Droplet size and stability of nano-emulsions produced by the temperature phase inversion method

We studied the formation and stability of n-decane in water nano-emulsions produced by the phase inversion temperature (PIT) emulsification method using polyoxyethylene lauryl ether as surfactant. The results obtained indicate that the droplet size and size distribution are strongly dependent on the methods of heating and cooling, and on the final temperature to which the mixture is cooled after phase inversion. Importantly, there exists an optimum storage temperature, at which the nano-emulsions are most stable, and develop ultra-small droplet sizes, ranging from 35 nm to 54 nm, with low polydispersity indices (0.2). This optimum temperature is about 20 °C below the PIT, and dependent on the surfactant concentration. Any departure in temperature from the optimum would result in increases in droplet sizes, polydispersity and instability by Ostwald ripening. Furthermore, nano-emulsions destabilized after a long period of storage at different temperatures can be rejuvenated simply by equilibration for a few minutes at the optimum temperature.     

Diosgenin-selective molecularly imprinted pearls prepared by wet phase inversion

Functional poly(acrylonitrile-co-acrylic acid) imprinted pearls, selective for diosgenin – a steroidal saponin with the ability to reduce cholesterol from blood – were prepared by wet phase inversion. Three copolymers with the monomer ratios AN:AA90:10, 80:20, and 70:30 where used to prepare the corresponding MIPs (molecularly imprinted polymers) and NIPs (non-imprinted polymers).The rheology studies showed that an 8 w% solution of copolymer in dimethylformamide lead fastest to robust, spherical pearls. Affinity centres were generated via non-covalent bonding between diosgenin’s hydroxyl groups and carboxyl moieties of the copolymer matrix. The presence and the quality of the selective binding sites in MIPs were highlighted by optic and electronic microscopy, infrared spectroscopy, thermal analyses, and batch rebinding tests. The imprinting factor (IF) values, ranging from 1.9 to 4.35, decrease with the increasing of the initial concentration of feed solution. When comparing the MIPs concerning the AN:AA ratio, the IF decreases in the order AN:AA80:20 > AN:AA70:30 > AN:AA90:10, suggesting that the 80:20 ratio is the optimum compromise between selectivity (given by AA) and resistance (given by AN). For the best imprinted MIP, 80:20, affinity tests were performed with three competitors, obtaining the average affinity 54%, compared with 31%, 11%, and 4% for the competitors.     

BaTiO3-based thermistor hollow fibers prepared using a phase inversion spinning process for energy efficient gas sorption

Positive temperature coefficient of resistivity (PTCR) hollow fibers that exhibit self-regulating heating characteristics have potential applications in temperature-swing adsorption systems (TSA), such as CO₂ recovery and drying of compressed air. La-doped BaTiO₃ hollow fibers displaying a PTCR effect were produced by phase inverting a casting solution consisting of N-methly-2-Pyrrolidone, polymethyl methacrylate, polyvinylpyrrolidone, BaTiO₃, TiO₂, and La₂O₃ through a spinneret into a coagulating waterbath. This was followed by polymer debinding, high temperature sintering between 1350?1400 °C and annealing in air at 1175 °C to produce hollow fibers of the composition Ba_0.9975La_0.0025TiO₃. Hydrothermal synthesis was implemented to deposit an adsorbent porous zeolite X layer within the hollow fiber lumen, which was confirmed by electron dispersive X-ray spectroscopy and CO₂ adsorption at 0 °C. Hence, these materials can be applied to energy efficient TSA gas separation processes. The results are discussed in terms of hollow fiber microstructure, adsorption characteristics and electrical properties.     

Fast determination of phase inversion in polymer blends using ultrasonic technique

Ultrasonic attenuation and velocity, together with SEM observation were used to investigate the morphology of some polymer blends. For miscible polymer blends of PVC/NBR, because there is no phase inversion but a homogeneous system a linear change (without discontinuity) of ultrasonic velocity and attenuation was observed in a whole composition ranges. For immiscible polymer blends, namely, PP/PS, PS/EPDM and PS/SBS system, the non-linear variation of ultrasonic velocity with composition indicates the immiscibility. On the other hand, the intensity of scattering attenuation changed from system to system depending on the size of dispersed phase, but a discontinuity of scattering attenuation was always observed as the phase inversion occurred. Our result suggests the sensitivity of ultrasonic attention vs phase inversion and may be served as a useful method to fast determine the phase inversion for immiscible polymer blends.     

Prediction of phase inversion in agitated vessels using a two-region model

Phase inversion in agitated vessels was studied using a two-region model. In this model, breakup and coalescence were assumed to take place in the vicinity of the impeller and away from that region, respectively. The mechanism of phase inversion was regarded as the result of an imbalance between the breakup and coalescence processes. Hence phase inversion was assumed to occur when the coalescence frequency exceeded that of breakup. In addition, the concept of a radial distribution function was adopted in the model in order to account for droplet coalescence in concentrated dispersions. Using the two-region model, the effect of interfacial tension, viscosity, density and impeller size on the width of the ambivalent range was investigated. The predictions agree well with experimental data particularly for the upper curve of the ambivalent range; however, the organic phase fraction of the lower curve is in some cases underestimated by the model.     

Experimental investigation of phase inversion in a stirred vessel using LIF

A non-intrusive dye tracing technique, laser-induced fluorescence (LIF), has been applied to investigate phase inversion in concentrated immiscible organic-aqueous liquid dispersions. The phase inversion process from oil-in-water (o/w) dispersion to water-in-oil (w/o) dispersion has been recorded by a high-speed video camera. Apart from phase inversion, secondary dispersion, drop coalescence and breakup mechanisms, have also been observed in great detail. The experimental results demonstrate that phase inversion is a gradual phenomenon: the process occurs only over 1-2 s, may not occur globally and depends on the local phase distribution. During phase inversion, two opposing pairs of processes, namely drop coalescence and break-up, and the inclusion and escape of small drops in larger drops, play a key role in phase inversion. The structure of the dispersion is extremely complex and a great number of secondary dispersions and multi-dispersions appear during phase inversion, which include water-oil-water secondary dispersions.     

Phase separation and phase inversion of polyurethane networks

A series of polyurethane networks were prepared from MDI (4,4¹-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a T_g (glass transition temperature) of –60 °C, and the aromatic hard segments display a T_g of about 128 °C. Two T_gs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.     

The effect of phase inversion during semibatch aromatic nitrations

The effect of phase inversion during semibatch aromatic nitrations is experimentally characterized and analysed. The influence of various parameters, i.e. interfacial area, effective heat-transfer coefficient and overall mass-transfer coefficient, is studied. The implications for optimizing nitrations are discussed from performance and safety points of view. The accumulation of unreacted nitric acid can be dangerous if accompanied by a phase inversion, owing to the fact that the rate may increase suddenly.     

水性聚氨酯自乳化过程中相反转及影响因素

概述了水性聚氨酯自乳化时的相反转过程,讨论了影响相反转的一些重要因素。     

Polyurethane membrane prepared via a dry/wet phase inversion method for protein adsorption

Hydroxyl‐terminated polybutadiene (HTPB)‐ and 4,4′‐dicyclohexyl‐methane (H₁₂MDI)‐based polyurethanes (PUs) were synthesized by solution polymerization. PU membranes were prepared by a dry/wet phase inversion method. Protein adsorption ratio of fibrinogen to albumin (F/A molar ratio) was measured. Low F/A molar ratio was found on these PUs. It was found that surface composition of these PUs has a subtle effect on F/A adsorption molar ratio. The F/A molar ratio was increased as the increase of hard segment content distributed on the surface. The variation of surface composition of these membranes and the effect on the F/A molar ratio were investigated by the difference in surface energy between nonpolar HTPB soft segment and polar hard segment, concentration, and temperature of coagulation medium, polymer content, and alcohol type. The CO/CC ratio, frequency shift, and difference (Δν) as a measure of polymer homogeneity and the average strength of interpolymer hydrogen bonds were utilized to study the surface composition. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1334–1340, 1999     

pH-triggered phase inversion and separation of hydrophobised bacterial cellulose stabilised Pickering emulsions

The pH-triggered transitional phase behaviour of Pickering emulsions stabilised by hydrophobised bacterial cellulose (BC) is reported in this work. Neat BC was esterified with acetic (C₂–), hexanoic (C₆–) and dodecanoic (C₁₂–) acids, respectively. We observed that C₆– and C₁₂–BC stabilised emulsions exhibited a pH-triggered reversible transitional phase separation. Water-in-toluene emulsions containing of 60 vol.% dispersed phase stabilised by C₆– and C₁₂–BC were produced at pH 5. Lowering the pH of the aqueous phase to 1 did not affect the emulsion type. Increasing the pH to 14, however, caused the emulsions to phase separate. This phase separation was caused by electrostatic repulsion between modified BC due to dissociable acidic surface groups at high pH, which lowered the surface coverage of the water droplets by modified BC. When the pH was re-adjusted to 1 again, w/o emulsions re-formed for C₆– and C₁₂–BC stabilised emulsions. C₂–BC stabilised emulsions, on the other hand, underwent an irreversible pH-triggered transitional phase separation and inversion. This difference in phase behaviour between C₂–BC and C₆–/C₁₂–BC was attributed to the hydrolysis of the ester bonds of C₂–BC at high pH. This hypothesis is in good agreement with the measured degree of surface substitution (DSS) of modified BC after the pH-triggered experiments. The DSS of C₂–BC decreased by 20% whilst the DSS remained constant for C₆– and C₁₂–BC.     

Influence of selective filling on rheological properties and phase inversion of two-phase polymer blends

We investigate the phase inversion of selectively filled polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends prepared by melt mixing. As we have shown by transmission electron microscopy analysis and by the calculation of different selectivity criteria, the filler used (glass spheres of submicron dimensions) resides exclusively in the PMMA-phase and modifies its rheological properties correspondingly.Four blend series made of PS and PMMA with different filler content are analyzed for the location of phase inversion concentration, φ_PI, and the width of the cocontinuity interval, CCI, in the concentration range where cocontinuity is predominant. Upon addition of filler a shift of φ_PI to higher concentrations of the filled PMMA-phase has been observed. This shift is in agreement with the predictions of a recently proposed equation defining the phase inversion concentration as that concentration where the maximum of the blends' extra elasticity occurs. The qualitative morphological analysis of these blends confirms this result.Moreover, it was found that the cocontinuity interval is widened significantly at increased filler content. We explain the appearance of a wider CCI for filled blends on the basis of a slowdown of processes leading to morphology destruction. Corresponding Tomotika experiments (stability of fibrils) substantiate these findings.     

Evaluation of the phase composition of amylose by FTIR and isothermal immersion heats

Amylose, a linear component of starch, has been shown to be directly responsible for many of starch's physical properties. In this study isothermal DSC assisted by FTIR spectroscopy was used to determine the phase composition of amylose under various pH conditions and while shear was used to disrupt chain-chain interactions. The analysis was based on a three-phase model consisting of crystalline (type B and single helices), amorphous, and network (physical entanglements and hydrogen bonds related) environments. Varying the pH of the water present in the samples enables the detection of the presence of the networks. Such networks, preferentially located in the amorphous phase, were found to be more reactive to chemical and probably thermal modifications. However, when chain entanglements or hydrogen bond networks are found near or in the helix of the crystalline phase, the polymer becomes more resistant to chemical and physical modification. Furthermore, it was observed that pH and shear could be used to control the morphology, orientation and phase content of amylose, which had a significant impact on the biodegradability of the treated samples.     

Formation,morphology and control of high-performance biomedical polyurethane porous membranes by water micro-droplet induced phase inversion

Biomedical polyurethane (BPU) porous membranes with controlled morphology and excellent permeability and mechanical properties were prepared via a method involving a phase inversion induced by water micro-droplets, which were generated by an ultrasonic atomizer. The cross-section morphology, air permeability and mechanical properties of the porous membranes were investigated. The SEM images demonstrated that the adjacent pores were connected by a micro-hole, serving as a “backdoor” for the pore. An interconnected porous structure was obtained, improving the air permeability of the BPU membrane relative to the membrane produced by immersion precipitation. Our studies indicated that the diameter of the pores in the membrane depended on the solution viscosity, allowing porous membranes with a desired morphology to be obtained by adjusting the polymer concentration and solution viscosity. The application of micro-droplets of water during membrane preparation reduced the exchange rate between the solvent and nonsolvent, resulting in the microphase separation of polymer molecules and the formation of a uniform porous structure in the membrane, which improved the air permeability and mechanical properties of the BPU porous membranes. This is a simple and effective preparation method for high-performance porous membranes with potential applications in tissue engineering scaffolds, controlled-release drug delivery and vascular grafts.     

Colour measurement as a proxy method for estimation of changes in phase and chemical composition of fly ash formed by combustion of coal

Influence of technology on colour changes of fly ashes was studied in relationships with their chemical and phase composition. Dry bottom boilers at the Detmarovice Power Plant (the Czech Republic) were selected for this study. Combustion tests were performed using mixture of coal and mineral oil residues at the minimum and maximum output of the power plant. Fly ashes for chemical analysis, phase analysis and colour measurements were sampled from the four sections of electrostatic fly ash precipitator. Colour parameters indicate relationships with concentrations of elements which are preferentially bound in silicate matrix. The maximum output of power plant increases the concentration of glass which has decisive influence on values of colour parameters. The changes of colour parameters can indicate the conditions of the technological process. Relationships between colour and constituents of the fly ash are expressed by CIE Lab colour parameters.     

Characteristics of PVdF-HFP/TiO2 composite membrane electrolytes prepared by phase inversion and conventional casting methods

Porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP)-based polymer membranes filled with various contents of titania (TiO₂) nanocrystalline particles are prepared by phase inversion technique and, along with conventional casting method for comparison. N-methyl-2-pyrrolidone (NMP) as a solvent is used to dissolve the polymer and to make the slurry with TiO₂. Cast film is obtained by spreading the slurry and evaporating NMP in a dry oven, while phase inversion membrane by promptly immersing the spread slurry into flowing water as a non-solvent. Physical and electrochemical characterizations, such as morphology, thermal and crystalline behavior, and other transport properties of lithium ionic species, are carried out for the polymer films/membranes and the polymer electrolytes with absorbing an electrolyte solution. Phase inversion polymer electrolytes are proved to show superior behaviors in electrochemical properties, such as ionic conductivity, electrochemical and interfacial stability, than cast film electrolytes. This is greatly owed to highly porous structure of phase inversion membranes. Even including the feature of interfacial resistance with lithium electrode, phase inversion polymer electrolytes of PVdF-HFP/(5-20 wt.% TiO₂) can be optimized as the adequate ones in applying to the electrolyte medium of lithium rechargeable batteries.     

Preparation of PVC/PVP composite polymer membranes via phase inversion process for water treatment purposes

In this work, new composite membranes were successfully prepared via phase inversion technique using polyvinyl chloride(PVC) and polyvinylpyrrolidone(PVP) as polymers and tetrahydrofuran(THF) and N-methyl-2-pyrrolidone(NMP) as solvents. The prepared membranes have been characterized by scanning electron microscope(SEM), and fourier transforms infrared spectroscopy(FTIR). The scanning electron microscope results prove that the prepared membranes are smooth and their pores are distributed throughout the whole surface and bulk body of the membrane without any visible cracks. The stress–strain mechanical test showed an excellent mechanical behavior enhanced by the presence of PVP in the prepared membranes. The membranes performance results showed that the salt rejection reached 98% with a high flux. This, in turn, makes the prepared membranes can be applied for sea and brackish water treatment through membrane distillation technology.     

XRD studies of the phase composition of the electrodeposited copper-rich Cu-Sn alloys

Studies of the phase and chemical compositions as well as of the surface morphology of Cu-Sn alloys electrodeposited in the sulphate solution containing laprol were carried out using the XRD, SEM, and EDX techniques. The multiphase composition—pure copper, the α-CuSn phase and the intermediate hcp phase were determined to be present in the deposits obtained at cathode potentials positive to that of the reversible of the Sn/Sn²⁺electrode. When the content of Sn in the deposit was higher than 12-13 at.%, the β and/or δ phases were determined to be present along with that mentioned above. The deposit obtained at the potentials negative to that of the reversible of the Sn/Sn²⁺ electrode presented the δ phase with low quantities of the pure Cu and α-CuSn phases. The grain size of deposits increased with the cathode potential until it was positive to that of the reversible of the Sn/Sn²⁺ electrode. The presence of Br⁻ ions in the solution hindered the granular electrocrystallization and reduced the Sn proportion in the alloy. It was assumed that underpotential deposition (UPD) of Sn on copper could be responsible for the formation of the multiphase composition and the intermediate hcp phase. It was concluded that the brightness of the studied Cu-Sn coatings was conditioned by the surface morphology.     

Population balance modelling of phase inversion in liquid-liquid pipeline flows

Population balance equations (PBEs) along with the equal surface energy criterion are used to predict phase inversion in liquid-liquid dispersed pipeline flows. Good agreement was found between theory and experiment. Our results suggest that an ambivalent range exists in terms of distance from the inlet (rather than volume fraction) which depends on system parameters.     

不定形耐火材料中的原位反应与相组成设计

阐明了原位耐火材料的定义 ,根据反应特征及其生成物进行了分类 ,同时分析了原位反应在不定形耐火材料中的应用原理 ,并且举例说明了在不定形耐火材料中的实际应用 ,说明利用原位反应原理可以指导不定形耐火材料的相组成设计。