Temperature Dependence Of Interaction Research Articles

First-principles study of vibrational entropy effects on the PbTe-SrTe phase diagram

We present first-principles calculations of the solid-state phase diagram of PbTe-SrTe that include both configurational and vibrational contributions to the free energy. These configurational and vibrational free energies were calculated using the cluster expansion (CE) approach and quasiharmonic phonon calculations, respectively. The coupled configurational and vibrational degrees of freedom were taken into account by including temperature-dependent CE interactions with the $T=0\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ values and temperature dependence of the interactions determined from total energies and phonon free energies, both calculated using density functional theory. This Hamiltonian was then employed in Monte Carlo simulations to obtain a quantitative prediction of the PbTe-SrTe phase diagram. The phase diagram consists of a miscibility gap with a maximum temperature of \ensuremath{\sim}500 K, with the inclusion of the vibrational entropy resulting in a more than fourfold increase in the calculated solubility limits of SrTe in PbTe. Our results suggest that the equilibrium solubility of this system is likely much larger than previously thought and deserves further experimental investigation.

Temperature-dependent Raman linewidths in transition-metal dichalcogenides

Using a semi-ab-initio theoretical method we examine the temperature-dependent linewidth of the Raman modes in bulk and monolayer transition-metal dichalcogenides (TMDs) ${\mathrm{MoS}}_{2}, {\mathrm{WS}}_{2}$, and ${\mathrm{MoTe}}_{2}$. It is found that different Raman modes show different linewidths and different temperature dependencies with respect to each other for a given sample and across different TMDs. We explain these characteristics as arising from a combination of phonon density of states, Raman mode frequency, and the relative contributions of temperature-independent mass-defect scattering and temperature-dependent intrinsic anharmonic interactions. Reported measurements for samples prepared under experimental conditions have been explained by adding frequency-dependent inhomogeneity-related background contribution to our theoretical results for the pure and homogeneous samples.

A geopolymeric composite of non-calcined rice husks made of metakaolin/sol–gel silica

In this work, the development of a composite material with geopolymer and a high content of rice husks without heat treatment was investigated to create and characterize a low-cost composite made with agro-industrial wastes. The ratio used was about 12/88 wt./% of sol–gel and metakaolin related to rice husks. This kind of composite geopolymer was designed as both a construction material for load or aesthetic finishing. X-ray diffraction studies reveal that the composite has an amorphous phase and a crystalline one, which is typical of geopolymeric materials. The scanning electron microscopy showed that the geopolymeric matrix completely wrapped the rice husks. The composite material has a compressive strength close to some mortars with a value of about 110 kg/cm2 (10.8 MPa). Laser scanning confocal microscopy reveals that there is a difference of emission in the visible spectrum between the inner and outer sides of the rice husks, which corroborates that they have a different chemical composition. Differential scanning calorimetry analysis confirmed that the composite material has combined characteristics of its raw materials. X-ray diffraction studies show that metakaolin with sol–gel solutions had temperature-dependent interactions besides that, after the dehydroxylation, the composite material is mostly amorphous. The material of high content of rice husk bound by geopolymer could be applicable in various areas of the construction industry and finishing.

Theories for Sequence-Dependent Phase Behaviors of Biomolecular Condensates.

Liquid-liquid phase separation and related condensation processes of intrinsically disordered proteins (IDPs), proteins with intrinsically disordered regions, and nucleic acids underpin various condensed-liquid droplets or gel-like assemblies in the cellular environment. Collectively referred to as condensates, these bodies provide spatial/temporal compartmentalization, often serving as hubs for regulated biomolecular interactions. Examples include certain extracellular materials, transcription complexes, and membraneless organelles such as germ and stress granules and the nucleolus. They are critically important to cellular function; thus misregulation of their assembly is implicated in many diseases. Biomolecular condensates are complex entities. Our understanding of their inner workings is only in its infancy. Nonetheless, insights into basic biophysical principles of their assembly can be gained by applying analytical theories to elucidate how IDP phase behaviors are governed by the properties of the multivalent, solvent-mediated interactions entailed by the proteins' amino acid sequences. Here we briefly review the background of the pertinent polymer theories and outline the approximations that enable a tractable theoretical account of the dependence of IDP phase behaviors on the charge pattern of the IDP sequence. Of relevance to the homeostatic assembly of compositionally and functionally distinct condensates in the cellular context, theory indicates that the propensity for populations of different IDP sequences to mix or demix upon phase separation is affected by the similarity or dissimilarity of the sequence charge patterns. We also explore prospects of extending analytical theories to account for dynamic aspects of biomolecular condensates and to incorporate effects of cation-π, π-π, and temperature-dependent hydrophobic interactions on IDP phase properties.

Temperature dependency of intraguild predation between native and invasive crabs.

Environmental factors such as temperature can affect the geographical distribution of species directly by exceeding physiological tolerances, or indirectly by altering physiological rates that dictate the sign and strength of species interactions. Although the direct effects of environmental conditions are relatively well studied, the effects of environmentally mediated species interactions have garnered less attention. In this study, we examined the temperature dependency of size-structured intraguild predation (IGP) between native blue crabs (Callinectes sapidus, the IG predator) and invasive green crabs (Carcinus maenas, the IG prey) to evaluate how the effect of temperature on competitive and predatory rates may influence the latitudinal distribution of these species. In outdoor mesocosm experiments, we quantified interactions between blue crabs, green crabs, and shared prey (mussels) at three temperatures reflective of those across their range, using two size classes of blue crab. At low temperatures, green crabs had a competitive advantage and IGP by blue crabs on green crabs was low. At high temperatures, size-matched blue and green crabs were competitively similar, large blue crabs had a competitive advantage, and IGP on green crabs was high. We then used parameter values generated from these experiments (temperature- and size-dependent attack rates and handling times) in a size-structured IGP model in which we varied IGP attack rate, maturation rate of the blue crab from the non-predatory to predatory size class, and resource carrying capacity at each of the three temperatures. In the model, green crabs were likely to competitively exclude blue crabs at low temperature, whereas blue crabs were likely to competitively and consumptively exclude green crabs at higher temperatures, particularly when resource productivities and rates of IGP were high. While many factors may play a role in delimiting species ranges, our results suggest that temperature-dependent interactions can influence local coexistence and are worth considering when developing mechanistic species distribution models and evaluating responses to environmental change.

Temperature-Dependent Species Interactions Shape Priority Effects and the Persistence of Unequal Competitors.

The order of species arrival at a site can determine the outcome of competitive interactions when early arrivers alter the environment or deplete shared resources. These priority effects are predicted to be stronger at high temperatures, as higher vital rates caused by warming allow early arrivers to more rapidly impact a shared environment. We tested this prediction using a pair of congeneric aphid species that specialize on milkweed plants. We manipulated temperature and arrival order of the two aphid species and measured aphid population dynamics and milkweed survival and defensive traits. We found that warming increased the impact of aphids on the quantity and quality of milkweed, which amplified the importance of priority effects by increasing the competitive exclusion of the inferior competitor when it arrived late. Warming also enhanced interspecific differences in dispersal, which could alter relative arrival times at a regional scale. Our experiment provides a first link between temperature-dependent trophic interactions, priority effects, and dispersal. This study suggests that the indirect and cascading effects of temperature observed here may be important determinants of diversity in the temporally and spatially complex landscapes that characterize ecological communities.

Hydrogen and Carbon Vapour Pressure Isotope Effects in Liquid Fluoroform Studied by Density Functional Theory

Abstract H/D and 12C/13C vapour pressure isotope effects (VPIEs) in liquid fluoroform (CHF3) were studied at the MPW1PW91/6-31 ++ G(d) level of theory. The CHF3 monomer and CHF3 molecules surrounded by other CHF3 molecules in every direction in CHF3 clusters were used as model molecules of vapour and liquid CHF3. Although experimental results in which the vapour pressure of liquid 12CHF3 is higher than that of liquid 12CDF3 and the vapour pressure of liquid 13CHF3 is higher than that of liquid 12CHF3 between 125 and 212 K were qualitatively reproduced, the present calculations overestimated the H/D VPIE and underestimated the 12C/13C VPIE. Temperature-dependent intermolecular interactions between hydrogen and fluorine atoms of neighbouring molecules were required to explain the temperature dependences of both H/D and 12C/13C VPIEs.

Dephasing mechanisms of optical transitions in rare-earth-doped transparent ceramics

We identify and analyze dephasing mechanisms that broaden the optical transitions of rare-earth ions in randomly oriented transparent ceramics. The study examines the narrow F_0^7 ↔ D_0^5 transition of Eu^(3+) dopants in a series of Y_2O_3 ceramic samples prepared under varying conditions. We characterize the temperature and magnetic field dependence of the homogeneous linewidth, as well as long-term spectral diffusion on time scales up to 1 s. The results highlight significant differences between samples with differing thermal treatments and Zr^(4+) additive concentrations. In particular, several distinct magnetic interactions from defect centers are observed, which are clearly distinguished from the broadening due to interactions with two-level systems and phonons. By minimizing the broadening due to the different defect centers, linewidths of the order of 4 kHz are achieved for all samples. The linewidths are limited by temperature-dependent interactions and by an interaction that is yet to be identified. Although the homogeneous linewidth can be narrowed further in these ceramic samples, the broadening is now comparable to the linewidths achieved in rare-earth-ion–doped single crystals. Thus, this work emphasizes the usefulness of studying ceramics to gain insights into dephasing mechanisms relevant to single crystals and suggests that ceramics may be an interesting alternative for applications in classical and quantum information processing.

Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions

Dynamic arrest transitions of colloidal suspensions containing nonspherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346-2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultrasmall angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. The adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.

ATR-IR Investigation of Solvent Interactions with Surface-Bound Polymers.

Solvent interactions with bulk and surface-bound polymer brushes are crucial for functionalities such as controlled friction and thermoresponsive adhesion. To study such interactions, the temperature-induced solvent-quality changes and the effect of surface tethering on the mechanical and tribological properties of poly(dodecyl methacrylate) (P12MA) brushes have been investigated by means of attenuated total reflection infrared spectroscopy (ATR-IR), as well as atomic force microscopy (AFM) and lateral force microscopy (LFM). These results have been compared with temperature-dependent UV–visible spectrophotometry (UV–vis) data for the corresponding bulk polymer solutions. The ATR-IR results clearly show that increasing temperature enhances ethanol uptake in P12MA, which results in film swelling. This is accompanied by a marked increase in both adhesion and friction. We have also shown that a combination of solvents, such as toluene and ethanol, can lead to a temperature-dependent solvent partitioning within the polymer brush. To our knowledge this is the first time preferential solvent uptake in a grafted-from brush has been monitored via in situ ATR-IR. Moreover, we have observed remarkably different behavior for polymer chains in solution compared to the behavior of similar chains bound to a surface. The presented findings on the temperature-dependent solvent interactions of surface-grafted P12MA reveal previously unknown solvation phenomena and open up a range of possible applications in the area of stimuli-responsive materials.

Theoretical Predictions of Temperature-Induced Gelation in Aqueous Dispersions Containing PEO-Grafted Particles.

In this work, we utilize classical polymer density functional theory (DFT) to study gelation in systems containing colloidal particles onto which polymers are grafted. The solution conditions are such that the corresponding bulk system displays a lower critical solution temperature (LCST). We specifically compare our predictions with experimental results by Shay et al. (J. Rheol. 2001, 45, 913-927), who investigated temperature response in aqueous dispersions containing polystyrene particles (PS), with grafted 45-mer poly(ethylene oxide) (PEO) chains. Our DFT treatment is based on a model for aqueous PEO solutions that was originally developed by Karlström for bulk solutions. In this model, monomers are assumed to be in either of two classes of states, labeled A and B, where B is more solvophobic than A. On the other hand, the degeneracy of B exceeds that of A, causing the population of solvophobic monomers to increase with temperature. In agreement with experimental findings by Shay et al., we locate gelation at temperatures considerably below TΘ, and far below the LCST for such chain lengths. This gelation occurs also without any dispersion interactions between the PS particles. Interestingly, the polymer-induced interaction free energy displays a nonmonotonic dependence on the grafting density. At high grafting densities, bridging attractions between grafted layers take place (considerably below TΘ). At low grafting densities, on the other hand, the polymers are able to bridge across to the other particle surface. Shay et al. conducted their experiments at very low ionic strength, using deionized water as a solvent. We demonstrate that even minute amounts of adsorbed charge on the surface of the particles, can lead to dramatic changes of the gelation temperature, especially at high grafting densities. Another interesting prediction is the existence of elongated (chainlike) equilibrium structures, at low particle concentrations. We emphasize that our model does not rely upon any temperature-dependent interactions.

Probing carbonyl-water hydrogen-bond interactions in thin polyoxazoline brushes.

Temperature-responsive oxazoline-based polymer brushes have gained increased attention as biocompatible surfaces. In aqueous environment, they can be tuned between hydrophilic and hydrophobic behavior triggered by a temperature stimulus. This transition is connected with changes in molecule-solvent interactions and results in a switching of the brushes between swollen and collapsed states. This work studies the temperature-dependent interactions between poly(2-oxazoline) brushes and water. In detail, thermoresponsive poly(2-cyclopropyl-2-oxazoline), nonresponsive hydrophilic poly(2-methyl-2-oxazoline), as well as a copolymer of the two were investigated with in situ infrared ellipsometry. Focus was put on interactions of the brushes' carbonyl groups with water molecules. Different polymer-water interactions could be observed and assigned to hydrogen bonding between C=O groups and water molecules. The switching behavior of the brushes in the range of 20-45 °C was identified by frequency shifts and intensity changes of the amide I band.

Non-monotonic temperature response of polymer mediated interactions.

In a recent publication, Feng et al. [Feng et al., Nat. Mater., 2015, 14, 61] reported a very interesting re-entrant solidification behaviour of colloidal particles in an aqueous solution containing polyethylene oxide (PEO). In this system, a crystalline colloidal phase, which is present at low temperatures, melts to a homogeneous fluid upon increasing the temperature. Further raising the temperature, however, eventually gives rise to a flocculated colloidal phase. Feng et al. proposed that the low-temperature crystalline phase is caused by polymer depletion while, at higher temperature, an increased attraction between polymers and particles leads to bridging attractions, and colloidal flocculation. The intermediate temperature regime sees the colloidal interactions dominated by charge repulsion, giving rise to a fluid phase. In the model by Feng et al., polymers are treated as hard spheres, which interact with the colloids via a phenomenological, temperature dependent potential. In this work, we develop a more detailed polymer density functional treatment, based on a model for aqueous PEO solutions that was originally developed by Karlström [Karlström, J. Phys. Chem., 1985, 89, 4962] for bulk solutions. In this model, monomers are assumed to be in either of two classes of states, labelled A and B, where B is more solvophobic than A. On the other hand, the degeneracy of the B states exceed that of A, causing the population of solvophobic monomers to increase with temperature. If the colloidal particles are also solvophobic, then this model displays the same qualitative temperature response as was observed by Feng et al. That is, at low temperatures, A type monomers predominate and one observes depletion interactions, whereas polymer bridging dominates at higher temperatures, due to the attraction between B-type monomers and the colloidal surface. Interestingly, the intermediate temperature regime is characterized by a polymer mediated interaction between colloids which is repulsive. That is, according to our model the homogeneous fluid phase would form even in the absence of repulsive electrostatic interactions. We emphasize that our model does not rely upon any temperature-dependent interactions. Furthermore, all possible polymer configurations are accounted for, subject to a mean-field Boltzmann weight. Finally, we show that interactions between colloids, mediated by neutral non-grafted polymers, generally follow the trend: attraction ⇒ repulsion (or vanishing interaction) ⇒ attraction as the surface affinity toward monomers proceeds from repulsive to attractive.

Molecularly imprinted polymer microprobes for manipulating neurological function by regulating temperature-dependent molecular interactions

We describe molecularly imprinted polymer (MIP) microprobes for manipulating neurological function by the thermoregulatory process. Some target and disease areas show raised temperature than normal temperature which are involved in neuronal diseases, such as Alzheimer’s, Parkinson’s and Huntington’s diseases. As well thermodynamic parameters can be obtained in the environments in vitro, which that the assay involves a temperature variable, at or beyond body temperature. We applied for studying molecular aspects of hypothalamus regulated physiology and behaviors. Steady-state binding was detected by fluorescence and Boltzmann energies-based fluorescence emission showed interactions of clozapine with altered energy levels. Dynamic spectra revealed dramatic effects on the fluorescence of the drug in dopamine imprint of MIPs exposed rat hypothalamic membranes at different temperatures. The MIPs that cooperatively occupied and provided the response to the neural proteins were not likely to be involved in the binding of clozapine within the cavity. The results indicated that the dynamics on the surface of proteins exposed to the drug–MIP with assembly, mediated specific function through temperature-dependent molecular interaction in the hypothalamus. Thus, this approach is applicable to processes of key importance of controlling the energy homeostasis and, plausibly, to selective signaling can affect in plasticity of the neural response.

Assessing Coupled Protein Folding and Binding Through Temperature-Dependent Isothermal Titration Calorimetry.

Broad interest in the thermodynamic driving forces of coupled macromolecular folding and binding is motivated by the prevalence of disorder-to-order transitions observed when intrinsically disordered proteins (IDPs) bind to their partners. Isothermal titration calorimetry (ITC) is one of the few methods available for completely evaluating the thermodynamic parameters describing a protein-ligand binding event. Significantly, when the effective ΔH° for the coupled folding and binding process is determined by ITC in a temperature series, the constant-pressure heat capacity change (ΔCp) associated with these coupled equilibria is experimentally accessible, offering a unique opportunity to investigate the driving forces behind them. Notably, each of these molecular-scale events is often accompanied by strongly temperature-dependent enthalpy changes, even over the narrow temperature range experimentally accessible for biomolecules, making single temperature determinations of ΔH° less informative than typically assumed. Here, we will document the procedures we have adopted in our laboratory for designing, executing, and globally analyzing temperature-dependent ITC studies of coupled folding and binding in IDP interactions. As a biologically significant example, our recent evaluation of temperature-dependent interactions between the disordered tail of FCP1 and the winged-helix domain from Rap74 will be presented. Emphasis will be placed on the use of publically available analysis programs written in MATLAB that facilitate quantification of the thermodynamic forces governing IDP interactions. Although motivated from the perspective of IDPs, the experimental design principles and data fitting procedures presented here are general to the study of most noncooperative ligand binding equilibria.

Nonadditivity of Temperature Dependent Interactions in Inorganic Ionic Clusters

Nonadditivity of interactions implies, in the chemical context, that binding of atoms cannot be fully predicted from interactions between atom pairs. This phenomenon determines the identity of our world, which would have been much poorer otherwise. Ionic systems provide a good example of the interaction nonadditivity, which arises in most cases due to electron transfer and delocalization effects. Using Born–Oppenheimer molecular dynamics simulations of LiCl, NaCl, and KCl at 300, 1500, and 2000 K, we show that interaction nonadditivity originates from interplay of thermal motion and cation nature. In the case of alkali cations, ionic nature plays a more significant role than thermal effects. The nonadditivity is significant in all systems and at all temperatures considered. Dipole moments increase at higher temperatures due to thermal fluctuations and thermal expansion of the clusters. At the same time, ionic charges change little. Our results contribute to the fundamental understanding of electronic effects in nanoscale and condensed phase ionic systems, and foster progress in physical chemistry and engineering.

Ultrafast core-loss spectroscopy in four-dimensional electron microscopy.

We demonstrate ultrafast core-electron energy-loss spectroscopy in four-dimensional electron microscopy as an element-specific probe of nanoscale dynamics. We apply it to the study of photoexcited graphite with femtosecond and nanosecond resolutions. The transient core-loss spectra, in combination with ab initio molecular dynamics simulations, reveal the elongation of the carbon-carbon bonds, even though the overall behavior is a contraction of the crystal lattice. A prompt energy-gap shrinkage is observed on the picosecond time scale, which is caused by local bond length elongation and the direct renormalization of band energies due to temperature-dependent electron–phonon interactions.

The temperature dependence of atomic incorporation characteristics in growing GaInNAs films

We have systematically studied the temperature dependence of incorporation characteristics of nitrogen (N) and indium (In) in growing GaInNAs films. With the implementation of Monte-Carlo simulation, the low N adsorption energy (−0.10 eV) is demonstrated. To understand the atomic incorporation mechanism, temperature dependence of interactions between Group-III and V elements are subsequently discussed. We find that the In incorporation behaviors rather than that of N are more sensitive to the Tg, which can be experimentally verified by exploring the compositional modulation and structural changes of the GaInNAs films by means of high-resolution X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, and secondary ion mass spectroscopy.

Effect of temperature on the interactions between low bandgap polymer and ionic liquids

Abstract In this paper, we have examined the effect of temperature on the interactions between imidazolium and ammonium based ionic liquids (ILs) and the low bandgap polymer (poly(2-heptadecyl-4-vinylthieno[3,4-d]thiazole) (PHVTT)). With the aim of exploring the utility of low bandgap polymers, we have carried out the interaction studies of the polymer with the ILs and investigated the behavior of polymer in the presence of ILs as the function of temperature. Recently, ILs have attracted extensive attention in polymer sciences. In this work, we have studied the temperature dependent interactions between the protic IL (1-methylimidazolium chloride ([Mim]Cl) from imidazolium family) and aprotic ILs (tributylmethylammonium methyl sulfate ([N1444][MeSO4]) from ammonium family and 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) from imidazolium family) with a low bandgap polymer. Our experimental data of UV–vis spectroscopy, photoluminescence (PL) spectroscopy, FT-IR spectroscopy, density (ρ) and speed of sound (u) as a function of temperature from 25 to 40 °C with the interval of 5 °C, clearly reveal that even at high temperature, [Bmim]Cl interacts strongly with the polymer as compared to other studied ILs.

Selective Turn-On Ammonia Sensing Enabled by High-Temperature Fluorescence in Metal–Organic Frameworks with Open Metal Sites

We show that fluorescent molecules incorporated as ligands in rigid, porous metal-organic frameworks (MOFs) maintain their fluorescence response to a much higher temperature than in molecular crystals. The remarkable high-temperature ligand-based fluorescence, demonstrated here with tetraphenylethylene- and dihydroxyterephthalate-based linkers, is essential for enabling selective and rapid detection of analytes in the gas phase. Both Zn2(TCPE) (TCPE = tetrakis(4-carboxyphenyl)ethylene) and Mg(H2DHBDC) (H2DHBDC(2-) = 2,5-dihydroxybenzene-1,4-dicarboxylate) function as selective sensors for ammonia at 100 °C, although neither shows NH3 selectivity at room temperature. Variable-temperature diffuse-reflectance infrared spectroscopy, fluorescence spectroscopy, and X-ray crystallography are coupled with density-functional calculations to interrogate the temperature-dependent guest-framework interactions and the preferential analyte binding in each material. These results describe a heretofore unrecognized, yet potentially general property of many rigid, fluorescent MOFs and portend new applications for these materials in selective sensors, with selectivity profiles that can be tuned as a function of temperature.