Nataly Belman

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. The rates of conversion to AAAC decreased with hydrocarbon chain length. Indexed powder X-ray diffractograms and the corresponding unit cells are presented for all phases of AAs and AAACs with chain lengths of 14, 16, and 18 carbons. Temperature-resolved powder X-ray diffraction of AAACs indicated anisotropic thermal expansion occurring exclusively along the a direction of the unit cell.

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.

Transmission electron microscopy of epitaxial PbS nanocrystals on polydiacetylene Langmuir films

Highly oriented arrays of lead sulfide (PbS) nanocrystals have been prepared in ambient conditions by the exposure of crystalline polydiacetylene (PDA) Langmuir films to H2S gas at the air–PbCl2 solution interface. The nanocrystals were studied by transmission electron microscopy (TEM), electron diffraction (ED), dark field TEM imaging (DF), high resolution TEM (HRTEM) and fast Fourier transform (FFT) analysis of HRTEM images. Three distinct, coexisting orientations were observed with typical nanocrystal morphologies corresponding to each orientation. The direction was aligned parallel to the PDA linear direction for all orientations, indicating a template-directed growth for the PbS/PDA system.

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.