Electric Conductivity and Phase Transition of a Polydiacetylene Gel: Poly[4,6-decadiyn-1,10-diol-bis(n-butoxy-carbonylmethyl urethane)] P(3BCMU)

Abstract

Electric conductivity and sol-gel transition behavior were studied for gels of a polydiacetylene poly[4,6-decadiyn-1,10-diol-bis(n-butoxy-carbonylmethyl urethane)] abbreviated to P(3BCMU). Two solvents with different dielectric constant were used, i.e., o-dichlorobenzene (o-DCB) and a mixed solvent of p-dichlorobenzene (p-DCB) and toluene (TOL). Temperature dependence of the shear moduli G′ was measured to determine the gel-to-sol transition temperatures Tt at which the moduli decreased steeply. The Tt was 378 K in o-DCB and 387 K in p-DCB/TOL (62/38). Both direct current (DC) conductivity σdc and alternating current (AC) conductivity σac at 1 kHz exhibited a maximum around 368 and 362 K in o-DCB and p-DCB/TOL, respectively. Dopant effects of an electron acceptor iodine and a donor tetrathiafulvalene TTF on σdc and σac were also studied. σac was enhanced approximately by 100 times with iodine but only by 5 times with TTF. The pronounced dopant effect indicates that the conduction in the gel state is partly due to electronic conduction through the P(3BCMU) chains. We also observed an appreciable strength of ionic conductivity in the sol and gel phases. The ionic conductivity in the gel phase was estimated from σac of the solvent containing the ions extracted from the gel phase. Then observed σac and σdc were separated into the contributions of ionic and electronic conductions. Electronic conductivity increased with increasing dielectric constant of the solvent. Transition temperature Tt where the color changed from blue to yellow was also determined by measuring the transmittance at 630 nm wave length. The temperature dependence of the transmittance indicated a hysteresis.