Carbon nanotube (CNT) reinforcement of polymer composites has not yielded optimum results in that the composite properties are typically compromised by poor dispersion and random orientation of CNTs in polymers. Given the short lengths available for nanotubes, opportunities lie in incorporating CNTs with other structural reinforcements such as carbon fibers (CFs) to achieve improvement over existing composite designs. Growth of vertically aligned CNTs (VACNTs) offers new avenues for designing high-performance composites by integrating CFs and nanotubes into layered 3D architectures. To obtain composites with high rigidity and damping, we have designed and fabricated VACNT-based sandwich composites from simply stacking the freestanding VACNTs and CF fabrics and infiltrating with epoxy matrix. Comparing with the CF/epoxy laminates, the VACNT-based sandwich composites exhibit higher flexural rigidity and damping, which is achieved due to the effective integration of the VACNTs as an interfacial layer between the CF stacks. Furthermore, the lighter weight of these VACNT-based sandwich composites offers advantages in aerospace and transportation applications.

Most materials respond either elastically or inelastically to applied stress, while repeated loading can result in mechanical fatigue. Conversely, bones and other biomechanical tissues have the ability to strengthen when subjected to recurring elastic stress. The cyclic compressive loading of vertically aligned carbon nanotube/poly(dimethylsiloxane) nanocomposites has revealed a self-stiffening response previously unseen in synthetic materials. This behavior results in a permanent increase in stiffness that continues until the dynamic stress is removed and resumes when it is reapplied. The effect is also specific to dynamic loads, similar to the localized self-strengthening that occurs in biological structures. These observations help to elucidate the complex interactions between matrix materials and nanostructures, and control over this mechanism could lead to the development of adaptable structural materials and active, load-bearing artificial connective tissues.

Biological tissues have the remarkable ability to remodel and repair in response to disease, injury, and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials which respond to external stresses through a permanent increase in stiffness are uncommon. Here, we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a nematic director which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement.

We describe a method to study diffusion of rhodamine 6G dye in single silica nanochannels using arrays of silica nanochannels. Dynamics of the molecules inside single nanochannel is found from the change of the dye concentration in solution with time. A 10(8) decrease in the dye diffusion coefficient relative to water was observed. In comparison to single fluorescent molecule studies, the presented method does not require fluorescence of the diffusing molecules.

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