Self-assembly of sulfonated amphiphiles for channel-like synthetic membranes

Self-assembly is one of the most useful techniques, which provide a facile strategy to construct structure-defined functional materials, such as ion-selective membranes. Highly selective membranes can eventually form a basis to replace some energy- or labor-intensive purificatiion processes and can also simplify specific detection problems in the fields of biochemical, medical and even environmental analytical technology. In this dissertation, a series of wedge-shaped sulfonic acid derivatives differing in substitution pattern and molecular symmetry as well as in the size of the cationic count-ions, were synthesized and characterized to give a better understanding of the self-assembly process. From the dependence of transition temperatures and enthalpies on the cation diameter, it is conclusive that the occurrence of mesophases of these compounds is more ruled by the geometric shape of the mesogen than by the ionic interactions between cation and sulfonate anion. For example, the symmetrical substituted alkali metal cationic sulfonates all exhibit columnar mesophases either on melting from the crystalline phase or on annealing at the proper temperature. The target molecule with polymerizable groups was also found to exhibit a hexagonal columnar mesophase between 115°C and 233°C, as well as in semi-polar methacrylate solvents as the concentration exceeded 70wt%. Photo-curing this hexagonal columnar mesophase results in a cross-linked polymer film covalently embedded with the cylinders network. The membranes with abundant sulfonate channels were obtained by photo-initiated polymerization in the state of lyotropic columnar mesophases without losing the ordered columnar arrangements. The ion-transport measurements showed their ability to transport small alkalic cations through the channels. The ion transport rates exhibited a decreasing tendency in the sequence of Lithium > Sodium > Potassium cation. Since in a free solution Lithium cation diffuses slower than sodium cation that diffuses slower than potassium cation, this opposite result is indicative of the transport through the supramolecular channels. It is confirmed that the diffusion became controlled by cation-sulfonate interactions during the transport through the supramolecular channels. In the last part of the dissertation, the sulfonated functional membranes with orientated columnar channels were achieved and used as a model system to investigate the mechanism of cation transport through the supramolecular sulfonated channels. Due to the possession of the geometrically defined superstructure, the presented strategy of constructing the channel-like functional membrane gives the potential to modify or tune the performance of the membranes for further application