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Mechanisms of ionic transport in ionically conducting polymers. Summary. 2. Mechanisms of ionic transport in ionically conducting polymers 2.1. Interaction between polymer and salt 2.1.1. Ion solvatation by the polymer 2.1.2. Hard - soft acid -base principle 2.1.3. Anions
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180º bond rotation at C-O bond A-B
Fiona M. Gray “Solid Polymer Electrolytes, Fundamentals and technological applications”
VCH Publishers, 1991.
R.G. Pearson J.Am.Chem.Soc. 85 (1963) 3533
R.G. Pearson J.Chem.Ed. 45 (1968) 581, 643
F->>Cl->Br->I- ~SCN->ClO4- ~CF3SO3->BF4- ~AsF6-
Most suitable choices of anions for aprotic
Low-dielectric-constant dipolar polymer-based SPE
P.G.Bruce et al. Solid State Ionics78 (1995) 191
It is generally accepted that anions are mobile and in some systems net cation mobility is vanishingly small (disappear)
Anions assist in cation transport
- by formation of ion pairs
- triple ions
- higher aggregates
With the assistance of polymeric chain segmental motion, the ionic cluster may itself move or it may act as transient center for the mobile species.
For higher salt concentration Ion pairs and aggregates can be formed
These species are less mobile and can promote a crosslink
a) via cation
b) via triple ion
To act as a successful polymer host, a polymer or the active part of a copolymer should generally have a minimum of three essential characteristics:
2) Low barriers to bond rotation so that segmental motion of the polymer chain can take place readily
3) A suitable distance between coordinating centers because the formation of multiple intrapolymer ion bonds appear to be important
Differences are due to the molecular conformation and crystalline structure (not chemical)
PEO crystalline structure is more open than PMO
Glass transition temp.
For high Mw, Tgs are of -65 to -60oC
Due to the intermolecular and intramolecular interractions - crosslink
Reduction of conductivity
for high salt concentration
ni – number of charge carriers (i)
qi - charge of each one
i - mobility
Z’- real part and Z” – imaginary part
Cation moving via intra-polymer coordenation
Cation moving via inter-polymer coordenation
for A=1cm2 and l=1cm Cb is a dielectric constant value of polymer
Generally of 5-20
(o permittivity of vacuum8,85*10-14 F/cm)
Ea- activation energy - linear fitting for semi-cristaline and amorphous systems
Log = log so + (-Ea / 2,303 RT)
R – ideal gas constant =8,31441 Jmol-1K-1
For the amorphous systems
Equivalent to VLF
viscoelastic properties also relaxation process (aT-deslocation factor)
C1 and C2 temperature dependent constants and To – WLF temperature reference