Nanorod alignment for optical asymmetry: The high polarizability of chiral nanoassemblies of plasmonic nanoparticles can lead to strong chiral dichroism, but strong light scattering causes the fraction of polarized photons generated, as measured by g-factors, to be much lower than that for chiral liquid crystals. Lu et al. used supramolecular interactions of gold nanorods with human islet amyloid peptides to assemble metallic superstructures with unusually high cholesteric order (see the Perspective by Nam and Kim). The long, straight helices increased the g-factor by 4600-fold, and this effect was used to screen small-molecule binding to amyloids. Science , this issue p. 1368 ; see also p. 1311

Complex chiral particles: Synthetic colloids are usually smooth, but nature can produce micrometer-scale particles with intricate structure and shape, such as the coccoliths produced by algae. Jiang et al. controlled the self-assembly of gold–cysteine nanoplatelets into a variety of chiral, hierarchically organized colloidal particles by changing the chiral fraction of cysteine and the nucleation temperature. Organic cations created electrostatic repulsions that favored edge assembly of the nanoplatelets, which in turn could create surfaces bearing twisted spikes. Science , this issue p. 642

The low melting point of room temperature ionic liquids is usually explained in terms of the presence of bulky, low-symmetry, and flexible ions, with the first two factors related to the lattice energy while an entropic effect is attributed to the latter. By means of molecular dynamics simulations, the melting points of 1-ethyl-3-methyl-imidazolium hexafluorophosphate and 1-decyl-3-methyl-imidazolium hexafluorophosphate were determined, and the effect of the molecular flexibility over the melting point was explicitly computed by restraining the rotation of dihedral angles in both the solid and the liquid phases. The rotational flexibility over the bond between the ring and the alkyl chain affects the relative ordering of the anions around the cations and results in substantial effects over both the enthalpy and the entropy of melting. For the other dihedral angles of the alkyl group, the contributions are predominantly entropic and an alternating behavior was found. The flexibility of some dihedral angles has negligible effects on the melting point, while others can lead to differences in the melting point as large as 20 K. This alternating behavior is rationalized by the different probabilities of conformation defects in the crystal.

Both viscosity and the shear-thinning of ionic liquids are determined mainly by ionic interaction, with density having a secondary effect.

Due to their physical properties including high thermal stability, very low vapor pressure, and high microwave absorption, ionic liquids have attracted great attention as solvents for the synthesis of nanomaterials, being considered as greener alternatives to traditional solvents. While usual solvents often need additives like surfactants, polymers, or other ligands to avoid nanoparticle coalescence, some ionic liquids can stabilize nanoparticles in dispersion without any additive. In order to quantify how the ionic liquids can affect both the aggregation thermodynamics and kinetics, molecular dynamics simulations were performed to simulate the evolution of concentrated dispersions and to compute the potential of mean force between nanoparticles of both hydrophilic and hydrophobic natures in two imidazolium-based ionic liquids, which differ from each other by the length of the cation alkyl group. Depending on the nature of the nanoparticle, structured layers of the polar and apolar regions of the ionic liquid can be formed close to its surface, and those layers lead to activation barriers for dispersed particles to get in contact. If the alkyl group of the ionic liquid is long enough to lead to domain segregation between the ionic and apolar portions of the solvent, the layered structure around the particle becomes more structured and propagates several nanometers away from its surface. This leads to stronger barriers close to the contact and also multiple barriers at larger distances that result from the unfavorable superposition of solvent layers of opposing nature when the nanoparticles approach each other. Those long-range solvent-mediated forces not only provide kinetic stability to dispersions but also affect their dynamics and lead to a long-range ordering between dispersed particles that can be explored as a template for the synthesis of complex materials.