ELECTRICAL CONDUCTANCE OF CHCL3 SOLUTIONS OF POLYETHYLENE OXIDE DOPEDWITH KCL

Citation
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
Citations number
44
Categorie Soggetti
Chemistry Physical
ISSN journal
00222860
Volume
416
Issue
1-3
Year of publication
1997
Pages
91 - 104
Database
ISI
SICI code
0022-2860(1997)416:1-3<91:ECOCSO>2.0.ZU;2-G
Abstract
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.