Marie Plazanet, Renato Torre, Paolo Bartolini, Bruno Deme, Caterina Petrillo, Francesco Sacchetti
Water or electrolyte filled nano-structures are often encountered in soft condensed matter. An example is the Nafion membrane, a particularly relevant system in which the confinement of water can be considered as model for electrolyte nano-confinement phenomena. This amphiphilic perfluorosulfonated polymer adopts a structural organisation made of channels and cavities, that water fills upon hydration. The sulfonate groups release the protons in water to form an electrolyte confined in the polymer matrix. The mechanism of water sorption/desorption and its connection with the temperature is still an open question. Performing neutron diffraction, we monitored the quantity of ice formed outside of the membrane as a function of temperature down to 180 K. The smooth and reversible behavior upon sorption or desorption of water is modelled on the basis of the freezing point depression of a solution. The quantitative agreement points out the origin of the phenomena, that could be more general in soft condensed systems.
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http://arxiv.org/abs/1305.0437
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