| Abstract
| - The low-frequency (0.01 Hz−10 MHz) dynamic characteristics of alkyl quaternary ammonium exchangedmontmorillonite (SC20A) were investigated to determine the correlation between temperature-dependentchanges in the interlayer structure and collective mobility of the surfactant. From 25 to 165 °C, SC20Aexhibits two interlayer transitions, one ascribed to the melting of the intercalated alkyl chains of the surfactant(20−40 °C) and another associated with an abrupt decrease in the interlayer's coefficient of thermal expansion(100 °C). For this temperature range, the excess surfactant and residual electrolytes present in commerciallymanufactured SC20A enhance the direct current conductivity and increase low-frequency space-chargepolarization, which is believed to occur across percolation paths established by the surfaces of the SC20Acrystallites. In contrast, a higher-frequency relaxation, which was less sensitive to process history and impuritycontent, is ascribed to relaxation within the interlayer at the surfactant−aluminosilicate interface electrostaticcouple. The temperature dependence of these dielectric relaxations indicated a drastic increase in mobility asthe interlayer organic phase transitions from static and glasslike into molten and mobile. Overall, SC20Adisplayed features of alternating current universality, including time−temperature superposition, common inother types of disordered ion-conducting media. The presence of long-range transport and its sensitivity tolow amounts of impurities imply that from a dynamic perspective the local environment of the surfactantsare substantially diverse and a minority fraction, such as at the edge of the crystallite (gallery and aluminosilicatelayer), may dominate the lower-frequency dielectric response.
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