Pickering emulsions stabilized with PANI-NP. Study of the thermoresponsive behavior under heating and radiofrequency irradiation

Micrometric Pickering emulsions in 1-octanol or cyclohexane were stabilized with water-dispersible electroactive polyaniline nanoparticles (PANI-NP). The emulsions were characterized by optical and electronic microscopy as well as spectroscopic techniques. It was demonstrated that nanoparticles maintain their functional properties (e.g., pH sensitivity and electromagnetic absorption) in the emulsion. Furthermore, as a proof of concept, smart Pickering emulsions employing PANI-NP stabilized with a thermosensitive polymer (PNIPAM) were obtained. The thermal behavior of the obtained structures was evaluated by turbidimetric techniques and an IR camera. The thermoresponsive emulsions have shown an important increment of the local temperature (>12°C) under radiofrequency (RF) irradiation. Phase transition of PNIPAM induced by heating or RF absorption provokes the breaking of the emulsions. In this context, the proposed systems herein could induce endothermal reactions carried out in organic solvents. Besides, Pickering emulsions formed by using electroactive PANI-NP could be applied in several medical or industrial applications.     

智能响应型Pickering乳液的制备及在物质分离中的应用进展

Pickering乳液是指由微纳米固体粒子代替传统表面活性剂作为乳化剂而稳定的乳液,具有较强的稳定性和超高油/水界面,能够为多相界面反应和物质传输提供高效稳定的场所。Pickering乳液的乳滴结构和性质与固体颗粒的尺寸形貌及表面性质密不可分,通过调控固体颗粒本身或表面的性质可以赋予Pickering乳液特定的响应性功能,拓宽其应用领域。本文对近年来不同响应型（磁性、CO₂、pH、光、温度等响应型）的Pickering乳液的主要研究成果进行了综述,重点介绍了Pickering乳液的稳定性原理、响应型Pickering乳液的制备方法和结构调控策略,以及近年来Pickering乳液在物质分离提取中的应用研究进展,最后对智能响应型Pickering乳液应用研究的发展趋势进行了展望。     

非共价改性纳米颗粒稳定Pickering乳液的制备及可逆调控

用具有氧化还原活性分子乙酰基二茂铁吖嗪(Fc⁺A)对磁性纳米颗粒Fe₃O₄@SiO₂进行非共价疏水改性,将改性颗粒作为乳化剂制备Pickering乳液。通过TEM、SEM、FTIR、XRD、接触角测量、光学显微镜等对纳米颗粒及Pickering乳液的结构、形貌和性能进行表征。结果表明：制备的核壳结构纳米颗粒粒径为150 nm左右,分散均匀;Fc⁺A成功修饰到纳米颗粒表面,且随Fc⁺A浓度的增加,改性颗粒的接触角明显增大;Fc⁺A浓度为12.5 mmol/L,乳化剂浓度为0.3%(质量),油水比为4∶6,搅拌速率为10000 r/min,得到的Pickering乳液具有良好的稳定性。而且,所得乳液具双重响应性,通过氧化还原和磁场可实现对乳液稳定性的可逆调控。     

高亲水性纳米二氧化硅颗粒稳定Pickering乳液

用未修饰的高亲水性纳米二氧化硅颗粒(SiO2 NPs)在其等电点附近制备Pickering乳液。结果表明,等电点(pH 2.7)条件下SiO2 NPs借助高能均质与油水界面剧烈混合,并在范德华引力的驱动下以弱吸附的状态在界面处负载,从而稳定得到O/W型Pickering乳液。增加SiO2 NPs的浓度或减小油相体积分数可提高单位油滴界面的颗粒负载率,增大连续相黏度并促进乳液液滴之间形成三维网络结构从而提高乳液稳定性。通过调节连续相的pH以促进SiO2 NPs表面的硅烷醇发生质子化与去质子化的转变,实现乳液多次pH响应循环。     

Au nanoparticle/graphene oxide hybrids as stabilizers for Pickering emulsions and Au nanoparticle/graphene oxide@polystyrene microspheres

Gold nanoparticle/graphene oxide hybrids (AuNP/GO) were easily fabricated by a redox reaction between GO and chloroauric acid without using any additional reductant and then used to stabilize Pickering emulsions. Factors affecting the properties of the emulsions were studied, including the HAuCl₄/GO mass ratio used to prepare the AuNP/GO, the oil/water ratio, the AuNP/GO concentration, the pH value, and the type and concentration of electrolytes. The emulsions were more stable when stabilized by AuNP/GO made from HAuCl₄/GO mass ratios of 0.375–0.5. High pH values and AuNP/GO concentrations that were too high or too low were unfavorable to the stability of the Pickering emulsions. Adding electrolytes to the systems improved the stability of the Pickering emulsions owing to the reduction of repulsive interactions between AuNP/GO sheets. The AuNP/GO stabilized Pickering emulsions were used to prepare AuNP/GO supported polystyrene (PS) microspheres (AuNP/GO@PS) by polymerizing the Pickering emulsion. The catalytic performance of AuNP/GO@PS for the reduction of 4-nitrophenol was then studied.     

A review on the application of nanofluids in enhanced oil recovery

Enhanced oil recovery (EOR) has been widely used to recover residual oil after the primary or secondary oil recovery processes. Compared to conventional methods, chemical EOR has demonstrated high oil recovery and low operational costs. Nanofluids have received extensive attention owing to their advantages of low cost, high oil recovery, and wide applicability. In recent years, nanofluids have been widely used in EOR processes. Moreover, several studies have focused on the role of nanofluids in the nanofluid EOR (N-EOR) process. However, the mechanisms related to N-EOR are unclear, and several of the mechanisms established are chaotic and contradictory. This review was conducted by considering heavy oil molecules/particle/surface micromechanics; nanofluid-assisted EOR methods; multiscale, multiphase pore/core displacement experiments; and multiphase flow fluid-solid coupling simulations. Nanofluids can alter the wettability of minerals (particle/surface micromechanics), oil/water interfacial tension (heavy oil molecules/water micromechanics), and structural disjoining pressure (heavy oil molecules/particle/surface micromechanics). They can also cause viscosity reduction (micromechanics of heavy oil molecules). Nanofoam technology, nanoemulsion technology, and injected fluids were used during the EOR process. The mechanism of N-EOR is based on the nanoparticle adsorption effect. Nanoparticles can be adsorbed on mineral surfaces and alter the wettability of minerals from oil-wet to water-wet conditions. Nanoparticles can also be adsorbed on the oil/water surface, which alters the oil/water interfacial tension, resulting in the formation of emulsions. Asphaltenes are also adsorbed on the surface of nanoparticles, which reduces the asphaltene content in heavy oil, resulting in a decrease in the viscosity of oil, which helps in oil recovery. In previous studies, most researchers only focused on the results, and the nanoparticle adsorption properties have been ignored. This review presents the relationship between the adsorption properties of nanoparticles and the N-EOR mechanisms. The nanofluid behaviour during a multiphase core displacement process is also discussed, and the corresponding simulation is analysed. Finally, potential mechanisms and future directions of N-EOR are proposed. The findings of this study can further the understanding of N-EOR mechanisms from the perspective of heavy oil molecules/particle/surface micromechanics, as well as clarify the role of nanofluids in multiphase core displacement experiments and simulations. This review also presents limitations and bottlenecks, guiding researchers to develop methods to synthesise novel nanoparticles and conduct further research.     

海藻酸辛酰胺的制备及其协同氨基SiO2纳米粒稳定液体石蜡/水乳液的研究

以辛胺为疏水改性剂,采用酰化法制得具有两亲性的海藻酸辛酰胺(ACA)。将ACA与采用修正Stber法制备的氨基二氧化硅(SiO_2-NH_2)纳米粒混合,在超声的作用下制得O/W型Pickering乳液。通过FT-IR,~1H NMR和荧光光谱对ACA的结构和性能进行表征。并采用激光粒度和Zeta电位分析仪、接触角测量仪和光学显微镜探究了ACA,SiO_2-NH_2及其协同水分散体系的胶体性能和相应的Pickering乳液的形貌。结果表明:ACA的取代度为0.29,在0.15 mol/L Na Cl水溶液中的临界聚集浓度(cac)为0.42 g/L,表现出较强的两亲性能。ACA通过静电作用力成功地吸附于SiO_2-NH_2纳米粒上,使水动力学粒径只有155 nm的SiO_2-NH_2纳米粒增长至386 nm,Zeta电位由+22.2 mV转变为-30.7 mV,在水溶液中能够表现出良好的稳定性。吸附于SiO_2-NH_2纳米粒表面的ACA可以抑制无机纳米粒的聚沉,而游离的ACA形成的胶束结构的疏水内腔能够增溶油滴,减少小油滴的聚并。光学显微镜中出现了粒径较大的Pickering乳液液滴和粒径较小的传统乳液液滴共存的现象,当ACA质量浓度在0.5 cac~1.0 cac时,2种乳液共存现象最为显著。     

基于纤维素纳米晶稳定的亚微米Pickering乳液制备

与传统表面活性剂稳定的乳液相比,固体纳米颗粒稳定的Pickering乳液具有较强的界面稳定性、多功能性、低毒性等优势,在生物医药领域具有较大的应用潜力。而相较于尺寸较大的微米级Pickering乳液,亚微米Pickering乳液具有更大的比表面积、更有效的递送效率,有望进一步拓展Pickering乳液在生物医药领域的应用。但由于Pickering乳液的制备影响因素众多,且相互制约,刚性的固体颗粒难以在较小的有限油水界面排布,增加了亚微米Pickering乳液的制备难度。本工作以制备稳定的亚微米Pickering乳液为研究目标,采用具有良好生物相容性的天然多糖–纤维素纳米晶(CNCs)为颗粒乳化剂,角鲨烯作为油相,考察了颗粒浓度、油水比例、水相成分、超声时间及频率对Pickering乳液粒径分布及稳定性的影响,最终得到了具有良好的储存稳定性和抗离心稳定性的粒径为638.7?8.40 nm的亚微米Pickering乳液(CNCs-PE)。通过激光共聚焦显微镜证实了CNCs吸附在油水界面,形成了Pickering乳液结构。利用CCK-8法评价了CNCs和CNCs-PE的细胞毒性,结果表明,两者都具有良好的细胞安全性。此外,将其用于吸附模型抗原OVA,吸附率达到约80%,且肌肉注射部位的切片结果也表明其注射安全性良好。此结果为亚微米Pickering乳液进一步研究提供了参考,并有望拓展CNCs稳定的亚微米Pickering乳液在生物医药领域的应用。     

阴离子多聚糖修饰Pickering乳液的制备及表征

为了提高淀粉纳米晶(SNC)与季铵盐壳聚糖(QCS)共同稳定的Pickering乳液在p H变化时的稳定性,以阴离子多聚糖海藻酸钠和果胶为原料,通过静电作用对乳液进行表面修饰,制得两种Pickering乳液。通过测定乳液粒径、Zeta电位和体外消化情况,对乳液的稳定性和消化特性进行了表征。结果显示:当水相中海藻酸钠和果胶质量分数均为0.1%(以水相为基准)时,修饰后的两种Pickering乳液在p H=2~7内均能保持粒径不变,且该乳液在25℃下放置90 d,粒径无变化,无乳析现象发生。此外,在体外模拟消化条件下,阴离子多聚糖的加入还能抑制Pickering乳液中油脂和淀粉的消化。     

Polymer‐coated nanoparticles for enhanced oil recovery

Enhanced oil recovery (EOR) processes aim to recover trapped oil left in reservoirs after primary and secondary recovery methods. New materials and additives are needed to make EOR economical in challenging reservoirs or harsh environments. Nanoparticles have been widely studied for EOR, but nanoparticles with polymer chains grafted to the surface—known as polymer‐coated nanoparticles (PNPs)—are an emerging class of materials that may be superior to nanoparticles for EOR due to improved solubility and stability, greater stabilization of foams and emulsions, and more facile transport through porous media. Here, we review prior research, current challenges, and future research opportunities in the application of PNPs for EOR. We focus on studies of PNPs for improving mobility control, altering surface wettability, and for investigating their transport through porous media. For each case, we highlight both fundamental studies of PNP behavior and more applied studies of their use in EOR processes. We also touch on a related class of materials comprised of surfactant and nanoparticle blends. Finally, we briefly outline the major challenges in the field, which must be addressed to successfully implement PNPs in EOR applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40576.     

Facile fabrication of nanocomposite microspheres with polymer cores and magnetic shells by Pickering suspension polymerization

Pickering suspension polymerization was used to prepare magnetic polymer microspheres that have polymer cores enveloped by shells of magnetic nanoparticles. Styrene was emulsified in an aqueous dispersion of Fe₃O₄ nanoparticles using a high shear. The resultant Pickering oil-in-water (o/w) emulsion stabilized solely by magnetic nanoparticles was easily polymerized at 70 °C without stirring. Fe₃O₄ nanoparticles act as effective stabilizers during polymerization and as building blocks for creating the organic–inorganic hybrid nanocomposite after polymerization. The fabricated magnetic nanocomposites were characterized by FTIR, XRD, TGA, DSC, GPC, XPS and SEM. The structures of the polymer core and the nanoparticle shell were analyzed. We investigated the effects on the products of the weight of Fe₃O₄ nanoparticles used to stabilize the original Pickering emulsions. Pickering suspension polymerization provides a new route for the synthesis of a variety of hybrid nanocomposite microspheres with supracolloidal structures.     

Multihollow nanocomposite microspheres with tunable pore structures by templating Pickering double emulsions

Micrometer-sized dual nanocomposite polymer microspheres with tunable pore structures were fabricated using a simple and straightforward method based on Pickering double emulsions. First, a primary water-in-styrene (oil) emulsion (w₁/o) was prepared using the hydrophobic silica nanoparticles as a particulate emulsifier without any molecular surfactants. Then, a water-in-styrene-in-water (w₁/o/w₂) Pickering emulsion was produced by the emulsification of the primary w₁/o emulsion into water using Fe₃O₄ nanoparticles as external emulsifier. The big styrene droplets containing small water droplets were polymerized after the formation of the double emulsions. Nanocomposite polystyrene microspheres with a multihollow structure were obtained and their morphological structures were studied by scanning electron microscopy (SEM). The pore structure of the microspheres could be tuned by the volume ratio of the internal water phase to the medium oil phase (w₁:o) of the primary emulsions. With increasing w₁:o from 1:8 to 4:1, the amount of the pores in one microsphere increased gradually and the pore structures changed from close to interconnected. The resulting multihollow microspheres had a responsive ability to magnetic stimulus due to the existence of Fe₃O₄ nanoparticles. This kind of multihollow hybrid polymer microspheres is expected to have a wide potential application in materials science and biotechnology.     

Enhanced oil recovery using nanoparticle-stabilized oil/water emulsions

We experimentally investigated nanoparticle-stabilized emulsions for enhanced oil recovery (EOR) applications. The emulsions were injected into a silica bead column containing mineral oil, and the oil recovery was calculated using a mass-balance approach. The experiments were carried out as follows: 1) The emulsions were injected into a column with 100% water saturation to investigate the mobility of the water and emulsions, 2) Water flooding was then carried out at initial oil and water saturation, and the emulsion flooding was injected to calculate the enhancement in the oil recovery rate. The results indicate that the nanoparticle-stabilized emulsions increased the oil recovery rate by 11% after water flooding. The mechanism for this is attributed to a greater pressure difference across the porous medium, leading to oil remaining in the pores being produced via a piston effect. These results indicate that nanoparticle-stabilized emulsions may be effective EOR agents.     

Effect of Nanoparticles on Viscosity and Interfacial Tension of Aqueous Surfactant Solutions at High Salinity and High Temperature

Surfactant flooding has widely been used as one of the chemically enhanced oil recovery (EOR) techniques. Surfactants majorly influence the interfacial tension, γ, between oil and brine phase and control capillary number and relative permeability behavior and, thus, influence ultimate recovery. Additives, such as nanoparticles, are known to affect surfactant properties and are regarded as promising EOR agents. However, their detailed interactions with surfactants are not well understood. Thus, in this work, we examined the influence of silica nanoparticles on the ability of surfactants to lower γ and to increase viscosity at various temperatures and salinities. Results show that the presence of nanoparticles decreased γ between n-decane and various surfactant formulations by up to 20%. It was found that γ of nanoparticles–surfactant solutions passed through a minimum at 35 °C when salt was added. Furthermore, the viscosity of cationic surfactant solutions increased at specific salt (1.5 wt.%) and nanoparticle (0.05 wt.%) concentrations. Results illustrate that selected nanoparticles–surfactant formulations appear very promising for EOR as they can lower brine/n-decane interfacial tension and act as viscosity modifiers of the injected fluids.     

Reactive Surfactants for Achieving Open-Cell PolyHIPE Foams from Pickering Emulsions

PolyHIPEs, highly porous polymers synthesized within high internal phase emulsions (HIPEs), emulsions with over 74% internal phase, are of interest for applications such as absorbents, reaction supports, and tissue engineering scaffolds. Typically, the surfactant contents for HIPE stabilization are relatively high, ranging from 20 to 30 wt% of the external phase, with the monomers usually being the remainder. One drawback of using surfactants for these applications is the potential for leachables, necessitating intensive purification processes for their removal. Pickering HIPEs, HIPEs stabilized using amphiphilic solid nanoparticles that spontaneously migrate to the oil–water interface, can be used as an alternative HIPE stabilization strategy. Although nanoparticles can add surface functionality advantageous for the application, polyHIPEs from Pickering HIPEs often lack the interconnecting holes needed for the high permeability required for such applications. This work describes a successful approach for designing an HIPE stabilization system that is based on a combination of nanoparticles and reactive surfactants and that generates the desired surface functionality, an interconnected porous structure, and a low leachable content. Such an approach can extend the applicative utility of such polyHIPEs by circumventing the need for extensive purification.     

Synthesis of Polystyrene/Hydrophobic SiO2 Composite Particles via Oil‐in‐Water Pickering Emulsion Polymerization

The aim of this work is to present a facile Pickering emulsion polymerization method for the synthesis of submicron polystyrene/SiO₂ core/shell composite particles. The commercial hydrophobic SiO₂ nanoparticles were used as stabilizing agent for creating a stable oil‐in‐water emulsion. Although the adsorption of hydrophobic SiO₂ nanoparticles in the emulsion system was unfavorable in terms of thermodynamics, by ultrasound treatment, self‐assembly of hydrophobic SiO₂ nanoparticles effectively stabilized oil‐in‐water Pickering emulsions during polymerization. Using 3 wt.% SiO₂ nanoparticles (based on styrene monomer) and 1:10 volume ratio of styrene monomer:water, the composite particles having average size of 790 nm and relatively narrow particles distribution were produced. With decreasing the volume ratio, smaller composite particles were created. Results from scanning electron microscope revealed that SiO₂ nanoparticles were located exclusively at the surface of the polystyrene latex particles. The SiO₂ content, determined by thermogravimetric analysis, was 12.6 wt.% in the composite particles. The route reported here may be used for the preparation of other composite nanostructures. POLYM. ENG. SCI., 59:E195–E199, 2019. © 2018 Society of Plastics Engineers     

疏水改性核壳结构颗粒对Pickering乳液的稳定作用

为了探究固体颗粒对乳液的稳定作用,采用双亲染料分子罗丹明B对核壳结构的Fe_3O_4@SiO_2纳米颗粒进行疏水改性,并将改性后的纳米颗粒作为稳定剂制备Pickering乳液。通过Zeta电位、FTIR、XRD、SEM、接触角测量、光学显微镜、电导率仪对Fe_3O_4@SiO_2纳米颗粒以及Pickering乳液的结构、形貌和性能进行表征与分析,结果表明:制备的纳米颗粒粒径小,约为150 nm,为单分散球形核壳结构;罗丹明B成功修饰到Fe_3O_4@SiO_2纳米颗粒表面,改性后颗粒接触角由30°增加至120°;随乳化剂颗粒质量浓度的增加,制备的乳液液滴的粒径减小。另外,所得Pickering乳液具有良好的磁场响应性,可通过外加磁场实现对乳液稳定性的可逆调控,且此过程可重复3次以上。     

纳米二氧化硅的疏水改性及其对Pickering乳液的稳定作用

为了探究固体粒子对乳液的稳定作用,采用L-赖氨酸作为催化剂合成纳米SiO2粒子,并用六甲基二硅胺烷(HMDS)对纳米SiO2粒子进行表面疏水改性,将经过HMDS改性后的纳米SiO2粒子作为稳定剂制备出Pickering乳液。通过粒径分析仪、场发射透射电子显微镜、FTIR、TG-DSC、接触角测量仪、光学显微镜、电导率仪分别对纳米SiO2的制备、表面改性和Pickering乳液的性能进行了表征。结果表明,成功合成出粒径小且形貌均一的硅球,具有疏水性的三甲基硅基成功接枝到纳米SiO2的表面;不同纳米SiO2浓度制备的Pickering乳液,发现随着SiO2浓度的增大,乳液的稳定性逐渐增强,乳液液滴直径呈现减小的趋势;不同油水比制备的Pickering乳液,发现随着油相体积的增大,乳液的稳定性呈现增大的趋势。     

TiO2纳米颗粒稳定的Pickering乳液用作防晒乳成分研究

采用烷基化改性的TiO_2纳米颗粒为稳定剂,化妆品级白油为油相,黄芪水溶液为水相,制备了一种载药Pickering乳液。利用TEM、接触角测试仪和光学显微镜对TiO_2纳米颗粒及载药Pickering乳液进行了表征。结果表明,该纳米颗粒分散性良好、尺寸均匀,具备良好的稳定乳液能力;通过紫外吸收测试,控制释放药物和清洗对照实验,表明该载药Pickering乳液具有较高的防晒效果和随光照时间控制释放药物以及易于从皮肤表面清洗的特性。     

Hydrophilic porous polymers based on high internal phase emulsions solely stabilized by poly(urethane urea) nanoparticles

Stable oil-in-water (o/w) Pickering high internal phase emulsions (HIPEs) having an internal phase of up to 95 vol% were prepared with a low-energy emulsification method. A poly(urethane urea) (PUU) aqueous nanodispersion was used as aqueous phase. The PUU nanoparticles of the aqueous nanodispersion acted as a mechanical barrier, and prevented droplet coalescence in the Pickering HIPEs. In addition, open porous hydrophilic polymer foams were obtained by polymerization of the Pickering HIPEs, and the morphology of the foams were tailored by changing the oil:water ratio, PUU nanoparticle and NaCl concentrations. The method used herein provides a simple way to prepare morphology controlled hydrophilic polymer foams using o/w Pickering HIPEs as template.