Development of thermal field-flow fractionation for the characterization of hybrid nanoparticles and polymers with complex architecture
Field-flow fractionation (FFF) is a family of analytical techniques designed for the separation of macromolecules and colloids on the nanometer to micron scale. The well-established theory governing FFF separations permits physiochemical properties to be calculated from measured analyte retention times. This allows FFF to be leveraged for not only separation of nanoparticles and polymers but also as a characterization tool to obtain physiochemical distributions. Thermal FFF is unique as the separation mechanism is based on the differential transport of analytes in the presence of a temperature gradient. This thermophoresis (or thermal diffusion - DT) is dependent on interactions at the analyte-solvent interface yielding transport driven by compositional differences. This permits the development of novel approaches to separating and characterizing complex polymers, functionalized, and hybrid nanoparticle systems. An in-depth assessment of competing thermophoretic theories was essential to identifying potential key levers (experimental conditions) that could manipulated to control ThFFF retention. This knowledge was leveraged to develop the unique analytical capabilities of ThFFF. First these principles were employed to separate and determine the compositional distributions of inorganic metal-metal oxide hybrids such as multi-lobed Pt-Fe3O4 nanoparticles. Results indicate that correlation of DT to both particle surface and bulk properties maybe dependent on the dielectric nature of the solvent. Subsequently, the role of solvent quality and presence of additives (salts, surfactants, ligands etc.) on polymeric particles and polymer stabilized metallic particles was studied. Results suggest that particle DT can be tuned via modification of a particle surface through the use of adsorbates. The affinity of the adsorbates for specific faceting on the analyte surface could be further exploited to enhance separations by morphology. Investigation of analyte-solvent interactions and the role of solvated conformations of organic-inorganic hybrids was strongly informed by studies of soluble polymer systems. The thermophoretic behavior of hyperbranched polyesters with various degrees of branching was examined showing that the presence of linear, cyclic, and branched polymers could be identified and polymer architecture distributions could be determined using ThFFF first principles. In conclusion, Thermal FFF has proven to be a unique technique capable of separating and characterizing complex colloidal solutions.
polymer architecture, thermal diffusion, thermophoresis, separations, hybrid nanoparticles, thermal field-flow fractionation
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