Thermal Field-Flow Fractionation of Polymers

Synthetic polymers are complex and multicomponent materials. Their development and further advancement is driven by the increasing demand for new functional materials with improved performance and tailored properties. Synthetic polymers are inherently complex materials as they can exhibit various distributions in properties such as molar mass (chain length), chemical composition, microstructure as well as molecular architecture and topology. As property distributions significantly influence the physical properties and end-use applications, proper monitoring and characterisation of distributions in key physical and physicochemical parameters is crucial for the improvement of polymer properties and performance. Most frequently, in order to characterise the various property distributions, a separation is required. As a result, fractionation techniques such as liquid chromatography and field-flow fractionation have become principal techniques for polymer characterisation.

ThFFF is the only FFF subtechnique that can separate analytes according to their composition and thus holds a great deal of potential for the characterisation of complex polymers. ThFFF uses the principle of thermal diffusion to drive analytes to the cold wall (accumulation wall) and the magnitude of this driving force is influenced by the chemical composition of the analyte as well as the carrier liquid. In this chapter, ThFFF is introduced and the fundamental parameters influencing the retention behaviour of polymers are addressed. In addition, some attention is given to how compositional information is obtained from ThFFF while recent advances and applications are also discussed.

This chapter discusses the characterisation of polymers by ThFFF in four main themes/examples. These include microstructure, solvent partitioning, self-assemblies and aqueous ThFFF. Furthermore, the experimental setup of the ThFFF system and the detection used in these examples are summarised.

This chapter concludes the book by discussing the importance of ThFFF as a powerful characterisation platform to address the growing analytical challenges facing the development of advanced materials.

This chapter discusses typical problems that can be encountered during the use of ThFFF. This chapter provides the reader with some guidelines to optimising ThFFF experiments as well as typical values for operating parameters. Experimental suggestions and recommendations are also included.

Before performing any analysis, the aims and objectives of the experiments must be clearly understood. This is especially relevant to ThFFF as it generally shows poor retention for low molar mass or small analytes unless high temperature drops or multicomponent carrier liquids are considered. In general, a good first approach to any FFF method development would be to perform a quick size analysis, e.g. by batch dynamic light scattering, beforehand in order to establish a general range of sizes in the sample. From this information, several parameters such as spacer thickness, temperature drop, temperature program and carrier composition can be selected accordingly.