6 research outputs found
Controlled Deposition of Oriented PbS Nanocrystals on Ultrathin Polydiacetylene Templates at the AirâSolution Interface
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<sub>18</sub>H<sub>37</sub>NH<sub>2</sub>) and hexadecylamine (HDA, C<sub>16</sub>H<sub>33</sub>NH<sub>2</sub>). 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 surfactantânanoparticle
inter-relations is very instrumental in understanding surfactant-assisted
nanoparticle synthesis and assembly
Reaction of Alkylamine Surfactants with Carbon Dioxide: Relevance to Nanocrystal Synthesis
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.e., through
physical interactions such as van der Waals forces or âionicâ
bonds). We have studied the behavior and effects of water on the structures
and surface energies of both chemisorbed octadecanethiol and physisorbed
octadecylamine SAMs on GaAs using a number of complementary techniques
including âdynamicâ contact angle measurements (with
important time and rate-dependent effects), AFM, and electron microscopy.
We conclude that both molecular overturning and submolecular structural
changes occur over different time scales when such SAMs are exposed
to water. These results provide new insights into the time-dependent
interactions between surfaces and colloids functionalized with SAMs
when synthesized in or exposed to high humidity or bulk water or wetted
by water. The study has implications for a wide array of phenomena
and applications such as adhesion, friction/lubrication and wear (tribology),
surfactantâsolid surface interactions, the organization of
surfactant-coated nanoparticles, etc