Directed coassembly of oriented PbS nanoparticles and monocrystalline sheets of alkylamine surfactant.

We demonstrate control over the orientation of PbS nanoparticles by way of directed assembly, which in turn affects the crystal structure of alkylamine surfactants such as octadecylamine (ODA, C(18)H(37)NH(2)) and hexadecylamine (HDA, C(16)H(33)NH(2)). This directed assembly method results in the arrangement of PbS nanoparticles with a well-defined epitaxial orientation on lamellar alkylamine sheets, which undertake a new crystal structure to accommodate these relations. Understanding these surfactant-nanoparticle inter-relations is very instrumental in understanding surfactant-assisted nanoparticle synthesis and assembly.

Origin of the contact angle hysteresis of water on chemisorbed and physisorbed self-assembled monolayers.

Self-assembled monolayers (SAMs) are known to form on a variety of substrates either via chemisorption (i.e., through chemical interactions such as a covalent bond) or physisorption (i.

Hierarchical superstructure of alkylamine-coated ZnS nanoparticle assemblies.

We describe methodology for producing highly uniform, ordered and reproducible superstructures of surfactant-coated ZnS nanorod and nanowire assemblies, and propose a predictive multiscale "packing model" for superstructure formation based on electron microscopy and powder X-ray diffraction data on the superstructure, as well as on individual components of the nanostructured system. The studied nanoparticles showed a hierarchical structure starting from the individual faceted ZnS inorganic cores, onto which the crystalline surfactant molecules are adsorbed, to the superstructure of the nanoparticle arrays. Our results point out the critical role of the surfactant headgroup and polarity in nanoparticle assembly, and demonstrate the relationship between the molecular structure of the surfactant and the resulting superstructure of the nanoparticle assemblies.

The temperature-dependent structure of alkylamines and their corresponding alkylammonium-alkylcarbamates.

In spite of the wide use of alkylamine (AA) surfactants, little attention has been paid to their spontaneous reactivity in air. Exposure of AA surfactants to CO(2) results in the formation of alkylammonium-alkylcarbamate (AAAC) molecular pairs. The effect of hydrocarbon chain length on the reactivity of AAs was followed by monitoring mass gain vs time under atmospheric conditions as well as in a saturated CO(2) environment.

Reaction of alkylamine surfactants with carbon dioxide: relevance to nanocrystal synthesis.

Exposure of tetradecylamine, hexadecylamine, and octadecylamine to CO(2) results in their transformation to alkylammonium alkylcarbamate (AAAC) pairs, which we find is a major source of irreproducibility in nanoparticle synthesis. Controlled exposure to CO(2) allows for highly uniform, ultranarrow ZnS nanorods coated with tetradecylamine to be reproducibly obtained in a single step. The crystal structures of the alkylamines and their AAAC analogs were investigated by powder X-ray diffraction and their isostructural three-dimensional unit cells are reported.

Hierarchical assembly of ultranarrow alkylamine-coated ZnS nanorods: a synchrotron surface X-ray diffraction study.

The packing of anisotropic ultranarrow nanoparticles ( r View Article and Find Full Text PDF

Normal and shear forces generated during the ordering (directed assembly) of confined straight and curved nanowires.

The effects of shape on nanowire interactions and shear-induced ordering were studied. Both the normal and lateral forces were sensitive to the particles' curvature. (i) No adhesion was observed between the confining surfaces, and the force profiles were short-ranged and mostly reversible for straight wires but longer-ranged and irreversible for curved wires.

Forces between surfaces across nanoparticle solutions: role of size, shape, and concentration.

Using a surface force apparatus, we have measured the normal forces between mica surfaces across various types of nanoparticles consisting of ZnS cores coated with a monolayer of physisorbed surfactant, dispersed in organic solvents. We focused on the effects of nanoparticle size, shape, and concentration on the force-distance profiles. Forces were exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles and were roughly linear when there was adhesion between the nanoparticle cores, i.