Eutectic Phase Behavior Research Articles

Phase diagrams and microstructure of mixtures of n-hentriacontane and saturated fatty acids

We determined the phase behavior and microstructure of binary mixtures of n-hentriacontane (C31) and one of three saturated fatty acids (SFA; myristic acid (MA), palmitic acid (PA), or stearic acid (SA)). Phase diagrams were developed through differential scanning calorimetry and X-ray diffraction. The C31/MA, C31/PA, and C31/SA systems all showed eutectic phase behavior. Below the solidus line, these systems consisted of a mechanical mixture of C31 crystals and SFA crystals in the C polymorph, irrespective of the C31/SFA ratio. The C31/SFA eutectic composition increased in C31 content with SFA chain length: XC31 = 0.06, XC31 = 0.37, and XC31 = 0.54 for MA, PA, and SA, respectively. Within specific concentration ranges, small amounts of SFA were incorporated into the C31 crystal lattice. Smaller crystals of C31 and SFA were obtained for mixtures close to the eutectic mixture composition.

Downward Oxidant Transport Through Europa's Ice Shell by Density‐Driven Brine Percolation

AbstractJupiter's moon Europa is thought to have an ocean beneath its ice shell and the habitability of the internal ocean depends on the availability of redox gradients. Downward transport of radiolytic materials produced at the surface through the ice shell sets the flux of oxidants into the ocean. Here, we propose that oxidants are transported through the ice shell by the drainage of near‐surface brines formed concurrently with chaotic terrains. We estimate that Europa's porous regolith contains 3.7 × 1014 to 5.6 × 1018 mol (1.2 × 1013 − 1.8 × 1017 kg) of trapped O2. Simulations of coupled melt‐migration and eutectic phase behavior show that brines drain before they refreeze, delivering ∼85% of the surface oxidants to the ocean on timescales of 2 × 104 years. From the distribution of chaotic terrains and from Europa's surface age we estimate that brine drainage could deliver O2 to the ocean at rates of 2.0 × 106 to 1.3 × 1010 mol/yr (0.002−13.2 kg/s).

Eutectic phase behavior induced by a simple additive contributes to efficient organic solar cells

Introducing a small amount of high boiling point solvent additive has been widely regarded as a feasible method to optimize the active layer morphology of organic solar cells (OSCs). However, current additives are initially developed for fullerene based OSCs and the development of additive engineering is lagging behind the development of non-fullerene acceptor based OSCs. Here, a simple and versatile solid additive, 1,4-diiodobenzene (DIB), is introduced to the non-fullerene OSCs. Due to the formation of a eutectic phase between the additive and the non-fullerene acceptor, a desired microstructure with tighter molecular stacking and more ordered molecular arrangement is achieved. As a result, DIB treated OSCs display significantly enhanced performance with a power conversion efficiency (PCE) of 17.72% for ternary device, 17.36% for binary device and 15.03% for thick-film (300 nm) device. Additional advantages of the DIB treatment include excellent device stability, toleration of a wide additive concentration range, and versatility in both polymer and small molecule OSCs. The results highlight the importance of additive engineering in high-performance OSCs and demonstrate the significance of supramolecular interactions.

Phase diagrams of mixtures of n-hentriacontane and saturated monoacid triacylglycerols

Gelation of vegetable oils with candelilla wax (CW) and saturated triacylglycerols (TAGs) is a promising strategy for engineering fat-based foods, cosmetics, and drug delivery systems. n-hentriacontane (C31) defines, to a large extent, the thermal properties of CW. Therefore, the phase behavior and microstructure of binary mixtures of C31 and trimyristin (MMM), tripalmitin (PPP), or tristearin (SSS) were studied to provide a better understanding of complex mixtures of CW and saturated fats. Phase diagrams were developed by differential scanning calorimetry and X-ray diffraction measurements. The mixtures showed a eutectic phase behavior, in which the C31-TAG mixtures below the solidus line were solid dispersions of crystals rich in C31 and crystals rich in the corresponding TAG. This segregation in the solid phase was attributed to the incompatible subcell-packing of the pure components in the stable polymorphic form, which was orthorhombic for C31, and monoclinic for TAGs in the β-polymorphic form. C31 had a major effect on TAGs microstructure. Morphological changes at the microstructural level were caused by the heterogeneous nucleation of MMM on C31 crystals. Conversely, microstructural changes for TAGs crystals in C31-PPP and C31-SSS mixtures were induced by the inhibition of crystal growth due to the transient adsorption of C31 molecules at the growing crystal surface.

Homocoupling Defects of a Small Donor Molecule for Organic Photovoltaics: Quantification of the Eutectic State Diagram by Rapid Heat–Cool Differential Scanning Calorimetry

The conjugated small donor molecule p-DTS(FBTTh2)2, leading to efficient bulk heterojunction organic photovoltaic devices with PC71BM, shows a eutectic phase behavior in combination with its homoco...

A centrifuge method to determine the solid-liquid phase behavior of eutectic mixtures.

The centrifuge method is a novel, equilibrium-based, analytical procedure that allows the construction of solid-liquid phase diagrams of binary eutectic mixtures. In this paper, the development, optimization, and successful verification of the centrifuge method are described. Contrary to common dynamic analysis techniques-differential scanning calorimetry and hot-stage microscopy-the studied mixtures are equilibrated at constant temperature. Therefore, the mixtures do not need to be recrystallized from the melt during analysis. This offers a great advantage for mixtures that exhibit strong supercooling behavior rather than direct crystallization. The centrifuge method was verified by reproducing the binary eutectic phase behavior of both the nearly ideal biphenyl-bibenzyl system and the strongly non-ideal deep eutectic solvent (DES) urea-choline chloride, which is prone to supercooling. Hence, the centrifuge method offers an alternative route to common dynamic analysis techniques for the quantification of the liquid range of DESs and other binary eutectic mixtures.

Polymorphism and Kinetic Behavior of Binary Mixtures of Trisaturated Triacylglycerols Containing Palmitic and Stearic Acid Under Non‐Isothermal Conditions

The kinetic phase behavior and phase transformation paths of pure tripalmitoylglycerol (PPP), 1‐palmitoyl‐2,3‐distearoyl‐sn‐glycerol (PSS), and 1,3‐dipalmitoyl‐2‐stearoyl‐sn‐glycerol (PSP) and binary mixtures thereof, are investigated at 10.0 °C min−1 (fast cooling) and 1.0 °C min−1 (slow cooling) cooling rates, and further re‐heating at 5.0 and 1.0 °C min−1. Mixtures are studied in terms of polymorphism, crystallization, and melting behavior. Kinetic phase diagrams are determined from DSC heating thermograms and XRD data. Independent of the cooling rate, most samples crystallized in the α‐polymorph and transformed into the more stable β′‐form via melt‐mediated crystallization or direct recrystallization from the α‐phase. Samples containing a high amount of PSP crystallized in the β′‐form at slow cooling rate and samples containing high PPP concentration ultimately transform to the most stable β‐form. The kinetic phase diagram of PPP‐PSS mixtures present an apparently typical eutectic behavior with a eutectic point at XPSS = 0.3, when the samples are melted at the higher heating rate, which shifts to higher concentration, XPSS = 0.5, when the lower heating rate is applied. The eutectic temperature (58.4 ± 0.3 °C) is independent of the cooling and heating rates used. The kinetic phase diagram of PSS‐PSP mixtures display two types of behaviors, a probable monotectic behavior in the most stable phase and a eutectic behavior in the meta‐stable phase when the samples are melted at higher heating rate. This study shows that PSS has a strong effect on the physical properties of PPP‐PSS blends and affects a large part of the phase behavior of this binary system. At lower PSS concentrations, the mixtures transform to the most stable β form, but at increasing PSS concentration, the samples stabilize in the β′‐phase. In the PSS‐PSP binary systems, all the mixtures stabilize in the β′‐phase, which is preferred in many food applications since it is associated with a smooth texture.Practical Applications: This research extends a previous study on the phase behavior of the most common trisaturated triacylglycerols and the results are useful for the food industry as they can help in understanding the functionality of hard fat based structuring agents in end applications, and in developing new triacylglycerol based crystallization and structuring agent for specific food applications.The kinetic phase behavior of trisaturated triacylglycerol containing stearic and palmitic acid were studied under three sets of conditions. The binary systems showed different behaviors at the conditions studied. An apparent eutectic phase behavior was obtained for mixtures containing mono‐acid and symmetric triacylglycerols. However, the samples containing asymmetric triacylglycerols showed a probable monotectic phase behavior in the most stable β′1‐phase.

Semifluorinated alkanes and alkanes: A phase study of the perfluorohexyloctane – Tetradecane system

The binary system perfluorohexyloctane (F6H8)–tetradecane (C14) was investigated in order to increase understanding of interactions of semifluorinated alkanes (SFAs) with hydrophobic molecules. The thermal phase behavior for F6H8 and C14 and their mixtures was determined using DSC. The activity coefficients for both components in the mixtures were calculated and Gibbs energy of mixing was determined. Furthermore, enthalpies of mixing were determined with ITC and structural investigations of the solid and the liquid phases were performed with SAXS and SWAXD. It was found that F6H8 displays one solid-solid transition at −42.3°C (ΔH=1.1kJ/mol) and one solid-liquid transition at −5.9°C (ΔH=16.6kJ/mol). Due to the low enthalpy of the solid-liquid transition it is likely that F6H8 is not fully crystallized in the solid phase but partly amorphous. The F6H8–C14 system displays a eutectic phase behavior and the liquid mixtures display a positive deviation from ideal mixing. C14 crystalizes in a triclinic unit cell as shown before, whereas crystallization of F6H8 in a lamellar rippled phase is shown for the first time. This ripple phase comprises a bilayer of tilted alternating heavily interdigitated F6H8 molecules in an oblique subunit cell.

Random Copolymers from Polyamide 11 and Polyamide 12 by Reactive Extrusion: Synthesis, Eutectic Phase Behavior, and Polymorphism

Random copolymers from polyamide 11 (PA11) and polyamide 12 (PA12) were obtained from the parent homopolymers by transamidation reactions during high-temperature reactive extrusion. Concomitantly, the product molecular weight increased by postcondensation reactions. With both species being crystallizable, eutectic phase behavior was observed and explained in terms of the Flory theory for random copolymer melting. Close to the eutectic composition, both species crystallize in a competitive mode, which induces mesomorphic phase formation. Although the crystal centers most likely remain PA11 or PA12 pure, it is argued that foreign comonomer units might be tolerated at the crystal borders, at least for PA11 crystals. To understand the copolymer crystallization behavior in general, large amounts of rigid amorphous material need to be created alongside the crystallites. Because of their low melting point and since the crystallinity and mechanical performance typical of the parent homopolymers are preserved, ran...

Phase Behavior of Binary Blends of Four Different Waxes

AbstractThe objective of this study was to investigate the phase behavior of binary blends of four waxes—beeswax (BW), paraffin wax (PW), sunflower wax (SFW), and rice bran wax (RBW)—using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Blends of BW/PW, RBW/PW, SFW/PW, SFW/RBW, SFW/BW, and RBW/BW were crystallized in a DSC, and their melting behavior was used to build binary phase diagrams. The microstructure of the crystalline networks formed in these blends was analyzed using PLM. BW/PW, SFW/PW, SFW/BW, and RBW/BW blends showed eutectic phase behavior, while RBW/SFW showed continuous solid solution and the RBW/PW blend showed monotectic behavior. Results from the box‐counting fractal dimension (Db) measurement of crystal morphology showed higher Db values for the 20 and 80 % wax blends, irrespective of crystallization temperature or wax type. Db values of single waxes decrease as temperature increases.

Dealloying Multiphase AgCu Thin Films in Supercritical CO2

Multiphase AgCu thin films were dealloyed using a mixture of hexafluoroacetylacetone (hfacH) and H2O2 dissolved in supercritical CO2. AgCu alloys exhibit eutectic phase behavior, allowing the composition of the two phases to be fixed while varying the average size of the phase domains from 250 to 1000 nm by increasing the annealing temperature. Selective removal of Cu from both phases was observed, and higher concentrations of the etching solution increased the etching rate between 45 and 75 °C, where the reaction exhibited an apparent activation energy of ∼38 kJ/mol. The morphology after dealloying was quantified using the fast Fourier transform power spectrum obtained from electron microscopy images. For phase domains smaller than ∼500 nm, Ag atoms released in the open regions that had been occupied by the Cu-rich phase diffused separately or as clusters to the Ag-rich phase, forming a nanostructured morphology that mimicked the starting microstructure. For larger domains, stable Ag clusters (50 nm diameter) formed in the open regions, because the diffusion limit was reached, yielding an estimate of 4 × 10–12 cm2/s for the surface diffusivity in supercritical CO2.

Second harmonic generation: applications in phase diagram investigations

Second harmonic generation (SHG) is a nonlinear optical effect occurring in crystals with non-centrosymmetric space groups [1]. The second harmonic generation efficiency of a given material depends mainly on (i) the intrinsic crystallographic features of the phase, (ii) the orientation of the crystal(s) (crystallographic axes) with reference to the fundamental beam orientation and polarization, (iii) the crystal size distribution. SHG was formerly proposed as a rapid, reliable and very sensitive test of non-centrosymmetry for powdered crystalline compounds [2] with applications to structure assignments and pre-screening of conglomerates [3]. It was also proposed as an efficient technique for the quantification of a crystalline phase inside an amorphous matrix [4] and, recently, we demonstrated that SHG can be used to assess the structural purity of an organic compound down to the ppm level [5]. Herein we investigate the SHG efficiency of several binary organic powder mixtures (recrystallized from a solvent) exhibiting eutectic phase behavior.

Solubilization of Genistein in Poly(oxyethylene) through Eutectic Crystal Melting

Solid-liquid phase diagrams of binary crystalline blends of genistein with poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG) were established experimentally and theoretically based on the combined Flory-Huggins free energy of liquid-liquid phase separation and the phase field free energy pertaining to crystal solidification. The liquidus lines obtained self-consistently were found to agree well with trends of depressed crystal melting transitions in genistein/PEO and genistein/PEG blends, exhibiting eutectic phase behavior. Of particular importance is the lowering of the eutectic temperature of the genistein/PEO blend by about 60 °C upon switching to the genistein/PEG system. The occurrence of interspecies hydrogen bonding between genistein molecules and both PEO and PEG chains, albeit weak, was noticed by Fourier transform infrared spectroscopy. The improved solubility of genistein in PEG can be attributed not only to lowering of the molecular weight of PEG utilized, but also to its terminal hydroxyl groups. This eutectic melting approach by PEG solvent is sufficiently effective in solubilizing genistein crystals that development of genistein-containing drugs might be feasible for injection and/or oral administration.

Effect of Multiple Adduct Fullerenes on Microstructure and Phase Behavior of P3HT:Fullerene Blend Films for Organic Solar Cells

The bis and tris adducts of [6,6]phenyl-C(61)-butyric acid methyl ester (PCBM) offer lower reduction potentials than PCBM and are therefore expected to offer larger open-circuit voltages and more efficient energy conversion when blended with conjugated polymers in photovoltaic devices in place of PCBM. However, poor photovoltaic device performances are commonly observed when PCBM is replaced with higher-adduct fullerenes. In this work, we use transmission electron microscopy (TEM), steady-state and ultrafast time-resolved photoluminescence spectroscopy (PL), and differential scanning calorimetry (DSC) to probe the microstructural properties of blend films of poly(3-hexylthiophene-2,5-diyl) (P3HT) with the bis and tris adducts of PCBM. TEM and PL indicate that, in as-spun blend films, fullerenes become less soluble in P3HT as the number of adducts increases. PL indicates that upon annealing crystallization leads to phase separation in P3HT:PCBM samples only. DSC studies indicate that the interactions between P3HT and the fullerene become weaker with higher-adduct fullerenes and that all systems exhibit eutectic phase behavior with a eutectic composition being shifted to higher molar fullerene content for higher-adduct fullerenes. We propose two different mechanisms of microstructure development for PCBM and higher-adduct fullerenes. P3HT:PCBM blends, phase segregation is the result of crystallization of either one or both components and is facilitated by thermal treatments. In contrast, for blends containing higher adducts, the phase separation is due to a partial demixing of the amorphous phases. We rationalize the lower photocurrent generation by the higher-adduct fullerene blends in terms of film microstructure.

Polymer-enforced crystallization of a eutectic binary hard sphere mixture

We prepared a buoyancy matched binary mixture of polydisperse polystyrene microgel spheres of size ratio Γ = 0.785 at a volume fraction of Φ = 0.567 just below the kinetic glass transition. In line with theoretical expectations, a eutectic phase behaviour was observed, but only a minor fraction of the samples crystallized at all. By adding a short non-adsorbing polymer we enforce inter-species fractionation into coexisting pure component crystals, which in turn also shows signs of intra-species fractionation. We show that in formerly inaccessible regions of the phase diagram binary hard sphere physics are made observable using attractive hard spheres.

In-Situ Monitoring of the Solid-State Microstructure Evolution of Polymer:Fullerene Blend Films Using Field-Effect Transistors

Organic field-effect transistors (OFETs) are used to investigate the evolution of the solid-state microstructure of blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) upon annealing. Changes in the measured field-effect mobility of holes and electrons are shown to reveal relevant information about the phase-segregation in this system, which are in agreement with a eutectic phase behavior. Using dual-gate OFETs and in-situ measurements, it is demonstrated that the spatial- and time-dependence of microstructural changes in such polymer:fullerene blend films can also be probed. A percolation-theory-based simulation is carried out to illustrate how phase-segregation in this system is expected to lead to a substantial decrease in the electron conductivity in an OFET channel, in qualitative agreement with experimental results.

The effect of NaCl on the eutectic phase behavior of aqueous poly(ethylene glycol) solutions

The phase behaviors of aqueous polymer solutions are known to be affected by the presence of ions even if the polymer itself does not have any charges. We studied the effect of salt (sodium chloride) on the eutectic phase behavior of non-ionic polymer, poly(ethylene glycol) (PEG) in aqueous solutions using differential scanning calorimetry. We observed that the addition of NaCl increased the liquidus temperature of PEG and decreased that of water. As a result, a steep rise (or fall) is induced in the liquidus around the eutectic point. A simple Flory–Huggins lattice model for the mixture (PEG–water–NaCl) was applied to the experimental results. The model quantitatively reproduced the change in the liquidus both with and without NaCl. The obtained interaction parameters suggest that the increase of the PEG melting temperature by NaCl can be understood as the depletion of NaCl around PEG, possibly due to the image charge repulsion.

Binary Organic Photovoltaic Blends: A Simple Rationale for Optimum Compositions

Polymer/small molecule binaries, such as P3HT:PC61BM display eutectic phase behavior with optimum photovoltaic performance at slightly hypoeutectic compositions (with respect to polymer content). Such hypoeutectic blends readily solidify into a finely phase-separated matrix surrounding primary crystals of the small-molecular species. The resulting large interfacial area and component connectivity is a desirable microstructure for bulk-heterojunction solar cells.

Dissolution enhancement of the anti-HIV drug UC 781 by formulation in a ternary solid dispersion with TPGS 1000 and Eudragit E100

The present research deals with the improvement of the dissolution properties of the anti-HIV drug UC 781. A ternary solid dispersion consisting of a high amount of TPGS 1000 and exhibiting good powder properties with respect to flowability was developed. Eudragit E100 was selected as a polymer based on supersaturation studies. DSC analysis of solid dispersions containing drug doses from 0 to 80% w/w revealed eutectic phase behaviour of the ternary TPGS 100–Eudragit E100–UC 781 mixture. The release of UC 781 in a medium simulating the gastrointestinal lumen was markedly enhanced, reaching a release of 70% w/w after 4 h. XRD results pointed to the presence of crystalline drug in the solid dispersion. The presence of UC 781 in the dispersion had an influence on the TPGS 1000–Eudragit E100 carrier, favoring folding of the polyethylene glycol chains in TPGS 1000. Moreover, the addition of UC 781 to the binary polymer–surfactant mixture was physically expressed by an increase in fluidity of the samples up to a drug load of 50% w/w. NMR was used to investigate this phenomenon, revealing a shielding and/or deshielding effect of the carrier on aromatic C atoms and methyl groups in UC 781. Polyethylene glycol chains present in TPGS 1000 seemed to play a role in this process. In addition, combining UC 781 with the TPGS 1000–Eudragit E100 mixture led to the appearance of TPGS 1000 clusters with a glass transition temperature well below the T g’s of the pure compounds.

Free flowing solid dispersions of the anti-HIV drug UC 781 with Poloxamer 407 and a maximum amount of TPGS 1000: Investigating the relationship between physicochemical characteristics and dissolution behaviour

Solid dispersions and physical mixtures made up of the poorly water-soluble drug UC 781, a polymer and a surfactant were prepared to contribute to the understanding of the relationship between physicochemical characteristics and dissolution behaviour. In addition, to facilitate downstream processing while still favouring drug dissolution to a maximum extent, formulation conditions were investigated to obtain a free flowing powder which contains a maximum amount of surfactant. Poloxamer 407, a polyethylene–polypropylene glycol block copolymer, was selected as a suitable polymer based on UC 781 supersaturation results. d-Alpha-tocopheryl polyethyleneglycol succinate 1000 (TPGS 1000) was preferred as a surfactant since it increased UC 781 dissolution when formulated in a self-micro emulsifying drug delivery system (SMEDDS), as compared to TPGS 400, TPGS 4000 and TPGS 6000. Based on flow properties, a TPGS 1000/Poloxamer 407 ratio of 80/20 was used to prepare solid dispersions by spray drying. Pure drugs, physical mixtures and solid dispersions were characterized by differential scanning calorimetry and X-ray powder diffraction. Eutectic phase behaviour was obtained in which the relative distribution of the polyethylene glycol folding was dependent on UC 781 concentration. Drug release was markedly increased when formulated as a solid dispersion with Poloxamer 407 and TPGS 1000. Formulation of solid dispersions did however not further improve the drug dissolution rate compared to that of physical mixtures. Nonetheless, variability of dissolution results was considerably reduced upon solid dispersion formulation.