Immiscible System Research Articles

Forming Nanoparticle Monolayers at Liquid-Air Interfaces by Using Miscible Liquids.

One standard way of forming monolayers (MLs) of nanoparticles (NPs) is to drop-cast a NP dispersion made using one solvent onto a second, immiscible solvent; after this upper solvent evaporates, the NP ML can be transferred to a solid substrate by liftoff. We show that this previously universal use of only immiscible solvent pairs can be relaxed and close-packed, hexagonally ordered NP monolayers can self-assemble at liquid-air interfaces when some miscible solvent pairs are used instead. We demonstrate this by drop-casting an iron oxide NP dispersion in toluene on a dimethyl sulfoxide (DMSO) liquid substrate. The NPs are energetically stable at the DMSO surface and remain there even with solvent mixing. Excess NPs coagulate and precipitate in the DMSO, and this limits NPs at the surface to approximately 1 ML. The ML domains at the surface nucleate independently, which is in contrast to ML growth at the receding edge of the drying drop, as is common in immiscible solvent pair systems and seen here for the toluene/diethylene glycol immiscible solvent pair system. This new use of miscible solvent pairs can enable the formation of MLs for a wider range of NPs.

Continuous melt granulation: Influence of process and formulation parameters upon granule and tablet properties

The pharmaceutical industry has a growing interest in alternative manufacturing models allowing automation and continuous production in order to improve process efficiency and reduce costs. Implementing a switch from batch to continuous processing requires fundamental process understanding and the implementation of quality-by-design (QbD) principles. The aim of this study was to examine the relationship between formulation-parameters (type binder, binder concentration, drug-binder miscibility), process-parameters (screw speed, powder feed rate and granulation temperature), granule properties (size, size distribution, shape, friability, true density, flowability) and tablet properties (tensile strength, friability, dissolution rate) of four different drug-binder formulations using Design of experiments (DOE). Two binders (polyethylene glycol (PEG) and Soluplus®) with a different solid state, semi-crystalline vs amorphous respectively, were combined with two model-drugs, metoprolol tartrate (MPT) and caffeine anhydrous (CAF), both having a contrasting miscibility with the binders. This research revealed that the granule properties of miscible drug-binder systems depended on the powder feed rate and barrel filling degree of the granulator whereas the granule properties of immiscible systems were mainly influenced by binder concentration. Using an amorphous binder, the tablet tensile strength depended on the granule size. In contrast, granule friability was more important for tablet quality using a brittle binder. However, this was not the case for caffeine-containing blends, since these phenomena were dominated by the enhanced compression properties of caffeine Form I, which was formed during granulation. Hence, it is important to gain knowledge about formulation behavior during processing since this influences the effect of process parameters onto the granule and tablet properties.

Thermocapillary Flow in an Annular Two-Layer Liquid System

By means of a hybrid lattice Boltzmann method, thermocapillary flow, driven by the surface tension owing to a horizontal temperature gradient along the interface in immiscible two-layer liquid system, is simulated numerically. The dynamic behavior of the interface is captured by using phase-field theory. The dependence of flow and interface deformation on the density ratio, Capillary number and aspect ratio, is investigated.

Morphology and properties of bio-based poly (lactic acid)/high-density polyethylene blends and their glass fiber reinforced composites

Poly (lactic acid) (PLA)/high-density polyethylene (HDPE) blends of various proportions and their glass fiber reinforced composites were prepared by melt-compounding. The miscibility, phase morphology, thermal behavior and mechanical properties of the blends were investigated. The blends were immiscible systems with two typical morphologies, spherical droplet and co-continuous, and could be obtained at various compositions. Water contact angle and SEM images indicated that PLA and HDPE are immiscible but can be successfully compatibilized by ethylene-butyl acrylate-glycidyl methacrylate (PTW). Thermal degradation of all blends led to two weight losses, for PLA and HDPE. The incorporation of HDPE improved the thermal stability of the blend. With the addition of 5 wt% PTW, the impact strength of PLA/HDPE/PTW blends (60/40/5 w/w/w) is increased to 18.0 kJ/m2. The effect of glass fiber (GF) on the morphology and mechanical properties of PLA/HDPE/PTW blends (60/40/5 w/w/w) was also investigated. The addition of GF improved the thermal stability of the PLA/HDPE/PTW blends to some extent. The tensile strength of these blends increased and impact strength decreased with increasing GF content.

The use of rheology to elucidate the granulation mechanisms of a miscible and immiscible system during continuous twin-screw melt granulation

Twin-screw hot melt granulation (TS HMG) is a valuable, but still unexplored alternative to granulate temperature and moisture sensitive drugs in a continuous way. Recently, the material behavior of an immiscible drug–binder blend during TS HMG was unraveled by using a rheometer and differential scanning calorimetry (DSC). Additionally, vibrational spectroscopic techniques proved the link between TS HMG and rheology since equal interactions at molecular level did occur in both processes. This allowed to use a rheometer to gain knowledge of the material behavior during hot melt processing of an immiscible drug–binder blend. However, miscibility of a drug–binder formulation and drug–binder interactions appear to influence the rheological properties and, hence conceivably also the granulation mechanism. The aim of this research was to examine if the TS HMG process of a miscible formulation system is comparable with the mechanism of an immiscible system and to evaluate whether rheology still serves as a useful tool to understand and optimize the hot melt granulation (HMG) process. The executed research (thermal analysis, rheological parameters and spectroscopic data) demonstrated the occurrence of a high and broad tan(δ) curve without a loss peak during the rheological temperature ramp which implies a higher material deformability without movement of the softened single polymer chains. Spectroscopic analysis revealed drug–polymer interactions which constrain the polymer to flow independently. As a result, the binder distribution step, which generally follows the immersion step, was hindered. This insight assisted the understanding of the granule properties. Inhomogeneous granules were produced due to large initial nuclei or adhesion of multiple smaller nuclei. Consequently, a higher granulation temperature was required in order to get the binder more homogeneously distributed within the granules.

Structural evolution of poly(l-lactide) block upon heating of the glassy ABA triblock copolymers containing poly(l-lactide) A blocks

Abstract Two triblock ABA copolymers poly( l -lactide- b -dimethylsiloxane- b - l -lactide) (PLLA- b -PDMS- b -PLLA) and poly( l -lactide- b -ethylene glycol- b - l -lactide) (PLLA- b -PEG- b -PLLA) containing poly( l -lactide) were synthesized by ring opening polymerization of l -lactide using bis(hydroxyalkyl) terminated PDMS and hydroxyl end-capped polyethylene glycol as macroinitiators, respectively. Both the triblock copolymers were melt-quenched to −40 °C to prepare the amorphous samples. The melt morphology of the triblock copolymers was preserved upon cooling the melt to −40 °C. PLLA and PDMS blocks are immiscible in the melt, and the amorphous triblock copolymer shows two distinct glass transition temperatures ( T g ) on heating. On the other hand, PLLA and PEG segments are miscible and the triblock copolymer shows the single T g . Structural evolution of PLLA during heating of the amorphous ABA triblock copolymers has been investigated by measuring the variable temperature small-angle and wide-angle X-ray scattering (SAXS and WAXS) and FTIR spectra. In the case of PLLA- b -PDMS- b -PLLA triblock copolymer (immiscible system), the mesophase of PLLA was found to appear just above the T g of PLLA block (∼45 °C), and on further heating the mesophase changed to the regular α form at around 90 °C. On the other hand, in PLLA- b -PEG- b -PLLA (miscible system), the mesophase of PLLA was found to appear at lower temperature i.e. −20 °C, because of the enhanced molecular mobility of PLLA chains in the presence of PEG. However, irrespective of the mesophase formation temperature, the ordered α form has appeared at around 90 °C. In this way, during heating of the amorphous triblock copolymers, the PLLA block was found to crystallize into the ordered α form always through the mesophase just above the T g of PLLA. These results are helpful in understanding the regularization process of semicrystalline polymers in different environments.

New insights on the formation of supersaturated Cu-Nb solid solution prepared by mechanical alloying

The deformation-driven alloying mechanisms in the immiscible Cu-Nb system during mechanical alloying (MA) process have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) observations. It is found that the dominating alloying mechanism changes at the different stages of milling. Initially, the alloying process is mainly governed by interfaces and dislocations, which supply fast diffusion channels between phases. In the intermediate stage, Nb particles with sizes below 8nm undergo a bcc to fcc allotropic transformation, and the interdiffusion between fcc-Nb and fcc-Cu is promoted due to the similarity of lattice structures. Further milling generates disclination defects, which contribute to the formation of fragments or subgrains with sizes below 5nm. The introduction of such defects and fragments benefits the formation of a complete Cu-Nb solid solution. The formation kinetics of solid solution is analyzed by Johnson-Mehl-Avrami equation, which suggests that the speed of the diffusion of Nb atoms into Cu is very slow.

Electroosmotic transport of immiscible binary system with a layer of non-conducting fluid under interfacial slip: The role applied pressure gradient.

We investigate the transport of immiscible binary fluid layers, constituted by one conducting (top layer fluid) and another non-conducting (bottom layer fluid) fluids in a microfluidic channel under the combined influences of an applied pressure gradient and imposed electric field. We solve the transport equation governing the flow dynamics analytically and obtain the closed-form expressions of the velocity fields. We bring out the alteration in the flow dynamics, mainly attributable to the non-linear interaction between interfacial slip and the electrical double layer effect over small scales as modulated by the applied pressure gradient. In particular, we show the augmentation in the net volume transport rate through the channel, emerging from an intricate competition among electrical forcing, applied pressure gradient and the viscous resistance as modulated by the interfacial slip. We believe that the results of this study may be of immense consequence for the design of various microfluidic devises, which are often used for the manipulation of two immiscible fluids in different biomedical/biochemical processes.

XNBR-grafted halloysite nanotube core-shell as a potential compatibilizer for immiscible polymer systems

Halloysite nanotubes (HNTs) grafted with carboxylated nitrile byutadiene rubber (XNBR) were synthesized via a sol-gel method. The HNTs as an inorganic cores were pre-treated with 3-Glycidoxypropyl trimethoxysilane, then successfully coated with the XNBR as an organic shell. The properties of XNBR-grafted HNTs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results suggested that the XNBR grafted to the surfaces of HNTs successfully. Then the TPE nanocomposites based on polyamide-6 (PA6) and nitrile butadiene rubber (NBR) containing various XNBR-grafted and pristine HNTs were prepared via a direct melt mixing method. The morphology, mechanical, dynamic mechanical and rheological properties of the prepared TPE nanocomposites were investigated. The results show that the XNBR-grafted HNTs can effectively improve the morphology and mechanical properties of the PA6/NBR TPEs. The morphology study of the prepared nanocomposites show that the effect of XNBR-grafted HNTs on the size reduction of NBR phase is markedly more effective than the pristine HNTs and rose by 50% in the same concentrations. Mechanical measurements show that the Young’s modulus of the TPE nanocomposites rose by 60% in just 7wt% of XNBR-grafted HNT loading. The results indicate that the introduction of HNT/XNBR core-shells into the PA6/NBR TPEs can enhances the interfacial interactions and provides a more fine rubber phase morphology and controlled mechanical properties in comparison with the accordingly TPE nanocomposites containing pristine HNTs.

Effects of ethyl cellulose on the crystallization and mechanical properties of poly(β-hydroxybutyrate)

Ethyl cellulose (EC) was blended with poly(β-hydroxybutyrate) (PHB), aiming at controlling crystallization and mechanical properties of PHB. The obtained PHB/EC blend is an immiscible system, and the discrete EC phase behaves dual characteristics in the PHB matrix, as the viscoelastic droplets during processing, and as the rigid filler particles during shear flow. This is confirmed by the rheological tests. The presence of EC domains acts as the tackifier, sharply increasing system viscosity from 1000Pas to 5000Pas, and as a result, has large influence on the spherulite morphology of PHB and its crystallization kinetics. The PHB spherulite growth rate reduces in the presence of inert EC, accompanied by decreased degree of crystallinity and reduced lamella defects. These affect the mechanical properties of PHB strongly, together with reinforcing effect of EC itself. At the lower content level, EC can act as both reinforcement and toughener. The presence of 1wt% EC enhances the tensile strength of PHB by about 22%, from 27.5MPa to 33.3MPa, accompanied by 15% increase of impact strength. This work provide an easy way to control the structure and properties of PHB using EC.

Novelties of selective triphasic synthesis of bis-(p-chlorobenzyl) sulfide using hydrogen sulfide and reusable phase transfer catalyst

The present investigation is based on the advancement in hydrogen sulfide (H2S) capture and utilization (HSCU). Commercially H2S is absorbed efficiently using alkanolamines such as methyldiethanolamine (MDEA). Aqueous H2S-rich MDEA is proposed to act as a sulfiding agent for aromatic halides such as p-chlorobenzyl chloride (p-CBC) to synthesize value-added thioethers. The objective of the present investigation is to synthesize bis-(p-chlorobenzyl) sulfide (BPCBS), a value-added thioether, selectively using p-CBC and H2S-laden aqueous MDEA. For the immiscible bi-phasic system, reusable solid phase transfer catalyst, polymer-bound tributylmethylammonium chloride (PBTBMAC) was employed under liquid-liquid-solid (L-L-S) mode in the presence of solvent toluene to enhance the reaction rate and product selectivity. Full conversion of p-CBC was obtained with 100% selectivity towards the desired product BPCBS at optimized specific level of process parameters. The catalyst has shown substantial activity even after three times of reuse, which leads to waste minimization and economic benefits. A generalized empirical kinetic model was developed and successfully validated against the experimental results. The triphasic reaction thus leads to process intensification, waste minimization and selectivity enhancement. The process can be utilized as an alternative to many other HSCU processes to utilize the sour gas in synthesizing value-added chemicals.

Atomic arrangement in immiscible Ag–Cu alloys synthesized far-from-equilibrium

Physical attributes of multicomponent materials of a given chemical composition are determined by atomic arrangement at property-relevant length scales. A potential route to access a vast array of atomic configurations for material property tuning is by synthesis of multicomponent thin films using vapor fluxes with their deposition pattern modulated in the sub-monolayer regime. However, the applicability of this route for creating new functional materials is impeded by the fact that a fundamental understanding of the combined effect of sub-monolayer flux modulation, kinetics and thermodynamics on atomic arrangement is not available in the literature. Here we present a research strategy and verify its viability for addressing the aforementioned gap in knowledge. This strategy encompasses thin film synthesis using a route that generates multi-atomic fluxes with sub-monolayer resolution and precision over a wide range of experimental conditions, deterministic growth simulations and nanoscale microstructural probes. Investigations are focused on structure formation within the archetype immiscible Ag-Cu binary system, revealing that atomic arrangement at different length scales is governed by the arrival pattern of the film forming species, in conjunction with diffusion of near-surface Ag atoms to encapsulate 3D Cu islands growing on 2D Ag layers. The knowledge generated and the methodology presented herein provides the scientific foundation for tailoring atomic arrangement and physical properties in a wide range of miscible and immiscible multinary systems.

Equation of state based on the hole-lattice theory and surface-charge density (COSMO): Part B – Vapor–liquid equilibrium for mixtures

In our previous study [1], an equation of state based on hole-lattice theory augmented with the surface charge-densities, i.e., σ-profiles, was developed and applied for pure components. Here, we extend this equation of state to mixtures in order to describe vapor–liquid equilibrium (VLE) data at low and high pressures. VLE data properties of 98 binary mixtures in (40 isobaric and 58 isothermal) at low pressures were predicted using only the pure components parameters obtained in previous work and σ-profiles calculations. This systems were divided in nonpolar–nonpolar, nonpolar–polar, polar–polar, practically immiscible and carboxylic acid systems. The performance of the proposed EoS were compared with those calculations from COSMO-SAC. For isobaric systems, the equation of state and COSMO-SAC showed, respectively, 0.6% and 0.5% average relative deviation for temperature, and 0.02 for vapor-phase mole fraction. For isothermic systems, the equation of state and COSMO-SAC presented an average relative deviation of 9.9% and 7.5% for pressure and absolute average deviation of 0.03 for vapor-phase mole fraction were reported. The equation of state was also tested for high pressure phase equilibria calculations. Satisfactory results were obtained for isothermal binary mixtures studied. This new equation of state can be used to predict VLE at low and high pressures.

Theoretical and experimental study of metastable solid solutions and phase stability within the immiscible Ag-Mo binary system

Metastable solid solutions are phases that are synthesized far from thermodynamic equilibrium and offer a versatile route to design materials with tailor-made functionalities. One of the most investigated classes of metastable solid solutions with widespread technological implications is vapor deposited ternary transition metal ceramic thin films (i.e., nitrides, carbides, and borides). The vapor-based synthesis of these ceramic phases involves complex and difficult to control chemical interactions of the vapor species with the growing film surface, which often makes the fundamental understanding of the composition-properties relations a challenging task. Hence, in the present study, we investigate the phase stability within an immiscible binary thin film system that offers a simpler synthesis chemistry, i.e., the Ag-Mo system. We employ magnetron co-sputtering to grow Ag1−xMox thin films over the entire composition range along with x-ray probes to investigate the films structure and bonding properties. Concurrently, we use density functional theory calculations to predict phase stability and determine the effect of chemical composition on the lattice volume and the electronic properties of Ag-Mo solid solutions. Our combined theoretical and experimental data show that Mo-rich films (x ≥ ∼0.54) form bcc Mo-Ag metastable solid solutions. Furthermore, for Ag-rich compositions (x ≤ ∼0.21), our data can be interpreted as Mo not being dissolved in the Ag fcc lattice. All in all, our data show an asymmetry with regards to the mutual solubility of Ag and Mo in the two crystal structures, i.e., Ag has a larger propensity for dissolving in the bcc-Mo lattice as compared to Mo in the fcc-Ag lattice. We explain these findings in light of isostructural short-range clustering that induces energy difference between the two (fcc and bcc) metastable phases. We also suggest that the phase stability can be explained by the larger atomic mobility of Ag atoms as compared to that of Mo. The mechanisms suggested herein may be of relevance for explaining phase stability data in a number of metastable alloys, such as ternary transition metal-aluminum-nitride systems.

ChemInform Abstract: A Route for Phase Control in Metal Nanoparticles: A Potential Strategy to Create Advanced Materials

AbstractReview: 124 refs.

Thermal properties and phase diagrams of water–hydrocarbon systems

The phase equilibria of immiscible binary systems (water–n-hexane, water–n-pentane) are investigated using a constant-volume piezometer. The measurements were performed under normal conditions, based on P,V,T,x-data obtained in the temperature range of 300–680 K, pressures up to 60 MPa, and in a wide range of densities. Based on the experimental data, we constructed phase diagrams in the P–T and T–x coordinates and determined the Krichevskii parameters for the system of water–n-hexane near the critical point of the pure solvent.

Recent Development in Counter-current Chromatography

Abstract Counter-current chromatography (CCC) is a quick preparative separation technique with immiscible liquid-liquid solvent systems. This paper reviews recent research progress in the instruments improvement of CCC and screening of solvent systems. Moreover, some applications and prospective about chiral resolution by CCC are discussed. Finally, the content and goal of further research in this field are also presented.

Large-scale room-temperature synthesis and optical properties of perovskite-related Cs4PbBr6fluorophores

An inhomogeneous interface reaction in a liquid–liquid immiscible two-phase system is developed to realize the large-scale room-temperature synthesis of perovskite-related Cs4PbBr6fluorophores.

Rapid solidification mechanism and magnetic property of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy

Rapid solidification is a typical non-equilibrium phase transition process, and the crystallization rate of liquid metal is larger than 1 cms-1. If the alloy is solidified in this case, the solute segregation is reduced or even eliminated and the solid solubility can be improved significantly. Rapid solidification technique can be used to refine the microstructures of alloys, which provides an effective method to prepare the novel metastable materials and improve their strengths, plasticities magnetic properties, etc. In this work, the rapid solidification mechanism and magnetic property of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy are investigated by drop tube and melt spinning techniques. It is known that Fe-Cu-Sn ternary alloy forms a typical immiscible system. However, the experimental results reveal that the liquid phase separation does not take place during the rapid solidification of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy. The solidification microstructures are all composed of primary Fe dendrites together with Cu3Sn and Cu6Sn5 phases. Under the free fall condition, as the drop tube technique provides microgravity and containerless states, the maximum surface cooling rate and maximum undercooling of alloy droplets are 1.3105 Ks-1and 283 K (0.19 TL), respectively. When the surface cooling rate reaches 1.9103 Ks-1, the primary Fe phase appears as coarse dendrites, and its maximum dendrite length is 41 m. Meanwhile, the Cu3Sn and Cu6Sn5 phases are distributed in the Fe interdendritic spacings. Once the surface cooling rate increases up to 3.3103 Ks-1, the morphology of the primary Fe phase transforms from coarse dendrites into broken dendrites. It is found that the cooling rate and undercooling greatly affect the solidification microstructure of alloy droplets. During the melt spinning experiments, since the large temperature gradient exists between the wheel surface and free surface, the solidification microstructure is subdivided into two crystal zones according to the different microstructure morphologies of Fe phase: fine grain (zone I) and coarse grain (zone II), where zone I is characterized by granular grains while zone II has some dendrites with secondary branch. Under the rapid cooling condition, the microstructures of ternary equiatomic Fe33.3Cu33.3Sn33.3 alloy ribbons are refined significantly and show soft magnetic characteristics. As the surface cooling rate increases from 8.9106 to 2.7107 Ks-1, the lattice constant of Fe solid solution rises rapidly and the coercivity increases from 93.7 to 255.6 Oe. Furthermore, the results indicate that the grain size of Fe phase is the main factor influencing the coercivity of alloy ribbons.

Multi-exponential inversion of T2 spectrum in NMR based on improved nonlinear fitting

Multi-exponential inversion algorithm of nuclear magnetic resonance (NMR) T2 spectrum is an important mathematical tool for the NMR relaxation study of complicated samples. The popular algorithm usually obtains the T2 spectrum by linear fitting under the prescribed distribution of T2. When the T2 spectrum is dispersed, such a procedure is inaccurate because of the lack of adaptive prescription and the limit of linear method. Nonlinear fitting method does not fix the T2 distribution, and it provides the positions and the weights of T2 simultaneously via the nonlinear fitting of multi-exponential function. In this case, the problem of multi-exponential inversion is transformed into a nonlinear optimization problem with non-negative constraints. The optimization objective function is the residual sum of squares (or residual sum of squares with regularization). The nonlinear optimization problem can usually be solved by Levenberg-Marquardt algorithm and evolutionary algorithm. But the results of Levenberg-Marquardt algorithm are dependent on initial values, and the calculation of evolutionary algorithm is complicated. We provide an optimal model for the nonlinear fitting in the inversion of dispersed T2 spectrum based on the linear regression and least-squares. The key idea is that the optimal weights of T2 can be calculated by least square when the positions of T2 are fixed, although the positions of T2 are adjusted adaptively. So we can relate the positions to weights appropriately to improve the popular nonlinear fitting algorithms. Such an improvement can reduce the searching inversion parameters, speed up its convergence and reduce the dependence on initial value. Incorporating it into the Levenberg-Marquardt algorithm or evolutionary algorithm can improve the inversion accuracy and make the algorithm more robust. The validity of our improvement is demonstrated by the inversions of simulation data and practical NMR data by combining Levenberg- Marquardt algorithm and differential evolution algorithm with our improvement. The inversion results of simulation data show that for dispersed T2 spectrum, the algorithm using this improvement can obtain more accurate T2 spectrum than previous ones, especially in the case of low signal-to-noise ratio (SNR) cases. The inversion results also indicate that the improvement can reduce the dependence on initial value of Levenberg-Marquardt algorithm, and can accelerate the convergence of differential evolution algorithm. The inversion results of practical NMR data show that the algorithm using the improvement can obtain more accurate T2 spectrum than the widely used CONTIN program in the case of low signal-to-noise ratio (SNR). The inversion results of oil-water mixture sample NMR data also demonstrate that the relaxation time T2 is independent of dispersion degree of immiscible system components.