Guiding conductive heat flux through thermal metamaterials

<div> <div> <div> <p>Experimental evidence of the bending of heat to desired purpose, in analogy to that of light, through designed placement and orientation of nominally isotropic material is presented. This was done by inducing anisotropy in an effective thermal medium through off-diagonal components in the thermal conductivity tensor. An upward or downward heat flux bending of up to +/- 26°, in close agreement with theoretical estimates, was obtained in a metamaterial constituted from thin, stacked layers of copper and stainless steel. Transient observations of heat flow indicate anisotropic energy transport hinging on the relative differences between the elements of the thermal diffusivity tensor. </p> </div> </div> </div

Estimating interfacial thermal conductivity in metamaterials through heat flux mapping

<div> <div> <div> <p>The variability of the thickness as well as the thermal conductivity of interfaces in composites may significantly influence thermal transport characteristics and the notion of a metamaterial as an effective medium. The consequent modulations of the heat flux passage are analytically and experimentally examined through a non-contact methodology using radiative imaging, on a model anisotropic thermal metamaterial. It was indicated that a lower Al layer/silver interfacial epoxy ratio of ~25 compared to that of a Al layer/alumina interfacial epoxy (of ~39) contributes to a smaller deviation of the heat flux bending angle. </p> </div> </div> </div

Layered thermal metamaterials for the directing and harvesting of conductive heat.pdf

<div> <div> <div> <p>The utility of a metamaterial, assembled from two layers of nominally isotropic mate- rials, for thermal energy re-orientation and harvesting is examined. A study of the underlying phenomena related to heat flux manipulation, exploiting the anisotropy of the thermal conductivity tensor, is a focus. The notion of the assembled metamaterial as an effective thermal medium forms the basis for many of these investigations and will be probed. An overarching aim is to implement in such thermal metamaterials, functionalities well known from light optics, such as reflection and refraction, which in turn may yield insights on efficient thermal lensing. Consequently, the harness and dissipation of heat, which are for example, of much importance in energy conservation and improving electrical device performance, may be accomplished. The possibilities of energy harvesting, through exploiting anisotropic thermopower in the metamaterials is also examined. The review concludes with a brief survey of the outstanding issues and insights needed for further progress. </p> </div> </div> </div

Enhanced solar evaporation of water from porous media, through capillary mediated forces and surface treatment

<div> <div> <div> <p> </p><div> <div> <div> <p>The relative influence of the capillary, Marangoni, and hydrophobic forces in mediating the evaporation of water from carbon foam based porous media, in response to incident solar radiation, are investigated. It is indicated that inducing hydrophilic interactions on the surface, through nitric acid treatment of the foams, has a similar effect to reduced pore diameter and the ensuing capillary forces. The efficiency of water evaporation may be parameterized through the Capillary number (Ca), with a lower Ca being preferred. The proposed study is of much relevance to efficient solar energy utilization.  </p> </div> </div> </div> </div> </div> </div

Femtomolar Level-Specific Detection of Lead Ions in Aqueous Environments, Using Aptamer-Derivatized Graphene Field-Effect Transistors

The detection of lead ion (Pb2+) contamination in aqueous media is relevant for preventing endemic health issues as well as damage to cognitive and physical health. Existing home kit tests are unable to achieve clinically relevant sensitivity and specificity. Here, a label-free graphene field-effect transistor sensor for detecting Pb2+ at the femtomolar (fM) level, discriminating between confounding ions, is reported. The sensing principle is based on electrically monitoring Pb2+-binding-mediated conformational changes of a specific aptamer tethered to graphene, modeled through the Hills–Langmuir mechanism. A record sensitivitythrough a limit of detection of ∼61 fM, for Pb2+ was demonstrated. For model verification, specific discrimination of Pb2+ from other ions at the 1 picomolar (pM) level was shown. The reported work provides motivation for development of portable, label-free, point-of-care devices with both high specificity and sensitivity