Structural analysis of high performance ion-gel comprising tetra-peg network

The structure of Tetra-PEG ion gel, which is tetra-arm poly(ethylene glycol) (Tetra-PEG) network in ionic liquid (IL) and has recently established in our group and possesses high ion conductivity and high mechanical properties, was investigated as functions of polymer concentration (Ï•) and molecular weight (M _w) by using small-angle neutron scattering (SANS) measurements. The results were compared with those of Tetra-PEG hydrogel. The macromer solutions of tetra-amine terminated PEG (TAPEG) macromers, which is one of the two constituents forming Tetra-PEG network, were found to interpenetrate each other in IL and exhibited a scaling relationship, ^-3/4, where is the correlation length. The SANS functions, I(q), for the ion gels made by cross-end-coupling of TAPEG and TNPEG (tetra-arm PEG with active ester groups) were represented by the so-called Ornstein-Zernike equation, suggesting absence of frozen inhomogeneites. The same scaling relationship to the macromer solutions, ^-3/4, was also obtained for the ion gels. Furthermore, the SANS curves were superimposed to a single master curve with I(q)/ ^5/3 irrespective of M _w and Ï•. In contrast, the Tetra-PEG ion gels made by reswelling of a dried hydrogel showed a large upturn, indicating that the ion gels made by the re-swollen method caused the network inhomogeneities.