Fluorinated building blocks for next-generation polymer electrolyte membrane fuel cells

The purpose of this thesis is to design, create and study basic building blocks for the construction of self-assembled nanostructured electrodes and membranes for PEMFC. The research described deals with the synthesis of polymerizable fluorosurfactant (1) and its non-polymerizable analogue (2) and the study of their self-assembly properties. Similarly, the (co)polymerization behavior of 1 and the polymer properties are described. The design of the polymerizable fluorosurfactant, 1 and the synthetic routes to obtain the desired functionalities and molecules are discussed in Chapter 1. The reaction pathways to create –SO3¯ as well as styryl groups are described. The syntheses of compounds 1 and 2 are described in Chapter 3. The key reactions viz. the copper mediated cross-coupling reactions to attach fluorocarbon molecules to aromatic moieties and the Wittig reactions to obtain styryl functionalities are described. The micellization properties of 1 and 2 are deliberated in Chapter 4. Unlike, several fluorinated sulfonic acid salt surfactants, both surfactants were soluble in water at room temperature. This is due to their hybrid character and the presence of bulky aromatic moieties in the surfactant tails. Both compounds 1 and 2 display comparable cmc values ~30 mM, and form spherical shaped micelles. The Gibbs energy of micellization of 1 and 2 are in the range of -24 to -26 kJ mol-1. The micelles were characterized by low aggregation numbers, in the range of 25 to 35. Entropy driven micelle formation and a U-shaped relation was observed between the Gibbs energy of micellization and experiment temperatures were observed. The LLC phase behavior of 2-water mixtures is described in Chapter 5 and two lyotropic phases in the range of 63 to 84 wt% 2 were identified and investigated. An unprecedented supramolecular columnar (Cs) phase made up by self-assembly of “Leek” shaped aggregates was observed in the concentration regime between 63 and 70 wt% 2, and a lamellar (L?) phase was observed from 70 to 84 wt% 2. The “Leeks” were shown to be formed by wrapping up of the 2-water bilayers. An interdigitated and/or tilted assembly of 2 molecules was suggested for both LLC phases based on SAXS data analysis. Homo and copolymers of compound 1 with model the perfluorinated comonomer, 3 or styrene were prepared by free radical method, and are discussed in Chapter 6. The strong incompatability of ionic groups and fluorocarbon moieties of poly-1 severely hampered the molecular weight determination by GPC. Homopolymer of 3 is insoluble in most of the polar as well as nonpolar solvents. 19F NMR experiments revealed that there are inhomogeneities within the copolymer samples synthesized from 1 and 3 because of the large compositional drifts with respect to the comonomer feed ratios occurred during the polymerization. Thermal stabilities of all polymers were slightly better compared to the thermal stability of polystyrene. Cryo-TEM P1-water solution revealed the formation of elongated worm-like micelles with ~5 nm diameter and length of up to 400 nm. These micelles were suggested to be formed by the lateral self- assembly of 2-3 extended polymer chains of P1.Chemical EngineeringApplied Science