Preparation of monodisperse crosslinked polymelamine microcapsules by phase separation method

Monodisperse polymelamine microcapsules were prepared by phase separation method. Control of microcapsule diameter was investigated using the uniform-sized oil-in-water emulsion droplets as the capsule core. The monodisperse emulsion droplets were prepared using the Shirasu porous glass (SPG) membrane emulsification technique. The effects of the diameter of the oil droplet and concentration of sodium dodecyl sulfate (SDS), which is a typical emulsifier in SPG membrane emulsification, on microencapsulation were investigated. The microcapsules were aggregated when oil droplets with small size were microencapsulated at high SDS concentration. To reduce the SDS concentration, the creamed emulsion was used. The monodisperse polymelamine microcapsules were successfully prepared by using the creamed emulsion. The microcapsule diameter was almost similar to the diameter of the encapsulated oil droplet. The coefficient of variation values was about 10% for all microcapsules prepared in this study. Control of microcapsule diameter was achieved in the range of 5–60 μm.     

Demulsification of water-in-oil emulsions by permeation through Shirasu-porous-glass (SPG) membranes

To investigate the effect of the droplet/pore size ratio on membrane demulsification, water-in-oil (W/O) emulsions with uniform-sized droplets was demulsified by permeation through Shirasu-porous-glass (SPG) membranes with a narrow pore size distribution at mean droplet/pore diameter ratios of 0.52–5.75. At transmembrane pressures above a critical pressure, the water droplets larger than the membrane pore size were demulsified, where the SPG membrane acted as a coalescer because the hydrophilic membrane surface had a high affinity for the water droplets. By contrast, at transmembrane pressures below the critical pressure, the larger water droplets were all retained by the membrane due to the sieving effect of the uniform-sized pores. When a W/O emulsion with a mean droplet diameter of 2.30 μm was allowed to permeate through a membrane with a mean pore diameter of 0.86 μm, the demulsification efficiency increased with increasing transmembrane pressure, to a maximum value of 91% at a transmembrane pressure of 392 kPa, and then decreased, while the transmembrane flux increased almost linearly with increasing transmembrane pressure. The demulsification efficiency was higher for higher water phase content and lower concentration of the surfactant, tetraglycerin condensed ricinoleic acid ester, in the emulsions due to the reduction of the emulsion stability.     

Influence of interfacial characteristics on Ostwald ripening in hydrocarbon oil-in-water emulsions

The influence of the nature of the interfacial membrane on the kinetics of droplet growth in hydrocarbon oil-in-water emulsions was investigated. Droplet growth rates were determined by measuring changes in the droplet size distribution of 1 wt % n-tetradecane or n-octadecane oil-in-water emulsions using laser diffraction. The interfacial properties of the droplets were manipulated by coating them with either an SDS layer or with an SDS-chitosan layer using an electrostatic deposition method. The emulsion containing SDS-coated octadecane droplets did not exhibit droplet growth during storage for 400 h, which showed that it was stable to Ostwald ripening because of this oils extremely low water-solubility. The emulsion containing SDS-coated n-tetradecane droplets showed a considerable increase in mean droplet size with time, which was attributed to Ostwald ripening associated with this oils appreciable water-solubility. On the other hand, an emulsion containing SDS-chitosan coated n-tetradecane droplets was stable to droplet growth, which was attributed to the ability of the interfacial membrane to resist deformation because of its elastic modulus and thickness. This study shows that the stability of emulsion droplets to Ostwald ripening can be improved by using an electrostatic deposition method to form thick elastic membranes around the droplets.     

Polymerization of electric field-centered double emulsion droplets to create polyacrylate shells

Porous and hollow particles are widely used in pharmaceuticals, as solid phases for chromatography, as catalyst supports, in bioanalytical assays and medical diagnostics, and in many other applications. By controlling size, shape, and chemistry, it is possible to tune the physical and chemical properties of the particles. In some applications of millimeter-scale hollow shells, such as in high energy density physics, controlling the shell thickness uniformity (concentricity) and roundness (sphericity) becomes particularly important. In this work, we demonstrate the feasibility of using electric field-driven droplet centering to form highly spherical and concentric polymerizable double emulsion (DE) droplets that can be subsequently photopolymerized into polymer shells. Specifically, when placed under the influence of an ～6 × 10(4) V(rms)/m field at 20 MHz, DE droplets, consisting of silicone oil as the inner droplet and tripropylene glycol diacrylate with a photoinitiator in N,N-dimethylacetamide as the outer droplet, suspended in ambient silicone oil, were found to undergo electric field-driven centering into droplets with ≥98% sphericity and ～98% concentricity. The centered DE droplets were photopolymerized in the presence of the electric field. The high degrees of sphericity and concentricity were maintained in the polymerized particles. The poly(propylene glycol diacrylate) capsules are just within the sphericity requirements needed for inertial confinement fusion experiments. They were slightly outside the concentricity requirement. These results suggest that electric field-driven centering and polymerization of double emulsions could be very useful for synthesizing hollow polymer particles for applications in high energy density physics experiments and other applications of concentric polymer shells.     

Study on the relationship between emulsion stability and droplet dynamics of a spontaneous emulsion for chemical enhanced oil recovery

Spontaneous emulsion (SE) has attracted increasing attention, especially in the development of low-permeability reservoirs (with an average throat radius of 0.1–2?µm) for enhanced oil recovery. In this work, based on multiple light scattering principles, the relationship between emulsion stability and the droplet dynamics of SEs was investigated. The results showed that the synergistic effect of surfactant and polymer was crucial for oil emulsification in brine, since the stability of the emulsion was greatly improved. The emulsion stability and droplet dynamics depend on the temperature, concentration, and type of emulsifier. The optimal combination system had the lowest Turbiscan stability index value, and the emulsion stability time was more than 2000s. The average droplet size was 1.50?µm, and the droplet migration rate was 7.21?mm/h. The stability of the emulsion was resulted from the microscopic droplet dynamics. By reducing the migration rate of the droplets, stability of the emulsion can be obtained. Finally, the stability and droplet dynamics mechanism of the system were explained by using a schematic representation of the various equilibriums in the spontaneous emulsification flooding system.     

Determination of the efficacy of preservation of non-eye area water-miscible cosmetic and toiletry formulations: collaborative study

A collaborative study was conducted to test a method developed to distinguish between adequately and inadequately preserved cosmetic formulations. Nineteen laboratories participated in the study. Samples tested included shampoos, hair conditioners, oil-in-water emulsions, and water-in-oil-emulsions. Triplicate samples of 4 adequately preserved and 4 inadequately preserved cosmetic products were tested by each collaborative laboratory. Results showed that all inadequately preserved shampoo and conditioner samples failed to meet the acceptance criteria for adequately preserved formulations. Of the 51 preserved samples, 49 shampoos and 48 conditioners met the criteria for adequate preservation. All samples of inadequately preserved water-in-oil emulsions and oil-in-water emulsions failed to meet the acceptance criteria, whereas all adequately preserved emulsion formulations met the acceptance criteria.     

Effect of hydrophobic modification of hydroxypropyl methylcellulose on silicone oil emulsions

To study the effect of hydrophobic modification of the emulsifier on the relationship between emulsion stability and polymer emulsifier concentration, silicone oil emulsions were prepared using hydroxypropyl methylcellulose (original HPMC) and HPMC stearoxy ether (hydrophobic HPMC) at concentrations around their overlap concentrations. Both HPMC types completely emulsified the silicone oil. However, the volume fraction of silicone oil in the emulsion prepared using hydrophobic HPMC was less than that that by the original HPMC, and the average oil droplet size in the former emulsion was less than that in the latter emulsion. Increasing HPMC concentration led to increase in both the amount of adsorbed polymer emulsifier and the storage moduli in the linear region, irrespective of which HPMC was used. Stress-strain sweep curves obtained by a rheo-optical method showed that emulsions stabilized by the hydrophobic HPMC flowed slowly, even beyond the yield stress, whereas emulsions prepared using the original HPMC flowed quickly beyond the yield stress. The storage moduli of the emulsions prepared by the hydrophobic HPMC were larger than those prepared using the original HPMC.     

Oil-in-water emulsions stabilized by whey protein aggregates: Effect of aggregate size,pH of aggregation and emulsion pH

Oil-in-water emulsions (60% oil (w/w)) were prepared using whey protein aggregates as the sole emulsifying agent. The effects of whey protein aggregate size (the diameter between 0.92 and 10.9?µm), the pH of emulsions (4–8.6) and storage time on physical properties, droplet size, and stability of emulsions were investigated. The results indicate that increment of whey protein aggregate size caused an increase in the firmness, droplet size, and viscosity of emulsions, and also a decrease in the emulsion creaming. The emulsion viscosity, firmness, and droplet size were reduced by increasing the emulsion pH; however, the creaming process was accelerated. Viscosity, creaming, and droplet size of emulsions were increased slightly during 21 days storage at 40°C.     

Characterization and Evaluation of Electrolyte Influence on Canola Oil/Water Nano‐Emulsion

Emulsion stability is controlled by the physicochemical properties of the adsorbed layers formed on the surface of the droplets. Zeta potential and droplet size measured initially and during storage can estimate O/W emulsion stability. The aim of this study was to characterize and evaluate the effects of different hydrolyzable compounds employed in pharmaceutical and cosmetic preparations on the zeta potential and droplet size of canola O/W nano‐emulsions and, consequently, the emulsion stability. The samples containing additives demonstrated significant change in zeta potential, but in spite of that, no macroscopic instability was observed. Yet the droplet size values did not undergo significant change.     

Effect of Emulsifier Type on the Characterization of O/W Emulsions Using a Spectroscopy Technique

The droplet size distribution (DSD) of emulsions is the result of two competitive effects that take place during emulsification process, i.e., drop breakup and drop coalescence, and it is influenced by the formulation and composition variables, i.e., nature and amount of emulsifier, mixing characteristics, and emulsion preparation, all of which affect the emulsion stability. The aim of this study is to characterize oil-in-water (O/W) emulsions (droplet size and stability) in terms of surfactant concentration and surfactant composition (sodium dodecyl benzene sulphonate (SDBS)/Tween 80 mixture). Ultraviolet-visible (UV-vis) transmission spectroscopy has been applied to obtain droplet size and stability of the emulsions and the verification of emulsion stability with the relative cleared volume technique (time required for a certain amount of emulsion to separate as a cleared phase). It is demonstrated that the DSD of the emulsions is a function of the oil concentration and the surfactant composition with higher stability for emulsions prepared with higher SDBS ratio and lower relative cleared volume with the time. Results also show that smaller oil droplets are generated with increasing Tween 80 ratio and emulsifier concentration.     

Droplet migration in emulsion systems measured using MR methods

The migration of emulsion droplets under shear flow remains a largely unexplored area of study, despite the existence of an extensive literature on the analogous problem of solid particle migration. A novel methodology is presented to track the shear-induced migration of emulsion droplets based on magnetic resonance imaging (MRI). The work is in three parts: first, single droplets of one Newtonian fluid are suspended in a second Newtonian fluid (water in silicone oil (PDMS)) and are tracked as they migrate within a Couette cell; second, the migration of emulsion droplets in Poiseuille flow is considered; third, water-in-silicone oil emulsions are sheared in a Couette cell. The effect of (a) rotational speed of the Couette, (b) the continuous phase viscosity, and (c) the droplet phase concentration are considered. The equilibrium extent of migration and rate of migration increase with rotational speed for two different emulsion systems and increased continuous phase viscosity, leads to a greater equilibrium extent of migration. The relationship between the droplet phase concentration and migration is however complex. These results for semi-concentrated emulsion systems and wide-gap Couette cells are not well described by existing models of emulsion droplet migration.     

New Polyurethane/Docosane Microcapsules as Phase‐Change Materials for Thermal Energy Storage

Polyurethane microcapsules were prepared by mini‐emulsion interfacial polymerization for encapsulation of phase‐change material (n‐docosane) for energy storage. Three steps were followed with the aim to optimize synthesis conditions of the microcapsules. First, polyurethane microcapsules based on silicone oil core as an inert template with different silicone oil/poly(ethylene glycol)/4,4′‐diphenylmethane diisocyanate wt % ratio were synthesized. The surface morphology of the capsules was analyzed by scanning electronic microscopy (SEM) and the chemical nature of the shell was monitored by Fourier transform infrared spectroscopy (FT‐IR). Capsules with the silicone oil/poly(ethylene glycol)/4,4′‐diphenylmethane diisocyanate 10/20/20 wt % ratio showed the best morphological features and shell stability with average particle size about 4 μm, and were selected for the microencapsulation of the n‐docosane. In the second stage, half of the composition of silicone oil was replaced with n‐docosane and, finally, the whole silicone oil content was replaced with docosane following the same synthetic procedure used for silicone oil containing capsules. Thermal and cycling stability of the capsules were investigated by thermal gravimetric analysis (TGA) and the phase‐change behavior was evaluated by differential scanning calorimetry (DSC).     

Influence of pH on the stability of oil-in-water emulsions stabilized by a splittable surfactant

A laboratory study was conducted to evaluate the effect of pH on the stability of oil-in-water emulsions stabilized by a commercial splittable surfactant Triton SP-190 by comparison with the results obtained by a common surfactant Triton X-100. The emulsion stability was explored by measuring the volume of oil phase separated and the size of the dispersed droplets. It was found that the addition of inorganic acids did not significantly affect the stability of emulsions stabilized by Triton X-100, but had a profound influence on the stability of emulsions stabilized by Triton SP-190. Moreover, the droplet size of a Triton X-100-stabilized emulsion and its dynamic interfacial activity were insensitive to acids. However, at lower pH the droplet size of the emulsions stabilized by Triton SP-190 was considerably increased. From the dynamic interfacial tension measurements the dynamic interfacial activity of Triton SP-190 at the oil/water interface was found to be strongly inhibited by the addition of acids, resulting in a slower decreasing rate of dynamic interfacial tension. The results demonstrate that the dramatic destabilization of Triton SP-190-stabilized emulsions could be realized by the use of acids, which evidently changed the interfacial properties of the surfactant and resulted in a higher coalescence rate of oil droplets.     

Effects of Surface Properties on Rheological and Interfacial Properties of Pickering Emulsions Prepared by Fumed Silica Suspensions Pre-Adsorbed Poly(N-Isopropylacrylamide)

The hydrophobic fumed silica suspensions physically pre-adsorbed poly(N-isopropylacrylamide) (PNIPAM) in water could prepare oil dispersed in water (O/W) Pickering emulsion by mixing of silicone oil. The resulting Pickering emulsions were characterized by the measurements of volume factions of emulsified silicone oil, adsorbed amounts of the silica suspensions, oil droplet size, and some rheological responses, such as stress-strain sweep curve and dynamic viscoelastic moduli as a function of the added amount of PNIPAM. Moreover, their characteristics were compared with those of the O/W Pickering emulsions prepared by the hydrophilic fumed silica suspensions pre-adsorbed PNIPAM. For the emulsions prepared by the hydrophobic silica suspensions, an increase in the added amount of PNIPAM led to (1) a decrease in the volume fraction of the emulsified oil in the emulsified phase, (2) both the size of oil droplets and the adsorbed amount of the corresponding silica suspensions being almost constant, except for the higher added amounts, and (3) both the storage modulus (G′) and the yield shear strain being constant. The term of 1 is the same for the emulsions prepared by the hydrophilic silica suspensions, whereas both the adsorbed amount of the corresponding silica suspension and the G′ value increase and both the droplet size and the yield shear strain decrease with an increase in the added amount of PNIPAM. The differences between the rheological properties of the emulsions prepared by the hydrophilic silica suspensions and those by the hydrophobic ones are attributed to the hydrophobic interactions of the flocculated silica particles in the Pickering emulsions.     

Creaming Stability of Flocculated Monodisperse Oil-in-Water Emulsions

The influence of droplet flocculation on the creaming stability of monodisperse n-hexadecane oil-in-water emulsions was studied. The creaming velocity of emulsions with different droplet radii (0.43 and 0.86 μm), droplet concentrations (1-67 vol%), and sodium dodecyl sulfate (SDS) concentrations (7-80 mM) were measured. Depletion flocculation was observed in the emulsions when the aqueous phase SDS concentration exceeded a particular level ( approximately 40 mM for 0.43-μm droplets and approximately 15 mM for 0.86-μm droplets). Creaming was monitored by measuring the back-scattered light from an emulsion as a function of its height. The creaming velocity increased with increasing flocculation and decreased with increasing droplet concentration. These results have important implications for the formulation of emulsion-based materials. Copyright 2000 Academic Press.     

Kinetics of colloidal templating using emulsion drop consolidation

The emulsion templating of ordered colloidal microsphere assemblies by Manoharan et al. involves a consolidation process where dispersed phase fluid is transported from droplets into a continuous phase. Consolidation can be approximated as a diffusion process with moving boundaries. The kinetics of consolidation are investigated here by following droplet shrinkage with time as a prelude to understanding rate effects on assembly structure. Consolidation kinetics are influenced by liquid diffusivity, the number of colloidal particles in a droplet, and the surfactant concentration. While surfactant exhibits little effect well below its critical micelle concentration (CMC) value, it significantly slows consolidation above the CMC. For a specific continuous phase (i.e., silicone oil and fluorinated silicone oil), with proper scalings, the droplet size shrinks with time following a power law independent of droplet diameter, surfactant concentrations, and particle number concentration. The power law exponent varies from 1/2 to 2/3 with different continuous oil phases as a result of concentration and interfacial effects. This study leads to an improved understanding of colloidal microstructure development at interfaces that can be applied in novel materials synthesis and drug delivery areas.     

Influence of environmental stresses on stability of oil-in-water emulsions containing droplets stabilized by beta-lactoglobulin-iota-carrageenan membranes

An oil-in-water emulsion (5 wt% corn oil, 0.5 wt% beta-lactoglobulin (beta-Lg), 0.1 wt% iota-carrageenan, 5 mM phosphate buffer, pH 6.0) containing anionic droplets stabilized by interfacial membranes comprising of beta-lactoglobulin and iota-carrageenan was produced using a two-stage process. A primary emulsion containing anionic beta-Lg coated droplets was prepared by homogenizing oil and emulsifier solution together using a high-pressure valve homogenizer. A secondary emulsion containing beta-Lg-iota-carrageenan coated droplets was formed by mixing the primary emulsion with an aqueous iota-carrageenan solution. The stability of primary and secondary emulsions to sodium chloride (0-500 mM), calcium chloride (0-12 mM), and thermal processing (30-90 degrees C) were analyzed using zeta-potential, particle size and creaming stability measurements. The secondary emulsion had better stability to droplet aggregation than the primary emulsion at NaCl 相似文献   

Emulsion Templating of Poly(lactic acid) Particles: Droplet Formation Behavior

Monodisperse poly(dl-lactic acid) (PLA) particles of diameters between 11 and 121 μm were fabricated in flow focusing glass microcapillary devices by evaporation of dichloromethane (DCM) from emulsion droplets at room temperature. The dispersed phase was 5% (w/w) PLA in DCM containing 0.1-2 mM Nile Red and the continuous phase was 5% (w/w) poly(vinyl alcohol) in reverse osmosis water. Particle diameter was 2.7 times smaller than the diameter of the emulsion droplet template, indicating very low particle porosity. Monodisperse droplets have only been produced under dripping regime using a wide range of dispersed phase flow rates (0.002-7.2 cm(3)·h(-1)), continuous phase flow rates (0.3-30 cm(3)·h(-1)), and orifice diameters (50-237 μm). In the dripping regime, the ratio of droplet diameter to orifice diameter was inversely proportional to the 0.39 power of the ratio of the continuous phase flow rate to dispersed phase flow rate. Highly uniform droplets with a coefficient of variation (CV) below 2% and a ratio of the droplet diameter to orifice diameter of 0.5-1 were obtained at flow rate ratios of 4-25. Under jetting regime, polydisperse droplets (CV > 6%) were formed by detachment from relatively long jets (between 4 and 10 times longer than droplet diameter) and a ratio of the droplet size to orifice size of 2-5.     

利用酯化淀粉和油酸甲酯制备高效氯氟氰菊酯水乳剂

以辛烯基琥珀酸淀粉钠和油酸甲酯分别为替代乳化剂和溶剂,采用浓缩乳化法制备了高度稳定的2.5％高效氯氟氰菊酯水乳剂,通过测定乳液油滴粒径分布,结合乳液外观研究了乳化方法、预处理液中辛烯基琥珀酸淀粉钠质量分数、转速和剪切时间等工艺条件对乳液稳定性的影响.研究结果表明,辛烯基琥珀酸淀粉钠对油酸甲酯具有较好乳化效果,以其为乳化剂可制备高度稳定的2.5％高效氯氟氰菊酯水乳剂,油滴平均粒径在1.2 μm左右,且加速试验[即(54±2)℃密封14 d]和常温储存6个月后平均粒径仅增长了0.1～0.3μm,外观无变化;采用浓缩乳化法且预处理液中辛烯基琥珀酸淀粉钠质量分数在15％～25％时乳液稳定性较好,提高转速可降低油滴平均粒径,但对乳液均一性无显著影响,延长剪切时间对油滴平均粒径影响不大,但有利于提高乳液均一性;辛烯基琥珀酸淀粉钠为乳化剂制备的高效氯氟氰菊酯水乳剂稳定性优于常规水乳剂.