Polymer Functionalized Graphene Oxide As Thermally Responsive Ion Permeable Membrane

A UCST polymer, poly(sulfobetaine) (PMABS), which exhibits upper critical solubility temperature (UCST) behavior, was successfully grown onto graphene oxide sheets with an atom-transfer polymerization process.  The modified graphene oxide sheets could be filtered to form free-standing papers that were then fabricated into a thermally-responsive membrane usable in non-aqueous solutions.  It was tested as a separator in a electrochemical cell, separating a Li foil and a reduced graphene oxide paper as the two electrodes in a configuration that was similar to a half-cell in a Li ion battery.  In the absence of the modified membrane, the specific storage capacitive for Li of the reduced graphene oxide paper increased ~30% when heated from 20^oC to 80^oC. In contrast, a PMABS-modified separator caused the storage capacity to decrease by over 50%.  The membrane were characterized using SEM, AFM, UV spectroscopy an quartz crystal microbalance. This reversible thermal reduction in ion permeability can be used to mitigate thermal runaway of a Li ion battery, or tune the thermal response of an ion sensor or an electrode, among other applications.