Neutral and Charged 1-Butyl-3-methylimidazolium Triflate Clusters: Equilibrium Concentration in the Vapor Phase and Thermal Properties of Nanometric Droplets

Ground state energy, structure, and harmonic vibrational modes of 1-butyl-3-methylimidazolium triflate ([bmim][Tf]) clusters have been computed using an all-atom empirical potential model. Neutral and charged species have been considered up to a size (30 [bmim][Tf] pairs) well into the nanometric range. Free energy computations and thermodynamic modeling have been used to predict the equilibrium composition of the vapor phase as a function of temperature and density. The results point to a nonnegligible concentration of very small charged species at pressures (P ~ 0.01 Pa) and temperatures (T 600 K) at the boundary of the stability range of [bmim][Tf]. Thermal properties of nanometric neutral droplets have been investigated in the 0 T 700 K range. A near-continuous transition between a liquidlike phase at high T and a solidlike phase at low T takes place at T ~ 190 K in close correspondence with the bulk glass point Tg ~ 200 K. Solidification is accompanied by a transition in the dielectric properties of the droplet, giving rise to a small permanent dipole embedded into the solid cluster. The simulation results highlight the molecular precursors of several macroscopic properties and phenomena and point to the close competition of Coulomb and dispersion forces as their common origin.

Incorporation of multiwalled carbon nanotubes to acrylic based bone cements: Effects on mechanical and thermal properties

Polymethyl methacrylate (PMMA) bone cement–multiwalled carbon nanotube (MWCNT) nanocomposites with a weight loading of 0.1% were prepared using 3 different methods of MWCNT incorporation. The mechanical and thermal properties of the resultant nanocomposite cements were characterised in accordance with the international standard for acrylic resin cements. The mechanical properties of the resultant nanocomposite cements were influenced by the type of MWCNT and method of incorporation used. The exothermic polymerisation reaction for the PMMA bone cement was significantly reduced when thermally conductive functionalised MWCNTs were added. This reduction in exotherm translated in a decrease in thermal necrosis index value of the respective nanocomposite cements, which potentially could reduce the hyperthermia experienced in vivo. The morphology and degree of dispersion of the MWCNTs in the PMMA matrix at different scales were analysed using scanning electron microscopy. Improvements in mechanical properties were attributed to the MWCNTs arresting/retarding crack propagation through the cement by providing a bridging effect into the wake of the crack, normal to the direction of crack growth. MWCNT agglomerations were evident within the cement microstructure, the degree of these agglomerations was dependent on the method used to incorporate the MWCNTs into the cement.

Animal-borne sensors successfully capture the real-time thermal properties of ocean basins

Climate change is perhaps the most pressing and urgent environmental issue facing the world today. However our ability to predict and quantify the consequences of this change is severely limited by the paucity of in situ oceanographic measurements. Marine animals equipped with sophisticated oceanographic data loggers to study their behavior offer one solution to this problem because marine animals range widely across the world's ocean basins and visit remote and often inaccessible locations. However, unlike the information being collected from conventional oceanographic sensing equipment, which has been validated, the data collected from instruments deployed on marine animals over long periods has not. This is the first long-term study to validate in situ oceanographic data collected by animal oceanographers. We compared the ocean temperatures collected by leatherback turtles (Dermochelys coriacea) in the Atlantic Ocean with the ARGO network of ocean floats and could find no systematic errors that could be ascribed to sensor instability. Animal-borne sensors allowed water temperature to be monitored across a range of depths, over entire ocean basins, and, importantly, over long periods and so will play a key role in assessing global climate change through improved monitoring of global temperatures. This finding is especially pertinent given recent international calls for the development and implementation of a comprehensive Earth observation system ( see http://iwgeo.ssc.nasa.gov/documents.asp?s=review) that includes the use of novel techniques for monitoring and understanding ocean and climate interactions to address strategic environmental and societal needs.

Thermal properties, sizes, and size distribution of Jupiter-family cometary nuclei

We present results from SEPPCoN, an on-going Survey of the Ensemble Physical Properties of Cometary Nuclei. In this report we discuss mid-infrared measurements of the thermal emission from 89 nuclei of Jupiter-family comets (JFCs). All data were obtained in 2006 and 2007 using imaging capabilities of the Spitzer Space Telescope. The comets were typically 4-5 AU from the Sun when observed and most showed only a point-source with little or no extended emission from dust. For those comets showing dust, we used image processing to photometrically extract the nuclei. For all 89 comets, we present new effective radii, and for 57 comets we present beaming parameters. Thus our survey provides the largest compilation of radiometrically-derived physical properties of nuclei to date. We have six main conclusions: (a) The average beaming parameter of the JFC population is 1.03 ± 0.11, consistent with unity; coupled with the large distance of the nuclei from the Sun, this indicates that most nuclei have Tempel 1-like thermal inertia. Only two of the 57 nuclei had outlying values (in a statistical sense) of infrared beaming. (b) The known JFC population is not complete even at 3 km radius, and even for comets that approach to ˜2 AU from the Sun and so ought to be more discoverable. Several recently-discovered comets in our survey have small perihelia and large (above ˜2 km) radii. (c) With our radii, we derive an independent estimate of the JFC nuclear cumulative size distribution (CSD), and we find that it has a power-law slope of around -1.9, with the exact value depending on the bounds in radius. (d) This power-law is close to that derived by others from visible-wavelength observations that assume a fixed geometric albedo, suggesting that there is no strong dependence of geometric albedo with radius. (e) The observed CSD shows a hint of structure with an excess of comets with radii 3-6 km. (f) Our CSD is consistent with the idea that the intrinsic size distribution of the JFC population is not a simple power-law and lacks many sub-kilometer objects.

Thermal properties and eutectic behaviour of dapivirine in combination with steroid hormones and other antiretrovirals

Background: Combination drug products can display thermal behaviour that is more complex than for the corresponding single drug products. For example, the contraceptive vaginal ring (VR) Nuvaring contains a eutectic (lowest melting) composition of etonogestrel (ETN) and ethinyl estradiol. Here we report the predisposition of dapivirine (DPV) to form reduced melting/eutectic mixtures when combined with other contraceptive hormones and antiretrovirals, and discuss the implications for development of combination microbicide and multipurpose prevention technology (MPT) products.
Methods: Binary mixtures of DPV with darunavir (DRV), levonorgestrel (LNG), ETN or maraviroc (MVC) were prepared either by physical mixing or by solvent evaporation. Selected binary mixtures were also incorporated into silicone elastomer (SE) VR devices. Thermal behavior of the mixtures was analyzed using differential scanning calorimetry (DSC) operating in standard heating ramp mode (10 °C/min). DSC data were used to construct two component phase diagrams for each binary system.
Results: Drug mixtures typically showed reduced melting transitions for both drug components, with clear evidence for a eutectic mixture at a well-defined intermediate composition. Eutectic temperatures and compositions for the various mixtures were: 40% DPV / 60% ETN - 170°C; 25% DPV / 75% MVC - 172°C; 65% DPV / 35% LNG - 192°C. In each case, the eutectic composition was also detected when the drug mixtures were incorporated into SE VRs. For the DPV/DRV system, the thermal behaviour is complicated by desolvation from the darunavir ethanolate polymorph.
Conclusions: When DPV is combined with small molecular weight hydrophobic drugs, the melting temperature for both drugs is typically reduced to a degree dependent on the composition of the mixture. At specified compositions, a low melting eutectic system results. The formation of eutectic behavior in binary drug systems needs to be carefully characterised in order to define product performance and drug release.

Structure and thermal properties of salicylate-based-protic ionic liquids as new heat storage media. COSMO-RS structure characterization and modeling of heat capacities

During this research, we present a study on the thermal properties, such as the melting, cold crystallization, and glass transition temperatures as well as heat capacities from 293.15 K to 323.15 K of nine in-house synthesized protic ionic liquids based on the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate ([H-Im-C₁OC_n][Sal]) with n = 3–11. The 3D structures, surface charge distributions and COSMO volumes of all investigated ions are obtained by combining DFT calculations and the COSMO-RS methodology. The heat capacity data sets as a function of temperature of the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate are then predicted using the methodology originally proposed in the case of ionic liquids by Ge et al. 3-(Alkoxymethyl)-1H-imidazol-3-ium salicylate based ionic liquids present specific heat capacities higher in many cases than other ionic liquids that make them suitable as heat storage media and in heat transfer processes. It was found experimentally that the heat capacity increases linearly with increasing alkyl chain length of the alkoxymethyl group of 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate as was expected and predicted using the Ge et al. method with an overall relative absolute deviation close to 3.2% for temperatures up to 323.15 K.

Thermal Properties of Alkyl-triethylammonium bis{(trifluoromethyl)sulfonyl}imide Ionic Liquids

In this work, we address the thermal properties of selected members of a
homologous series of alkyltriethylammonium bisf(trifluoromethyl)sulfonylgimide ionic
liquids. Their phase and glass transition behavior, as well as their standard isobaric heat
capacities at 298.15 K, were studied using differential scanning calorimetry (DSC),
whereas their decomposition temperature was determined by thermal gravimetry analysis.
DSC was further used to measure standard molar heat capacities of the studied ionic liquids
and standard molar heat capacity as a function of temperature for hexyltriethylammonium,
octyltriethylammonium, and dodecyltriethylammonium bisf(trifluoromethyl)sulfonylgimide
ionic liquids. Based on the data obtained, we discuss the influence of the alkyl chain
length of the cation on the studied ionic liquids on the measured properties. Using viscosity
data obtained in a previous work, the liquid fragility of the ionic liquids is then discussed.
Viscosity data were correlated by the VTF equation using a robust regression along a
gnostic influence function. In this way, more reliable VTF model parameters were obtained than in our previous work and a good estimate of the liquid fragility of the ionic liquids was made.

Effect of poly ethylene glycol on the mechanical and thermal properties of bioactive Poly (ε–caprolactone) melt extrudates for pharmaceutical applications

This paper investigates the effects of polyethylene glycol (PEG), on the mechanical and thermal properties of nalidixic acid/ploy ε-caprolactone (NA)/PCL blends prepared by hot melt extrusion. The blends were characterized by tensile and flexural analysis, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. Experimental data indicated that the addition of NA caused loss of the tensile strength and toughness of PCL. Thermal analysis of the PCL showed that on addition of the thermally unstable NA, thermal degradation occurred early and was autocatalytic. However, the NA did benefit from the heat shielding provided by the PCL matrix resulting in more thermally stable NA particles. Results show that loading PEG in the PCL had a detrimental effect on the tensile strength and toughness of the blends, reducing them by 20-40%. The partial miscibility of the PCL-PEG system, causes an increase in Tg. While increases in the crystallinity is attributed to the plasticisation effect of PEG and the nucleation effect of NA. The average crystal size increased by 8% upon PEG addition.