Characterization of Monomer Emulsions in Terms of Droplet Size and Stability: Effect of Emulsifier Concentration

In emulsification processes, the estimation of the droplet size distribution is important data not only because it is linked with the manufacturing process, but also because it is an important parameter affecting the emulsion stability. The aim of this research is to use the ultraviolet-visible transmission spectrum as a tool for emulsion characterization (droplet size and stability) to be a function of monomer concentration, and to verify of emulsion stability using the volume of separated phase's technique. Both techniques are applied to monomer emulsions as a function of emulsifier concentration. Results show correlations between droplet size measurements and stability of emulsions using the spectroscopy technique; results were also found to be in agreement using the cleared volume method.     

Characterization of Emulsions: A Systematic Spectroscopy Study

Emulsification processes results in the generation of droplets populations produced from the dynamic equilibrium between the breakup and coalescence phenomena determined primarily by the formulation and composition variables, mixing characteristics and emulsion preparation. The information contained in the UV‐vis spectrum on the absorption and scattering properties of the emulsions lead to the interpretation of the spectra in terms of the particle size distribution, the particle shape, and the chemical composition of the oil and emulsifier. This article reports analysis of emulsions on transmission spectrum as function of the oil concentration and physicochemical variables. The quantitative interpretation of the transmission spectrum is performed in the portion where no absorption is present (300–820 nm) leading to reliable estimated of droplet size populations in the range of 1 to 20 µm. The possibility of obtaining information from a single multiwavelength measurement makes UV‐vis spectroscopy a powerful tool for characterization of dispersed systems.     

Continuous Spectroscopy Characterization of Emulsions

In emulsion polymerization, the formation of particles has an important effect on the rate of reaction and on the final properties of the latex. To investigate particle nucleation mechanisms in emulsion polymerization it is necessary to establish the initial conditions of the emulsified system before the reaction takes place. This research reports on a technique to continuously monitor the droplet size distribution of liquid-liquid emulsions using spectroscopy. The on-line particle characterization methodology is based on an integrated sampling and dilution strategy combined with spectroscopy methods. It is shown that the sampling system integrated with a multiwavelength turbidity detector provides reliable estimates of droplet populations as function of the dispersed phase concentration in emulsions of saturated hydrocarbons. The results provide not only the groundwork necessary for the elucidation of particle nucleation during emulsion polymerization process but also suggests the potential of this combined technology to further our understanding of liquid-liquid emulsions.     

Encapsulation and Prolonged Release Behaviour of W/O/W Type Multiple Emulsions

W/O/W type multiple emulsions were prepared by two step emulsification procedures using an oily lymphographic agent, lipiodol, as an inner oil phase and Pluronic F-68 as a hydrophilic emulsifier contained in the outer aqueous phase. Span 80, Pluronic L-64 and HCO-60 were used as emulsifiers incorporating them into the inner oil phase. The phase volume of the inner and outer aqueous phases and the yield of the w/o/w type multiple emulsions were studied. The dissolution behaviour of the w/o/w type multiple emulsions were determined by a dialysis method employing cellulose tubing. The effect of emulsifier type and the amount of HCO-60 on the stability and prolonged release behavior of the w/o/w type multiple emulsions with or without lecithin, was also examined. The results indicate the HCO-60 is a better emulsifier than Span 80 or Pluronic L-64. Its use improves the stability and the prolonged release behavior of w/o/w type multiple emulsions.     

Stability of W/O Emulsions Encapsulating Polysaccharides

In the frame of formulation of W/O emulsions entrapping polysaccharides devoted to agricultural applications, the aim of this work was to study the stability over time of these emulsions, stabilized with either soybean lecithin or polyglycerol polyricinoleate (PGPR) as emulsifiers. Emulsifiers were dissolved in oil phase, and polysaccharides (carboxymethycellulose (CMC), guar, xanthan) in ultrapure water. Emulsions stability was studied through natural aging tests and accelerated aging tests, using bottle tests, microscopy and calorimetry. Experiments showed that PGPR was more efficient than lecithin to stabilize emulsions containing the polysaccharides studied, and that emulsions prepared with CMC showed the best stability.     

Alteration of Interfacial Stability of Oil-in-Water Emulsions Using Bio-Derived Additives

Oil-in-water (O/W) emulsions are widely used in the preparation of many cosmetics, foods, and pharmaceutical products. Microstructure and stability of such emulsions are of utmost importance for their acceptability by the end user. In the present work, we studied the O/W emulsions to know the effects of two bio-derived additives—juice of Coriander sativam L., and milk of Cocos nucifera L, which have good nutrient value for their use in food emulsions. Addition of Cocos nucifera L. milk resulted in enhanced stability with decrease in the polydispersity of dispersed droplets in the emulsions due to the presence of proteins in it. Addition of Coriander sativam L. provided better stability against pH variation from 4 to 8.     

W／O／W乳液的渗透溶胀与夹带溶胀

研究了W/O/W乳液的溶胀,实验结果表明,渗透溶胀随内外相溶液间的渗透压差、表面活性剂及载体浓度的增大而增加,但随膜粘度的增加而降低,渗透压差较高时,水渗透的影响大于夹带的影响;膜相中含氧化合物对溶胀的影响大于含氮化合物,采用Span 80作乳化剂时,比采用E 644渗透溶胀约高6倍,夹带溶胀也较高;重复聚结再分散使夹带溶胀急剧增加,因而多级混合澄清槽对液膜操作似不适用。     

醇醚糖苷与纳米膨润土颗粒稳定乳状液的协同作用

以表面活性剂醇醚糖苷(AEG)和纳米膨润土颗粒(NPT-2)为乳化剂,制备了油酸甲酯乳状液,考察了AEG与NPT-2的配比对乳液体系稳定性和乳液粒径的影响,并通过表面张力和zeta电位测量对二者复配稳定乳液的机理进行了讨论。结果表明,单一使用表面活性剂AEG或者纳米膨润土颗粒NPT-2均不能得到稳定的油酸甲酯乳状液,将二者复配则乳液的稳定性有显著提高。固定AEG量逐渐增加NPT-2乳液粒径先增大后又减小,固定NPT-2量逐渐增加AEG,乳液体系粒径逐渐变小;AEG与NPT-2复配前后体系的表面张力曲线"滞后"现象及zeta电位的升高表明,AEG分子在纳米颗粒NPT-2上发生了吸附,协同稳定乳状液。     

Jojoba Oil/Water Emulsions Stabilized by BSA and Egg Proteins: A Study Using Conductivity Technique

Stability of jojoba oil/water emulsion systems was investigated using the conductivity technique. Egg white, egg yolk, and bovine serum albumin (BSA) proteins were used as emulsifiers. Stability of above emulsions was investigated using several protein concentrations (0.05–0.50 mg/ml) and several oil volume fractions, OVF, (0.25; 0.50). It was concluded from the results that the investigated emulsions stability, when using BSA, was higher than when using egg white or egg yolk. In addition, emulsion stability did not show a strong dependence on OVF, except at the higher protein concentration of 5.0 mg/ml, where ES increased significantly with increasing OVF. Finally, emulsifier activity was found to increase with increasing OVF.     

酯化淀粉乳化剂制备的高效氯氟氰菊酯O/W乳液的稳定机制

通过测定辛烯基琥珀酸淀粉钠的用量、盐离子、pH值和温度等因素对油滴Zeta电位及表面吸附量的影响,分析了以酯化淀粉辛烯基琥珀酸淀粉钠为乳化剂制备的5％高效氯氟氰菊酯水乳剂的稳定机制.结果表明,辛烯基琥珀酸淀粉钠质量分数为7％时,Zeta电位达到最大值,油滴表面吸附量接近饱和;Na+、Mg2+和Al3+压缩油滴表面的双电层,降低Zeta电位,削弱静电排斥作用,增加辛烯基琥珀酸淀粉钠分子柔性,提高辛烯基琥珀酸淀粉钠表面吸附量,且随着Na+、Mg2、Al3+离子强度依次增大,压缩双电层能力依次增强,Zeta 电位降低和表面吸附量增加程度依次增大;pH值影响辛烯基琥珀酸淀粉钠在水中的解离,在碱性范围内解离出较多羧酸根,静电排斥力较大,Zeta电位较高,但表面吸附量有所降低;温度升高,辛烯基琥珀酸淀粉钠在水溶液中溶解度增大,呈舒展状态,且辛烯基琥珀酸淀粉钠从油滴表面逃逸的趋势增加,油滴表面Zeta电位和表面吸附量均随着温度升高而降低,在低温区差别不大,温度越高二者变化越明显.辛烯基琥珀酸淀粉钠通过吸附于油滴表面为其提供较强的静电斥力和空间位阻作用而维持O/W乳液稳定.     

O/W Moisturizing Emulsions with Saccharose Palmitate and Saccharose Stearate

The ability of two saccharose esters, saccharose palmitate (SMP) and saccharose stearate (SMS), to form lamellar structure in oil/water/glyceryl stearate mixtures was investigated through ternary phase diagrams. Three different oils have been tested: fluid paraffin, C12‐15 alkylbenzoate, and cetearyl octanoate. On the basis of the phase behaviors several emulsions with liquid crystalline structure were obtained and then characterized. Furthermore the most stable ones were added with a moisturizing active, lauryl pyrrolidone (LP), or sodium‐D,Lpyroglutamate (PCA). After the addition, the stability of the emulsions was assessed: It was observed that PCA‐containing emulsions resulted as less stable compared to LP‐containing ones.     

Effects of compositions on the stability of polyols-in-oil-in-water (P/O/W) multiple emulsions

Polyols-in-oil-in-water (P/O/W) multiple emulsions were successfully prepared by using polyols as inner aqueous phase to avoid instabilities caused by water. The influence of polyols, oils and emulsifiers on the morphology and stability of P/O/W multiple emulsions were studied and the stability mechanisms of this new kind of multiple emulsions were also explored. Glycerol that has the worst solubility in oil phase contributed to the formation of stable inner droplets which agree with the Ostwald Ripening theory. Mineral oil worked well with the system proving that oils possessing similar solubility parameters with the hydrophobic group of emulsifiers benefited for system stability. Several typical surfactants had been investigated in this article, and it turned out that emulsifiers Cetyl PEG/PPG-10/1 Dimethicone and the block copolymer Poloxamer 407 were suitable for the P/O/W system. The stability of the system affected by different compositions was evaluated based on microscopic observation and rheological measurements. The novel multiple emulsions will provide enlightening recommendations for future investigations and applications in cosmetic, food and pharmaceuticals, including drug delivery and the encapsulation of hydrophilic actives and actives that are soluble in polyols.     

用混合乳化剂UE20/PVA制备的水包油型生漆乳液的性能

以漆酚基乳化剂(UE20)和聚乙烯醇(PVA)为混合乳化剂制备了水包油(O/W)型生漆乳液(RLE), 研究了UE20与PVA的质量比、混合乳化剂质量分数(wME)、水与天然生漆(RL)的质量比、温度和贮存时间对RLE性能的影响, 并用透射电镜观察了wME对RLE粒子的大小及形态的影响. 结果表明, RLE的黏度随着PVA的增加而增大; 当wME≤6.7%时, RLE表现出假塑性流体的特征, 其黏度随着wME的增大而增大, 乳液的稳定性增强; 而当wME≥10.0%时, RLE则表现出膨胀型流体的特征, 乳液的黏度较低; 随着温度的升高及水的用量增加, RLE粒子间相互作用减弱, 乳液的稳定性降低. 正交实验结果表明, 影响RLE的黏度及稳定性的顺序为wME＞mH2O∶mRL＞mUE20∶mPVA＞乳化温度. 随着wME的增大, RLE粒子的粒径减小, 其形态也由不规则的形状转变为球形粒子.     

Preparation and Optimization of O/W Emulsions Stabilized by Triglycerol Monolaurate for Curcumin Encapsulation

Curcumin is one of the most studied chemo-preventive agents, which may cause suppression, retardation, or inversion of carcinogenesis. But its application is currently limited because of its poor water-solubility and bioaccessibility. A curcumin O/W emulsion was prepared by high-pressure homogenization, using triglyceride monolaurate as an emulsifier and medium chain triglycerides (MCT) as the oil phase. The effects of emulsifiers, emulsifier concentration, oil type, oil-to-water ratio, and homogenization pressure and processing cycles on the physical stability and droplet size distribution of curcumin-encapsulated O/W emulsions were evaluated in this study. The results showed that the mean droplet size of the O/W emulsions remained remarkably stable during 60 days of storage under both light and dark conditions. Curcumin retentions in O/W emulsions after 60 days of storage under light and dark conditions were 97.9% and 81.6%, respectively. In addition, during the simulated gastrointestinal digestion process, the mean droplet size of the O/W emulsions increased from 260 nm to 2743 nm after incubation with simulated gastric fluid (SGF) for 24 h, while the mean droplet size remained unchanged after incubation with simulated intestinal fluid (SIF). The results displayed negligible changes in curcumin content during incubation with simulated gastrointestinal fluids, indicating that effective protection of curcumin was achieved by encapsulation in the O/W emulsion. It is expected that curcumin will acquire high bioaccessibility and bioavailability when the O/W emulsion is to be used in clinical applications.     

Preparation and Characterization of Styrene/Butyl Acrylate Emulsifier-Free Latex with 2-Acrylamido-2-Methyl Propane Sulfonic Acid as a Reactive Emulsifier

A kind of emulsifier-free latex (FL) was successfully synthesized from styrene (St) and butyl acrylate (BA) with 2-acrylamido-2-methyl propane sulfonic acid (AMPS) as a reactive emulsifier. The particle size of latex particles, stability against electrolytes, minimum film forming temperature (MFT) and water contact angle (CA) were evaluated and compared with a conventional latex (CL). Test results show that FL has larger particle size, better stability against electrolytes and lower MFT value compared with CL; higher AMPS content leads to smaller particle size and smaller water CA.     

非离子型可聚合聚氨酯/苯乙烯的超浓乳液聚合

研究了以非离子型可聚合聚氨酯(PUAG)和苯乙烯(St)为混合单体的超浓乳液聚合, 并且考察了n(NCO)/n(OH)摩尔比、复合乳化剂体系质量浓度[E]、不同乳化剂的种类、引发剂质量浓度[I]、单体体积分数(或分散相体积分数, 也称内相比Φ)、聚合温度等因素对聚合稳定性、动力学的影响. 同时结合光相关光谱(PCS)测定了聚合物乳胶粒子大小和粒径分布, 用透射电子显微镜(TEM)观察了粒子形态, 结果表明: 当n(NCO)/n(OH)＝2∶1, T＝328 K, Φ＝80.39%, [I]＝0.8% g/g (PUAG-St), [E]＝0.22 g/mL H₂O, m(MS-1)/m(CA)＝2∶1, PVA＝0.01 g/mL H₂O时, 超浓乳液不仅有较好的聚合稳定性和较快的聚合速率, 而且粒径小分布均匀. 同时, 在此条件下的表观动力学表达式和表观活化能分别确定为R_p＝k[I]^0.50[E]^0.73[M]^0.54和 E_a＝29.7 kJ/mol. 热失重分析(TGA)进一步表明: 调节PUAG的含量可以达到对聚苯乙烯的改性, 提高聚苯乙烯的热稳定性.     

Synthesis and Characterization of Nano-silica/Polyacrylate Composite Emulsions by Sol-gel Method and in-situ Emulsion Polymerization

Organic nano-silica was firstly synthesized by sol-gel method with methyl methacrylate (MMA) and butyl acrylate (BA) in the micelles as dispersing media, tetraethoxysilicate (TEOS) as precursor, hydrochloric acid as catalyst and methacryloylpropyl trimethoxysilane (A174) as modifier. Subsequently, the nano-silica/polyacrylate composite emulsions were directly prepared by in-situ emulsion polymerization under the action of the initiator. The structure and properties were characterized by Fourier transform infrared spectroscopy (FTIR), dynamic light-scattering (DSL), thermogracvimetry (TG) and transmission electron microscopy (TEM). The results showed that A174-modified nano-silica was successfully synthesized in the acrylate-based emulsions by the sol-gel method. The nano-silica was encapsulated by polyacrylate, and the composite latex particles exhibited an apparent core-shell structure. The A174 could improve the lipophilicity of nano-silica and increase the grafting efficiency of polyacrylate on nano-silica particles. The nano-silica/polyacrylate composite latex film had better thermal stability, and the composite latex particles had greater average size and broader size distribution in contrast to those of pure polyacrylate emulsions.     

Role of emulsifier on the particle size and polymer particle size distribution using multiwavelength spectroscopy measurements

Latex emulsions depend strongly on the polymer composition, and particle size distribution, which in turn, is a function of the preparation of the latex and on the formulation and composition variables. This study reports measurements of particle size and particle size distribution of latex emulsions as function of the reaction time and the type and concentration of emulsifier by using the multiwavelength spectroscopy technique. Results show changes in the particle size of latex emulsions with the reaction time, obtaining larger particles and broader distributions with increasing of Tween 80 ratio. The steric stabilization provides the sole nonionic emulsifier is not enough to protect the polymer particle, causing the flocculation among the interactive particles, resulting in unstable latex. However, latex emulsions prepared with Tween 80 ratio <70 wt.% can stabilize efficiently the nucleated particles, probably due to the effects provided by both, the electrostatic and steric stabilization mechanisms. The same effect is shown in the curves of conversion (%) as a function of reaction time, resulting in slower polymerization rate for Tween 80 ratio >70 wt.%. On the other hand, smaller polymer particles, in all range of emulsifier mixture, have been obtained to higher emulsifier concentration.     

离心-电导联用法快速评价O/W乳状液稳定性

建立了乳状液在重力场和离心力场中的沉降/分层速率模型,利用离心加速乳状液的沉降/分层,根据分层后富水相的电导随离心时间的变化关系得到乳状液在离心场中的稳定时间tc,进而推算出乳状液在重力场中的稳定时间tg。这种离心-电导联用方法可快速评价O/W乳状液的稳定性。例如,以质量分数为4%Pluronic F68、1.2%卵磷脂、8%甘露醇和10%IPM配置的乳状液,在8000r/min离心下测得tc为22min,计算出tg为69d;定性分析得到离心分层常数KA=48.0%,结果表明,该配方可得到稳定的O/W乳状液。