Unidirectional rotation of micromotors on water powered by pH-controlled disassembly of chiral molecular crystals.

Biological and synthetic molecular motors, fueled by various physical and chemical means, can perform asymmetric linear and rotary motions that are inherently related to their asymmetric shapes. Here, we describe silver-organic micro-complexes of random shapes that exhibit macroscopic unidirectional rotation on water surface through the asymmetric release of cinchonine or cinchonidine chiral molecules from their crystallites asymmetrically adsorbed on the complex surfaces. Computational modeling indicates that the motor rotation is driven by a pH-controlled asymmetric jet-like Coulombic ejection of chiral molecules upon their protonation in water.

The role of steric interactions in dispersion of carbon nanotubes by poly(3-alkyl thiophenes) in organic solvents.

The dispersion mechanism of carbon nanotubes (CNTs) in organic solutions of poly(3-alkyl thiophenes, P3ATs) was examined in a study that combines experimental investigation of the dispersion mechanism and molecular theory calculations of the effective intertube potential for polymer wrapped CNTs. The minimal polymer concentration required for dispersion of CNT served as a comparative measure of the efficiency of P3AT derivatives that differ in the length of the alkyl side chains or the regiochemistry of the monomers in three solvents: 1,2 and 1,3 dichlorobenzene and chloroform. While previous studies focused on the adsorption mechanism of P3ATs onto SWNT, we find that the dispersing efficiency depends not only on the stacking of the polymer backbone onto the CNT ("wrapping"), but also on the steric repulsion among the side chains of adsorbed P3ATs.

Salting-in effect in organic dispersions of poly(3-hexyl thiophene)-carbon-nanotubes.

Addition of small concentrations of different inorganic salts to THF solutions of poly(3-hexyl thiophene), which contain non-dispersed powder of Multi-Walled Carbon Nanotubes (MWNTs), was found to "salt-in" the precipitated tubes leading to the formation of a stable dispersion of the MWNTs. This effect seems to result from a salt-induced conformational change of polymer chains adsorbed onto the CNTs, resulting in the onset of (entropic) steric repulsion among polymer-decorated chains.