Electromechanical actuators based on sheets of single-walled carbon nanotubes were shown to generate higher stresses than natural muscle and higher strains than high-modulus ferroelectrics. Like natural muscles, the macroscopic actuators are assemblies of billions of individual nanoscale actuators. The actuation mechanism (quantum chemical–based expansion due to electrochemical double-layer charging) does not require ion intercalation, which limits the life and rate of faradaic conducting polymer actuators. Unlike conventional ferroelectric actuators, low operating voltages of a few volts generate large actuator strains. Predictions based on measurements suggest that actuators using optimized nanotube sheets may eventually provide substantially higher work densities per cycle than any previously known technology

Porous carbons that are three-dimensionally periodic on the scale of optical wavelengths were made by a synthesis route resembling the geological formation of natural opal. Porous silica opal crystals were sintered to form an intersphere interface through which the silica was removed after infiltration with carbon or a carbon precursor. The resulting porous carbons had different structures depending on synthesis conditions. Both diamond and glassy carbon inverse opals resulted from volume filling. Graphite inverse opals, comprising 40-angstrom-thick layers of graphite sheets tiled on spherical surfaces, were produced by surface templating. The carbon inverse opals provide examples of both dielectric and metallic optical photonic crystals. They strongly diffract light and may provide a route toward photonic band-gap materials.

Rare crystal phases that expand in one or more dimensions when hydrostatically compressed are identified and shown to have negative Poisson's ratios. Some of these crystals (i) decrease volume and expand in two dimensions when stretched in a particular direction and (ii) increase surface area when hydrostatically compressed. Possible mechanisms for achieving such negative linear and area compressibilities are described for single crystals and composites, and sensor applications are proposed. Materials with these properties may be used to fabricate porous solids that either expand in all directions when hydrostatically compressed with a penetrating fluid or behave as if they are incompressible.

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The force-constant matrix of an oligomer, composed of five or more repeat units with appropriate terminal groups, can be used to construct the force-constant matrix of the corresponding planar or helical polymer. The calculations on some typical polymers (polymeric sulfur, polyacetylene, and polyethylene) show that the oligomer approach is accurate enough to duplicate the vibrational frequencies of frozen-phonon calculations. The oligomer approach has much more predictive power if used in conjunction with some form of empirical scaling (scaled quantum-mechanical oligomer force field for polymers). ir and Raman selection rules for helical polymers are also discussed. Vibrational frequencies and intensities of polymeric sulfur and polyethylene have been calculated at the ab initio STO-3G, 4-31G, 6-31G, and 6-31G* basis-set levels. The agreement of frequencies with experiment is excellent. The quality of calculation is limited by the basis set and theoretical model used rather than the oligomer approach.

We present an ab initio based, scaled quantum mechanical oligomer force field (SQMOFF) method for modeling the structure and vibrational spectra of doped poly(p-phenylene). By integrating this theoretical method and Raman spectroscopic technique, we are able to investigate quantitatively the structural evolution of poly(p-phenylene) upon doping. On the basis of our periodic quinonoid model and the observed inter-ring stretching frequency, we find heavily doped PPP to have only about 30% quinonoid character on the average. Accordingly, the average inter-ring C-C bond length decreases from 1.501 to 1.45(2) Á upon doping. This structural information, available for the first time, is fundamental in understanding the effects of doping. Additionally, we find that the corresponding force constant increases from 4.573 to 5.475 mdyn/A upon doping. The intensity ratios of the four Ag modes are predicted by the SQMOFF method to be primarily dependent on the quinonoid structure of the doped polymer. The role of charge transfer in this context is primarily to increase the quinonoid character of the structure. A discussion on intensity ratios with respect to the effective conjugation coordinates theory is also presented.