No abstract

A detailed study of the dehydration process of hydrated Nafion−Na membranes has been performed using thermogravimetric analysis (TGA) and time-dependent (TD) FTIR, with the aim of investigating the water loss process during dehydration. The TGA data provide the absolute water weight loss, and TD FTIR spectra yield the relative IR intensity loss. Both TGA profiles and TD FTIR traces can be well fitted by second-order exponential decay, which implies two different dehydration processes, depending on water content. The fast process is attributable to high water level Nafion−Na (HWLN), with percolation structure and thus higher water diffusivity. The slow process is characteristic of low water level Nafion−Na (LWLN), with specific isolated cluster structure and lower diffusivity. For LWLN, the relative IR intensity loss of water bands is significantly faster and more extensive than the corresponding relative weight loss obtained by TGA. This deviation seriously calls into question the use of IR spectra as a quantitative measurement of water content in Nafion. The apparent dependence of the IR spectrum on the size of the nanoscale water clusters is in agreement with Gebel's mechanism of water swelling in Nafion.

Nafion membranes have been studied using dynamic mechanical analysis in the controlled force mode and clamp of tension film measurements for as received commercial Nafion membranes with different solvent contents and with different cations (Li+, Na+, K+, Rb+ and Cs+). In comparison with as-received Nafion membranes, the initial slope of the stress-strain curves decreases with increasing water contents in the Nafion membrane and also with the addition of methanol, ethanol and ethanol/water (50/50%, v/v) mixture. The initial slope decreases also with increasing temperatures. On the other hand, the initial slope increases when the cation is replaced, in the following order: Li+, Na+, K+, Cs+ and Rb+. Nafion in salt form normally shows an increase in the initial slope from room temperature up to approximately 90ºC, after which the slope decreases with increasing temperatures

A 9-year-old girl developed hidradenitis suppurativa 3 months after the first signs of adrenarche. Such a close temporal relationship is consistent with the hypothesis that the disease is androgen dependent. Less than 2% of patients have onset of the disease before the age of 11 years. The exceptionally early age of onset in our patient may be partly explained by the fact that she had an early puberty.