Janus纳米金稳定的Pickering乳液界面催化氧化性能

Janus纳米粒子的结构设计和简易合成是Pickering乳液界面催化的关键. 本文通过在Pickering乳液保护法中操纵共轭亚油酸的自组装、 自交联性和弱还原性, 合成了Janus型自交联吸附胶束修饰的纳米Fe₃O₄ (SCA-Fe₃O₄), 并在其表面原位还原金后, 合成了Janus型催化剂Au-SCA-Fe₃O₄, 考察其同时作为乳化剂和催化剂在乳液界面催化苯甲醇氧化生成苯甲醛的性能. 结果表明, 该Janus纳米粒子的金修饰量(质量分数)仅为0.66%, 兼具乳化性、 催化性和磁响应性. Au-SCA-Fe₃O₄可制备外观稳定(100 μm)和热稳定(90 ℃)的苯甲醇/水型Pickering乳液, 可显著提高互不相溶反应物与催化剂间的接触面积, 使其催化活性达到均匀纳米催化剂的2倍和非乳液催化时的3倍, 其在界面的不可转动性使苯甲醛的选择性高于99.9%, 避免了苯甲醛被过度氧化成苯甲酸.     

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。     

多功能Fe3O4@SiO2 Janus颗粒

采用溶剂热法和溶胶-凝胶法制备了顺磁性Fe₃O₄@SiO₂颗粒,以Pickering乳液界面保护法实现颗粒表面分区获得Fe₃O₄@SiO₂ Janus颗粒,进一步选区复合生长Pt或Ag纳米颗粒制备Fe₃O₄@SiO₂-Pt和Fe₃O₄@SiO₂-Ag Janus颗粒.Fe₃O₄@SiO₂-Pt Janus颗粒的Pt一侧进行催化过氧化氢的反应,具有自驱动功能.因其顺磁性和两亲性,Fe₃O₄@SiO₂-Ag Janus颗粒能够作为磁响应颗粒乳化剂稳定油水乳液,并将Ag的催化功能引入界面.     

肉桂酸改性透明质酸颗粒乳化剂的制备及性能

将具有紫外吸收性能的单体肉桂酸(CA)引入天然大分子透明质酸(HA)中,制得疏水性改性HA(HA-CA),然后在二甲亚砜与水的混合溶剂中自组装制备HA-CA胶体粒子,并以之为颗粒乳化剂稳定油水界面制备Pickering乳液。通过紫外、核磁、纳米粒度仪、透射电镜、光学显微镜等方法对HA-CA、HA-CA胶体粒子及其所稳定的乳液进行表征。结果表明,HA-CA可以在选择性溶剂中自组装形成粒径约为95nm的球形胶体粒子;所得的HA-CA胶体粒子可以有效地稳定油/水界面,制备水包油(O/W)型的Pickering乳液,且所得乳液具有良好的耐盐性和细胞相容性;此外该胶体粒子可稳定多种油/水体系,具有一定普适性。     

Papain/HA-Phe自组装复合纳米粒子及乳化性能

用L-苯丙氨酸乙酯(L-Phe)改性透明质酸(HA)双亲性生物大分子(HA-Phe)负载生物活性分子木瓜蛋白酶(papain),HA-Phe和Papain通过静电、氢键和疏水相互作用自组装形成生物基Papain/HA-Phe复合纳米粒子.用动态光散射(DLS)和透射电镜(TEM)对复合纳米粒子的尺寸和形貌进行表征.结果显示,形成的复合纳米粒子为球形结构,粒径约308 nm.以此复合纳米粒子为颗粒乳化剂稳定白油,形成水包油型Pickering乳液.乳液的扫描电镜(SEM)显示,复合纳米粒子吸附在油水界面,形成复合纳米粒子的吸附层以稳定乳液.详细研究了pH和盐浓度对复合纳米粒子性质和复合纳米粒子乳化性能的影响.结果表明,随着pH增加,复合纳米粒子在油滴表面的吸附数目减少,乳化性能降低;随着盐浓度增加,复合纳米粒子的形变能力增强,乳化性能提高.进一步研究了乳液中木瓜蛋白酶的活性及美白效果.研究表明,制备的乳液保留了一定的活性,且具有一定的美白效果.     

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.     

纳米粒子的界面自组装

近年来,随着纳米技术的发展及Pickering乳液在食品、化妆品、医药等领域中的应用,纳米粒子的界面自组装现象引起了人们的广泛关注。界面能的降低是纳米粒子液液界面自组装的主要驱动力。通过改变纳米粒子的尺寸和表面配体的化学性质,可控制纳米粒子的界面自组装行为。本文综述了不同类型纳米粒子实现界面自组装的研究工作,包括均质纳米粒子、Janus纳米粒子、棒状纳米粒子以及生物纳米粒子。最后,对纳米粒子的界面组装这一领域的可能发展做了展望。     

CO2响应型Pickering乳液的构筑及应用

互不相溶的油/水两相在固体颗粒的作用下,其中一相以小液滴形式溶于另一相中形成的乳液称为Pickering乳液。由于其制备成本低、稳定性强且环境友好,目前已应用于医药、食品及化妆品等多个领域。在实际的应用中,具有长期稳定性质和可快速乳化/破乳的乳液在石油开采、催化等领域需求广泛,因而制备具有环境刺激响应性质的Pickering乳液迫在眉睫。与pH、磁场、温度、光等刺激手段相比,CO₂响应型乳液具有廉价易得、无污染、响应迅速、生物相容性好等优势,是解决产品循环回收问题的有效策略。目前CO₂刺激响应型Pickering乳液体系仍处于研究的初级阶段,且该乳液的响应机制、构筑策略仍有待明确和拓展。本文总结了Pickering乳液的稳定/响应机制,综述了CO₂响应型Pickering乳化剂的种类及构筑策略,列举了其在乳液聚合、界面催化、生物医药领域的应用进展,并展望了其未来的发展前景。     

Janus粒子的制备及功能化应用

Janus粒子是指表面具有两种或两种以上不同化学组成或性质的不对称粒子,目前Janus粒子的制备方法仍在发展中,同时也逐渐形成了Janus粒子在生物医药、催化、材料以及防污等领域功能化应用的研究重点。本文从Janus粒子制备和应用两个方面方法来介绍Janus粒子的研究进展。制备方法主要包括表面选择性修饰法、晶种生长法、微流控法、嵌段共聚物自组装法和电化学沉积法等。应用方面则着重介绍了Janus粒子在生物医药、界面催化、表面活性剂、复合材料、微米马达和防污等方面的功能化应用,并对Janus粒子未来的发展趋势做了展望。     

Pickering乳滴模板法制备超粒子结构有机/无机杂化微球

Pickering乳滴模板法制备有机/无机杂化的核壳微球越来越引起人们的关注,主要因为该方法制备出的微球具有以无机粒子为壳层的超粒子结构(supracolloidal structure),能够赋予微球独特的功能.胶体粒子在乳滴表面自组装形成有序的球面胶体壳,得到稳定Pickering乳液,固定乳滴表面的胶体粒子来制备核壳结构的微球或者以胶体粒子为壳层的微胶囊(colloidosome).本文综述了我们课题组以Pickering乳滴模板法制备超粒子结构有机/无机杂化微胶囊包括实心微球方面的工作.我们选择具有不同性能、种类的胶体粒子以及具有不同性质和功能的核材料,采用Pickering乳滴模板法,对吸附在乳滴表面的胶体粒子用不同的固定方法制备具有不同结构和性能的微球和微胶囊,利用基于多重Pickering乳液的聚合技术制备双纳米复合的超粒子结构多核聚合物微球.     

Pickering emulsions: Versatility of colloidal particles and recent applications

The versatility of colloidal particles endows the particle stabilized or Pickering emulsions with unique features and can potentially enable the fabrication of a wide variety of derived materials. We review the evolution and breakthroughs in the research on the use of colloidal particles for the stabilization of Pickering emulsions in recent years for the particle categories of inorganic particles, polymer-based particles, and food-grade particles. Moreover, based on the latest works, several emulsions stabilized by the featured particles and their derived functional materials, including enzyme immobilized emulsifiers for interfacial catalysis, 2D colloidal materials stabilized emulsions as templates for porous materials, and Pickering emulsions as adjuvant formulations, are also summarized. Finally, we point out the gaps in the current research on the applications of Pickering emulsions and suggest future directions for the design of particulate stabilizers and preparation methods for Pickering emulsions and their derived materials.     

In situ formed Mg(OH)2 nanoparticles as pH-switchable stabilizers for emulsions

Different from traditional methods for preparing pH-switchable Pickering emulsifiers, a simple and straightforward approach is established on the basis of a reversible process between in situ formation and dissolution of Mg(OH)(2) nanoparticles (MHp). It was found that when pH value was above 9.5, emulsions of liquid paraffin-in-water can be stabilized by the resulting surface-active particles. Below this pH, emulsions demulsify, resulting in a reversible Pickering emulsifier. Based on the strongly pH-dependent precipitation of metal hydroxide nanoparticles, this procedure offers a new way to design pH-switchable emulsifiers without aid of any other organic matters.     

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.     

Supramolecular Polymer Emulsifiers for One-step Complex Emulsions

Complex emulsions,such as double emulsions and high-internal-phase emulsions,have shown great applications in the fields of drug delivery,sensing,catalysis,oil-water separation and self-healing materials.Their controllable preparation is at the forefront of interface and material science.Surfactants and polymers have been widely used as emulsifiers for building complex emulsions.Yet some inherent disadvantages exist including multi-step emulsifications and low production efficiency.Alternatively,supramolecular polymer emulsifier for complex emulsions via one-step emulsification is rising as a new strategy due to the ease of preparation.In this feature article,we review our recent progresses in using supramolecular polymer emulsifiers for the preparation of complex emulsions.Double emulsions and high-internal-phase emulsions are successfully prepared via one-step emulsification with the help of different supramolecular interactions including electrostatic,hydrogen bond,coordination interaction and dynamic covalent bond,which will be particularly emphasized in detail.In the end,a comprehensive prospect is given for the future development of this field.This article is expected to provide new inspirations for preparing complex emulsions via supramolecular routes.     

Simple, reversible emulsion system switched by pH on the basis of chitosan without any hydrophobic modification

Chitosan without hydrophobic modification is not a good emulsifier itself. However, it has a pH-tunable sol-gel transition due to free amino groups along its backbone. In the present work, a simple reversible Pickering emulsion system based on the pH-tunable sol-gel transition of chitosan was developed. At pH > 6.0, as adjusted by NaOH, chitosan was insoluble in water. Chitosan nanoparticles or micrometer-sized floccular precipitates were formed in situ. These chitosan aggregates could adsorb at the interface of oil and water to stabilize the o/w emulsions, so-called Pickering emulsions. At pH < 6.0, as adjusted by HCl, chitosan was soluble in water. Demulsification happened. Four organic solvents (liquid paraffin, n-hexane, toluene, and dichloromethane) were chosen as the oil phase. Reversible emulsions were formed for all four oils. Chitosan-based Pickering emulsions could undergo five cycles of emulsification-demulsification with only a slight increase in the emulsion droplet size. They also had good long-term stability for more than 2 months. Herein, we give an example of chitosan without any hydrophobic modification to act as an effective emulsifier for various oil-water systems. From the results, we have determined that natural polymers with a stimulus-responsive sol-gel transition should be a good particulate emulsifier. The method for in situ formation of pH-responsive Pickering emulsions based on chitosan will open up a new route to the preparation of a wide range of reversible emulsions.     

High internal phase Pickering emulsions

Macroemulsions rendered stable by adsorbed colloidal particles are termed Pickering emulsions. If the volume fraction of dispersed phase exceeds around 0.75, the emulsions are named high internal phase Pickering emulsions abbreviated to HIPPEs, which present new properties and potential applications. We review here the recent progress in preparing and studying HIPPEs of both oil-in-water and water-in-oil types. This includes discussion of the range of solid particle emulsifiers, the choice of the two immiscible liquids and methods for their preparation. As a result of their high interfacial area and long-term stability, HIPPEs are being put to use in many potential applications including drug delivery, catalysis, and in the production of novel porous materials.     

Pickering乳液模板法制备Janus粒子

本文以SiO₂粒子稳定的水包油(O/W)型Pickering乳液作为模板, 在乳液连续相进行SI-ATRP, 将聚合物刷接枝到SiO₂粒子外半表面, 破乳得到半修饰的Janus粒子.     

CO2-triggered switchable Pickering emulsion stabilized by guanidine-functionalized silica particles

The guanidine group-modified silica particles were used as emulsifier to obtain a CO₂-responsive Pickering emulsion. To compare the wettability effect of the particles on the stability of the emulsion, both guanidine and alkyl chain were attached on the surface of silica particles. The influences of tension, particles concentration, oil-water fraction, NaCl concentration, and CO₂ on Pickering emulsion properties were investigated. Although the particles did not decrease the surface and interfacial tensions of the air/oil-water interfaces, they attached on the oil–water interfaces and stabilized the emulsions at room temperature for at least 4 weeks. Addition of salt increased the emulsion stability and induced phase inversion at high salt concentration. The stabilization–destabilization cycles of the emulsion could be successively controlled by alternative CO₂/heating triggers due to the protonation-deprotonation of guanidine groups on the particle surfaces.     

Synergistic interaction in emulsions stabilized by a mixture of silica nanoparticles and cationic surfactant

Using a range of complementary experiments, a detailed investigation into the behavior of dodecane-water emulsions stabilized by a mixture of silica nanoparticles and pure cationic surfactant has been made. Both emulsifiers prefer to stabilize o/w emulsions. At high pH, particles are ineffective emulsifiers, whereas surfactant-stabilized emulsions become increasingly stable to coalescence with concentration. In mixtures, no emulsion phase inversion occurs although synergism between the emulsifiers leads to enhanced stability at either fixed surfactant concentration or fixed particle concentration. Emulsions are most stable under conditions where particles have negligible charge and are most flocculated. Freeze fracture scanning electron microscopy confirms the presence of particle flocs at drop interfaces. At low pH, particles and surfactant are good emulsifiers alone. Synergism is also displayed in these mixtures, with the extent of creaming being minimum when particles are most flocculated. Experiments have been undertaken in order to offer an explanation for the latter synergy. By determining the adsorption isotherm of surfactant on particles in water, we show that surfactant addition initially leads to particle flocculation followed by re-dispersion. Using suitable contact angle measurements at oil-water-solid interfaces, we show that silica surfaces initially become increasingly hydrophobic upon surfactant addition, as well as surfactant adsorption lowering the oil-water interfacial tension. A competition exists between the influence of surfactant on the contact angle and the tension in the attachment energy of a particle to the interface.     

A novel formulation of the pickering emulsion stabilized with silica nanoparticles and its thermal resistance at high temperatures

Stabilization of emulsions with solid particles can be used in several fields of oil and gas industry because of their higher stability. Solid particles should be amphiphilic to be able to make Pickering emulsions. This goal is achieved by using surfactants at low concentrations. Oil-in-water (o/w) emulsions are usually stabilized by surfactant but show poor thermal stability. This problem limits their applications at high-temperature conditions. In this study, a novel formulation for o/w stabilized emulsion by using silica nanoparticles and the nonionic surfactant is investigated for the formulation of thermally stable Pickering emulsion. The experiments performed on this Pickering emulsion formula showed higher thermal stability than conventional emulsions. The optimum wettability was found for DME surfactant and silica nanoparticles, consequently, in that region; Pickering emulsion showed the highest stability. Rheological changes were evaluated versus variation in surfactant concentration, silica concentration and pH. Scanning electron microscopy images approved the existence of a rigid layer of nanoparticle at the oil-water interface. Finally, the results show this type of emulsion remains stable in harsh conditions and allows the system to reach its optimum rheology without adding any further additives.