Melting Temperature Depression Research Articles

Influence of water of crystallization on the ternary phase behavior of a drug and deep eutectic solvent

Deep eutectic solvents (DESs) are mixtures of two solid components that interact via hydrogen bonds causing a large melting temperature depression. DESs are promising drug carriers and solvents for drugs with poor aqueous solubility. The presence of water within DESs is reported to change physicochemical properties, which could influence molecular interactions with drugs. It is therefore essential to study the influence of water of crystallization within one of the DES components on the drug loading capacity. In this study the influence of water of crystallization on the properties of two DESs containing xylitol and betaine anhydrate or monohydrate was investigated. Furthermore, the binary and ternary phase diagrams as well as the interplay between acetylsalicylic acid and the DES components were characterized to identify the maximum drug loading and elucidate the solvation mechanism. The presence of water of crystallization did not change the phase behavior of the binary DES, which had a eutectic melting temperature of 35–36 °C. Betaine anhydrate and acetylsalicylic acid formed a co-crystal after ball milling for 5 min with a melting temperature of 78 °C. Betaine monohydrate and acetylsalicylic acid formed a eutectic mixture with a melting temperature of 35 °C. Due to different interactions between the two crystal forms of betaine, the ternary phase behavior was significantly influenced by water of crystallization. The highest drug loading for the betaine anhydrate containing DES was 10 n/n% and was found at the eutectic composition of the DES. For the betaine monohydrate containing DES, the highest drug loading was 39 n/n% at a non-eutectic composition of the DES. These results demonstrated the importance of investigating the ternary phase behavior and influence of water of crystallization.

Pani‐Ag/PVA nanocomposite: Gamma induced changes in the thermal and optical characteristics

AbstractThe gamma (γ) induced modifications in the synthesized Pani‐Ag/PVA nanocomposite (NCP) thermal and optical characteristics have been depicted. The induced effect was investigated applying X‐ray diffraction, differential scanning calorimetry, and UV‐spectroscopy. Further, the color intensity (ΔE) of the irradiated NCP and blank has been estimated. The γ radiation decreases the optical band gap value from 2.65 to 1.54 eV owing to the randomly amorphous dominance in the irradiated NCP. Moreover, γ radiation induced noticeable defects generation, splitting the crystals, leading to depressed melting temperature.

Phase Behavior of Carbon Dioxide and Polyhedral Oligomeric Silsesquioxanes with Two Different Functional Groups

Phase behavior of carbon dioxide and polyhedral oligomeric silsesquioxanes (POSS) modified with two different functional groups is studied in the temperature range of 308-323 K, up to 22 MPa. Different than the common types, one of the eight functional groups attached to the Si atoms of these POSS is a CO2-philic functional group, methacryl, while the rest are branched alkyl chains, either isooctyl (MIOPOSS) or isobutyl (MIBPOSS). Methacrylisobutyl POSS-CO2 binary system exhibits pressure-induced melting temperature depression. Both molecules have higher solubilities in scCO2 compared to their counterparts with single type of functionality, octaisobutyl POSS, isooctyl POSS and methacryl POSS. The measured highest solubility of MIBPOSS is 0.006 mole fraction at 323 K and 16.8 MPa, while it is 0.0017 mole fraction at 323 K and 22.1 MPa for MIOPOSS. Various density-based semi-empirical models used to model the solubility data gave good correlations with AARD of about 4%.

Melting behaviour of tri-phasic Bi44In32Sn23 alloy nanoparticle embedded in icosahedral quasicrystalline matrix

Tri-phasic nanoscaled (Bi,In,Sn) alloy nanoparticles (NPs) embedded in the icosahedral quasicrystalline (IQC) matrix were synthesized by the rapid solidification route. The microstructure of the NPs was analyzed using transmission electron microscopy (TEM), which typically reveals the combination of three phases; rhombohedral (Bi), body-centered tetragonal BiIn and hexagonal (γ-Sn) in each NP. TEM study also indicates that (Bi) and BiIn bear a reasonably good lattice match with surrounding IQC, whereas (γ-Sn) does not develop any specific orientation relationship. In order to understand the melting behavior of tri-phasic NPs, extensive DSC (differential scanning calorimetry), in-situ TEM (transmission electron microscopy) and in-situ XRD (X-ray diffraction) has been carried out. The DSC result reveals substantial depression of melting temperature (∼20 °C) as compared to bulk. In-situ studies also indicate the solid-state transformation of (γ-Sn) into (β-Sn) prior to melting. As the temperature advances, melting initiates at the triple junction of (Bi)/BiIn and matrix. BiIn first melts completely, and the melt front grows into the (β-Sn) phase of the NP. Subsequently, the melt propagates into the interior of (Bi) rich region. The present study provides an insight into the formation of non-equilibrium (γ-Sn) phase instead of (β-Sn) and the mechanism of the melting behaviour of three-phase NP embedded in IQC.

Melting temperature depression due to the electronic spin transition of iron

AbstractThe electronic spin transition of iron has been shown to strongly affect many thermoelastic properties of the host mineral. However, the response of melting temperatures to the spin transition remains largely unexplored. Here, we study the melting of lower mantle minerals, ferropericlase and bridgmanite, using Lindemann's Law. This empirical law predicts a negligible melting temperature depression for Earth-relevant bridgmanite but a substantial depression for Earth-relevant ferropericlase across the spin transition of iron, consistent with extant experimental results. This melting depression can be explained within the framework of Lindemann's Law for a Debye-like solid. The transition of iron from high- to low-spin configuration reduces the molar volume and the bulk modulus of the crystal, leading to a decrease in Debye frequency and consequently lowering the melting temperature. Thermodynamically, the melting depression likely derives from a more negative Margules parameter for a liquid mixture of high- and low-spin end-members as compared to that of a solid mixture. This melting depression across the spin transition of iron may be the process responsible for the formation of a deep molten layer during the crystallization of a magma ocean in the past, and a reduced viscosity layer at present.

Melting curve of iron to 290 GPa determined in a resistance-heated diamond-anvil cell

The Earth's core is composed mainly of iron. Since the liquid core coexists with solid at the inner core boundary (ICB), the melting point of iron at 330 GPa offers a key constraint on core temperatures. However, previous results using a laser-heated diamond-anvil cell (DAC) have been largely inconsistent with each other, likely because of an intrinsic large temperature gradient and its temporal fluctuation. Here we employed an internal-resistance-heated DAC and determined the melting temperature of pure iron up to 290 GPa, for the first time above 200 GPa by static compression experiments. A small extrapolation of the present experimental results yields a melting point of 5500 ± 220 K at the ICB, higher than 4850 ± 200 K reported by previous laser-heated DAC by Boehler (1993) but is lower than 6230 ± 500 K by Anzellini et al. (2013). Accounting for the melting temperature depression due to core-alloying elements, the upper bounds for the temperature at the ICB and the core–mantle boundary (CMB) are estimated to be 5120 ± 390 K and 3760 ± 290 K, respectively. Such low present-day CMB temperature suggests that the lowermost mantle has avoided global melting, at least since early Proterozoic Eon.

Hydrophobic eutectic mixtures as volatile fatty acid extractants

Organic waste streams can be converted into volatile fatty acids (VFAs) via fermentation. VFAs can be used as intermediates in the synthesis of added-value chemicals. In this work, hydrophobic eutectic mixtures were designed for the liquid-liquid extraction of VFAs from dilute aqueous solutions. The eutectic behaviour was screened for over 100 combinations of 16 hydrophobic components that were selected based on a set of predetermined criteria. Mixtures of dihexylthiourea and trioctylphosphine oxide (TOPO) showed the best extraction performance and were stable over a wide pH range. The extraction efficiency increased with increasing hydrophobicity of the VFAs, and only undissociated acids were extracted. Upon increasing the TOPO content of the eutectic mixture, the extraction performance could be improved, confirming the tuneable nature of eutectic solvents. However, the extraction performance was less than that for solutions of TOPO in hydrophobic solvents, even though mole fractions of TOPO were higher in the eutectic mixtures. It was hypothesized that the intermolecular VFA–TOPO interactions required for extraction are suppressed by the inter-component interactions in the eutectic mixture. The inter-component interactions are responsible for the negative deviation from ideality of the melting temperature depressions that extend the liquid window of the mixtures towards the extraction temperature. Hence, the design of novel hydrophobic extractants based on eutectic mixtures was demonstrated. Their performance might be improved by selecting counterparts that interfere less with the interactions required for VFA extraction.

Development of poly(ε‐caprolactone)/pine resin blends: Study of thermal, mechanical, and antimicrobial properties

Blends of poly(ε‐caprolactone) (PCL) with pine resin, an extract from the plant Pinus caribaea—Hondurensis was prepared by melt mixing in mass ratios from 90/10 to 50/50. The thermal, crystallization, morphological, and mechanical properties of the blends were studied by differential scanning calorimetry, Fourier transform infrared spectroscopy, polarized optical microscopy, scanning electron microscopy, and tensile test. Enzymatic degradation of the blends was investigated using porcine pancreatic and Candida rugosa lipase. Antimicrobial activity of the blends was tested against four strains of bacteria; Staphylococcus aureas, Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa using the zone inhibition method. Miscibility of the blends was confirmed by the depression in the equilibrium melting temperature () of PCL estimated from Hoffman–Weeks plot and the presence of extinction rings in the spherulites of blended PCL. Interactions between the two components involved the carbonyl and the C‐O‐C groups. The tensile strength of the blends with low pine resin content was comparable to PCL but decreased with higher pine gum content. Enzymatic degradation of the blends increased with increasing pine resin content. The blends showed antimicrobial property with all the bacteria except E. coli. The developed biomaterial shows promising candidacy in medical applications. POLYM. ENG. SCI., 59:E32–E41, 2019. © 2018 Society of Plastics Engineers

Molecular Structure and Crystallization Dynamics of Poly(3-hydroxyl alkanoate) with Medium-Chain Length Biosynthesized from Pseudomonas putida

The molecular structure of poly(3-hydroxyalkanoate) (P3HA) with medium-chain length, biosynthesized from Psuedomonas putida (P. putida), was investigated by thermal analysis, X-ray diffraction, and infrared spectrum. Cultivation in a medium of nonanoic acid and a mixed substrate of nonanoic acid and glycerin as carbon sources provided P3HA with monomer units of 7 and 9 carbons (P3HAn) and 5, 6, 7, 8, 9, and 10 carbons (P3HAmix). Since these P3HA has comparatively long side chains, the crystallinity was as low as about 10%. It was suggested that the hydrogen bonding plays an important role in constructing the crystal. The lamellar thickness was 1.20 nm, estimated from the melting temperature depression. This lamellar thickness corresponds to two repeating units. Crystallinity depending on time was observed by the CO stretching mode in the infrared spectrum, and then Avrami’s theory was applied to analyze the crystallization mechanism. The crystallization rate of P3HAn was very low, on the order of a few hours. An Avrami exponent of 1.45 was estimated from the slope of the Avrami plot. This shows that the conformational arrangement is presumably promoted along the chain axis. The slow crystallization is attributed to the long side chain, which prevents aggregation of the polymer chains.

The Role of Polyfunctionality in the Formation of [Ch]Cl-Carboxylic Acid-Based Deep Eutectic Solvents

Aiming at providing an extensive characterization of the solid–liquid equilibria (SLE) of deep eutectic solvents (DESs), the phase diagrams of nine eutectic mixtures composed of choline chloride ([Ch]Cl) and (poly)carboxylic acids, commonly reported in the literature as DESs, were measured experimentally. Contrarily to the behavior reported for eutectic mixtures composed of [Ch]Cl (hydrogen-bond acceptor, HBA) and monofunctional hydrogen-bond donors (HBD) such as fatty acids and fatty alcohols, which have recently been shown to be almost ideal mixtures, a significant decrease of the melting temperature, at the eutectic point, was observed for most of the systems studied. This melting temperature depression was attributed to a pronounced nonideality of the liquid phase induced by the strong hydrogen-bond interactions between the two mixture components. Perturbed-chain statistical associating fluid theory (PC-SAFT) was used to describe these interactions physically. PC-SAFT allowed accurately modeling the e...

Impact of Molecular Weight on the Thermal Stability and the Miscibility of Poly(ε-caprolactone)/Polystyrene Binary Blends

Poly(e-caprolactone) (PCL) and two different molecular weight (6K and 650K) of polystyrene (PS) were mixed in solution to prepare binary blends of PCL/PS with various compositions. The impact of the molecular weight of PS in the blends was studied on thermal stability and miscibility by the thermogravimetric analysis (TGA) and the differential scanning calorimetry (DSC) method. The TGA results under dynamic conditions in an inert atmosphere show that the thermal stability of the blends depends on the length of PS molecules. The increase of the low molecular weight PS into the PCL/PS blend reduces the thermal stability while the high molecular weight PS improves the thermal stability. The crystallization peak temperature, enthalpy, and crystallinity of the blends are found molecular weight dependent; these parameters with blend compositions deviate from linearity of additive law for low molecular weight PS, while they do follow the additive law for high molecular weight PS. A significant melting point depression of PCL crystals with composition was observed for the blends with the incorporation of the low molecular weight PS, while the no significant melting temperature depression was observed for the high molecular weight PS. The experimental results clearly indicate that in the PCL/PS blends, the thermal stability and the interaction between the neat components strongly depend on the molecular weight of the PS.

Effect of Pore Size Distribution on Dissociation Temperature Depression and Phase Boundary Shift of Gas Hydrate in Various Fine-Grained Sediments

Capillarity in small, confined pores has a pronounced effect on the depression of the dissociation temperature of gas hydrates, known as the Gibbs–Thomson effect. However, this effect remains poorly understood in natural fine-grained sediments with wide pore size distributions. This study investigated the effect of pore size distributions of fine-grained sediments on the dissociation temperature of a gas hydrate. A gas hydrate was synthesized under partially water-saturated conditions in nanosized silica gels and in various natural fine-grained sediment samples, including sand, silt, diatoms, a diatom–sand mixture, and clayey sediment. The synthesized hydrate samples were thermally dissociated under isochoric conditions, while the melting temperature depression and the shifted phase boundaries were monitored. We observed a dissociation temperature depression of approximately 0.1–0.3 °C in silt, 0.2–0.4 °C in the diatom sample, and 1.2–1.5 °C in clayey silt, while no temperature depression was observed in ...

Engineered Cellular Uptake and Controlled Drug Delivery Using Two Dimensional Nanoparticle and Polymer for Cancer Treatment.

Two major problems in chemotherapy, poor bioavailability of hydrophobic anticancer drug and its adverse side effects causing nausea, are taken into account by developing a sustained drug release vehicle along with enhanced bioavailability using two-dimensional layered double hydroxides (LDHs) with appropriate surface charge and its subsequent embedment in polymer matrix. A model hydrophobic anticancer drug, raloxifene hydrochloride (RH), is intercalated into a series of zinc iron LDHs with varying anion charge densities using an ion exchange technique. To achieve significant sustained delivery, drug-intercalated LDH is embedded in poly(ε-caprolactone) (PCL) matrix to develop intravenous administration and to improve the therapeutic index of the drug. The cause of sustained release is visualized from the strong interaction between LDH and drug, as measured through spectroscopic techniques, like X-ray photoelectron spectroscopy, infrared, UV-visible spectroscopy, and thermal measurement (depression of melting temperature and considerable reduction in heat of fusion), using differential scanning calorimeter, followed by delayed diffusion of drug from polymer matrix. Interestingly, polymer nanohybrid exhibits long-term and excellent in vitro antitumor efficacy as opposed to pure drug or drug-intercalated LDH or only drug embedded PCL (conventional drug delivery vehicle) as evident from cell viability and cell adhesion experiments prompting a model depicting greater killing efficiency (cellular uptake) of the delivery vehicle (polymer nanohybrid) controlled by its better cell adhesion as noticed through cellular uptake after tagging of fluorescence rhodamine B separately to drug and LDH. In vivo studies also confirm the sustained release of drug in the bloodstream of albino rats using polymer nanohybrid (novel drug delivery vehicle) along with a healthy liver vis-à-vis burst release using pure drug/drug-intercalated LDHs with considerable damaged liver.

Multiple Thermal Gelation of Hydroxypropyl Methylcellulose and Kappa-Carrageenan Solutions and their Interaction with Salts

The multiple gelation behavior of aqueous solutions of kappa-carrageenan (KCG) and low molecular weight hydroxypropyl methylcellulose (HPMC) was studied with the presence of various salts. Multiple gelation behavior of aqueous solutions of HPMC/KCG/salt mixture were found. The shear viscosity of HPMC/KCG blend increased by one orders of magnitude, while the viscosity of HPMC/KCG/potassium chloride (KCl) mixture increased by three orders of magnitude as compared to HPMC solution at temperatures below apparent gelation. The dynamic elastic modulus of HPMC/KCG blend increased by two orders of magnitude, while the elastic modulus of HPMC/KCG/potassium chloride (KCl) mixture increased by three orders of magnitude as compared to HPMC solution at temperatures below apparent gelation temperature. The gel elastic modulus of the solution blend of HPMC/KCG/salt mixture decreased in the order of KCl > NaCl > CaCl2. Thermal analysis revealed a linear relationship between the depression of melting temperature and the salt concentrations, which is independent of KCG. The free water content computed by enthalpy data showed that free water content decreased with increasing salt concentrations. The secondary peak which typically associated with bound water appeared in the mixture of HPMC and KCG in the presence of KCl. As the concentrations of KCl salt increased, the bound water peak also amplified and lifted to a higher temperature.

Thermal Control of Confined Crystallization within P3EHT Block Copolymer Microdomains

The local, nanoscale organization of crystallites in conjugated polymers is often critical to determining the charge transport properties of the system. Block copolymer geometries, which offer controlled nanostructures with tethering of chains at interfaces, are an ideal platform to study the local organization of conjugated polymer crystallites. The model conjugated polymer poly(3-(2′-ethyl)hexylthiophene) (P3EHT) features a depressed melting temperature relative to the widely studied poly(3-hexylthiophene) (P3HT), which allows it to robustly form microphase-separated domains that confine the subsequent P3EHT crystallites. Importantly, P3EHT crystallization in confinement is coupled to a rubbery second block via interfacial tethering, mechanical properties, and chain stretching. Here, the impact of thermal processing on the diblock copolymer structure is examined to elucidate the key driving forces controlling the final coupled diblock copolymer and crystalline structures. Surprisingly, the diblock copol...

Molecular simulation and experimental studies of the miscibility of PLA/PLAx-PEGy-PLAx blends

To design a more efficient plasticizer for PLA based on PEG derivative, the miscibility enhancement of PLA/PLAx-PEGy-PLAx blends were investigated by both atomistic and mesoscale simulations. Flory-Huggins interaction parameters (χ ij ) of PLAx-PEGy-PLAx blends, with PLA block fractions = 0.1–0.5, were calculated using molecular dynamic (MD) simulation to determine the miscibility of PLA/PLAx-PEGy-PLAx blends and compared with PLA/PEG blends (Takhulee et al. J Polym Res 24:8, 2017). Based on the calculated χ ij and radial distribution functions, PLA/PLAx-PEGy-PLAx showed better miscibility compared to PLA/PEG. The values of χ ij for PLA/PLAx-PEGy-PLAx blends are always lower than those for PLA/PEG blends at the same PEG composition. For PLA/PLAx-PEGy-PLAx blends, χ ij increased as a function of PLA block fractions. Mesoscale properties of PLA/ PLAx-PEGy-PLAx blends were then determined using dissipative particle dynamic (DPD) simulation. Smaller PEG domain in PLA/PLAx-PEGy-PLAx blends was observed, compared to that in PLA/PEG blend. Miscibility behavior of PLA/PLAx-PEGy-PLAx blends was investigated by experiments at selected conditions based on the simulation results. By differential scanning calorimetry measurements, acceleration of the crystallization of PLA matrix by blending PLAx-PEGy-PLAx was observed. Although PLA/PEG 70/30 (wt/wt) blend was phase separated when slowly cooled from the melt, due to the crystallization of PEG component, this phenomenon was not observed in PLA/PLAx-PEGy-PLAx blends. The melting temperature (T m ) depression of PLA/PLAx-PEGy-PLAx blends was also more pronounced. From dynamic mechanical analysis, the storage (G′) and loss moduli (G′′) curves in terminal region were determined. The slope of G′ curves for PLA/PEG 75/25 and 70/30 (wt/wt) was less than 2 while this deviation was found only at 70/30 (wt/wt) for PLA/PLAx-PEGy-PLAx. These results indicate that PLAx-PEGy-PLAx is better miscible with PLA.

Three-Phase Melting Curves in the Binary System of Carbon Dioxide and Water

Invariant, three-phase melting curves, of ice VI in equilibrium with solid CO2, of ice VII in equilibrium with solid CO2, and of solid CO2 in simultaneous equilibrium with a majority aqueous and a majority CO2 fluid, were explored in the binary system of carbon dioxide and water. Diamond-anvil cells were used to develop pressures of 5 GPa. Water exhibits a large melting temperature depression (73°C less than its pure melting temperature of 253°C at 5 GPa) indicative of large concentrations of CO2 in the aqueous solution. The melting point of water-saturated CO2 does not show a measureable departure from that of the pure system at temperatures lower than ∼200°C and only 10°C at 5 GPa (from 327°C).

Miscibility Study of Poly(Butylene Succinate) and Pine-Gum Blends

Miscibility between poly (butylene succinate) [PBS], a semi-crystalline polymer with a natural gum extracted from the pine tree (Pinus Caribaea – Hondurensis), was investigated in solution cast blends using Differential Scanning Calorimetry [DSC] and Fourier Transform Infrared Spectroscopy [FTIR]. The spherulite morphology of PBS in the blends was observed with polarized optical microscopy [POM]. Depression in the equilibrium melting temperature of PBS in the blends was determined using the Hoffman-Weeks plot method. The depression in the crystallization temperature of the blends with increasing pine gum ratio and the emergence of extinction rings in the spherulites of the blends confirmed the blends to be miscible at the molecular level. Infrared spectroscopy indicated that interactions occurred between the hydroxyl groups of the pine-gum and the carbonyl group of PBS.

Computational perspectives on structure, dynamics, gas sorption, and bio-interactions in deep eutectic solvents

We present a snapshot of the current status of understanding structure, dynamics, and molecular interactions within deep eutectic solvents (DESs) gained from a computational perspective. The simulations reported thus far have been largely aimed at unravelling the relationship between the molecular features within a DES and the depressed melting temperature at its eutectic composition. Computational efforts consistently reveal that the addition of hydrogen bond donors significantly disrupts long-range ordering of the cation–anion arrangement in choline chloride, resulting in significant moderation of the interaction energies between the components of the DES. These studies paint a picture of DES formation being accompanied by hydrogen-bond directed charge transfer processes yielding transient cage-like formation and nanoscale ordering entailing segregation of the ionic and molecular domains. Computational insights further uncover how unique solvation features present within DESs may lead to enhanced biomolecular (e.g., protein, nucleic acid, polysaccharide) stability and/or activity while also offering advantages as environmentally-responsible gas sorbents.

Measurement and PC-SAFT modeling of solid-liquid equilibrium of deep eutectic solvents of quaternary ammonium chlorides and carboxylic acids

In this study the solid-liquid equilibria (SLE) of 15 binary mixtures composed of one of three different symmetrical quaternary ammonium chlorides and one of five different fatty acids were measured. The experimental data obtained showed extreme negative deviations to ideality causing large melting-temperature depressions (up to 300 K) that are characteristic for deep eutectic systems. The experimental data revealed that cross-interactions between quaternary ammonium salt and fatty acid increase with increasing alkyl chain length of the quaternary ammonium chloride and with increasing chain length of the carboxylic acid. The pronounced decrease of melting temperatures in these deep eutectic systems is mainly caused by strong hydrogen-bonding interactions, and thermodynamic modeling required an approach that takes hydrogen bonding into account. Thus, the measured phase diagrams were modeled with perturbed-chain statistical associating fluid theory based on the classical molecular homonuclear approach. The model showed very good agreement with the experimental data using a semi-predictive modeling approach, in which binary interaction parameters between quaternary ammonium chloride and carboxylic acid correlated with chain length of the components. This supports the experimental findings on the phase behavior and interactions present in these systems and it allows estimating eutectic points of such highly non-ideal mixtures.