基于Ugi多组分反应的海藻酸酰胺衍生物改性二氧化硅纳米粒子的制备

采用海藻酸酰胺衍生物通过Ugi多组分反应制备了新颖的聚合物-二氧化硅(Oct-Alg-Si O_2)纳米粒子.通过氢核磁共振波谱(~1H NMR)和X射线光电子能谱(XPS)对Oct-Alg-Si O_2的结构和表面元素组分进行了表征.采用透射电子显微镜(TEM)、Zeta电位和激光粒度分析仪对Oct-Alg-Si O_2的形貌、粒径和胶体性能进行了探索.结果表明,海藻酸酰胺衍生物共价接枝到氨基二氧化硅(Si O_2-NH_2)纳米粒子的表面,提高了其平均直径,调控了其Zeta电位,在水介质中能够表现出良好的分散稳定性.以10%的液体石蜡为油相,采用Oct-Alg-Si O_2制备了Pickering乳液.在油水界面能够形成液滴粒径为5.7μm的稳定Pickering乳液.随着水相p H值的增大,乳液体积分数增大,稳定性增强.细胞相容性实验结果表明,Oct-Alg-Si O_2纳米粒子具有极好的生物相容性.     

含不同氨基酸反相微乳体系中胆红素钙的形成与稳定性

在聚乙二醇辛基苯基醚(OP)/正己醇/环己烷/水反相微乳液和甘氨酸、精氨酸、组氨酸3种含不同氨基酸的反相微乳液体系中成功地制备了胆红素钙,考察了氨基酸对胆红素钙的组成、形貌、配位方式及稳定性的影响。采用透射电子显微镜、表面Zeta电位、红外光谱和紫外光谱等测试技术对样品进行了表征。结果表明,此反相微乳体系中所得球形颗粒为中性胆红素钙,平均粒径80nm,在水分散体系中颗粒的稳定性随分散体系pH值的升高而先降低后增加,当pH=4.9时,颗粒表面Zeta电位值为0。3种亲水性氨基酸的加入促进胆红素钙颗粒的成核,最终影响胆红素钙的微结构、颗粒形貌和稳定性。当加入的氨基酸为组氨酸、甘氨酸时,所得胆红素钙球形颗粒形貌无明显变化,但平均粒径依次减小至60和40nm,其水分散体系中的稳定性明显增加;当加入的氨基酸为精氨酸时,所得胆红素钙颗粒形貌不规则,粒径非常小,不稳定,易形成聚集体。     

Brij类表面活性剂与Laponite纳米颗粒的相互作用及其稳定乳液的研究

通过表面张力、Zeta电位和流变学参数的测定, 研究了聚氧乙烯烷基醚类非离子型表面活性剂(Brij 30和Brij 35)在合成锂皂石(Laponite)纳米颗粒表面的吸附及对Laponite水分散体系中颗粒间相互作用和体系粘度的影响. 结果表明, 这类表面活性剂能显著地吸附在Laponite颗粒表面上, 且吸附量随其分子中POE链长短而不同. 这种吸附没有改变Laponite粒子的带电性质, 但一定程度地降低了Laponite颗粒Zeta电位; 吸附也会减弱颗粒间的相互作用, 降低体系的粘度. 实验以Laponite和Brij为乳化剂, 制备了O/W型乳状液. 乳液稳定性变化和乳液粒径分布结果表明, 体系中Brij的浓度较低时, 乳液的性质主要是由Laponite颗粒决定的; 而Brij浓度较高时, 则主要取决于Brij表面活性剂. 高速剪切含Brij的Laponite水分散体系, 剪切后表面张力随时间的变化表明, 剪切作用会使得吸附在Laponite颗粒表面的Brij分子不同程度地解吸下来. 这也意味着乳液制备时, 高速剪切作用也会造成Brij分子自Laponite颗粒表面的脱附, 这可能是非离子表面活性剂与阳离子表面活性剂对负电固体颗粒稳定乳液影响不同的原因.     

纳米玉米醇溶蛋白微球稳定的O/W型Pickering乳液

利用相分离工艺制备玉米醇溶蛋白(zein)纳米微球,微球粒径可控制在40 nm左右;经旋转蒸发制得zein溶胶体系,zein溶胶具有明显的丁达尔现象,静置数月不聚沉,Zeta电位法测得zein微球在pH值为4.0时分散性能最佳。以纳米zein微球为固相稳定剂制备O/W型Pickering乳液,考察了zein胶体加入量、油水体积比等因素对乳液稳定性的影响。实验结果表明,zein胶体加入量的质量分数控制为0.4%,高油水体积比将有利于Pickering乳液的长时间稳定。基于zein分子的两亲结构和界面组装特点,提出了zein微球稳定Pickering乳液的作用机制。     

马来松香酸和纳米氧化铝颗粒协同稳定具有pH响应性的Pickering乳液

使用有机颗粒稳定Pickering乳液受到越来越多的关注, 润湿性可调的有机颗粒且结合纳米无机颗粒协同稳定不同类型的Pickering乳液却鲜有报道. 系统研究了基于具有多羧酸基团的松香基衍生物马来松香(MPA)与纳米Al₂O₃颗粒在不同pH条件下形成的乳液类型及相关机理. 研究发现, 在单一MPA颗粒体系条件下, pH可以诱导乳液的类型由W/O Pickering乳液到O/W Pickering乳液, 到最后O/W乳液的转变, MPA的亲水性随着pH升高而增强是该乳液转变的原因. 当纳米Al₂O₃颗粒加入到MPA中后, 吸附在MPA颗粒上的亲水性Al₂O₃导致MPA颗粒亲水性增加, 从而可以使W/O Pickering乳液转变为O/W Pickering乳液(pH=1). 当pH=6时, MPA分子与纳米Al₂O₃颗粒同时具有较强的亲水性且分别无法形成稳定的乳液, 但两者的混合体系可以形成稳定的W/O Pickering乳液, 这是因为MPA分子与纳米Al₂O₃颗粒可以在水溶液中形成疏水性较强的络合物. 另外, 研究了MPA浓度及油相体积分数对乳液外观及粒径的影响, 发现随着MPA浓度增加Pickering乳液的粒径逐渐减小, 增加油相的体积分数会引起粒径的增大. 最后, 利用Zeta电势、颗粒在油水界面吸附率、接触角及表/界面张力研究了稳定Pickering乳液的稳定机理, 在油水界面上吸附的类似盔甲状颗粒层及颗粒层之间形成的网状结构是乳液液滴保持稳定的原因. 为Pickering乳液的绿色化制备提供了一种新的途径, 将在化妆品、医药及新材料等领域得到重要应用.     

以单分散P(DC-TMPTA)聚合物微球为Pickering乳液稳定剂制备石蜡乳液和石蜡微球

以三羟甲基丙烷三丙烯酸酯(TMPTA)和1-十二烯(DC)为单体,不使用任何乳化剂或分散稳定剂,通过沉淀聚合制备了高度单分散P(DC-TMPTA)的聚合物微球颗粒.以此聚合物微粒为Pickering稳定剂,不添加任何化学助剂,以乙醇-水混合介质在70℃下通过恒速振荡制得了单分散石蜡Pickering乳液.将该体系迅速降温至石蜡熔点之下,制得了窄分布的固体石蜡微球.研究了连续相水含量、振荡频率及稳定粒子尺寸对Pickering乳液及石蜡微球的影响,优化了石蜡乳液和微球的制备条件.利用扫描电子显微镜对石蜡微球的表面和内部形貌进行了表征,结果表明P(DC-TMPTA)微球全部聚集在石蜡液滴和固化后的石蜡微球表面.基于石蜡微球和聚合物稳定粒子的尺寸,计算了不同条件下石蜡微球表面聚合物粒子的数量.通过聚合物粒子在石蜡-乙醇和水混合溶液界面的三相接触角以及石蜡-乙醇和水混合溶液界面张力的测定,计算了聚合物粒子在石蜡-乙醇和水混合溶液界面吸附能,为解释该体系Pickering乳液的稳定性提供了理论支持.     

Pickering乳液的制备和应用研究进展

Pickering乳液是一种由固体粒子代替传统有机表面活性剂稳定乳液体系的新型乳液。与传统乳液相比,Pickering乳液具有强界面稳定性、减少泡沫出现、可再生、低毒、低成本等优势,在化妆品、食品、制药、石油和废水处理等行业具有广阔的应用前景,受到越来越多研究者们的关注。本文综述了近年来Pickering乳液的研究进展,先介绍Pickering乳液相对于表面活性剂乳液的特色与优势,然后介绍Pickering乳液的制备研究进展,最后介绍Pickering乳液的应用研究进展。     

NiFe2O4与TiO2稳定的多重Pickering乳液的制备

由沉淀法和溶胶-凝胶法分别制备了Ni Fe_2O_4和Ti O_2,并用XRD和SEM对两种粒子进行了表征,结果表明成功制备了粒径大小较为均匀的目标产物。用CTAB对Ni Fe_2O_4进行了改性,并由IR和Zeta电位测试予以确认。以改性Ni Fe_2O_4和Ti O_2作为稳定粒子,由两步法制备了W/O/W型多重Pickering乳液,采用数码照片和光学显微照片观察所制备的乳液的宏观与微观形貌。研究表明,制备的单重Pickering乳液粒径较为均匀,多重Pickering乳液粒径范围稍宽,但两者稳定性能都非常良好。     

软颗粒在液-液界面吸附及界面催化

正Pickering乳液是由吸附在水油两相界面上的颗粒稳定的乳状液,而这些颗粒的界面脱附往往需要很高的热力学脱附能,使得Pickering乳液具有良好的稳定性~1。相比于传统的表面活性剂稳定的乳液,颗粒在液液界面的存在不仅有效阻止了乳滴间的聚结合并,还赋予了乳液环境响应性,如pH、温度~2。因此,Pickering乳液被广泛应用于医药、催化、材料、能源、食品等领域~(3–5)。诸多颗粒被证明可以作为Pickering乳液的乳化剂,如二氧化硅纳米球、聚苯乙烯微球、碳酸钙颗粒等。除此以外,软颗粒稳定的Pickering乳液越来越引起了研究者的兴趣,而最具代表性的便是微凝胶粒子(microgel) ~6和蛋白质颗粒。     

Pickering多重乳状液的一步法合成及形成机理研究

使用锂皂石层状纳米颗粒与表面活性剂（Span80）复配制备乳状液的过程中,在乳化之前对锂皂石颗粒水分散体系进行稀释,则可以通过一步法制备出性能稳定的W/O/W型Pickering多重乳状液.研究了Span80浓度、锂皂石浓度以及稀释用水的量对生成乳状液的类型及稳定性的影响规律,对一步法合成Pickering多重乳状液的...     

Effect of dispersion pH on the formation and stability of Pickering emulsions stabilized by layered double hydroxides particles

Using positively charged plate-like layered double hydroxides (LDHs) particles as emulsifier, liquid paraffin-in-water emulsions stabilized solely by such particles are successfully prepared. The effects of the pH of LDHs aqueous dispersions on the formation and stability of the emulsions are investigated here. The properties of the LDHs dispersions at different pHs are described, including particle zeta potential, particle aggregation, particle contact angle, flow behavior of the dispersions and particle adsorption at a planar oil/water interface. The zeta potential decreases with increasing pH, leading to the aggregation of LDHs particles into large flocs. The structural strength of LDHs dispersions is enhanced by increasing pH and particle concentration. The three-phase contact angle of LDHs also increases with increasing pH, but the variation is very small. Visual observation and SEM images of the interfacial particle layers show that the adsorption behavior of LDHs particles at the planar oil/water interface is controlled by dispersion pH. We consider that the particle-particle (at the interface) and particle-interface electrostatic interactions are well controlled by adjusting the dispersion pH, leading to pH-tailored colloid adsorption. The formation of an adsorbed particle layer around the oil drops is crucial for the formation and stability of the emulsions. Emulsion stability improves with increasing pH and particle concentration because more particles are available to be adsorbed at the oil/water interface. The structural strength of LDHs dispersions and the gel-like structure of emulsions also influence the stability of the emulsions, but they are not necessary for the formation of emulsions. The emulsions cannot be demulsified by adjusting emulsion pH due to the irreversible adsorption of LDHs particles at the oil/water interface. TEM images of the emulsion drops show that a thick particle layer forms around the oil drops, confirming that Pickering emulsions are stabilized by the adsorbed particle layers. The thick adsorbed particle layer may be composed of a stable inner particle layer which is in direct contact with the oil phase and a relatively unstable outer particle layer surrounding the inner layer.     

Pickering emulsions stabilized solely by layered double hydroxides particles: the effect of salt on emulsion formation and stability

The formation and stability of liquid paraffin-in-water emulsions stabilized solely by positively charged plate-like layered double hydroxides (LDHs) particles were described here. The effects of adding salt into LDHs dispersions on particle zeta potential, particle contact angle, particle adsorption at the oil-water interface and the structure strength of dispersions were studied. It was found that the zeta potential of particles gradually decreased with the increase of salt concentration, but the variation of contact angle with salt concentration was very small. The adsorption of particles at the oil-water interface occurred due to the reduction of particle zeta potential. The structural strength of LDHs dispersions was strengthened with the increase of salt and particle concentrations. The effects of particle concentration, salt concentration and oil phase volume fraction on the formation, stability and type of emulsions were investigated and discussed in relation to the adsorption of particles at the oil-water interface and the structural strength of LDHs dispersions. Finally, the possible stabilization mechanisms of emulsions were put forward: the decrease of particle zeta potential leads to particle adsorption at the oil-water interface and the formation of a network of particles at the interface, both of which are crucial for emulsion formation and stability; the structural strength of LDHs dispersions is responsible for emulsion stability, but is not necessary for emulsion formation.     

Double inversion of emulsions induced by salt concentration

The effects of salt on emulsions containing sorbitan oleate (Span 80) and Laponite particles were investigated. Surprisingly, a novel double phase inversion was induced by simply changing the salt concentration. At fixed concentration of Laponite particles in the aqueous phase and surfactant in paraffin oil, emulsions are oil in water (o/w) when the concentration of NaCl is lower than 5 mM. Emulsions of water in oil (w/o) are obtained when the NaCl concentration is between 5 and 20 mM. Then the emulsions invert to o/w when the salt concentration is higher than 50 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When the salt concentration is low in the aqueous dispersion of Laponite, the particles are discrete and can move to the interface freely. Therefore, the emulsions are stabilized by particles and surfactant, and the type is o/w as particles are in domination. At intermediate salt concentrations, the aqueous dispersions of Laponite are gel-like, the viscosity is high, and the transition of the particles from the aqueous phase to the interface is inhibited. The emulsions are stabilized mainly by lipophilic surfactant, and w/o emulsions are obtained. For high salt concentration, flocculation occurs and the viscosity of the dispersion is reduced; thus, the adsorption of particles is promoted and the type of emulsions inverts to o/w. Laser-induced fluorescent confocal micrographs and cryo transmission electron microscopy clearly confirm the adsorption of Laponite particles on the surface of o/w emulsion droplets, whereas the accumulation of particles at the w/o emulsion droplet surfaces was not observed. This mechanism is also supported by the results of rheology and interfacial tension measurements.     

Interfacial properties of emulsions stabilized with surfactant and nonsurfactant coated boehmite nanoparticles

The properties of emulsions stabilized with surface-modified boehmite particles of 26 and 8 nm in diameter have been investigated. The surface-modified particles were prepared by mixing aqueous dispersions of cationic boehmite particles with aqueous solutions of the surfactant p-dodecylbenzenesulfonic acid (DBSA) or the nonsurfactant p-toluenesulfonic acid (TSA). For the 26 nm particles, interfacial tension measurements indicate that p-dodecylbenzenesulfonic acid partitions between the particle surface and the oil-water interface, while p-toluenesulfonic acid remains on the particle surface. The partitioning of p-dodecylbenzenesulfonic acid supports the formation of emulsions, although in the absence of the particles the same surfactant concentration is not sufficient for emulsion stabilization. Due to the fast exchange kinetics, p-dodecylbenzenesulfonic acid is gradually replaced by particles. At equilibrium, the interfacial tension in the presence of the surface-modified particles is between the values for the pure particles and the pure surfactant solutions. However, the interfacial tension is independent of the surfactant concentration used in the preparation of the particles. Reducing the particle size to 8 nm leads to increased emulsion stability, and thus, the minimum particle concentration required to prepare stable emulsions was reduced to 0.1 g/L. However, above approximately 3.5 mmol/L of the sulfonic acids, the small particles dissolve slowly, and the emulsion stability is lost. This mechanism can be used to trigger the collapse of the emulsions.     

Naturally occurring spore particles at planar fluid interfaces and in emulsions

We have investigated the potential of utilizing naturally occurring spore particles of Lycopodium clavatum as sole emulsifiers of oil and water mixtures. The preferred emulsions, prepared from either oil-borne or aqueous-borne dispersions of the monodispersed particles of diameter 30 microm, are oil-in-water. The particles act as efficient stabilizers for oils of different polarity. Droplets as large as several millimeters are stable to coalescence indefinitely, despite the low coverage of interfaces by particles observed microscopically. Consistent with the emulsion findings, we discover that particles spontaneously adsorb to bare oil-water interfaces of single drops from oil dispersions, whereas adsorption is less spontaneous and extensive from aqueous dispersions. Monolayers of the spore particles at both air-water and oil-water planar interfaces contain particles in an aggregated state forming clusters and chains. The influence of particle concentration, oil/water ratio, and additives in the aqueous phase is studied.     

Synergistic stabilization of emulsions by a mixture of surface-active nanoparticles and surfactant

The stability and rheology of tricaprylin oil-in-water emulsions containing a mixture of surface-active hydrophilic silica nanoparticles and pure nonionic surfactant molecules are reported and compared with those of emulsions stabilized by each emulsifier alone. The importance of the preparation protocol is highlighted. Addition of particles to a surfactant-stabilized emulsion results in the appearance of a small population of large drops due to coalescence, possibly by bridging of adsorbed particles. Addition of surfactant to a particle-stabilized emulsion surprisingly led to increased coalescence too, although the resistance to creaming increased mainly due to an increase in viscosity. Simultaneous emulsification of particles and surfactant led to synergistic stabilization at intermediate concentrations of surfactant; emulsions completely stable to both creaming and coalescence exist at low overall emulsifier concentration. Using the adsorption isotherm of surfactant on particles and the viscosity and optical density of aqueous particle dispersions, we show that the most stable emulsions are formed from dispersions of flocculated, partially hydrophobic particles. From equilibrium contact angle and oil-water interfacial tension measurements, the calculated free energy of adsorption E of a silica particle to the oil-water interface passes through a maximum with respect to surfactant concentration, in line with the emulsion stability optimum. This results from a competition between the influence of particle hydrophobicity and interfacial tension on the magnitude of E.     

Effect of electrolyte in silicone oil-in-water emulsions stabilised by fumed silica particles

Partially hydrophobised fumed silica particles are used to make silicone oil-in-water emulsions at natural pH of the aqueous phase. The stability and rheological properties of the emulsions and suspensions are studied at NaCl concentrations in the range 0-100 mM. It is found that all emulsions are very stable to coalescence irrespective of the NaCl concentration. However, a strong effect of electrolyte on the creaming and rheological properties is observed and linked to the particle interactions in aqueous suspensions. The creaming rate and extent are large at low electrolyte concentrations but both abruptly decrease at salt concentrations exceeding the critical flocculation concentration of the suspension (approximately 1 mM NaCl). The drastic improvement of the stability to creaming is attributed to the formation of a visco-elastic three-dimensional network of interconnected particles and emulsion droplets.     

Particle zips: vertical emulsion films with particle monolayers at their surfaces

Vertical emulsion films with particle monolayers at their surfaces have been studied by direct microscope observations. The effects of particle wettability and surface coverage on the structure and stability of water films in octane and octane films in water have been investigated. Monodisperse silica particles (3 microm in diameter) hydrophobized to different extents have been used. It is found that the structure and stability of emulsion films strongly depend on the film type (water-in-oil or oil-in-water), the particle contact angle, the interactions between particles from the same and the opposite monolayer, and the monolayer density. Stable films are observed only when the particle wettability fulfills the condition for stable particle bridges--in agreement with the concept that hydrophilic particles can give stable oil-in-water emulsions, whereas hydrophobic ones give water-in-oil emulsions. In the case of water films with dilute disordered monolayers at their surfaces, the hydrophilic particles are expelled from the film center toward its periphery, giving a dimple surrounded by a ring of particles bridging the film surfaces. In contrast, the thinning of octane films with dilute ordered monolayers at their surfaces finally leads to the spontaneous formation of a dense crystalline monolayer of hydrophobic particles bridging both surfaces at the center of the film. The behaviors of water and octane films with dense close-packed particle monolayers at their surfaces are very similar. In both cases, a transition from bilayer to bridging monolayer is observed at rather low capillary pressures. The implications of the above finding for particle stabilized emulsions are discussed.     

Double phase inversion of emulsions containing layered double hydroxide particles induced by adsorption of sodium dodecyl sulfate

A liquid paraffin-water emulsion was investigated using layered double hydroxide (LDH) particles and sodium dodecyl sulfate (SDS) as emulsifiers. Both emulsifiers are well-known to stabilize oil-in-water (o/w) emulsions. Surprisingly, a double phase inversion of the emulsion containing LDH particles is induced by the adsorption of SDS. At a constant LDH concentration, the emulsion is o/w type when SDS concentrations are low. At intermediate SDS concentrations, the first emulsion inversion from o/w to w/o occurs, which is attributed to the enhanced hydrophobicity of LDH particles caused by the desorption of the second layer of surfactant, leaving a densely packed SDS monolayer on the LDH exterior surfaces. The second inversion from water-in-oil (w/o) to o/w occurs at higher SDS concentrations, which may be due to the competitive adsorption at the oil/water interfaces between the LDH particles modified by the SDS bilayers and the free SDS molecules in the bulk solution, but the free SDS molecules dominate and determine the emulsion type. Laser-induced fluorescent confocal micrographs clearly confirm the adsorption of LDH particles on the surfaces of the initial o/w and intermediate w/o emulsion droplets, whereas no LDH particles were adsorbed on the final o/w emulsion droplet surfaces. Also, transmission electron microscopy (TEM) observations indicate that the shape of the final o/w emulsions is similar to that of the monomeric SDS-stabilized emulsion but different from that of the initial o/w emulsions. The adsorption behavior of SDS on LDH particles in water was investigated to offer an explanation for the emulsion double phase inversion. The zeta potential results show that the particles will flocculate first and then redisperse following surfactant addition. Also, X-ray diffraction (XRD) measurements indicate that SDS adsorption on the LDH interior surfaces will be complete at intermediate concentrations.     

离子型共聚单体参与下的全氟丙烯酸酯无皂乳液共聚

离子型共聚单体参与下的全氟丙烯酸酯无皂乳液共聚;全氟烷基丙烯酸酯;无皂乳液;离子型共聚单体