title: Evaporation assisted CdSe nanorod assembly by small angle X-ray scattering and langmuir adsorption.
abstract: Using evaporative assembly of dilute (<3 wt %) CdSe nanorod solutions, we combine Langmuir adsorption and small-angle X-ray scattering (SAXS) to estimate the onset of nanorod alignment instigated by the dipolar character of CdSe nanorods. SAXS demonstrates that the peak scattering intensity increases along the diameter toward the center of each dry assembly. By agreement of SAXS and profilometry results, we have established a practical access window into the lyotropic feature of emergent orientational order or alignment in nanorod solutions. With a mean field approach involving the rod-rod or dipole-dipole interaction, i.e., Keesom interaction, and the observation that the nanorod dipole moment scales with nanorod volume, we demonstrate that reaction constants result in nanometer scale interparticle separations which increase with aspect ratio or excluded volume. We compute a SAXS weighted intensity alignment parameter, which improves with aspect ratio, to indicate edge-to-center orientational ordering within dry nanorod assemblies.
authors.affiliation: Department of Physics and Astronomy, Howard University , 2355 Sixth Street NW, Washington, District of Columbia 20059, United States.
authors.forename: Kimani A
authors.initials: KA
authors.lastname: Stancil