Dilru Ratnaweera

The impact of lignin source on its self-assembly in solution

Recently, there has been a growing interest in developing value added uses for lignin, including the utilization of lignins as a precursor for carbon materials. Proper understanding of the association behavior of lignins during solution processing provides important structural information that is needed to rationally optimize the use of lignins in industry in a range of value added applications. In these experiments, we follow the assembly of lignin molecules from a variety of sources in dimethyl sulfoxide, a good solvent for lignins, using small angle neutron scattering. In order to mimic industrial processing conditions, concentrations of lignins were kept above the overlap concentration. At small length scales, short lignin segments with ∼4–10 monolignol units associate to form rigid rod-like/cylindrical building blocks, where the number of repeat units in a cylindrical segment decreases with increasing lignin concentration. These cylindrical building blocks associate to form aggregates with low cross-linking densities and a random coil or network like structures from highly branched lignin structures. The degree of branching of the base lignin molecule, which varies with source, plays a crucial role in determining their association behavior. The overall sizes of the aggregates decrease with increasing concentration at low cross-linking densities, whereas the opposite trend is observed for highly branched lignins.

Microfluidic Synthesis of Monodisperse Nanoporous Oxide Particles and Control of Hierarchical Pore Structure

Particles with hierarchical porosity can be formed by templating silica microparticles with a specially designed surfactant micelle/oil nanoemulsion mixture. The nanoemulsion oil droplet and micellar dimensions determine the pore size distribution: one set of pores with diameters of tens of nanometers coexisting with a second subset of pores with diameters of single nanometers. Further practical utility of these nanoporous particles requires precise tailoring of the hierarchical pore structure. In this synthesis study, the particle nanostructure is tuned by adjusting the oil, water, and surfactant mixture composition for the controlled design of nanoemulsion-templated features. We also demonstrate control of the size distribution and surface area of the smaller micelle-templated pores as a consequence of altering the hydrophobic chain length of the molecular surfactant template. Moreover, a microfluidic system is designed to process the low interfacial system for fabrication of monodisperse porous particles. The ability to direct the assembly of template nanoemulsion and micelle structures creates new opportunities to engineer hierarchically porous particles for utility as electrocatalysts for fuel cells, chromatography separations, drug delivery vehicles, and other applications.

In Situ Self Assembly of Nanocomposites: Competition of Chaotic Advection and Interfacial Effects as Observed by X-Ray Diffreaction

The effects of chaotic advection on the in situ assembly of a hierarchal nanocomposite of Poly Amide 6, (nylon 6 or PA6) and platelet shape nanoparticles (NPs) were studied. The assemblies were formed by chaotic advection, where melts of pristine PA6 and a mixture of PA6 with NPs were segregated into discrete layers and extruded into film in a continuous process. The process assembles the nanocomposite into alternating pristine-polymer and oriented NP/polymer layers. The structure of these hierarchal assemblies was probed by X-rays as a processing parameter, N, was varied. This parameter provides a measure of the extent of in situ structuring by chaotic advection. We found that all assemblies are semi-crystalline at room temperature. Increasing N impacts the ratio of α to γ crystalline forms. The effects of the chaotic advection vary with the concentration of the NPs. For nanocomposites with lower NP concentrations the amount of the γ crystalline form increased with N. However, at higher NP concentrations, interfacial effects of the NP play a significant role in determining the structure, where the NPs oriented along the melt flow direction and the polymer chains oriented perpendicular to the NP surfaces.