(271e) Peo Mobility in Nanoparticle-Filled Polymer Electrolytes as Measured by Neutron Scattering

The mobility of poly(ethylene
oxide) [PEO] is measured for solid polymer electrolyte systems of PEO/LiClO₄
and PEO/LiClO₄/Al₂O₃, where LiClO₄
is the lithium salt and Al₂O₃ is the nanoparticle filler
(average diameter, 11nm).  While the addition of nanoparticles has been shown
to improve conductivity in solid polymer electrolytes, the molecular mechanism
is not clear.  Some authors suggest that the addition of nanoparticles
increases PEO mobility and hence Li⁺ ion mobility.  However, other
authors suggest that nanoparticles act like crosslinkers, pinning PEO at the
ether oxygen atoms, and creating a more direct route for Li⁺ ions. 
This mechanism suggests that PEO mobility is decreased.  The glass transition
temperatures [T_g] of polymer electrolytes filled and unfilled with
nanoparticles differs by only a few degrees, making it difficult to interpret
the influence of nanoparticle fillers on PEO mobility.  However, PEO mobility
can be measured directly by quasielastic neutron scattering [QENS], and has
previously been used to measure a system of PEO/LiClO₄.  We measure
PEO mobility using the NG2 High-Flux Backscattering Spectrometer [HFBS] and the
Disk Chopper Time-of-Flight Spectrometer [DCS] at the NIST Center for Neutron
Research in Gaithersburg, Maryland.  HFBS measures motion on a timescale
between 240 ps and 2 ns, and DCS between 0.1 ps and 40 ps.  PEO mobility is
measured for filled and unfilled solid polymer electrolytes at 295K, 323K and
348K.  Results indicate that the addition of nanoparticle filler decreases PEO
mobility.  Therefore, the influence of nanoparticle filler on conductivity
supercedes that of increased segmental relaxations of PEO.