Quenched microemulsions: a new route to proton conductors

Cecile Noirjean (1) , Fabienne Testard (1) , Jacques Jestin (2) , Olivier Tache (1) , Christophe Dejugnat (3) , David Carriere (1)

1 LIONS - Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire
2 LLB - UMR 12 - Laboratoire Léon Brillouin
3 IMRCP - Interactions moléculaires et réactivité chimique et photochimique

Solid-state proton conductors operating under mild temperature conditions (T < 150 [degree]C) would promote the use of electrochemical devices as fuel cells. Alternatives to the water-sensitive membranes made of perfluorinated sulfonated polymers require the use of protogenic moieties bearing phosphates/phosphonates or imidazole groups. Here, we formulate microemulsions using water, a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) and a fatty acid (myristic acid, MA). The fatty acid acts both as an oil phase above its melting point (52 [degree]C) and as a protogenic moiety. We demonstrate that the mixed MA-CTA film presents significant proton conductivity. Furthermore, bicontinuous microemulsions are found in the water-CTAB-MA phase diagram above 52 [degree]C, where molten MA plays both the role of the oil phase and the co-surfactant. This indicates that the hydrogen-bond rich MA-CTA film can be formulated in the molten phase. The microemulsion converts into a lamellar phase upon solidification at room temperature. Our results demonstrate the potential of such self-assembled materials for the design of bulk proton conductors, but also highlight the necessity to control the evolution of the nanostructure upon solidification of the oil phase.

Domaines: Chimie-Physique [physics.chem-ph]; Matériaux; Chimie

Cecile Noirjean, Fabienne Testard, Jacques Jestin, Olivier Tache, Christophe Dejugnat, et al.. Quenched microemulsions: a new route to proton conductors. Soft Matter, 2014, 10 (32), pp.5928-5935. ⟨10.1039/c4sm00849a⟩. ⟨hal-01157193⟩