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。     

Sustainable food-grade Pickering emulsions stabilized by plant-based particles

This review summarizes the major advances that have occurred over the last 5 years in the use of plant-based colloidal particles for the stabilization of oil-in-water and water-in-oil emulsions. We consider the characteristics of polysaccharide-based particles, protein-based particles and organic crystals (flavonoids) with respect to their particle size, degree of aggregation, anisotropy, hydrophobicity and electrical charge. Specific effects of processing on particle functionality are identified. Special emphasis is directed towards the issue of correctly defining the stabilization mechanism to distinguish those cases where the particles are acting as genuine Pickering stabilizers, through direct monolayer adsorption at the liquid–liquid interface, from those cases where the particles are predominantly behaving as ‘structuring agents’ between droplets without necessarily adsorbing at the interface, for example, in many so-called high internal phase Pickering emulsions. Finally, we consider the outlook for future research activity in the field of Pickering emulsions for food applications.     

Pickering emulsion polymerization kinetics of styrene: Comparison of bare and surface modified SiO2 nanoparticles

A step towards the understanding of some mechanistic events occurring in the styrene Pickering emulsions, using a SiO₂ dispersion, is presented. Polymerizations at 80°C with different levels of a water soluble initiator were performed. The emulsion polymer content was ca. 15% with conversions close to 90%. With conversion and particle size measurements, the particle density was estimated for bare and surface modified SiO₂ particles. Then, the average number of radicals per particle was inferred, yielding a pseudo-bulk type polymerization. It was found that bare SiO₂ nanoparticles do not participate in the nucleation mechanism; however, they, along with the initiator, promote an enhanced oligomer coagulation. On the other hand, the hexadecyltrimethylammonium bromide modified SiO₂ nanoparticles do participate in the nucleation and coagulation mechanisms, yielding more stable and smaller poorly-covered polymer particles. This approach allowed untangling some events such as: particle nucleation, radical entry to particles, particle density, coagulation and vitreous and Trommsdorff effects.     

Synthesis of ZnO/polystyrene composites particles by Pickering emulsion polymerization

ZnO/polystyrene composite particles were synthesized by Pickering emulsion polymerization. ZnO nanoparticles were first prepared by reaction of zinc acetate and sodium hydroxide in ethanol medium. Then different amount of styrene monomer was emulsified in water in the presence of ZnO nanoparticles either by mechanical stirring or by sonication, followed by polymerization of styrene. Two kinds of initiators were used to start the polymerization, azobisisobutyronitrile (AIBN) and potassium persulfate (KPS). The X-ray diffraction pattern verified the crystal structure of ZnO and FT-IR spectra evidenced the existence of ZnO and polystyrene (PS) in ZnO/polystyrene composite particles. Different morphologies were observed for the composite particles when using different initiators. From TEM photographs, AIBN-initiated system produced mainly core-shell composite particles with PS as core and ZnO as shell, while KPS-initiated system showed both composite particles and pure PS particles. Two schemes of reaction mechanism were proposed to explain the morphologies accordingly. Both systems of composite particles showed good pH adjusting ability.     

具有二氧化碳响应性的纳米球形聚电解质刷的制备及其乳化性能

以聚苯乙烯(PS)纳米球为核,利用紫外光引发聚甲基丙烯酸N,N-二甲基氨基乙酯(PDMAEMA)接枝到PS纳米球上,得到对CO_2有刺激响应的聚甲基丙烯酸N,N-二甲基氨基乙酯刷(PS-PDMAEMA)。动态光散射(DLS)、电导率结果表明PS-PDMAMEA具有CO_2刺激响应性。该微粒可以作为Pickering乳液的乳化剂,通过导入CO_2或N_2作为开关,进而破坏或稳定Pickering乳液。用数码照片、偏光显微镜等方法表征了乳液的稳定情况。结果表明:PS-PDMAEMA具有很好的CO_2刺激响应性,利用PS-PDMAEMA作为乳化剂稳定Pickering乳液,仅仅依靠气体开关(CO_2或N_2)就可改变乳液的稳定性。     

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。     

Pickering emulsions stabilized by ultrashort nanotubes

We describe a simple method to prepare high-efficiency ultrashort nanotube Pickering emulsifiers. The polydivinylbenzene (PDVB) nanotubes with a slight degree of sulfonation, then interrupted to several microns in length, can stabilize hundred times their own mass of oil or water phase and form different Pickering emulsion types. The emulsion is very stable and can be stored for more than half a year without demulsification. A layer of magnetic Fe₃O₄ nanoparticles can be grown on the surface of the ultrashort sulfonated PDVB nanotubes. After being emulsified, oil-phase and magnetic nanotubes can be collected using a magnet, which have huge potential application for separation and recovery of organic solvents in environmental protection.     

Phase inversion of the Pickering emulsions stabilized by plate-shaped clay particles

We investigated the phase inversion of Pickering emulsions stabilized by plate-shaped clay particles. Addition of water induced a phase inversion from a water-in-oil (W/O) emulsion to an oil-in-water (O/W) emulsion when the amount of the oil phase exceeded a limiting amount of oil absorption to solid particles. On the other hand, a phase inversion from a powdery state to an O/W emulsion state through an oil-separated state is observed when the amount of an oil phase is less than the limiting amount of the oil absorption. Interestingly, the oil separated is re-dispersed as emulsion droplets into the O/W emulsion phase. This type of phase inversion, which is a feature of the Pickering emulsions stabilized by the clay particles, is caused by a change in the aggregate structures of particles.     

Pickering emulsions stabilized by hydrophobically modified alginate nanoparticles: Preparation and pH-responsive performance in vitro

pH-responsive Pickering emulsions were prepared, taking the hydrophobic modified calcium alginate nanoparticles (MCA) of pH sensitivity as emulsifiers. The MCAs were obtained via gelation between Ca²⁺ in emulsion and alginate sodium that reacted with diacetone acrylamide since alginate sodium was too hydrophilic to be used as a stabilizer. The effect of MCA characteristics, Ca²⁺ content, and pH on the preparation and property of emulsion was evaluated. Then, the released behaviors of MCA-stabilized emulsion loading oil-soluble drug of curcumin were investigated in vitro. The results demonstrated that Pickering emulsions released curcumin intestine-specifically (37% in 4 hours with a pH of 6.8), compared with the one in the gastric fluid (3% in 4 hours with a pH of 1.5), proving that MCA had similar pH sensitivity to alginates and probably as the promising candidate in oral drug controllable release.     

CO2 Hydrogenation Catalyzed by Graphene-Based Materials

In the context of an increased interest in the abatement of CO₂ emissions generated by industrial activities, CO₂ hydrogenation processes show an important potential to be used for the production of valuable compounds (methane, methanol, formic acid, light olefins, aromatics, syngas and/or synthetic fuels), with important benefits for the decarbonization of the energy sector. However, in order to increase the efficiency of the CO₂ hydrogenation processes, the selection of active and selective catalysts is of utmost importance. In this context, the interest in graphene-based materials as catalysts for CO₂ hydrogenation has significantly increased in the last years. The aim of the present paper is to review and discuss the results published until now on graphene-based materials (graphene oxide, reduced graphene oxide, or N-dopped graphenes) used as metal-free catalysts or as catalytic support for the thermocatalytic hydrogenation of CO₂. The reactions discussed in this paper are CO₂ methanation, CO₂ hydrogenation to methanol, CO₂ transformation into formic acid, CO₂ hydrogenation to high hydrocarbons, and syngas production from CO₂. The discussions will focus on the effect of the support on the catalytic process, the involvement of the graphene-based support in the reaction mechanism, or the explanation of the graphene intervention in the hydrogenation process. Most of the papers emphasized the graphene’s role in dispersing and stabilizing the metal and/or oxide nanoparticles or in preventing the metal oxidation, but further investigations are needed to elucidate the actual role of graphenes and to propose reaction mechanisms.     

Application of CO2-Triggered Switchable Surfactants to Form Emulsion with Xinjiang Heavy Oil

Owing to the high acid number of Xinjiang heavy oil and incomplete demulsification after pipelining, this article discusses the application of CO₂-triggered switchable surfactants to the emulsified transport of several Xinjiang heavy oils in the pipeline. Results show that CO₂-triggered switchable surfactants promote the formation and stabilization of oil-in-water (O/W) emulsion in the absence of CO₂ as a base. The property parameters of heavy oils fundamentally influence the indigenous emulsifying agents. The emulsion is stable when the heavy oil has a high acid number and low asphaltene content, which is also affected by some physical factors.     

A pH-responsive TiO2-based Pickering emulsion system for in situ catalyst recycling

Through tuning the surface wettability of interfacially active TiO₂ particles, a pH-responsive Pickering emulsion system is formed, as in situ separation and recycling of the nano-catalysts system.     

Effect of emulsification processes on the stability of Pickering emulsions stabilized by organomontmorillonites

In this paper, effect of emulsification processes on the properties of Pickering emulsions stabilized by organomontmorillonites (OMts) was studied. Results of micro-morphology and X-ray diffraction showed that the structure of OMt in emulsion depended on the emulsification processes and had an effect on the stability of emulsion. We propose a schematic diagram to reveal the relationship between emulsification processes-OMt laminates structure-stability of Pickering emulsion. In emulsion prepared by ultrasonic, OMt showed uniform dispersion, loose structure, and irregular crystalline. In emulsion prepared by vortex mixing method, OMt illustrated stacking and coagulation structure. In emulsion prepared by microwave method, OMt showed interacting structure and had a little interaction with oil/water interface, and thus the properties of emulsion prepared by microwave was weakly related to oil/water ratios. Emulsification processes had a profound effect on the structure of OMt and stability of Pickering emulsion, which can be used as a trigger to prepare emulsion for various applications.     

Hollow microspheres with covalent‐bonded colloidal and polymeric shell by Pickering emulsion polymerization

Hollow microspheres with SiO₂/polymer binary shell were fabricated from Pickering emulsion stabilized solely by methacryloxypropyltrimethoxysilane‐modified SiO₂ particles, and were characterized by optical microscopy, scanning electron microscopy, Fourier transformation infrared spectrum, thermogravimetric analysis (TGA), and energy dispersive X‐ray spectroscopy. The microspheres were templated by the Pickering droplets and the inner structure was affect by the proportion of crosslinking reagent. TGA result indicated that 60.3% of polymer in the shell was connected with SiO₂ by covalent bond which was formed by copolymerization of styrene and the reactive C?C group on SiO₂ stabilizer. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

A CO2-Switchable Polymer Surfactant Copolymerized with DMAEMA and AM as a Heavy Oil Emulsifier

A CO₂-switchable polymer surfactant was synthesized with acrylamide (AM) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). The changes in conductivity, particle size, and ζ-potential were adopted to illustrate its switchability. The CMC of the surfactant was determined by the break point of the curve of surface tension versus concentration. An oil emulsion with 8 g/L surfactant almost reached the highest stability. The thermodynamic stability of the emulsion decreased sharply upon increase of the temperature. Adding an inorganic salt was hard to affect the emulsion stability because the surfactant is non-ionic. The emulsion could maintain its stability even if the concentration of NaCl was as high as 10 g/L. The emulsion could easily be broken by bubbling CO₂. Its dehydration rate was 155 times faster than that without the presence of CO₂, and the amount of residual oil in water was only 32.22 ppm, which displayed brilliant performance of de-emulsification.     

Characterization of silicone oil emulsions stabilized by TiO2 suspensions pre-adsorbed SDS

To study the effects of pre-adsorbed emulsifier on Pickering emulsion stability, the preparation of silicone oil emulsions by TiO₂ suspensions pre-adsorbed sodium dodecyl sulfate (SDS) at the fixed TiO₂ concentration of 0.15 g was carried out below a fiftieth of critical micelle concentration (cmc) of SDS, where all added amounts of SDS are adsorbed on the TiO₂ particles. The stability of the Pickering emulsions incorporating TiO₂ suspensions pre-adsorbed SDS was investigated by measuring the volume fraction of emulsified silicone oil, adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS, oil droplet size, and some rheological responses such as the stress-strain sweep curve and strain and frequency dependences of dynamic viscoelastic moduli. The silicone oil was almost emulsified by TiO₂ suspensions pre-adsorbed SDS above cmc/10³. Increasing in the adsorbed amount of SDS on the TiO₂ particles leads to an increase in the adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS. Such silicone oil emulsions for the first time showed two yield stresses in the stress-strain sweep curve as well as the oscillatory stress-strain curve. The respective yield stresses also increase with an increase in the adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS. From such characteristic rheological properties and a partial sedimentation of some TiO₂ particles remained in the dispersion medium, we proposed the formation of a three dimensional network of the flocculated TiO₂ particles pre-adsorbed SDS on the silicone oil droplets.     

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。     

Noncovalent modification of self-assembled functionalized COF by PNIPAM and its properties of Pickering emulsion

Based on a facile and universal method using noncovalent bonding, here, polymer-modified covalent organic framework materials (COFs) were rapidly prepared. PNIPAM-modified COF (COF-PNIPAM) was synthesized by electrostatic self-assembly between COF prepared by low-cost melamine and terephthalaldehyde and carboxyl-terminated poly(N-isopropylacrylamide) (PNIPAM) prepared via reversible addition-fragmentation chain transfer polymerization. The carboxyl-terminated PNIPAM was characterized by Gel Permeation Chromatography and Ultraviolet and Visible Spectroscopy (UV–vis). COF and COF-PNIPAM were characterized by Fourier Transform Infrared Spectroscopes, Scanning Electron Microscope, Transmission Electron Microscope, X-Ray Diffractomer (XRD), and Brunner-Emmet-Teller (BET) measurements. The results showed that the COF-PNIPAM was successfully prepared. The Pickering emulsion properties of the COF-PNIPAM in a water-to-toluene mixed system were studied, and when the water-to-oil ratio is 2:1, a stable emulsion can be obtained. However, the results show that the PNIPAM chains of COF-PNIPAM nearly lose their temperature responsiveness.     

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.