Pl. Huyskens et al., ELECTRICAL CONDUCTANCE OF CHCL3 SOLUTIONS OF POLYETHYLENE OXIDE DOPEDWITH KCL, Journal of molecular structure, 416(1-3), 1997, pp. 91-104
CHCl3 solutions containing a few percent polyethylene oxide PEO (M-W =
200000) or the low-molecular model dioxane are stirred at 50 degrees
C during more than 100 h in the presence of small amounts of KCl. The
specific conductance, the viscosity and the density of the solutions a
re measured at 25 degrees C as a function of time. Both PEO and dioxan
e act as ligands improving the solubility of KCl. The relaxation times
are of the order of several hours. After 40 h or more the viscosity o
f the solutions increases in a spectacular way. However, the most stri
king observation is that the specific conductance of the polymeric sol
utions at 25 degrees C is systematically 5% higher than the value meas
ured with the same sample at 45 degrees C, just as for metals. The eff
ect of the dilution of the primary stirred solutions either in the pur
e solvent or in the initial polymer solution is investigated. These re
sults are discussed in terms of a three-step mechanism in the polymer
systems: (1) Loading of the coils to polymeric cations with a full ele
mentary charge, as a consequence of charge transfer interactions of th
e crown-ether type with numerous K+ ions penetrating into the coils; (
2) Electron tunnelling conduction of the Hamill-Ceulemans type from on
e positive coil to the neighbouring one; (3) Alteration of the structu
re of the coils and of their hydrodynamic radius by the motions of Kin the coils. These 'brachiation' motions by a hopping mechanism resul
t from an increased mobility of the complexed K+ ions, which is also t
he origin of the Zundel effect, They do not directly contribute to the
conductance but are responsible for the delayed increase of the visco
sity. (C) 1997 Elsevier Science B.V.