Author
Carlos Gracia-Fernández
Bio: Carlos Gracia-Fernández is an academic researcher from University of Vigo. The author has contributed to research in topics: Differential scanning calorimetry & Glass transition. The author has an hindex of 16, co-authored 41 publications receiving 782 citations.
Papers
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TL;DR: The rheological behavior was determined for both nanofluids at nanoparticle mass concentrations up to 25%, including flow curves and frequency-dependent storage and loss moduli, using a cone-plate rotational rheometer.
Abstract: Homogeneous stable suspensions obtained by dispersing dry TiO2 nanoparticles in pure ethylene glycol were prepared and studied Two types of nanocrystalline structure were analyzed, namely anatase and rutile phases, which have been characterized by scanning electron microscopy The rheological behavior was determined for both nanofluids at nanoparticle mass concentrations up to 25%, including flow curves and frequency-dependent storage and loss moduli, using a cone-plate rotational rheometer The effect of temperature over these flow curve tests at the highest concentration was also analyzed from 28315 to 32315 K Furthermore, the influence of temperature, pressure, nanocrystalline structure, and concentration on the volumetric properties, including densities and isobaric thermal expansivities, were also analyzed
124 citations
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TL;DR: This is the highest Tt reported so far for a perovskite-like formate that is thus a promising candidate to display electric order very close to room temperature.
Abstract: We report that the hybrid organic–inorganic compound [(CH3)2NH2][Mg(HCOO)3] shows a marked dielectric transition around Tt ∼ 270 K, associated to a structural phase transition from SG Rc (centrosymmetric) to Cc (non-centrosymmetric). This is the highest Tt reported so far for a perovskite-like formate that is thus a promising candidate to display electric order very close to room temperature.
109 citations
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TL;DR: In this paper, isobaric specific heat capacity measurements were performed for five different nanofluid sets designed as dispersions up to 15% mass concentrations of MgO, ZnO, and ZrO 2 in pure ethylene glycol as well as ZnOs, ZOs and ZRs in an ethanol glycol+water mixture at 50:50% in volume.
101 citations
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TL;DR: In this article, the same frequency and temperature using quasi-isothermal conditions in both instruments were compared with three different polymer samples and it was found that when choosing a suitable response parameter, i.e. the phase angle, the dynamic glass transition temperature values obtained by both methods are practically the same.
81 citations
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TL;DR: In this article, the authors compared the results obtained by rheometry and dielectric analysis to those obtained using the Flory equation and found a reasonable agreement between the two techniques that lead to gel conversion values very close to the ones obtained using DEA.
54 citations
Cited by
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TL;DR: The International Nanofluid Property Benchmark Exercise (INPBE) as discussed by the authors was held in 1998, where the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids" was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady state methods, and optical methods.
Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.
881 citations
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TL;DR: Hybrid organic-inorganic perovskites (HOIPs) as mentioned in this paper can have a diverse range of compositions including halides, azides, formates, dicyanamides, cyanides, and Dicyanometallates.
Abstract: Hybrid organic–inorganic perovskites (HOIPs) can have a diverse range of compositions including halides, azides, formates, dicyanamides, cyanides and dicyanometallates. These materials have several common features, including their classical ABX3 perovskite architecture and the presence of organic amine cations that occupy the A-sites. Current research in HOIPs tends to focus on metal halide HOIPs, which show promise for use in solar cells and optoelectronic devices; however, the other subclasses also exhibit a diverse range of physical properties. In this Review, we summarize the chemical variability and structural diversity of all known HOIP subclasses. We also present a comprehensive account of their intriguing physical properties, including photovoltaic and optoelectronic properties, dielectricity, magnetism, ferroelectricity, ferroelasticity and multiferroicity. Moreover, we discuss the current challenges and future opportunities in this exciting field. Hybrid organic–inorganic perovskites (HOIPs) comprise a diverse range of chemical compositions from halides and azides to formates, dicyanamides, cyanides and dicyanometallates. In this Review, advances in the synthesis, structures and properties of all HOIP subclasses are summarized and their future opportunities are discussed.
788 citations
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TL;DR: In this paper, a review of recent advances in the measurement and modeling of thermophysical properties at the nanoscale (from the solid state to colloids) is presented, including thermal conductivity, dynamic viscosity, specific heat capacity, and density.
322 citations
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TL;DR: In this article, the effects of temperature and nanoparticles concentration on the rheological behavior of Fe 3 O 4 -Ag/EG hybrid nanofluid have been experimentally investigated.
309 citations
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TL;DR: Crystal structure and solid-state NMR studies reveal a switchable property between low and high dielectric states around 245 K, which originates from an order-disorder phase transition of the system, changing the dynamics of the polar dimethylammonium cation.
Abstract: The inclusion compound [(CH3)2NH2]2[KCo(CN)6] exhibits a marked temperature-dependent dielectric constant and can be considered as a model of tunable and switchable dielectric materials. Crystal structure and solid-state NMR studies reveal a switchable property between low and high dielectric states around 245 K. This originates from an order–disorder phase transition of the system, changing the dynamics of the polar dimethylammonium (DMA) cation. Furthermore, the tuning of the dielectric constant at temperatures below the phase transition point is related to increasing angular pretransitional fluctuations of the dipole moment of DMA.
284 citations