Heat effects and rates and molecular mechanisms of water sorption by perfluorinated polymer materials bearing functional groups

The heat effects and the rates and equilibrium quantities of H2O vapour sorbed and desorbed on polymeric perfluorinated materials (functional groups -SO3H, -SO3Na, -SO3K) and on material treated with FeCl3 solution as sorbent were investigated. Sorbed H2O may be completely desorbed in vacuum at 443 K. The material bearing -SO3H has maximum sorption affinity: the molar heat of -SO3H wetting is close to that of H2SO4 wetting. The differential heat of sorption decreases from 68 kJ mol(-1) at n congruent to 0 (n = H2O/-SO3H) to 45 kJ mol(-1) at n congruent to 5, but not below the heat of H2O condensation. The -SO3H samples sorb H2O vapour in the presence of liquid H2O at 293 K up to n = 17. The -SO3K material has minimum affinity for H2O: the equilibrium quantity sorbed in room air is less by a factor of 4 than that for the -SO3H material. The spatial arrangement of H2O molecules near the sulpho groups is considered.