聚合物分散剂对氟虫脲水悬浮剂分散稳定性的影响

通过测定药物颗粒界面Zeta电位和平均粒径, 研究了聚合物分散剂苯乙烯磺酸聚合物钠盐(GY-D08)用量、pH和盐离子对氟虫脲水悬浮剂分散稳定性的影响, 研究结果表明, 分散剂GY-D08的加入量与水悬浮剂分散效果密切相关, 制备质量分数为5%氟虫脲水悬浮剂的GY-D08最佳用量为2%, GY-D08用量过多或过少都会使分散效果下降; pH影响分散剂GY-D08在水中的电离能力, 当pH=9时, GY-D08分子完全电离, 能为颗粒提供较大的静电位阻, 水悬浮剂分散稳定性最好; Mg²⁺或Ca²⁺压缩颗粒界面的双电层, 降低Zeta电位, 使颗粒因带电量减少而聚结, 导致水悬浮剂分散稳定性变差, 且Mg²⁺或Ca²⁺浓度愈大, 其分散稳定性愈差; 当离子浓度相同时, Ca²⁺压缩双电层的能力比Mg²⁺强, 添加Ca²⁺后的水悬浮剂的分散稳定性更差.     

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.     

分子动力学模拟电解质对阴非离子表面活性剂界面行为的影响

通过分子动力学(MD)方法研究了不同类型电解质对阴非离子表面活性剂C₁₂EO₃C油水界面性能的影响。运用z轴质量密度分布、径向分布函数、分子间相互作用配位数、空间分布函数及均方根位移五种模拟参数来分析电解质与阴非离子表面活性剂的相互作用情况。研究表明,三种离子的加入均对水分子与表面活性剂亲水基形成的水化层结构产生影响,且从微观层面验证三种离子对表面活性剂亲水基相互作用强度大小顺序为Na⁺ < Ca²⁺ < Mg²⁺。通过扩散模拟结果可以较好地解释离子加入对界面张力平衡时间的影响情况。这对指导实验方向、制订最佳复配方案具有重要意义。     

毛细管区带电泳同时测定化妆品中的阴阳离子

Natural Sea Beauty系列化妆品富含来自Dead Sea水中的矿物质,对皮肤有较好的治疗和滋养作用.本文采用毛细管区带电泳的技术,电迁移双端进样,5 mmol/L咪唑-2 mmol/L硝酸为背景电解质,以富马酸调至pH 4.1,UV间接测定法(214nm),在6min内同时检测了化妆品中的阴阳离子(K⁺、Na⁺、Ca²⁺、Mg²⁺、Cl^-、Br^-),与离子色谱法所得结果进行了对照.此方法可为鉴别不同品牌的化妆品提供一定的依据.     

冠醚对生物化学影响的研究(Ⅲ)——五种冠醚化合物对小麦幼苗根系吸收与运转42K、24Na、45Ca离子的影响

本文用放射性同位素⁴²K、²⁴Na、⁴⁵Ca作示踪,配以P^K、P^Na离子选择电极测量溶液的电导率和电位变化。研究五种冠醚化合物对南大八号小麦幼苗根系吸收与运转无机离子(K⁺、Na⁺、Ca^艹)的作用。实验结果表明,五种冠醚化合物对小麦幼苗根系具有不同程度的促进吸收和加速运转K⁺、Na⁺、Ca^艹的作用,其中以1号冠醚化合物作用最为明显,在K⁺、Na⁺、Ca⁺艹>中对K⁺的作用最为突出。     

离子效应对纳滤膜表面Zeta电位测定的影响

采用流动电位法,用固体表面电位测定仪考察电解质溶液种类、浓度、p H对纳滤膜表面Zeta电位的影响。结果表明,二价离子溶液比一价离子溶液对纳滤膜表面Zeta电位作用明显,同价态离子的离子半径越小,Zeta电位越大;随着离子强度的增加,Zeta电位越小,在低离子浓度下Zeta电位值稳定性,重复性好;随着溶液p H的变化(3~10),纳滤膜的表面呈现两性性质,等电位点在p H 4.5~5.0之间。在测试纳滤膜表面Zeta电位时,推荐选择0.001mol/L的KCl电解质溶液。     

钽掺杂六方相氧化钨对Sr2+的吸附:Zeta电位的测量及吸附机理的研究

研究Ta掺杂六方相氧化钨(hex-WO₃)材料在吸附Sr²⁺过程中其表面zeta电位的变化情况,并进一步探讨了吸附过程的热力学及吸附机理。结果表明：(1)在实验pH值范围内,Ta掺杂hex-WO₃悬浮液的zeta电位值随溶液中电解质的价态增大而增大;(2)且zeta电位随体系中离子强度的增加而增大;(3) Ta掺杂hex-WO₃对Sr²⁺的吸附容量随着温度降低而增大,随着离子强度的增加而减少;(4)吸附过程的吸附焓为－47 kJ·mol^-1,且Sr²⁺离子与材料表面之间主要为化学相互作用;(5) Ta掺杂hex-WO₃对Sr²⁺吸附过程主要为材料表面吸附及材料孔道内离子交换共同作用。     

Ca2+诱导的淀粉液化芽孢杆菌α-淀粉酶分子的生物活性和结构变化

在研究Ca²⁺对淀粉液化芽孢杆菌α-淀粉酶分子生物活性影响的基础上, 采用荧光光谱法和傅里叶变换红外光谱法研究了Ca²⁺诱导的酶分子结构变化. 结果表明, 当溶液中Ca²⁺浓度低于25.0 mmol/L时, Ca²⁺对酶分子具有激活作用; 而当Ca²⁺浓度高于25.0 mmol/L时, Ca²⁺对酶分子的生物活性具有抑制作用. 在Ca²⁺诱导的淀粉液化芽孢杆菌α-淀粉酶分子结构变化过程中, 酶分子仅发生二级结构的变化, 并不涉及其三级结构. 当Ca²⁺对酶分子具有激活作用时, 酶分子中的无规卷曲结构及β-折叠结构的含量下降, 而α-螺旋结构及β-转角结构的含量上升; 而当Ca²⁺对酶分子生物活性具有抑制作用时, 酶分子中的α-螺旋结构及β-转角结构的含量下降, 而无规卷曲结构及β-折叠结构的含量上升.     

PEO基聚合物电解质及其锂硫电池性能研究

锂硫电池由于具有高的理论比能量引起了广泛关注,然而传统液态锂硫电池由于多硫化物的“穿梭效应”以及安全问题而限制了其应用,全固态锂硫电池可显著提高电池安全性能并有望解决多硫化物的穿梭问题. 本文采用传统的溶液浇铸法制备了具有不同的[EO]/[Li⁺]的PEO-LiTFSI聚合物电解质,并将其应用于锂硫电池. 研究发现,虽然[EO]/[Li⁺] = 8的聚合物电解质具有更高的离子电导率,但是[EO]/[Li⁺] = 20的电解质与金属锂负极间的界面阻抗更低,界面稳定性更好. Li|PEO-LiTFSI([EO]/[Li⁺]=20)|Li对称电池在60 °C,电流密度为0.1 mA·cm^-2时可稳定循环超过300 h,而Li|PEO-LiTFSI ([EO]/[Li⁺]=8)|Li对称电池循环75 h就出现了短路现象. 基于PEO-LiTFSI([EO]/[Li⁺]=20)电解质的锂硫电池首圈放电比容量为934 mAh·g^-1,循环16圈后放电比容量为917 mAh·g^-1以上. 而基于PEO-LiTFSI ([EO]/[Li⁺]=8)电解质的锂硫电池,由于与锂负极较低的界面稳定性不能够正常循环,首圈就出现了严重过充现象.     

苯乙烯-马来酸酐共聚物对20%除虫脲水悬浮剂分散稳定性的影响

以过氧化苯甲酰为引发剂,采用溶液共聚法在不同温度下合成了一系列苯乙烯-马来酸酐共聚物,经磺化制得不同相对分子质量的聚苯乙烯-马来酸酐磺酸钠(SSMA)。 通过测定平均粒径、Zeta电势、黏度等考察了SSMA对20%除虫脲悬浮剂分散稳定性的影响。 结果表明,最佳分散剂为75 ℃聚合得到的SSMA,其质量分数为3%时,水悬浮剂的分散稳定性最好;当pH=9时SSMA分子完全电离,能为颗粒提供较大的空间势垒,水悬浮剂分散稳定性最好;Na+或Ca2+压缩颗粒界面的双电层,降低Zeta电势的绝对值,使颗粒因带电量减少而聚结,导致水悬浮剂分散稳定性变差;当离子浓度相同时,Ca2+的聚沉能力强于Na+,添加Ca2+后的水悬浮剂的分散稳定性更差。     

Effect of process parameters and methylcellulose supplementation on the properties of n-undecane emulsions

Study was made on the influence of processing parameters on droplet size during emulsification with an Ultra-Turrax homogenizer. Emulsions of undecane in water, stabilized with nonionic Igepals, were prepared at the optimum hydrophilic-lipophilic balance (HLB) of 11.5 and oil-to-water (O/W) ratio of 5/95; the sizes of emulsion droplets were measured at intervals from the commencement of emulsification. Results showed that the optimum emulsification conditions, as pertaining to minimum particle size, arose at 13 400 rpm and 20 minutes of Ultra-Turrax treatment. Additionally, effects exerted by the presence of methylcellulose, time and storage temperature on the emulsions were determined. Emulsions prepared at the optimal processing parameters revealed that the smallest particle sizes (lower than 200 nm) and the best emulsion stability were demonstrated at the oil/water ratios of 3/97 and 5/95, with 3% surfactant content, an HLB value of 10 to 11 and the storage temperature of 25°C, irrespective of the content of methylcellulose.     

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.     

Structures and stability of lipid emulsions formulated with sodium caseinate

The physicochemical properties of emulsions play an important role in food systems as they directly contribute to texture, sensory and nutritional properties of foods. Sodium caseinate (NaCas) is a well-used ingredient because of its good solubility and emulsifying properties and its stability during heating. One of most significant aspects of any food emulsion is its stability. Among the methods used to study emulsion stability it may be mentioned visual observation, ultrasound profiling, microscopy, droplet size distribution, small deformation rheometry, measurement of surface concentration to characterize adsorbed protein at the interface, nuclear magnetic resonance, confocal microscopy, diffusing wave spectroscopy, and turbiscan. They have advantages and disadvantages and provide different insights into the destabilization mechanisms. Related to stability, the aspects more deeply investigated were the amount of NaCas used to prepare the emulsion, and specially the oil-to-protein ratio, the mobility of oil droplets and the interactions among emulsion components at the interface. It is known that the amount of protein required to stabilize oil-in-water emulsions depends, not only on the structure of protein at the interface, and the average diameters of the emulsion droplets, but also on the type of oils and the composition of the aqueous phase. Several authors have investigated the effect of a thickening agent or of a surface active molecule. Factors such as pH, temperature, and processing conditions during emulsion preparation are also very relevant to stability. There is a general agreement among authors that the most stable systems are obtained for conditions that produce size reduction of the droplets, an increase in viscosity of the continuous phase and structural changes in emulsions such as gelation. All these conditions decrease the molecular mobility and slow down phase separation.     

Spreading of partially crystallized oil droplets on an air/water interface

The influence of crystalline fat on the amount and rate of oil spreading out of emulsion droplets onto either a clean or a protein-covered air/water interface was measured for β-lactoglobulin stabilized emulsions prepared with either anhydrous milk fat or a blend of hydrogenated palm fat and sunflower oil. At a clean interface, liquid oil present in the emulsion droplets was observed to completely spread out of the droplets unimpeded by the presence of a fat crystal network. Further, the presence of a fat crystal network in the emulsion droplets had no effect on the rate of oil spreading out of the droplets. At a protein-covered interface, the spreading behavior of emulsion droplets containing crystalline fat was evaluated in terms of the value of the surface pressure (Π_AW) at the point of spreading; Π_AW at spreading was unaffected by the presence of crystalline fat. We conclude it is unlikely that the role of crystalline fat in stabilizing aerated emulsions such as whipped cream is to reduce oil spreading at the air/water interface. However, the temperature of the system did have an effect: spontaneous spreading of emulsion droplets at clean air/water interfaces occurred for systems measured at 5 °C, but not for those measured at 22 or 37 °C. Thus, temperature may play a more important role in the whipping process than commonly thought: the entering and spreading of emulsion droplets was favored at lower temperatures because the surface pressure exerted by protein adsorbed at the air/water interface was reduced. This effect may facilitate the whipping process.     

Stabilization of Water‐Soluble Antioxidant in Water‐in‐Oil‐in‐Water Double Emulsions

Abstract

In this study, we are introducing a method that can effectively stabilize antioxidants in water‐in‐oil‐in‐water (W/O/W) double emulsions. Preliminarily, stable W/O/W double emulsions were produced by manipulating the characteristics of internal aqueous phase via two‐stage emulsification, resulting consequently in the formation of fine internal water droplets in the dispersed oil droplets. From conductivity measurements that can determine the elution amount of internal aqueous phase, it was confirmed that the double emulsion stability could be improved by treating the internal aqueous phase with a hydroxypropyl‐beta‐cyclodextrin. In this study, kojic acid, 5‐hydroxy‐2‐(hydroxymethyl)‐4‐pyrone was selected as a model antioxidant. The stabilization of kojic acid was attempted by locating it in the internal water droplets of the stable W/O/W double emulsions. The stability of kojic acid in the double emulsion system could be maintained at 90% for 10 weeks at high temperature. We believe that these stable W/O/W double emulsions could be used meaningfully as a carrier for many unstable antioxidants.     

Electrostatic stabilization of colloids in carbon dioxide: electrophoresis and dielectrophoresis

Over the past decade, steric stabilization has been achieved for a variety of inorganic and organic colloids in supercritical fluid carbon dioxide (scCO2). Herein we demonstrate that colloids may also be stabilized in CO2 by electrostatic forces, despite the ultralow dielectric constant of 1.5. Zeta potentials of micrometer-sized water droplets, measured in a microelectrophoresis cell, reached -70 mV corresponding to a few elementary charges per square micrometer of droplet surface. This degree of charge was sufficient to stabilize water/CO2 emulsions for an hour, even with water volume fractions of 5%. Hydrogen ions partition preferentially, relative to bicarbonate ions, from the emulsion droplets to the cores of surfactant micelles in the diffuse double layer surrounding the droplets. The micelles, formed with a low molecular weight branched hydrocarbon surfactant, prevent ion pairing of the hydrogen counterions to the negatively charged emulsion droplets. Dielectrophoresis of the water droplets at a frequency of 60 Hz leads to chains containing a dozen droplets with lengths of 50 mum. The ability to form electrostatically stabilized colloids in carbon dioxide is particularly useful in practical applications, because steric stabilization in CO2 is often limited by the poor solvation of the stabilizers.     

Water pH and surfactant addition effects on the stability of an Algerian crude oil emulsion

In many oil production sites water injection is used as a piston to push the crude out of the well. As the age of the field progresses, the ratio of water to oil produced increases. Agitation of a water and crude oil mixture may give stable water-in-oil emulsion in which the water remains dispersed for a long period of time. These emulsions can cause severe problems in production and transport processes since they normally possess high stability and viscosity. The most important water properties which may contribute to the emulsion stability include pH and additive content. In this study, we report on the effect of both, water pH and the presence of surfactant molecules (anionic, cationic or non-ionic) on the stability of an Algerian crude oil (Haoudh el Hamra well) aqueous emulsion prepared by a mechanical agitation procedure. The stability was followed by the test-bottle method to measure the resolved water separated from the emulsion, and optical microscopy to visualize the dispersed water droplets in the oil phase. The results of the effects of varying the aqueous-phase pH suggest that the neutral medium is more efficient than acidic or basic environment for stabilizing the emulsions. The addition of non-ionic surfactants has a better potential to improve crude oil emulsion stability with respect to both cationic and anionic surfactants which do not show any improvement in the oil/water phase compatibility.     

SiO2纳米颗粒与聚氧乙烯对Pickering乳液的协同稳定作用简

研究了聚氧乙烯(PEO)与SiO2纳米颗粒对水/二甲苯体系Pickering乳液的协同稳定作用. 实验发现,PEO的存在减小了乳液液滴的平均直径,抑制了乳液的相反转,有效阻止了乳液的熟化,使乳液具有更好的稳定性. 进一步对纳米颗粒膜的流变性质进行研究,结果表明,PEO高分子促进了纳米颗粒形成更大尺寸的聚集结构,提高了其在界面上的吸附性,增强了颗粒膜的力学性能,在较小颗粒用量条件下使得Gibbs稳定性判据得到满足.