The low-frequency (0.01 Hz-10 MHz) dynamic characteristics of alkyl quaternary ammonium exchanged montmorillonite (SC20A) were investigated to determine the correlation between temperature-dependent changes in the interlayer structure and collective mobility of the surfactant. From 25 to 165 degrees C, SC20A exhibits two interlayer transitions, one ascribed to the melting of the intercalated alkyl chains of the surfactant (20-40 degrees C) and another associated with an abrupt decrease in the interlayer's coefficient of thermal expansion (100 degrees C). For this temperature range, the excess surfactant and residual electrolytes present in commercially manufactured SC20A enhance the direct current conductivity and increase low-frequency space-charge polarization, which is believed to occur across percolation paths established by the surfaces of the SC20A crystallites. In contrast, a higher-frequency relaxation, which was less sensitive to process history and impurity content, is ascribed to relaxation within the interlayer at the surfactant-aluminosilicate interface electrostatic couple. The temperature dependence of these dielectric relaxations indicated a drastic increase in mobility as the interlayer organic phase transitions from static and glasslike into molten and mobile. Overall, SC20A displayed features of alternating current universality, including time-temperature superposition, common in other types of disordered ion-conducting media. The presence of long-range transport and its sensitivity to low amounts of impurities imply that from a dynamic perspective the local environment of the surfactants are substantially diverse and a minority fraction, such as at the edge of the crystallite (gallery and aluminosilicate layer), may dominate the lower-frequency dielectric response.

Over the last decade, the utility of inorganic nanoparticles as additives to enhance polymer performance has been established and now provides numerous commercial opportunities, ranging from advanced aerospace systems to commodity plastics.[1] Low-volume additions (1±5 wt.-%) of highly anisotropic nanoparticles, such as layered silicates or carbon nanotubes, provide property enhancements with respect to the neat polymer that are comparable to those achieved by conventional loadings (15±40 wt.-%) of traditional fillers. The lower loadings facilitate processing and reduce component weight. In addition, unique value-added properties not normally possible with traditional fillers are also observed, such as reduced permeability, tailored biodegradability, optical clarity, self-passivation, electrical conductivity, electrostatic discharge, remoteactuated shape recovery, and flammability, oxidation, and ablation resistance.[2] Many references to this technology utilize the moniker nanocomposites', which invokes parallels to traditional fiber-reinforced composite technology and the ability to spatially engineer, design, and tailor' materials performance for a given application. However, development of chemical and processing procedures to disrupt the low-dimensional crystallites (tactoids and ropes) and achieve uniform distribution of the nanoelement (layered silicate and single wall carbon nanotube, respectively) is system specific and, in general, inadequate. Even less developed are approaches to provide spatial and orientational control of the hierarchical morphology with precision comparable to that conventionally obtained through fiber plies and weaving. Herein, we demonstrate the utility of AC electric fields to direct the morphology of polymer±inorganic nanocomposites, specifically epoxylayered silicate systems, through dielectrophoretic effects. [3] This provides an unprecedented ability to tailor physical properties of bulk nanocomposites such as modulus, thermal expansivity, and optical clarity and to develop detailed structure±property relationships through tuning of the nanoscale orientational distribution of nanoelements. Previous morphology±processing studies of polymer± layered silicate nanocomposites have focused on the influence of shear and elongational forces on nanoelement orientation. For example, Krishnamoorti and co-workers have extensively examined and correlated the impact of layered silicate dispersion on melt rheometry and relaxation dynamics.[4] In parallel, recent studies have indicated that shear-induced orientation of these semi-rigid plates, even in simple shear flows, is highly complex, potentially exhibiting tumbling and kayaking behavior reminiscent of the behavior of complex fluids such as liquid crystals and block copolymers. [5] This complexity restricts the general utility of shear forces for precision morphology to uniaxial in-plane alignment, for applications such as ultra-high barrier films. Optimization for other potential applications, such as dielectric under-fills for electro...