Crystallization Of Blends Research Articles

Synergistic Effect of Solvent and Epitaxy on the Formation of Anisotropic Structures of P3HT and P3HT/PCBM Films.

Oriented organic semiconductor blends can confer desirable properties, such as enhanced charge transport properties and polarized light emission or absorption. A technique that is not only adapted to solution processing but also producing anisotropic conducting blend films is realized by epitaxial crystallization of blends on oriented polymer substrate. The epitaxial structure of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) on oriented polyethylene (PE) substrate is affected by the boiling point of the used solvent. The P3HT spin-coated from o-dichlorobenzene with a high boiling point on PE forms a "side-on" and "face-on" molecular chain orientation with c-axis parallel to the c-axis of PE. While the orientation of the side-on and face-on is poor when P3HT is spin-coated from chloroform with a low boiling point. The addition of PCBM does not affect the epitaxial crystallization behavior of P3HT. Moreover, the anisotropic structure of PCBM is also obtained on the PE substrate. The PE substrate efficiently increases the amount of the face-on structure and the ratio of the face-on to side-on is 7 times that on the PSS:PEDOT substrate. Anisotropic structures lead to anisotropic absorption and photoluminescence properties. The anisotropic optical properties are better for the sample spin-coated from o-dichlorobenzene with the dichroic ratio of 2. The technique of employing oriented PE film to regulate the formation of oriented conducting polymer combined with the analytical method provides guidance to the fabrication and characterization of anisotropic functional film.

Enzymatic Hydrolysis of Poly (Caprolactone) and its Blend with Styrene–Butadiene–Styrene (40% PCL/60% SBS)

In this study, we aim to evaluate the effect of enzymatic hydrolysis on aliphatic polyester and on its shape memory blend. Therefore, the hydrolysis of poly (ɛ-caprolactone) (PCL) and of its shape memory polymer (SMP) blend [40% PCL/60% styrene–butadiene–styrene (SBS)] in a solution containing an Amano lipase from pseudomonas fluorescence and a phosphate buffered saline (PBS), is achieved. An appropriate characterization helps to better understand the behaviour of these polymers. So, the properties of these materials prior and after hydrolytic degradation are investigated. When they are submitted to enzymatic hydrolysis, the physico-chemical and mechanical properties of PCL and its blend (PCL/SBS) change. PCL undergoes a significant decrease in weight during enzymatic hydrolysis. Yet, blending PCL with SBS considerably reduces its degradation rate in terms of weight drop, compared with pure PCL. The enzymatic hydrolysis causes chains splitting, which rises their mobility and facilitates their reorientation. Consequently, for PCL and its blend, the degree of crystallinity Xc rises during hydrolytic degradation, which confirms that the amorphous regions of PCL are more susceptible to hydrolysis. Besides, this continuous rise in crystallinity causes the augmentation of PCL and its blend melting, crystallization and glass transition temperatures. Moreover, the PCL brittleness increases, and the blend ductility decreases with the enzymatic hydrolysis time. For both, PCL and its blend, the young modulus displays two opposite effects; it goes up due the growth of crystallinity, but at the end of hydrolysis, its value goes down because of weight loss.

Fractional Crystallization Kinetics and Formation of Metastable β-Form Homocrystals in Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Blends Induced by Precedingly Formed Stereocomplexes

Stereocomplex (SC) crystallization has been an effective way to improve the physical performance of polymer materials. However, SC crystallization of stereocomplexable polymer blends with complemen...

Crystal phase control in self-catalyzed InSb nanowires using basic growth parameter V/III ratio

In this work, the influence of V/III ratio on self-catalyzed InSb nanowire (NW) crystal structure is investigated using metal organic chemical vapor deposition. The effective balance of V/III ratio determines the change of InSb NW crystal structure from zincblende to wurtzite. Particularly, as group-V molar flow varies from 6.4 × 10−5 to 8.0 × 10−5 mol/min, wurtzite segment length of InSb NW increases from 16 ± 9 nm to 89 ± 9 nm, whereas zincblende crystal phase is observed for other molar flows. We interpret the observed phase transition to a lower surface energy of In-Sb alloy droplet than pure In-droplet, which makes triple phase line nucleation energetically favorable. This study gives insight on single growth parameter (V/III ratio) change to the InSb NW crystal control, such a technique is essential to selectively tune the crystal phase of single NW for various applications.

About the Crystallization of Abiotic Coded Matter.

The crystallization of digitally encoded polyurethanes was studied by electron diffraction. A series of oligomers with different primary structures was analyzed in this work. They all form hydrogen-bonding-directed lamellar single crystals with a base-centered orthorhombic unit cell. Although crystal morphology was the same in all cases, the digital coding of the oligomers has a small influence on the intersheet distance in the crystals. The crystal lattices allow calculation of the volume occupied by one basic information unit, which is in the range 148-188 Å3. Interestingly, this volume is about 3× smaller than that occupied by a coded nucleotide in a DNA double helix. Furthermore, crystallization of blends of oligourethanes with different coded primary structures was investigated. Oligomers with drastically different monomer compositions form structures that are not cocrystals but more probably segregated crystals containing distinct domains of different composition.

Zinc solubility, speciation and deposition: A role for liquid hydrocarbons as ore fluids for Mississippi Valley Type Zn-Pb deposits

Although the ore fluid for Mississippi Valley Type (MVT) deposits is universally considered to be a basinal brine, the common occurrence of liquid hydrocarbons as inclusions in one of the ore minerals (sphalerite) raises the question of whether liquid hydrocarbons could play a role in metal transport. Here we explore the potential of liquid hydrocarbons to act as an ore fluid by determining the steady-state concentration of zinc in crude oil and evaluating the factors that promote its dissolution. To this end, zinc wires were reacted with a series of oils (labelled oils A, B and C) at 150, 200 and 250 °C, and the steady-state concentration of Zn was determined. Zinc concentrations were observed to increase with temperature and with the Total Acid Number (TAN) of the oils, the latter of which is strongly correlated to the carboxylic acid content of crude oil. Crude oil B, the highest TAN oil, dissolved 1700 ± 0.8 ppm at 250 °C, which is comparable to the highest Zn concentration inferred to have been dissolved in brines interpreted to represent MVT ore fluids. X-ray Photoelectron Spectroscopic (XPS) analyses performed on the residual oil coating the zinc wires after the reaction supported the conclusion that Zn has a strong chemical affinity for carboxylic acids in crude oil. Finally, an experiment designed to precipitate sphalerite crystals from a Zn-rich synthetic oil at room temperature showed that sphalerite precipitation from liquid hydrocarbons proceeds efficiently in a carbonate-buffered, H2S -rich environment.

High‐temperature crystallization of immiscible polymer blends induced by the shear flow in injection molding

High‐temperature crystallization of immiscible polymer blends induced by the shear flow in injection molding

Effect of iron concentration on the crystallization and electronic structure of sphalerite/marmatite: A DFT study

In this work, various sphalerite crystal models with different iron (Fe) concentrations were selected for theoretical calculations to determine the influence rules of Fe concentration on the crystallization and electronic structure of sphalerite crystals. The results showed that with increasing Fe concentration, the lattice parameters generally gradually decreased. In other words, the crystal structure contracted slightly. Meanwhile, with the gradual decrease of the bond length between Fe and sulfur (S), the force between Fe and S slowly strengthened. The electrical conductivity of the crystals continuously rose and followed the changing trend from semiconducting to semimetallic and then to metallic conductivity. Fe substitution induced obvious electron rearrangement, causing charge redistribution in the entire crystal structure. The Fe d orbital made a major contribution to the Fermi level.

The substitution mechanism of Au in In-, Fe- and In-Fe-bearing synthetic crystals of sphalerite, based on the data from EPMA and LA-ICP-MS study

Research subject.Sphalerite (ZnS) is a widespread mineral that can be found in various depositional environments. During formation, this mineral can accumulate minor and trace impurities, with gold being one of the most valuable component. The issue of the chemical state of Au in sphalerite has been much discussed recently.Methods.Samples of In-, Fe- and In-Febearing sphalerite with a composition ranging from 0 to 2.5 mol.% In2S3 and 0 – 40 mol.% FeS were synthesized in an Ausaturated system using gas transport and salt flux techniques. The resulting products were subsequently investigated using EPMA and LA-ICP-MS.Results.All the elements under investigation are found to be homogeneously distributed within the sphalerite matrix. After quenching, sphalerite is shown to retain Au. Our data indicates that the observed increase in Au concentration is caused by the presence of In (up to 1.02 wt % Au) and, to a lesser extent, by that of Fe (up to ≈600 ppm Au). These elements substitute Zn in the crystal structure of sphalerite following the scheme Au+ + In3+(Fe3+) ↔ 2Zn2+, which is in good agreement with previous data obtained using the XAS method.Conclusions.A higher sulphur fugacity in the system leads to a more significant accumulation of Au in sphalerite. The concentration of Au in pure sphalerite does not exceed 10 ppm under our experimental conditions and does not depend on the activity of sulphur in the system.

Impact of different sugar and cocoa powder particle sizes on crystallization of fat used for the production of confectionery products

The effect of solid particle size distribution (PSD) on the crystallization and microstructure of fat blends was evaluated. Samples were prepared as suspensions of sugar and cocoa particles of different sizes in a palm oil fraction and textural and rheological characteristics were determined. Solid fat content (SFC) was measured using pulsed nuclear magnetic resonance and confocal laser scanning microscopy was used to study the microstructure. Particle size reduction accelerated the crystallization process and resulted in final hardness increase. These systems also had the highest values of G′ and crystallization onset at the highest temperature during cooling. PSD did not affect the final SFC. SFC results showed significant difference only in samples with sugar particles. Results from this study highlight that the nucleation ability of solid particles is important for fat crystallization and strength of the underlying fat crystal network. Microstructure analysis showed that the amount of liquid oil decreased as particle size decreased. Practical applications Chocolate and other confectionery products are suspensions of solid particles, sugar and cocoa, in fat matrix. Understanding the effect of different particle sizes on physical characteristics of these products and defining a desirable particle size gives an opportunity to producers to adjust properties of a product. Namely, many undesirable occurrences may be prevented (fat blooming, loss of flavor, changed appearance, etc.) during the production process, and adequate final product texture could be achieved.

Application of High Intensity Ultrasound to Accelerate Crystallization of Anhydrous Milk Fat and Rapeseed Oil Blends

In this study, the impact of high intensity ultrasound (HIU) treatment on anhydrous milk fat and milk fat/rapeseed oil blends with 10–30 w/w% rapeseed oil is examined. Effects of HIU treatment on crystallization kinetics, thermal behavior, microstructure, texture, and oxidation are evaluated. HIU treatment results in an acceleration of the crystallization process, especially for blends with a high rapeseed oil content. HIU treatment reduces the crystal size, however, HIU treatment does not have any significant effects on the melting behavior or hardness. No significant effects of HIU treatment on secondary oxidation products are observed, indicating that lipid oxidation is not facilitated by the HIU treatment.Practical Application: A great potential exists for the use of use of high intensity ultrasound in the food industry to obtain a shorter and more controllable fat crystallization process. Results from this demonstrate how the impact of ultrasound treatment is affected by diluting a hard fat with liquid oil. Such effects are of great importance in, for instance, the dairy industry, where high intensity ultrasound potentially provides an additional processing tool in the production of spreadable blends based on milk fat and rapeseed oil. Ultrasound treatment is introduced in a circulating flow system, a more realistic representation of an industrial setting compared with commonly used probe based bath systems.High intensity ultrasound accelerates the crystallization kinetics of anhydrous milk fat and rapeseed oil blends, resulting in the formation of smaller crystals but no differences in melting properties or hardness. This is obtained in a circulating flow cell, without detection of increased levels of secondary oxidation products.

Monte Carlo Simulation of Strain-Enhanced Stereocomplex Polymer Crystallization.

We performed dynamic Monte Carlo simulations to investigate strain-induced polymer crystallization under separate enhancements of the driving forces for homocomponent and stereocomplex crystallization in the half-half symmetric racemic polymer blends. The results showed that the polymer strain significantly enhances the stereocomplex crystallization, in comparison to the parallel cases of template-induced crystal growth without any strain in the previous simulations. We attributed the results to the strain-induced polymer crystallization favoring intermolecular crystal nucleation at high temperatures, which benefits the stereocomplex crystallization. Our observations provided a molecular-level interpretation to the strain- or shear-enhanced stereocomplex crystallization in the racemic polylactide blends.

The influence of blend composition and filler on the microstructure, crystallization, and mechanical behavior of polymer blends with multilayered structures

The preparation of multilayered structures has been thought as a complicated process until our recent study illustrating an effective method through high speed thin wall injection molding (HSTWIM) of polypropylene (PP) and polyethylene (PE) based blends. Current study investigates the effect of blends composition as well as the addition of carbon nanotubes (CNT) on the structure and properties of these blends. It is observed that a close ratio of high density polyethylene (HDPE) and impact copolymer polypropylene (ICP) triggers the formation of a multilayered structure. Meanwhile, PE is migrated into the rubber phase in ICP, leading to the distribution of some rubber phase on the interface between PP and PE, which is thought as beneficial for the interfacial interaction. Meanwhile, epitaxial growth of PE crystals on PP substrate is also observed. The presence of rubber phase on the interface, multilayered structure and epitaxial growth of PE crystals on PP are thought to be responsible for the observed mechanical enhancement in tensile strength as well as strain at break. Furthermore, the addition of CNTs leads to enhanced strength, reduced strain at break and anisotropic conductive network.

Preparation and Fluorescence Property of Water-dispersible ZnSe:Co/ZnSe/ZnS Quantum Dots

In this paper, water-dispersible, L-cysteine-capped Co-doped ZnSe/ZnSe/ZnS core/shell/shell quantum dots are prepared via a simple epitaxial growth approach by depositing ZnS on the superficial layer of the Co-doped ZnSe/ZnSe core/shell QDs. The crystal structure as well as fluorescence performance of the as-prepared Co-doped core/shell/shell QDs have been testified through X-ray power diffraction, Infrared spectrum, Ultraviolet-visible spectrum and photoluminescence spectrum. The results exhibit that the Co-doped ZnSe/ZnSe/ZnS core/shell/shell quantum dots have a cubic sphalerite crystal and the size about 3.4nm. After coating ZnS shell with appropriate thickness around the Co-doped ZnSe/ZnSe core/shell QDs, the fluorescence intensity of Co-doped ZnSe/ZnSe/ZnS core/shell/shell QDs has been improved greatly.

Pressure and composition dependence of thermodynamic properties of zinc-blende AlyGa1-yAs alloy

The moment method in statistical mechanics is applied to study the thermodynamic properties of the zinc-blende AlyGa1-yAs compound. The lattice parameter, isothermal bulk modulus, specific heats at the constant volume and constant pressure of the zinc-blende AlyGa1-yAs crystal are investigated in detail as functions of pressure and Al composition up to 10 GPa at room temperature. Numerical calculations have been performed using the many-body Pearson-Takai-Halicioglu-Tiller potential to describe atomic interactions in the AlyGa1-yAs system. Our work shows that the lattice parameter and specific heats of the AlyGa1-yAs alloy increase almost linearly with the Al composition. Nevertheless, when pressure goes up, while lattice parameter and specific heats decrease gradually, the isothermal bulk modulus increases drastically. Present results can be used as reference data for future experiments and theoretical works. Furthermore, this research proposes the potential of statistical moment method on investigation of thermodynamic and mechanical properties of ternary alloys.

Wear resistant all-PE single-component composites via 1D nanostructure formation during melt processing

Melt-flow-induced crystallization of polyethylene blends having tailored ultrabroad molar mass distribution affords extended-chain ultrahigh molar mass (UHMWPE) nanophases resembling nanofibers which effectively reinforce the polyethylene matrix. Unparalleled by state-of-the-art high density polyethylene (HDPE), the resulting melt-processable “all-polyethylene” single component composites exhibit simultaneously improved wear resistance, toughness, stiffness and strength. Key intermediates are trimodal blends prepared by melt compounding HDPE with bimodal UHMWPE/HDPE wax reactor blends (RB) readily tailored by ethylene polymerization on supported two-site catalysts. Whereas HDPE wax, varied up to 54 wt.-%, serves as processing aid lowering melt viscosity, UHMWPE varied up to 63 wt.-% accounts for improved blend properties. UHMWPE platelet-like nanophase separate during ethylene polymerization and readily melt during injection molding of RB/HDPE blends producing extended-chain fiber-like UHMWPE nanostructures of 100 nm diameter as shish which nucleate HDPE and HDPE wax crystallization to form shish-kebab-like structures. At 32 wt.-% UHMWPE content shish-kebab-like reinforcing phases account for massive polyethylene self-reinforcement as reflected by improved Young's modulus (+420%), tensile strength (+740%) and notched Izod impact strength (+650%) without impairing HDPE injection molding. All-PE composites exhibit high wear resistance entering ranges typical for polyamide and monomodal UHMWPE which is not processable by injection molding under identical conditions.

Solvent-free preparation of porous poly(l-lactide) microcarriers for cell culture

Porous polymeric microcarriers are a versatile class of biomaterial constructs with extensive use in drug delivery, cell culture and tissue engineering. Currently, most methods for their production require potentially toxic organic solvents with complex setups which limit their suitability for biomedical applications and their large-scale production. Herein, we report an organic, solvent-free method for the fabrication of porous poly(l-lactide) (PLLA) microcarriers. The method is based on the spherulitic crystallization of PLLA in its miscible blends with poly(ethylene glycol) (PEG). It is shown that the PLLA spherulites are easily recovered as microcarriers from the blends by a water-based process. Independent control over microcarrier size and porosity is demonstrated, with a higher crystallization temperature leading to a larger size, and a higher PLLA content in the starting blend resulting in a lower microcarrier porosity. Microcarriers are shown to be biocompatible for the culture of murine myoblasts and human adipose stromal/stem cells (hASC). Moreover, they support not only the long-term proliferation of both cell types but also hASC differentiation toward osseous tissues. Furthermore, while no significant differences are observed during cell proliferation on microcarriers of two different porosities, microcarriers of lower porosity induce a stronger hASC osteogenic differentiation, as evidenced by higher ALP enzymatic activity and matrix mineralization. Consequently, the proposed organic-solvent-free method for the fabrication of biocompatible porous PLLA microcarriers represents an innovative methodology for ex vivo cell expansion and its application in stem cell therapy and tissue engineering. Statement of SignificanceWe report a new solvent-free method for the preparation of porous polymeric microcarriers for cell culture, based on biocompatible poly(l-lactide), with independently controllable size and porosity. This approach, based on the spherulitic crystallization in polymer blends, offers the advantages of simple implementation, biological and environmental safety, easy adaptability and up-scalablility. The suitability of these microcarriers is demonstrated for long-term culture of both murine myoblasts and human adipose stromal/stem cells (hASCs). We show that prepared microcarriers support the osteogenic differentiation of hASCs, provided microcarriers of properly-tuned porosity are used. Hence, this new method is an important addition to the arsenal of microcarrier fabrication techniques, which will contribute to the adoption, regulatory approval and eventually clinical availability of microcarrier-based treatments and therapies.

Second order nonlinear optical processes in [111] cubic crystals for terahertz optoelectronics

In this paper, we give an overview of emission and detection of terahertz electromagnetic pulses using, respectively, optical rectification and electro-optic effect in [111] zinc blende crystals. This crystal orientation allows us to generate and read any polarization state of the THz beam only by controlling the polarization state of the laser beam that excites or probes the emitting and receiving crystals. This technique is very useful for polarimetric terahertz spectroscopic studies.

Isothermal Crystallization Kinetics of Palm Oil as Influenced by Addition of a Commercial Phytosterol Ester Mixture.

In literature there is good agreement on the health-promoting effects of phytosterols. However, addition of phytosterol esters (PEs) to lipid (containing food products) may influence its crystallization behavior. This study investigated the crystallization kinetics of palm oil (PO) after addition of PEs in high concentrations (≥10%). The isothermal crystallization of the PE-PO blends was analyzed at a temperature of 20 °C and at a supercooling of 18.7 °C using differential scanning calorimetry and time-resolved synchrotron X-ray diffraction. At increasing PE concentrations, PO crystallization at an isothermal temperature of 20 °C started later and was slower and a smaller amount of crystals were formed. Furthermore, a delay in polymorphic transition from α to β' was observed. When the blends were isothermally crystallized at a supercooling of 18.7 °C, only two of these effects remained: the delay in polymorphic transition and the decrease in crystalline content.

Improved miscibility of PA6 and chitosan by the electric-field assisted phase inversion

A facile and efficient method for the improved miscibility of natural polymer/synthetic polymer blends is reported here based on the electric-field-driven phase inversion. We have employed bioderived chitosan (CS) and Polyamide-6 (PA6) as an example since their blends are known to always result in a large scale phase separation (i.e. CS settles to the bottom of the blends as sediment) during phase inversion procedure. The condensed structure of the polymer blends has been well characterized, notably by the polarized attenuated total reflectance infrared spectroscopy and proton longitudinal relaxation time (T1) distribution. The application of an electric field can orient the polar groups which will hinder the crystallization of blends and also increase the interphase interaction between PA6 and CS. The miscibility of the PA6/CS blends has been characterized by scanning electron microscopy and confocal Raman spectroscopy. It is shown that this controllable hydrogen bonding environment, induced by the presence of electric field, indeed greatly hinder the sedimentation of CS without destroying its chemical structure. The improved miscibility of PA6/CS blends can thus significantly increase the toughness and generate a somewhat larger tensile strength.