Melting Is Well-Known, but Is It Also Well-Understood?

Contrary to continuous phase transitions, where renormalization group theory provides a general framework, for discontinuous phase transitions such a framework seems to be absent. Although the thermodynamics of the latter type of transitions is well-known and requires input from two phases, for melting a variety of one-phase theories and models based on solids has been proposed, as a generally accepted theory for liquids is (yet) missing. Each theory or model deals with a specific mechanism using typically one of the various defects (vacancies, interstitials, dislocations, interstitialcies) present in solids. Furthermore, recognizing that surfaces are often present, one distinguishes between mechanical or bulk melting and thermodynamic or surface-mediated melting. After providing the necessary preliminaries, we discuss both types of melting in relation to the various defects. Thereafter we deal with the effect of pressure on the melting process, followed by a discussion along the line of type of materials. Subsequently, some other aspects and approaches are dealt with. An attempt to put melting in perspective concludes this review.</p

On the Use of Probe Liquids for Surface Energy Measurements

To assess the surface energy of solids, normally a set of probe liquids comprising polar and apolar compounds is used. Here we survey the surface tension of some frequently used probe liquids as given in the literature, for which a significant scatter appears to be present, and compare them with experimentally determined values. We discuss the influence of the liquid purity as well as the contact angle between the liquid and the Wilhelmy plate, which is commonly used for surface tension measurements. For hygroscopic polar probe liquids such as dimethyl sulfoxide, ethylene glycol, and formamide, water impurities appear to be of limited importance. Similarly, the amount of halogen impurities is of minor importance for diiodomethane and 1-bromonaphthalene, which decompose under the influence of light. Conversely, the influence of the contact angle for liquids that do not fully wet the plate, such as diiodomethane, is large in many cases, rendering a rather accurate determination of the contact angle necessary. Some discrepancies in the literature are indicated, and brief recommendations for future studies using such liquids are given.</p

On the Use of Probe Liquids for Surface Energy Measurements

To assess the surface energy of solids, normally a set of probe liquids comprising polar and apolar compounds is used. Here we survey the surface tension of some frequently used probe liquids as given in the literature, for which a significant scatter appears to be present, and compare them with experimentally determined values. We discuss the influence of the liquid purity as well as the contact angle between the liquid and the Wilhelmy plate, which is commonly used for surface tension measurements. For hygroscopic polar probe liquids such as dimethyl sulfoxide, ethylene glycol, and formamide, water impurities appear to be of limited importance. Similarly, the amount of halogen impurities is of minor importance for diiodomethane and 1-bromonaphthalene, which decompose under the influence of light. Conversely, the influence of the contact angle for liquids that do not fully wet the plate, such as diiodomethane, is large in many cases, rendering a rather accurate determination of the contact angle necessary. Some discrepancies in the literature are indicated, and brief recommendations for future studies using such liquids are given.</p

Grain size effect on the switching current in soft ferroelectric lead zirconate titanate

Recently, we reported on the appearance of a double peak in the switching current during the reverse poling. In the present paper, the switching current measurements have been carried out on a soft lead zirconate titanate as a function of grain size. While in small grains only a small single switching peak is observed, large grains, however, showed double peak switching, as commonly observed in this material. The pyroelectric coefficient curves show a consistent trend with the switching curves. This behavior is attributed to non-180° domain switching during the reversed poling case as a result of residual stresses developed during forward poling. ©2007 American Institute of Physic

Iron phosphate mediated magnetite synthesis:a bioinspired approach

The biomineralization of intracellular magnetite in magnetotactic bacteria (MTB) is an area of active investigation. Previous work has provided evidence that magnetite biomineralization begins with the formation of an amorphous phosphate-rich ferric hydroxide precursor phase followed by the eventual formation of magnetite within specialized vesicles (magnetosomes) through redox chemical reactions. Although important progress has been made in elucidating the different steps and possible precursor phases involved in the biomineralization process, many questions still remain. Here, we present a novelin vitromethod to form magnetite directly from a mixed valence iron phosphate precursor, without the involvement of other known iron hydroxide precursors such as ferrihydrite. Our results corroborate the idea that phosphate containing phases likely play an iron storage role during magnetite biomineralization. Further, our results help elucidate the influence of phosphate ions on iron chemistry in groundwater and wastewater treatment.</p

Graphene-Flakes Printed Wideband Elliptical Dipole Antenna for Low Cost Wireless Communications Applications

This letter presents the design, manufacturing and operational performance of a graphene-flakes based screenprinted wideband elliptical dipole antenna operating from 2 GHz up to 5 GHz for low cost wireless communications applications. To investigate radio frequency (RF) conductivity of the printed graphene, a coplanar waveguide (CPW) test structure was designed, fabricated and tested in the frequency range from 1 GHz to 20 GHz. Antenna and CPW were screen-printed on Kapton substrates using a graphene paste formulated with a graphene to binder ratio of 1:2. A combination of thermal treatment and subsequent compression rolling is utilized to further decrease the sheet resistance for printed graphene structures, ultimately reaching 4 Ohm/sq. at 10 {\mu}m thicknesses. For the graphene-flakes printed antenna an antenna efficiency of 60% is obtained. The measured maximum antenna gain is 2.3 dBi at 4.8 GHz. Thus the graphene-flakes printed antenna adds a total loss of only 3.1 dB to an RF link when compared to the same structure screen-printed for reference with a commercial silver ink. This shows that the electrical performance of screen-printed graphene flakes, which also does not degrade after repeated bending, is suitable for realizing low-cost wearable RF wireless communication devices.Comment: Accepted, in press (online preview available

Time-Resolved Cryo-TEM Study on the Formation of Iron Hydroxides in a Collagen Matrix

The mineralization of collagen via synthetic procedures has been extensively investigated for hydroxyapatite as well as for silica and calcium carbonate. From a fundamental point of view, it is interesting to investigate whether collagen could serve as a generic mineralization template for other minerals, like iron oxides. Here, bio-inspired coprecipitation reaction, generally leading to the formation of magnetite, is used to mineralize collagen with iron hydroxides. Platelet-shaped green rust crystals form outside the collagen matrix, while inside the collagen, nanoparticles with a size of 2.6 nm are formed, which are hypothesized to be iron (III) hydroxide. Mineralization with nanoparticles inside the collagen solely occurs in the presence of poly(aspartic acid) (pAsp). In the absence of pAsp, magnetite particles are formed around the collagen. Time-resolved cryo-TEM shows that during the coprecipitation reaction, initially a beam-sensitive phase is formed, possibly an Fe3+-pAsp complex. This beam-sensitive phase transforms into nanoparticles. In a later stage, sheet-like crystals are also found. After 48 h of mineralization, ordering of the nanoparticles around one of the collagen sub-bands (the a-band) is observed. This is very similar to the collagen-hydroxyapatite system, indicating that mineralization with iron hydroxides inside collagen is possible and proceeds via a similar mechanism as hydroxyapatite mineralization. </p

Local quantification of mesoporous silica microspheres using multiscale electron tomography and lattice Boltzmann simulations

The multiscale pore structure of mesoporous silica microspheres plays an important role for tuning mass transfer kinetics in technological applications such as liquid chromatography. While local analysis of a pore network in such materials has been previously achieved, multiscale quantification of microspheres down to the nanometer scale pore level is still lacking. Here we demonstrate for the first time, by combining low convergence angle scanning transmission electron microscopy tomography (LC-STEM tomography) with image analysis and lattice Boltzmann simulations, that the multiscale pore network of commercial mesoporous silica microspheres can be quantified. This includes comparing the local tortuosity and intraparticle diffusion coefficients between different regions within the same microsphere. The results, spanning more than two orders of magnitude between nanostructures and entire object, are in good agreement with bulk characterization techniques such as nitrogen gas physisorption and add valuable local information for tuning mass transfer behavior (in liquid chromatography or catalysis) on the single microsphere level