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.     

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.     

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.     

Fabrication and performance of microencapsulated phase change materials with hybrid shell by in situ polymerization in Pickering emulsion

Microencapsulated phase change materials (MePCMs) using melamine–formaldehyde resin/SiO₂ as shell were investigated in this paper. Organically modified SiO₂ particles were employed to stabilize Pickering emulsion, and in situ polymerization of melamine and formaldehyde was carried out to form hybrid shell. The performances of resultant MePCMs with hybrid shell were investigated comparatively with the MePCMs with polymer shell. SiO₂ particles raise the microencapsulation efficiency by improving the stability of emulsion and providing a precipitation site for melamine–formaldehyde resin. Also, the mechanical strength, thermal reliability, and anti‐osmosis performance of MePCMs were improved significantly by SiO₂ particles in the shell. Our study shows that Pickering emulsion is a simple and robust template for MePCMs with polymer‐inorganic hybrid shell. Copyright © 2015 John Wiley & Sons, Ltd.     

Ca2+ Responsive Microgel-Stabilized Pickering Emulsions

As an ionic cross-linker that can change the size of poly(N-isopropylacrylamide-co-acrylic acid) microgel, Ca²⁺ is applied as a trigger to demulsify microgel-stabilized oil/water Pickering emulsions. The influence of Ca²⁺ induced intra-particle ionic cross-linking and inter-particle aggregation on the stability of microgel-stablized “Pickering” emulsion is described. At low and mediate concentration of Ca²⁺, ionic cross-linking can change the internal elasticity of the microgel, and cause the coarsening of the oil droplets. At high concentration of Ca²⁺, microgels flocculate due to the salt out effect and the emulsion is destabilized. This work provide a facile method to control the stability of the Pickering emulsions at ambient condition.     

Particle self-assembly in oil-in-ionic liquid Pickering emulsions

We have studied polydimethylsiloxane (PDMS)-in-1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]) Pickering emulsions stabilized by polystyrene microparticles with different surface chemistry. Surprisingly, in contrast to the consensus originating from oil/water Pickering emulsions in which the solid particles equilibrate at the oil-water droplet interfaces and provide effective stabilization, here the polystyrene microparticles treated with sulfate, aldehyde sulfate, or carboxylate dissociable groups mostly formed monolayer bridges among the oil droplets rather than residing at the oil-ionic liquid interfaces. The bridge formation inhibited individual droplet-droplet coalescence; however, due to low density and large volume (thus the buoyant effect), the aggregated oil droplets actually promoted oil/ionic liquid phase separation and distressed emulsion stability. Systems with binary heterogeneous polystyrene microparticles exhibited similar, even enhanced (in terms of surface chemistry dependence), bridging phenomenon in the PDMS-in-[BMIM][PF(6)] Pickering emulsions.     

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.     

Particle self-assembly at ionic liquid-based interfaces

This review presents an overview of the nature of ionic liquid (IL)-based interfaces and self-assembled particle morphologies of IL-in-water, oil- and water-in-IL, and novel IL-in-IL Pickering emulsions with emphasis on their unique phenomena, by means of experimental and computational studies. In IL-in-water Pickering emulsions, particles formed monolayers at ionic liquid–water interfaces and were close-packed on fully covered emulsion droplets or aggregated on partially covered droplets. Interestingly, other than equilibrating at the ionic liquid–water interfaces, microparticles with certain surface chemistries were extracted into the ionic liquid phase with a high efficiency. These experimental findings were supported by potential of mean force calculations, which showed large energy drops as hydrophobic particles crossed the interface into the IL phase. In the oil- and water-in-IL Pickering emulsions, microparticles with acidic surface chemistries formed monolayer bridges between the internal phase droplets rather than residing at the oil/water–ionic liquid interfaces, a significant deviation from traditional Pickering emulsion morphology. Molecular dynamics simulations revealed aspects of the mechanism behind this bridging phenomenon, including the role of the droplet phase, surface chemistry, and inter-particle film. Novel IL-in-IL Pickering emulsions exhibited an array of self-assembled morphologies including the previously observed particle absorption and bridging phenomena. The appearance of these morphologies depended on the particle surface chemistry as well as the ILs used. The incorporation of particle self-assembly with ionic liquid science allows for new applications at the intersection of these two fields, and have the potential to be numerous due to the tunability of the ionic liquids and particles incorporated, as well as the particle morphology by combining certain groups of particle surface chemistry, IL type (protic or aprotic), and whether oil or water is incorporated.     

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.     

颗粒乳化剂的研究及应用

近年来,颗粒乳化剂因其在食品、采油、化妆品、医药、催化以及功能纳米材料制备等领域具有潜在应用前景而备受关注。本文综述了近来颗粒乳化剂的研究进展,归纳了颗粒乳化剂的种类,包括:无机纳米粒子、表面改性或杂化的无机粒子、有机纳米粒子以及特殊的颗粒乳化剂Janus粒子;并对颗粒乳化剂能够在油水界面稳定吸附的热力学机理和动力学行为进行了阐述,颗粒乳化剂在油水界面接触角以及粒径大小是其在界面稳定吸附的关键参数,而颗粒在油水界面的排布方式则主要受粒子之间相互作用的影响。重点介绍了颗粒乳化剂的热点应用,包括:(1)利用颗粒乳化剂制备Pickering乳液,以及通过对颗粒乳化剂的功能化,使得Pickering乳液具备环境响应性(即pH、盐浓度、温度、紫外光、磁场敏感响应性);(2)以颗粒乳化剂为构筑基元、以Pickering乳液为模板制备Janus颗粒、Colloidosome、具有多级结构的粒子或膜,以及多孔结构材料;(3) Janus粒子在催化领域的应用。     

Cross‐Linking Density and Temperature Effects on the Self‐Assembly of SiO2—PNIPAAm Core–Shell Particles at Interfaces

SiO₂–PNIPAAm core–shell microgels (PNIPAAm=poly(N‐isopropylacrylamide)) with various internal cross‐linking densities and different degrees of polymerization were prepared in order to investigate the effects of stability, packing, and temperature responsiveness at polar–apolar interfaces. The effects were investigated using interfacial tensiometry, and the particles were visualized by cryo‐scanning electron microscopy (SEM) and scanning force microscopy (SFM). The core–shell particles display different interfacial behaviors depending on the polymer shell thickness and degree of internal cross‐linking. A thicker polymer shell and reduced internal cross‐linking density are more favorable for the stabilization and packing of the particles at oil–water (o/w) interfaces. This was shown qualitatively by SFM of deposited, stabilized emulsion droplets and quantitatively by SFM of particles adsorbed onto a hydrophobic planar silicon dioxide surface, which acted as a model interface system. The temperature responsiveness, which also influences particle–interface interactions, was investigated by dynamic temperature protocols with varied heating rates. These measurements not only showed that the particles had an unusual but very regular and reversible interface stabilization behavior, but also made it possible to assess the nonlinear response of PNIPAAm microgels to external thermal stimuli.     

Preparation of poly(methyl methacrylate)/CaCO3/SiO2 composite particles via emulsion polymerization

A novel method to prepare organic/inorganic composite particles, i.e. poly(methyl methacrylate)/CaCO₃/SiO₂ three-component composite particles, using emulsion polymerization of methyl methacrylate with sodium lauryl sulfate as a surfactant in an aqueous medium was reported. CaCO₃/SiO₂ two-component inorganic composite particles were obtained firstly by the reaction between Na₂CO₃ and CaCl₂ in porous silica (submicrometer size) aqueous sol and the specific surface area of the particles was measured by the Brunauer–Emmett–Teller (BET) method. The results show that the BET specific surface area of the CaCO₃/SiO₂ composite particle is much smaller than that of the silica particle, indicating that CaCO₃ particles were adsorbed by porous silica and that two-component inorganic composite particles were formed. Before copolymerization with methyl methacrylate, the inorganic composite particles were coated with a modifying agent through covalent attachment. The chemical structures of the poly(methyl methacrylate)/CaCO₃/SiO₂ composite particles obtained were characterized by Fourier transform IR spectroscopy and thermogravimetric analysis. The results show that the surface of the modified inorganic particles is grafted by the methyl methacrylate molecules and that the grafting percentage is about 15.2%.     

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.     

Preparation of SiO2/PMMA composite particles via conventional emulsion polymerization

A series of SiO₂/PMMA composite particles with different morphologies were prepared by conventional emulsion polymerization by the aid of acid–base interaction between the silanol groups of unmodified silica particles and the amino groups of 4‐vinylpyridine. In this approach, no surface treatment for nanosilica particles was required. The morphologies of composite particles, for example, multicore–shell, raspberry‐like, and conventional core–shell, could be controlled by modulating emulsifier content, monomer/silica ratio, silica size, and monomer feed method. The possible particle formation mechanisms were discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3807–3816, 2006     

The Effect of Nano-SiO2 Colloid on Soap-free Emulsion Polymerization of Methyl Methacrylate and Hydroxyethyl Methacrylate

Soap-free emulsion polymerization of methyl methacrylate (MMA) and hydroxyethyl methacrylate (HEMA) was carried out in the presence of colloidal nano-SiO₂ particles. The effect of nano-SiO₂ level on the monomer conversion, polymerization rate (Rp), and emulsion stability was investigated. The viscosity, particle size distribution of the emulsions, surface tension, and ionic conductivity of these systems were determined. Upon the introduction of the nano-SiO₂ particles into this system, the Rp and monomer conversion increased and the average particle size of the P(MMA-HEMA) emulsion decreased in comparison to emulsions formed in the absence of nano-SiO₂. However, the particle size distribution became broader to some degree. Scanning electron microscope observations demonstrated that the shape of these latex particles were uniformly spherical. The surface tension and ionic conductivity of the system increased significantly after polymerization, but the presence of nano-SiO₂ resulted in an increase in surface tension and a decrease in ionic conductivity in comparison to the particle–free system.     

Oil-in-water Pickering emulsion destabilisation at low particle concentrations

Droplet evolution in unstable, dilute oil-in-water Pickering emulsions was characterised using a combination of light scattering, confocal microscopy and rheology. Emulsions were formed at concentrations of silanised fumed silica particles that are not sufficient to prevent destabilisation. The key result is that destabilisation initially occurs via a combination of droplet flocculation and permeation. Close contact between the drops enhances oil transfer from smaller drops to the larger ones. The large drops swell over time until the attached particle density is insufficient to protect the drops against coalescence. Examination of the emulsion microstructure revealed the relationship between drop stability and the structural characteristics of the aggregates formed due to coagulation of the silica particles in the emulsions. The implications of these results for controlling Pickering emulsion stability are discussed.     

Comparison of binding behavior for molecularly imprinted polymers prepared by hierarchical imprinting or Pickering emulsion polymerization

The aim of this study was the evaluation of the binding performances and selectivity of molecularly imprinted beads prepared toward several penicillins (i) by hierarchical bulk polymerization in the pores of template‐grafted silica microbeads (hMIPs) and (ii) by Pickering emulsion polymerization in the presence of template‐decorated silica nanobeads (pMIPs). 6‐Aminopenicillanic acid was chosen as the common fragmental mimic template. Both approaches produced micron‐sized polymeric beads with good recognition properties toward the target ligands whereas the selectivity pattern appeared quite different. The polymer prepared by the Pickering emulsion approach showed binding properties similar to imprinted beads prepared by hierarchical approach. Equilibrium binding constants changed their values from 0.1–0.2 × 10⁶ (hMIPs) to 0.2–0.6 × 10⁶ M^?1 (pMIPs), while the binding site densities changed from 3.7–4.8 (hMIPs) to 0.3–0.55 μmol/g (pMIPs). Compared to the hierarchical polymerization, Pickering emulsion polymerization represents a more practical approach when a template mimic needs to be used.     

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.     

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.     

Assembly of a Metal–Organic Framework into 3 D Hierarchical Porous Monoliths Using a Pickering High Internal Phase Emulsion Template

3D Hierarchical porous metal–organic framework (MOF) monoliths are prepared by using Pickering high internal phase emulsion (HIPE) template. Pickering HIPEs were stabilized solely by UiO‐66 MOF particles with internal phase up to 90 % of the volume. The effects of internal phase type and volume, as well as MOF particle concentration on the stability of resulting Pickering HIPEs were investigated. Furthermore, by adding small amount of polyvinyl alcohol (PVA) as binder or polymerization in the continuous aqueous phase, followed by freeze‐drying, two types of MOF‐based 3D hierarchical porous monoliths with ultralow density (as low as 12 mg cm^?3) were successfully prepared. This Pickering HIPE template approach provides a facile and practical way for assembling of MOFs into complex structures.