Vibrational and thermal characterization of Flemion® membranes

Author(s)

Wilson Mantovani Grava

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2008-02-29

Examining board members

Yoshio Kawano; Adhemar Colla Ruvolo Filho; Márcia Laudelina Arruda Temperini; Roberto Manuel Torresi; Hélio Wiebeck

• Advisor: Yoshio Kawano

Abstract

The behavior of Flemion® membranes on their many applications (among them, fuel cells) is function of series of parameters like how the ionic side groups arrange themselves inside the so called interconnected \'clusters\' inside the material. Such arrangement is also function of types and intensities of ionic interactions inside the clusters and how the membranes are treated before use. Besides the characterization of membranes with differents side group densities (Equivalent Weigth - EW), the work also evaluates the behavior of clusters under two different effects: treatment with H2O2 and ionic exchange. On the first part it is shown that pre-treatment with H2O2 at 80ºC, a very followed procedure on literature, changes the clusters by intercrossing S-O-S bond formation, but with no sulfonate groups losses. Membranes tend to rise their cluster size and keep their structure up to higher temperatures. There are also alteration on thermal decomposition mechanism and mechanical stability rising. As lower the side group density, lower these effects tend to be, revealing that higher-EW membranes tend to be less changeable. Concerning ion exchange, results were generated by observation of effects promoted by mono (alkaline), bi (arkaline-earth) an trivalent cations: the 1:1 charge ratio of alkaline cations make their individual z/R relation play a fundamental role on cation/membrane interactions; with different thermal, mechanical and cluster stabilization that are optimized for K+. On this first case, side groups density affects little the observed behavior. On bivalent cations case, 2:1 ratio alters a lot the ionic interaction reflexes on membranes behavior. It is possible to evaluate differences on cluster inserted water and S-O stretching bands displacement on infra-red spectra induced by coupling of different groups. In this case, results show that membranes don\'t get as much thermal stabilization as guaranteed by alkaline cations, sometimes showing even opposite results comparing to the former ones. Also, side group density effects are more relevant in this case, given the need of side groups to accommodate around larger z/R ratios. On both trivalent cations studied, membranes respond differently according to their side group densities, showing that larger z/R and cations with larger charge balance ratio accommodation tend to be more effective as the material has larger side group density and, for so, larger clusters as well. (AU)