Web Release Date: May 25,
Effect of Molecular Weight on the Mechanical and Electrical Properties of Block Copolymer Electrolytes
Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, Berkeley, California 94720; Department of Chemical Engineering, University of California, Berkeley, Berkeley, California 94720; Materials Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, Berkeley, California 94720; Department of Chemistry, University of Athens, Panepistimiopolis Zografou, 157 71 Athens, Greece; and Australian Synchrotron Research Program, Bldg 343, Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
Received December 25, 2006
Revised Manuscript Received March 23, 2007
Abstract:
The relationship between ionic conductivity, morphology, and rheological properties of polystyrene-block-poly(ethylene oxide) copolymers (SEO) doped with a lithium salt, Li[N(SO2CF3)2], is elucidated. We focus
on lamellar samples with poly(ethylene oxide) (PEO) volume fractions, 
, ranging from 0.38 to 0.55, and PEO
block molecular weights, MPEO, ranging from 16 to 98 kg/mol. The low-frequency storage modulus (G') at 90 
C
increases with increasing MPEO from about 4 × 105 to 5 × 107 Pa. Surprisingly, the conductivity of the SEO/salt
mixtures with the molar ratio of Li to ethylene oxide moieties of 0.02 
, also increases with increasing MPEO,
from 6.2 × 10-5 to 3.6 × 10-4 S/cm at 90 C. We compare with the conductivity of pure PEO/salt mixtures,
PEO, and find that /[PEO] of our highest molecular weight sample is close to 0.67, the theoretical upper limit
for transport through randomly oriented lamellar grains.
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