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Heat conduction mechanisms in nanofluids, fluids seeded with nanoparticles, have been extensively scrutinized in the past decades to explain some experimental observations of their enhanced thermal conductivity beyond the effective medium theory. Although many mechanisms such as Brownian motion, clustering, ballistic transport, and internanoparticle potential are speculated, experimental proof of any of the mechanisms has been difficult. Here, we investigate the mechanisms experimentally by thermal conductivity measurements and structural analysis for the same materials in both liquid and solid states. These studies strongly suggest that clustering holds the key to the thermal conductivity enhancement of nanofluids.

Many neutrophil functions are regulated by phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) that mediates protein membrane translocation via binding to pleckstrin homolog (PH) domains within target proteins. Here we show that inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), a cytosolic small molecule, bound the same PH domain of target proteins and competed for binding to PtdIns(3,4,5)P3. In neutrophils, chemoattractant stimulation triggered rapid elevation in Ins(1,3,4,5)P4 concentration. Depletion of Ins(1,3,4,5)P4 by deleting the gene encoding InsP3KB, which converts Ins(1,4,5)P3 to Ins(1,3,4,5)P4, enhanced membrane translocation of the PtdIns(3,4,5)P3-specific PH domain. This led to enhanced sensitivity to chemoattractant stimulation, elevated superoxide production, and enhanced neutrophil recruitment to inflamed peritoneal cavity. On the contrary, augmentation of intracellular Ins(1,3,4,5)P4 concentration blocked PH domain-mediated membrane translocation of target proteins and dramatically decreased the sensitivity of neutrophils to chemoattractant stimulation. These findings establish a role for Ins(1,3,4,5)P4 in cellular signal transduction pathways and provide another mechanism for modulating PtdIns(3,4,5)P3 signaling in neutrophils.

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A new sort of nanofluid phase-change material (PCM) is developed by suspending a small amount of nanoparticles in melting paraffin. Cu, Al, and C/Cu nanoparticles were selected to add to the melting paraffin to enhance the heat-transfer rate of paraffin. Cu nanoparticles have the best performance for heat transfer. Five dispersants were chosen to make Cu nanoparticles stably suspended in melting paraffin. The nanofluids with Cu nanoparticles show good stability in melting paraffin under the action of Hitenol BC-10, even suspending for 12 h in a constant temperature trough. The Fourier transform infrared (FTIR) spentrum shows that it is a physical interaction among Cu, paraffin, and Hitenol BC-10. The differential scanning calorimetric (DSC) results reveal that the latent heats of Cu/paraffin shift to lower values compared to those of pure paraffin; however, the melting and freezing temperatures are kept almost the same as pure paraffin. The latent heats and phase-change temperatures change very little after 100 thermal cycles. Furthermore, the heating and cooling rates of PCMs were significantly improved upon the addition of Cu nanoparticles. For composites with 1 wt % Cu nanoparticle, the heating and cooling times can be reduced by 30.3 and 28.2%, respectively.

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