Ryan S. Justice

Simplified tube form factor for analysis of small-angle scattering data from carbon nanotube filled systems

This work presents an analysis method for small-angle scattering data utilizing a simplified tube (hollow cylinder) form factor. The simplified form factor captures the rod-like character of a tube at long length scales (one-dimensional), the sheet-like character of the tube wall at intermediate length scales (two-dimensional), and the surface characteristics of a tube at small length scales while suppressing the deep minima seen in the exact form factor. Ultra-small-angle X-ray scattering data from composites made with multi-walled carbon nanotubes and a bismaleimide resin are analyzed using the simplified form factor and compared with scanning electron micrographs. Although a hollow core is not evident via microscopy, a solid rod form factor does not fit the data. However, a tube form factor does fit the data and generates reasonable geometric parameters. At higher concentrations, evidence for aggregation is seen in the data. Aggregation is accommodated by including a fractal structure factor within the simplified approach, allowing facile analysis of data from aggregated (poorly dispersed) fillers.

Calcium alginate barrier films modified by montmorillonite clay

The goal of decreasing the permeation of small molecules through calcium alginate films is addressed by incorporating small amounts of montmorillonite clay into the polymer. Incorporation is achieved by (i) blending up to 3 wt% pre‐exfoliated montmorillonite into sodium alginate polymer solutions, (ii) casting thin films, (iii) cross‐linking the chains with calcium chloride solution into insoluble calcium alginate, and (iv) drying the resulting cross‐linked materials. Exfoliation and dispersion of the montmorillonite platelets is assessed by light scattering and small‐angle X‐ray scattering. The barrier properties of the impregnated films were gauged by permeation of benzaldehyde using a Hanson‐Research diffusion cell. Decreased permeability is found at clay loadings below 3 wt%. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.

Large-Scale Morphology of Dispersed Layered Silicates

Ultra small angle x-ray scattering is used to probe the morphology of highly dispersed montmorillonite (MMT) in water and polyamide-66. In water the scattered intensity, I(q) shows a q -2 dependence for q > 0.01 A -1 , where q is the magnitude of the scattering vector. This is as expected for a two dimensional sheet-like object. On larger scales (smaller q) mass-fractal character is evident up to the radius-of-gyration of the individual scattering entities. The scattering profile is interpreted using a semi-flexible sheet model in which flat, disk-like entities of radius = 80 A (an areal persistence length) are fractally distributed on large scales with a mass fractal dimension of 2.65. These size scales correspond to a scattering entity comprised of one or a few crumpled sheets. No evidence of inter-particle correlations is found at concentrations below the gel point. In polyamide-66 loaded with organically modified MMT long-range fractal behavior is also observed but with larger fractal dimension.

D-96 Characterization of Nanocomposite Filler Morphology Using Ultra Small-Angle X-ray Scattering

Loading polymer matrices with nanoscale fillers is widely believed to have the potential to push polymer properties to extreme values. Realization of anticipated properties, however, has proven elusive. Recent nanocomposite research suggests better characterization of the large-scale morphology will provide insight explaining these shortfalls. This work will present ultra-small angle X-ray scattering as a viable tool for elucidating the hierarchical filler morphology that exists within polymer nanocomposites. Scattering analysis tools developed by our group will be applied to scattering data from nanocomposites filled with carbon nanotubes, layered silicates, and colloidal silica. The relationship between imaging data and scattering data will be discussed in the context of filler dispersion. Finally, the impact of large-scale filler morphology on mechanical and electrical properties will be discussed.