We report the disentanglement of bulk and interfacial contributions to the thermally excited magnon spin current in the spin Seebeck effect under static heating. For this purpose, we have studied the dependence of the inverse Spin Hall voltage and the thermal conductivity on the magnetic layer thickness. Knowledge of these quantities allows us to take into account the influence of both sources of thermal spin current in the analysis of the voltage dependence. The magnetic layer thickness modulates the relative magnitude of the involved thermal drops for a fixed total thermal difference throughout the sample. In the end, we attain the separate contributions of both sources of thermal spin current -bulk and interfacial-and obtain the value of the thermal magnon accumulation length scale in maghemite, which we find to be 29(1) nm. According to our results, bulk magnon accumulation dominates the spin Seebeck effect in our studied range of thicknesses, but the interfacial component is by no means negligible.
We present the analysis of the thermal conductivity, κ, and heat capacity, C, of a wide variety of liquids, covering organic molecular solvents, ionic liquids and water-polymer mixtures. These data were obtained from ≈0.6 μL samples, using an experimental development based on the 3ω method, capable of the simultaneous measurement of κ and C. In spite of the different type and strength of interactions, expected in a priori so different systems, the ratio of κ to the sound velocity is approximately constant for all of them. This is the consequence of a similar atomic density for all these liquids, notwithstanding their different molecular structures. This was corroborated experimentally by the observation of a C/V ≈ 1.89 × 10 J K m (≈3R/2 per atom), for all liquids studied in this work. Finally, the very small volume of the sample required in this experimental method is an important advantage for the characterization of systems like nanofluids, in which having a large amount of the dispersed phase is sometimes extremely challenging.
Here we show that by adjusting the concentration of tetrabutyl ammonium and phosphonium salts in water (% 1.5-2.0 m), hydrophobic solvation triggers the formation of a unique, highly incompressible supramolecular liquid, with a dynamic structure similar to clathrates, involving essentially all H 2 O molecules of the solvent. Despite the increasing local order, the thermal diffusivity, and compressibility of these supramolecular liquids is strongly decreased with respect to bulk water due to slower relaxation dynamics. The results presented in this paper open an avenue to design a new family of supramolecular fluids, stable under atmospheric conditions, which can find important technological applications in energy storage and conversion. Dissolving small non (or moderate)-polar molecules in water induces the formation of local ice-like structures around them. [1-4] Above a certain concentration of the solute, and under conditions of high pressure and low temperature, these host-guest hydrates can form crystalline solids, so-called clathrate hydrates, a vast class of materials with important applications in gas separation, storage and transportation. [5-7] When the host molecule takes part within the multi-polyhedral structure of hydrogen-bonded water, semi-clathrate hydrates are formed. This is the case for tetrabutyl ammonium bromide (TtBABr) and other quaternary ammonium salts, in which the anions incorporate into
Developing systems that can be switched between states with different thermal conductivities is one of the current challenges in materials science. Despite their enormous diversity and chemical richness, molecular materials...
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