Chris J. Cornelius

Water dynamics in rigid ionomer networks

The dynamics of water within ionic polymer networks formed by sulfonated poly(phenylene) (SPP), as revealed by quasi-elastic neutron scattering (QENS), is presented. These polymers are distinguished from other ionic macromolecules by their rigidity and therefore in their network structure. QENS measurements as a function of temperature as the fraction of ionic groups and humidity were varied have shown that the polymer molecules are immobile while absorbed water molecules remain dynamic. The water molecules occupy multiple sites, either bound or loosely constrained, and bounce between the two. With increasing temperature and hydration levels, the system becomes more dynamic. Water molecules remain mobile even at subzero temperatures, illustrating the applicability of the SPP membrane for selective transport over a broad temperature range.

Heat Treatment of TiO 2 /SiO 2 Electrospun Ceramic Fibers

Nano-TiO2 is currently one of the most interesting topics of study in materials science and beyond, and is being used in a wide variety of applications [1]. However, producing crystalline TiO2 nanostructures, other than simple powders, can pose significant challenges: growing such structures in the crystalline state tends to be slow and expensive, and while this can be overcome by fabricating amorphous structures quickly and cheaply, handling these materials after the subsequent heat treatment will reduce them to a powder. Dispersing TiO2 particles on a mechanically robust support is a common method for overcoming this issue. One processing pathway for doing so is to electrospin a TiO2/SiO2 solution into fibers followed by heat treatment, which causes the two immiscible materials to phase separate and the TiO2 to crystallize [2, 3]. A forthcoming publication describes how this process has recently been improved to drastically increase the TiO2 content of such fibers [4]; this work is concerned with the details of the phase separation of the TiO2 and SiO2 during heat treatment and the crystallization of the TiO2.