soluble in 5CB and the "A" endblocks are polystyrene, which is LC-phobic and microphase separates to produce a physically cross-linked, thermoreversible, macroscopic polymer network.

Self-assembled liquid-crystalline gels designed from the bottom up.

Liquid crystals are often combined with polymers to influence the liquid crystals' orientation and mechanical properties, but at the expense of reorientation speed or uniformity of alignment. We introduce a new method to create self-assembled nematic liquid-crystal gels using an ABA triblock copolymer with a side-group liquid-crystalline midblock and liquid-crystal-phobic endblocks. In contrast to in situ polymerized networks, these physical gels are homogeneous systems with a solubilized polymer network giving them exceptional optical uniformity and well-defined crosslink density.