Melt Crystallization Research Articles

Influence of low contents of cellulose nanocrystals on the crystallization behavior of biobased Poly(propylene 2,5-furandicarboxylate)

To address the slow crystallization problem of poly(propylene 2,5-furandicarboxylate) (PPF), fully biobased PPF/cellulose nanocrystals (CNC) composites were prepared via a solution and casting method in this work at low CNC contents. The influence of CNC on the crystallization of PPF was studied in detail under various conditions, including nonisothermal and isothermal melt crystallization as well as nonisothermal and isothermal cold crystallization. The results revealed that the crystallization of PPF was enhanced under various crystallization conditions by CNC due to the heterogeneous nucleating agent role. From the isothermal crystallization kinetics study, the presence of CNC did not alter the crystallization mechanism of PPF. In addition, the thermogravimetric analysis results showed that both PPF and PPF/CNC composites displayed an excellent thermal stability. On the basis of the wide angle X-ray diffraction study, CNC did not change the crystal structure of PPF.

Melt crystallization and thermal degradation profile of the antichagasic drug nifurtimox

Despite nifurtimox (NFX) being a traditional drug for treating Chagas disease, some of its physicochemical properties are still unknown, especially its thermal behavior, which brings important outcomes regarding stability and compatibility. In this work, a comprehensive study of NFX’s thermal properties was conducted to assist incremental innovations that can improve the efficacy of this drug in novel pharmaceutical products. For this purpose, thermal analyses associated with spectroscopy and spectrometry techniques were used. DSC analyses revealed that the melt crystallization of the NFX led to its amorphous form with the possible formation of a minor fraction of a different crystalline phase. Coats-Redfern method using TGA results indicated the activation energy of NFX non-isothermal degradation as 348.8 ± 8.2 kJ mol−1, which coincides with the C-NO2 bond dissociation energy of the 2-nitrofuran. Investigation of the isothermal degradation kinetics using FTIR 2D COS showed the possible detachment of radical NO2 and ethylene from the NFX structure, which could affect its mechanism of action. A preliminary mechanism for the thermal degradation of this drug was also proposed. The results enhanced the understanding of NFX's thermal properties, providing valuable insights, especially for developing NFX-based pharmaceutical products that involve thermal processing.

Trace element partitioning in strongly peraluminous rare-metal silicic magmas – Implications for fractionation processes and for the origin of the Macusani Volcanics (SE Peru)

The Macusani Volcanics and related rocks (SE Peru) are well known examples of erupted strongly peraluminous rare-metal rich silicic magmas. We used the phenocryst/matrix glass method to determine relevant mineral/melt partition coefficients to facilitate modeling of such systems. Concentrations of trace (Li, Be, B, Al, P, Ti, Mn, Zn, Ge, Rb, Sr, Zr, Nb, Sn, Cs, Ba, La, Sm, Eu, Gd, Yb, Ta, W, Pb and U) and major elements were measured in obsidians, matrix glasses, glass inclusions, phenocrysts and phases from biotite reaction zones by Laser-Ablation ICP-MS and Electron Microprobe Analysis. The derived phenocryst/melt partition coefficients for quartz, plagioclase, sanidine, biotite, muscovite, andalusite and ilmenite are compared with values from reference silicic magmas and literature. Mineral/biotite partition coefficients are calculated for tourmaline and hercynite. The database is then applied to model chemical fractionation in Macusani magmas. Fractional crystallization and partial melting trends (with the B concentration used as a proxy for the fraction of residual liquid) generate progressively more evolved (higher Rb, Nb, Sn, Cs and Ta and lower Sr, Ba and Pb) residual liquids. The trace element concentrations in obsidians are reproduced for 50–70% crystallization of matrix glasses from ash-flow tuffs. This demonstrates that differentiation of magmas parental to the ash-flow tuffs can generate the highly evolved obsidian-forming liquids. Based on this, we present an updated model for crustal melting and the generation of the Macusani magmas. A metapelitic component dominates the source region but calcic plagioclase cores enriched in Sr, Ba and La suggest an affiliation with mafic magmas, which were likely potassic to ultrapotassic. The presence of a mafic component is consistent with the high heat fluxes in the source region and accounts for specific magmatic variables (i.e., middle crustal anatectic zone, very reducing fO2, high F). Petrogenetic processes differ significantly between Macusani Volcanics suites and two-mica leucogranites despite both having nearly identical source rocks, mineral assemblages and compositions.

Deep segregation and crystallization of ultra-depleted melts in the sub-ridge mantle

Partial melting of mantle peridotite from which considerable amounts of melt have been extracted during prior melting episodes generates melts characterized by low incompatible element contents and very low ratios of highly to moderately incompatible elements, so-called ‘ultra-depleted’ melts. Reaction of peridotite with percolating ultra-depleted melts has been inferred from petrological-geochemical studies of abyssal peridotites and ophiolites. But so far, direct evidence for the existence of ultra-depleted melts, only comes from rare melt inclusions. Here, we show that a pyroxenite layer within abyssal peridotite from the Mid Atlantic Ridge (8°N, Doldrums Fracture Zone) formed by crystallization of a segregated melt that is highly depleted in incompatible elements, at >27 km-depth beneath the ridge axis (at T ∼ 1250 °C), and with little or no modification by interaction with the host harzburgite. During exhumation, the pyroxenite experienced decompression and partial re-equilibration under plagioclase-facies conditions (∼1060 °C and ∼ 15 km depth). The high Hf isotope ratio (εHf = 40.3) of the pyroxenite clinopyroxene is inherited from a melt sourced from an ultra-depleted peridotite that evolved with high Lu/Hf. The associated MORB-like Nd isotope ratios (εNd = 10.6), however, imply a long-term evolution of the source peridotite with composition moderately depleted in incompatible elements (rather low Sm/Nd). These compositions are different from the host harzburgite, but typical for peridotites that have melted and partially reacted with migrating melts in ancient times. Hence, the pyroxenite investigated here is a partial melt from an ultra-depleted peridotite that has become re-enriched in incompatible elements and clinopyroxene. This melt crystallized in the oceanic lithosphere, and partially re-equilibrated at low pressure during exhumation. Overall, our results show that renewed melting of ultra-depleted peridotites with a complex history of prior melting and melt-rock reaction occurs, and that such melts migrate through the sub-ridge mantle, and can thus contribute to mid ocean ridge magmatism, although to a still unknown extent.

Paleovolcanism of the eastern Magnitogorsk megazone, Southern Urals: Petrology, geochemistry, and gold-bearing perspectives

The geological-petrographic and petrogeochemical features of volcanic rocks are considered of the Gumbeika zone in the Southern Urals, that is the frontal easternmost portion of the East Magnitogorsk paleo-island arc. The volcanites are united into the Gumbeika volcanic association. The association is shown to be represented by the basalt– andesite–dacite–rhyodacite “uninterrupted” homodrom igneous series. The compositional features of the volcanics allow confident assigning them to the island-arc calc-alkaline series, or more precisely, to formations of “developed” island arcs. It is concluded that the main process that determines the general appearance and composition of the unified petrogenetic series of rocks of the Gumbeika association was the fractional crystallization of the parental basaltic melts in deep-seated chambers and, then, in near-surface peripheral ones. The emplacement of some of the magmatic bodies was also accompanied by in situ gravitational differentiation. The general similarity of the volcanics-associated gold-silver deposits with the analogs within recent island arcs allows us to suggest a great perspectives for gold-silver mineralization throughout the Gumbeika zone. Two forecasted ore fields have been identified.

Doping of n-type Bi2Se3 single crystal with Fe, Ru, Os, and Mo

Doping is one of the most suitable methods for tuning the electronic properties of topological insulators and a promising approach for band gap opening in surface states. In this study, we developed a reliable method for preparing high-quality single crystal substrates comprising Bi2Se3 doped with VIIIB and VIB column elements. We combined experimental photoelectron spectroscopy (X-ray photoelectron spectroscopy, angle resolved photoelectron emission spectroscopy, and ultraviolet photoelectron spectroscopy) and theoretical (ab initio) methods to analyze the electronic properties and chemical states of atoms in the substitutional position and native defects in the topological insulator, which can be achieved using the free melt crystallization method for sample growth. The relationship between the position of the Dirac cone and valence band maximum was explored and discussed.

Wollastonite-containing glass-ceramics from the CaO–Al2O3–SiO2 and CaO–MgO–SiO2 ternary systems

Glass-ceramics (GCs) are polycrystalline materials produced from parent glasses by the controlled crystallization that results in crystalline phase(s) embedded in a residual amorphous matrix. Typically, GCs are produced by a conventional glass route with subsequent crystallization for which two heat treatments are usually applied, the former to generate nuclei and the latter being a crystal growth stage. Alternatively, another technically viable route for manufacturing GCs involves sintering of glass-powder compacts followed by crystallization (sinter-crystallization).Wollastonite-containing GCs from the CaO–Al2O3–SiO2 and CaO–MgO–SiO2 systems find a wide variety of uses in different technological fields, including construction, architecture, medical and high-tech fields. For example, a special type of wollastonite-containing GC marketed under the name of Neoparies®, which is stronger and lighter than natural stone, features high resistance to weathering/chemical attack and is manufactured on a large scale for construction and architectural applications. In the biomedical field, the well-known Cerabone® products have been used in bone-contact applications for many years.The main goal of this brief review is to provide a critical analysis of the experimental trials focusing on the synthesis of wollastonite-containing GC materials and to discuss the various fields of their application. Constitution of phase diagram of CaO–Al2O3–SiO2 and CaO–MgO–SiO2 systems are comprehensively discussed with connection to melt crystallization path and crystalline phase formation. Furthermore, special emphasis will be given to the production of wollastonite-containing GCs for construction and architectural purposes from natural raw materials and wastes, as well as to the recent advancement in developing wollastonite-containing GC biomaterials for bone repair.

Influence of heat treatment on the structure and mechanical properties of zirconium dioxide crystals partially stabilized by samarium oxide

The effect of high-temperature treatment in different media on the phase composition, microhardness and fracture toughness of (ZrO2)1-х(Sm2O3)х crystals with x = 0.02÷0.06 has been studied. The crystals have been grown using direction melt crystallization in a cold skull. The crystals have been heat treated at 1600 °C for 2 h in air and in vacuum. The phase composition of the crystals has been studied using X-ray diffraction and Raman scattering. We show that samarium cations enter the ZrO2 lattice mainly in a trivalent charge state and do not change their charge after air or vacuum annealing. The as-annealed phase composition has changed in all the test crystals except for the (ZrO2)0.94(Sm2O3)0.06 composition. After air or vacuum annealing the (ZrO2)1-x(Sm2O3)x crystals with 0.002 ≤ x ≤ 0.05 contain a monoclinic phase. The (ZrO2)0.94(Sm2O3)0.06 crystals contain two tetragonal phases (t and t´) with different tetragonality degrees. After air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals the lattice parameters of the t and t´ phases change in opposite manners, suggesting that the tetragonality degree of the t phase increases whereas the tetragonality degree of the t´ phase decreases. The microhardness and fracture toughness of the as-annealed crystals depend on the Sm2O3 concentration in the solid solutions. The formation of the monoclinic phase in the (ZrO2)1-х(Sm2O3)х crystals with 0.037 ≤ x ≤ 0.05 significantly reduces the microhardness and fracture toughness of the crystals. Annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals triggers more efficient hardening mechanisms and thus increases the fracture toughness of the crystals. We show that air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals increases the fracture toughness of the crystals by 1.5 times as compared with that of the as-grown crystals.

Exploring the relationship between interfacial adhesion, molecular dynamics, and the brill transition in fully bio-based polyamide 1010 nanocomposites reinforced by two-dimensional materials

One of the greatest goals of modern polymer science can be considered the production of high-performance polymer nanocomposites from renewable sources due to the growing interest in environmental and sustainability issues. Within that scope, a good strategy is to pair the processability of thermoplastic materials with the outstanding characteristics of 2D nanomaterials. However, the final performance of the produced nanocomposite is mainly attributed to the interphase, i.e., the volume fraction of the bulk polymer that has its molecular dynamics affected by interactions with the surface of the filler. Therefore, we aim to investigate how different 2D nanomaterials, i.e., graphene oxide (GO), hexagonal-boron nitride (h-BN), and molybdenum disulfide (MoS2) affect the molecular dynamics of a fully bio-based polyamide 1010 (PA 1010) by a new correlation between experimental results from differential scanning calorimetry, broadband dielectric spectroscopy, and dynamic mechanical analysis. For that, nanocomposites based on single and hybrid-fillers were produced through melt mixing. It was observed that, although all nanofillers seem to hinder the molecular relaxation of the polymer chains, GO and h-BN were more effective than MoS2. This remained true when the fillers were applied individually and in the hybrid form. This effect has been attributed to the following aspects: (I) higher enthalpy related to the melting of the polyamide crystals after the Brill transition, which indicates lower thermal motion being gained before the transition takes place; (II) higher activation energy of the glass transition, which was estimated from the fitting of the dielectric spectra to the Havriliak-Negami function and then to the Vogel-Fulcher-Tammann model; (III) lower values of the “adhesion factor”, which is calculated from the decrease in intensity of the mechanical tan(δ) in the nanocomposites with respect to the neat polymer, indicating higher adhesion for the composites filled with GO and h-BN. To confirm the trends observed experimentally for each nanomaterial, molecular dynamics simulations, which enabled the investigation of the adhesion force as a function of nanosheet displacement, were also carried out. The simulations corroborated with the experimental observations, in which h-BN leads to a more intense force of separation, followed by GO, and lastly by MoS2. Since the level of interfacial interactions is what mainly dictates the performance of polymer nanocomposites, it is suggested that GO, and especially h-BN, might present greater promise for novel bionanocomposites based on PA 1010.

Characterization of calumite-modified melaphyre glass in terms of mineral fibres and glass-ceramic materials production

The possibility of utilizing calumite (BSF) in the glass-ceramic industry was analyzed in this study. The properties of melaphyre glasses modified with 25 % and 50 % of calumite were determined after the post-melting and directional crystallization process. The produced glasses were subjected to microstructural analysis using light LM and scanning electron microscopy SEM. Their chemical composition was determined using XRF spectroscopy. After melting and directional crystallization, the glasses' structural tests were performed using FTIR spectroscopy and XRD phase analysis. The characteristic temperatures and the thermal stability of the glasses were determined with thermal analysis (DTA/TG) and dilatometric tests, which analysis was also valuable to determine the parameters of the directional crystallization process of melaphyre glasses. The results showed that unmodified melaphyre glasses demonstrate a low crystallization ability and do not crystallize even at 900 °C, while incorporating calumite into their composition increases their crystallization ability. The study showed that calumite significantly influences the chemical and structural characteristics of melaphyre glasses, which gives it the chance to be successfully used as a raw material for producing glass crystalline materials or mineral fibres. Notably, the findings underscore the potential utility of calumite as a proficient raw material for fabricating glass crystalline fibrous or insulating materials.

Thermally stable Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal with tunable luminescence

By using the melt crystallization process, Dy2O3/Sm2O3 co-doped glass ceramics (GCs) containing La2Sn2O7(LSO) crystal were successfully prepared. By using X-ray diffraction (XRD), the sample's phase was determined, and scanning electron microscopy (SEM), the sample's morphology was examined. The optimal heat treatment condition of glass ceramics was determined to be 650 °C/1.5 h. Under 362 nm excitation, the energy transfer of Dy3+→Sm3+ was observed in Dy2O3/Sm2O3 co-doped glass ceramic samples from the emission spectrum. Electric dipole-electric dipole interaction is identified as the mechanism of energy transfer from Dy3+ to Sm3+ according to the Dexter formula for energy transfer. The emission spectra of 0.5%Dy2O3-0.4%Sm2O3 co-doped glass ceramic samples in a range from 298 K to 458 K show that the samples have high thermal stability, and the thermal quenching activation energy at 575 nm has been estimated to be 0.265 eV. According to chromaticity coordinates and correlated color temperature, warm white light emission may be achieved by co-doping Dy2O3/Sm2O3 glass ceramics. The findings demonstrate Dy2O3/Sm2O3 co-doped glass ceramics containing La2Sn2O7 crystal have a potential application prospect in warm white light-emitting diodes (w-LEDs).

Comparison of chlorination resistance of biodegradable microplastics and conventional microplastics during the disinfection process in water treatments

Nowadays, microplastics (MPs) widely exist in the environment, and water treatment plants are important sources of MPs. Chlorine is widely used in the disinfection process in water treatment plants and has strong oxidation, however, the chemical and physical properties changes of MPs during chlorination were unclear. Thus, in this study, based on the actual used chlorine concentrations, different chlorination conditions were simulated to study the variation of MPs after chlorination. Meanwhile, the produced disinfection by-products were monitored. The results showed that under high chlorination concentration conditions, functional groups of polyethylene (PE), polystyrene (PS), and polylactic acid (PLA) changed, while no peak shift or change of poly (butyleneadipate-co-terephthalate) (PBAT) could be detected. Moreover, after chlorination, partial yellowing and cracks appeared on PS, PLA, and PBAT, while PE remained white and showed little morphological changes. Besides, chlorination led to the narrowing of the cold crystallization peak and melting peak of PLA, while chlorination had little influence on the crystal structure of PE and PBAT. Furthermore, the reaction between PLA and chlorine mostly produced more trichloromethane than other types of MPs. Consequently, when chlorine concentrations were in the range of 2.5 to 5000 mg/L, the chlorination resistance was PBAT/PE > PLA > PS. Specifically, PBAT had the strongest chlorination resistance in terms of chemical properties, while PE had the strongest chlorination resistance in terms of physical properties. Therefore, the degradability of biodegradable MPs is not higher than that of conventional MPs in all cases. Moreover, it should be noted that most changes occurred only in high chlorine concentrations. Thus, neither conventional MPs nor biodegradable MPs can be completely degraded during the chlorination process in water treatments.

Synthesis and thermal investigation of poly(propylene terephthalate-co-2,5-furan dicarboxylate) copolyesters

Herein, we report the synthesis of new poly(propylene terephthalate-co-2,5-furan dicarboxylate) (PPTF) copolyesters with high molecular weight. Copolymers having various PT/PF molar fractions were synthesized via a two-stage melt polycondensation reaction from the dimethyl esters of terephthalic acid (TPA) or 2,5-furandicarboxylic acid (FDCA) with 1,3-propanediol. The combination of the crystallization ability of PPT with the biobased nature of PPF could make the PPTF copolyesters very appealing. Based on nuclear magnetic resonance spectroscopy, the structure and the actual molar composition of the copolyesters were identified and all the copolymers were found to be random. The investigation of the cocrystallization behavior with XRD showed that isodimorphism predominates, and DSC confirmed the random nature of the copolymers by the presence of a minimum value of the melting temperature as a function of copolymers’ composition. Moreover, isothermal melt crystallization studies were conducted. The melting point depression was investigated through the implementation of a plethora of thermodynamic models, and it was found that the incorporation of the PF units into the PPT crystal was preferred. In all cases, the effect of the furan ring was noticeable, as the copolyesters with higher PT content demonstrated higher crystallization rates. Finally, through polarized light microscopy the spherulitic morphology of the polymers was examined.

The origin of calcite in calc‐silicate rocks from the Kokchetav ultrahigh‐pressure metamorphic complex

AbstractUnderstanding calcite genesis in ultrahigh‐pressure crustal rocks is a key to the reconstruction of the evolution of ultrahigh‐pressure metacarbonate rocks. Here, we present new data and a new model on the genesis and the P–T conditions of the formation of calcite found in the ultrahigh‐pressure calc‐silicate rocks from the Kokchetav massif. In the studied sample aragonite inclusions coexist with Type A calcite inclusions (previously interpreted as mineral inclusions) and the inclusions of Type B calcite (previously interpreted as derived from the crystallization of carbonatitic melt) in cores of garnet porphyroblasts. The most Mg‐rich calcite from Type A inclusions coexisting with aragonite inclusions in one garnet growth zone shows XCa = 0.935 implying their crystallization during a retrograde metamorphic stage at P ~ 2.3 GPa and T ~ 870°C along the P–T path. Type A calcite and aragonite inclusions were also found coexisting in one growth zone with K‐bearing clinopyroxene inclusion (ω[K2O] = 0.5 wt.%). Such a high K2O‐content in clinopyroxene testify that the pressure of inclusion capture exceeded 3.5 GPa, which contradicts the P–T conditions estimated by XCa in magnesian calcite. Thus, Type A calcite inclusions were initially captured as an aggregate of aragonite+ magnesian calcite at ultrahigh pressure metamorphic stage (P ≥ 3.5 GPa, T = 900–1,000°C) and then re‐equilibrated at lower conditions (P ≤ 2.3 GPa and T ≤ 870°C). The trace element composition of aragonite and Type A and Type B calcite from inclusions was also studied to clarify calcite genesis in these inclusions. Aragonite shows high LREE (5–57 ppm) and Sr‐content (600–800 ppm). Calcite from Type A inclusions shows low LREE (2.9–19.8 ppm) and Sr‐content (490–670 ppm). Calcite from Type B inclusions forms two groups according to the LREE and Sr content distribution (Type B1 and Type B2). Trace element distribution in Type B1 calcite is identical to that of Type A calcite, while Type B2 calcite shows high LREE (6.8–64.9 ppm) concentrations along with low Sr‐content (180–340 ppm). Type A and Type B1 calcite is interpreted to have been re‐equilibrated. Type B2 calcite inclusions crystallized from the hydrous carbonatitic melt.

Ionic thermoelectric effect in Cu2-δSe during phase transition

The ionic Seebeck coefficient was studied in copper selenide with Cu1.99Se, Cu1.95Se and Cu1.8Se stoichiometry which was synthesized with a melt crystallization method. To measure the ionic Seebeck coefficient of copper ions, 0.15C6H12N4CH3I + 0.85CuI solid-state electrolyte was prepared. Electrolyte layers were pressed with copper selenide powder into a sandwich-like structure. At the temperature of 410 K, the materials have ionic Seebeck coefficient values close to each other, about 1100 μV/K. In the case of β-phase structure (Cu1.8Se material), changes in the measured Seebeck coefficient were observed—with decreasing temperature, the ionic thermopower firstly increased reaching about 1230 μV/K and then decreased to 950 μV/K at 355 K. In the Cu1.99Se material, a phase transition to the α-phase was observed during cooling. The ionic Seebeck coefficient values gradually increased from 1030 to 1220 μV/K at 370 K, when the material is in the low-temperature phase. The measured difference between the ionic thermopower of the two phases well matches calculations based on the entropy of the transition (presence part of the Seebeck coefficient) and different activation energies of ionic transport (transport part).Graphical abstract

On the Effect of Non-Thermal Atmospheric Pressure Plasma Treatment on the Properties of PET Film.

The aim of the work was to investigate the effect of non-thermal plasma treatment of an ultra-thin polyethylene terephthalate (PET) film on changes in its physicochemical properties and biodegradability. Plasma treatment using a dielectric barrier discharge plasma reactor was carried out in air at room temperature and atmospheric pressure twice for 5 and 15 min, respectively. It has been shown that pre-treatment of the PET surface with non-thermal atmospheric plasma leads to changes in the physicochemical properties of this polymer. After plasma modification, the films showed a more developed surface compared to the control samples, which may be related to the surface etching and oxidation processes. After a 5-min plasma exposure, PET films were characterized by the highest wettability, i.e., the contact angle decreased by more than twice compared to the untreated samples. The differential scanning calorimetry analysis revealed the influence of plasma pretreatment on crystallinity content and the melt crystallization behavior of PET after soil degradation. The main novelty of the work is the fact that the combined action of two factors (i.e., physical and biological) led to a reduction in the content of the crystalline phase in the tested polymeric material.

Order-disorder transition and thermal behavior of paracelsian-type MGa2Ge2O8 (M = Sr, Ba) compounds

Two Ga–Ge disordered feldspar-related compounds MGa2Ge2O8 (M = Sr, Ba) with paracelsian topology were synthesized for the first time using the melt crystallization methods (1300–1400 °C) and rapid cooling. Their stability was studied under high-temperature conditions using in situ single-crystal (up to 1000 °C) and powder (up to 1050 °C) X-ray diffraction. Both compounds are stable in the studied temperature range. The refinement of the crystal structure of BaGa2Ge2O8 at different temperatures does not demonstrate any ordering processes. The thermal expansion of both compounds has anisotropic character (αmax/αmin = 3.7 and 3.9 for SrGa2Ge2O8 and BaGa2Ge2O8, respectively), wherein the maximum and minimum expansion is observed within the bc plane. The anisotropy degree of MGa2Ge2O8 increases as the size of extraframework cation increasing. Simultaneously this process leads to the decreasing of MGa2Ge2O8 stability range. The influence of the crystallization procedure on order-disorder process of MGa2Ge2O8 is discussed.

Two-Step Melting in a Bulk Crystal via Intermediate Metastable Liquid.

The mechanism of melting is significant, as it links the structure and dynamics between crystal and liquid. In two dimensions, the crystal could first melt into a hexatic liquid before finally reaching a disordered liquid. However, such a hexatic liquid phase is unstable in three dimensions, and melting is recognized as a one-step process. Here we report a two-step melting process in a three-dimensional system, (S)-(+)-ibuprofen. The crystal melts through an indirect pathway that first transforms into an intermediate liquid phase exhibiting an extremely long lifetime followed by the transition to the ordinary liquid phase at a spinodal point with the occurrence of long-range fluctuations. Such observations suggest that the complexity of liquid could affect the transition pathway of melting. These results could lead us to hypothesize the existence of continuous melting in three dimensions.

Effects of NANH as a nucleation agent on the performance of PLLA

In this research, N,N′-bis(nicotinic) 1,4-naphthalenedicarboxylic acid dihydrazide (NANH) as a new synthetic organic nucleating agent was employed to overcome the slow crystallization rate of poly(L-lactide) (PLLA). Melt crystallization showed that the crystallization ability of PLLA was significantly enhanced by NANH, with NANH still being able to accelerate PLLA crystallization at a cooling rate of 50°C/min. Additionally, when the final melting temperature was 170°C, the onset melt-crystallization temperature and melt-crystallization peak temperature of PLLA/3% NANH were up to 160.0 and 155.1°C, respectively. Isothermal crystallization showed that the half-time of the overall crystallization of PLLA/3% NANH was dramatically reduced, from 71.9 min at 135°C for the virgin PLLA to the minimum value of 0.3 min. This advanced nucleation effect was speculated to be due to chemical nucleation through the theoretical analysis of frontier orbital energy. Melting behaviors under different conditions further confirmed the crystallization-accelerating effect of NANH for PLLA crystallization, and the melting processes were affected by the crystallization temperature and heating rate. Although NANH decreased the thermal decomposition temperature of PLLA in air, the thermal decomposition temperatures of all PLLA/NANH blends were higher than 330°C, which could meet daily usage requirements. Finally, the addition of NANH enhanced PLLA fluidity; however, light transmittance was seriously weakened.

The Micro-Capacitance Enhancement of Polyionic Liquids Grafted Onto Carbon Nanotubes on the Piezoelectric Properties of Poly(Vinylidene Fluoride) Films and Their Sensor Applications

The increased micro-capacitance of a poly (vinylidene fluoride) (PVDF) matrix can effectively improve the piezoelectric properties of the composite material. This work used chemically modified carbon nanotubes (CNTs) as the main reinforcement material. Atom transfer radical polymerization (ATRP) was used to graft polyionic liquids (PILs) with different hydrophilic anions to the CNTs’ surfaces. Solution casting and compressive melt molding were used to prepare the PVDF-composite piezoelectric films. Micro-capacitance formed by the PIL grafted CNTs dispersed well in the PVDF matrix, and their effects on the crystalline form and piezoelectric properties were studied. The hydrophobic hexafluorophosphate anion (-PF6 -) can significantly improve the CNTs dispersion and enhance the micro-capacitance formation in the PVDF matrix. During solution crystallization, the synergistic effect of CNTs and PIL on the PVDF and the solvent effect made the content of β phase of PVDF/CNTs@PIL-PF6 film reach 80.2%, resulting in a high dielectric constant of 188 and a piezoelectric coefficient of 36. In the process of melt crystallization, due to shear stretching and extrusion, the CNTs@PIL-PF6 had an obvious nucleation effect on the polar crystalline phase of PVDF, with a β phase content up to 99.3%, leading to the higher dielectric constant of 530 and the piezoelectric coefficient of 31. The current discovery provides a development direction for smart piezoelectric polymer matrix composites, which have great potential in preparing piezoelectric energy storage materials.