Simple models for the thermal conductivity enhancements in carbon nanotube (CNT) composites are presented as analytical functions of volume fraction, anisotropic thermal conductivities, aspect ratio, nonstraightness, and interfacial thermal resistance of the CNTs. The model predictions agree very well with the measured thermal conductivities of CNT composites available in the literature. It is shown that using CNTs with higher aspect and straightness ratios is an efficient means to get much better thermal conductivity enhancements for CNT composites. The models are further extended to account the effects of either the random or aligned orientation of CNTs and the interaction among CNTs on thermal conductivity of CNT composites.
In this article, we review our recent work on mid-infrared (mid-IR) photonic materials and devices fabricated on silicon for on-chip sensing applications. Pedestal waveguides based on silicon are demonstrated as broadband mid-IR sensors. Our low-loss mid-IR directional couplers demonstrated in SiNx waveguides are useful in differential sensing applications. Photonic crystal cavities and microdisk resonators based on chalcogenide glasses for high sensitivity are also demonstrated as effective mid-IR sensors. Polymer-based functionalization layers, to enhance the sensitivity and selectivity of our sensor devices, are also presented. We discuss the design of mid-IR chalcogenide waveguides integrated with polycrystalline PbTe detectors on a monolithic silicon platform for optical sensing, wherein the use of a low-index spacer layer enables the evanescent coupling of mid-IR light from the waveguides to the detector. Finally, we show the successful fabrication processing of our first prototype mid-IR waveguide-integrated detectors.
High-performance sealants using rubber composites containing multiwalled carbon nanotubes (MWNTs) were developed in order to probe and excavate oil in deeper wells. However, the stress-strain behavior and the reinforcing mechanism of highly concentrated MWNT/rubber composites subjected to large deformation remain largely unexplored. Here we report on the complete stress-strain relationships of MWNT/rubber composites under uniaxial tension before rupture, with a suggestion of a novel reinforcement effect of high concentration of MWNTs. A theoretical model is developed to understand the reinforcing mechanism and estimate the mechanical properties of MWNT/rubber composites under large deformation. We have demonstrated that persistence length and reorientation of MWNTs during stretch have a significant impact on mechanical properties, such as the modulus of the rubber composite. These results provide guidelines for developing MWNT-reinforced composites to achieve desired nonlinear and extreme mechanical performance for a wide range of applications.
Experiments on electrical properties of carbon nanotube (CNT) composites have shown that addition of CNTs may greatly enhance the electrical conductivity of the matrix. It has been a key but unresolved issue for years how to develop an analytical model of effective electrical conductivity of CNT composites that takes account of not only the CNT concentration and percolation, but also CNT conductivity anisotropy, aspect ratio, and nonstraightness. Such a model is established in this letter. The model predictions agree well with the measured data available in literatures and are also extended to account the effect of the orientation distribution of CNTs.
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