开关型Pickering乳液体系

Pickering乳液以胶体尺寸的固体粒子代替传统表面活性剂作为稳定剂,具有超稳定,生物相容性好以及对环境友好等优点。开关型Pickering乳液可随pH值、CO₂/N₂浓度、温度、磁场强度及光强度等条件的变化而改变固体乳化剂的表面润湿性,实现在“乳化”与“破乳”之间的快速转换,在非均相催化、乳液聚合等诸多领域有广泛的应用前景。本文全面总结了近年来开关型Pickering乳液的研究进展及其在界面催化系统、液膜处理有机废水、药物的包封与释放等方面的应用。     

Pickering乳状液的研究进展

随着纳米技术的发展以及Pickering乳液在食品、化妆品、医药等领域的潜在应用前景,人们对Pickering乳液给予了关注。本文全面总结了近些年来Pickering乳液的研究进展,对本课题组在Pickering乳液研究领域所取得的成果进行了介绍。本文主要分为4个部分:第一部分概述了Pickering乳液的研究现状;第二部分全面考察了Pickering乳液的各种影响因素;第三部分介绍了Pickering乳液的转相特性;最后综述了颗粒和表面活性物质协同稳定乳液的研究进展。这些研究成果促进了乳液基础理论的发展,并且拓展了乳液的应用范围。     

两亲性Janus粒子的合成及其在Pickering乳液中的应用

Janus粒子由于在光、电、力、磁及表面亲/疏水性等方面表现出各向异性,因此在稳定乳液、生物医药及功能涂层等方面展现出广阔的应用价值。两亲性Janus粒子是指一侧具有亲水性、另一侧具有疏水性的不对称材料,由于同时具有表面活性剂的性质和固体颗粒的效应,在稳定Pickering乳液方面极具优势。基于此,本文对两亲性Janus粒子的制备方法进行了综述,并对比分析了其优缺点,同时总结了两亲性Janus粒子对Pickering乳液稳定性的影响,最后对其今后的发展进行了展望。     

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。     

MOFs在乳液中的可控生长

金属有机框架(Metal organic frameworks, MOFs)材料是金属离子与有机配体自组装形成的形貌可控的多孔晶体材料。表面活性剂的乳化作用是形成乳液的关键,其自组装形成不同形貌的胶束控制最终产物的形貌。因此,在MOFs的制备中,不同乳液体系中的胶束亦可以作为反应模板,从而调控MOFs的形貌。本文简要介绍了传统乳液、反相微乳液、无皂乳液和Pickering乳液的形成机理和特点。重点综述了近年来MOFs在不同乳液体系中可控生长研究。其中,利用无皂乳液法和Pickering乳液法是构建MOFs复合材料的理想思路。     

Pickering乳液在功能高分子材料研究中的应用

功能高分子材料制备的瓶颈问题是如何解决多重材料的相容性问题,传统的物理共混技术和聚合添加技术无法保证材料的稳定性及均一性。 Pickering乳液具有成本低、毒性小、环境友好、稳定性好、制备的多重材料结构稳定等优点,在制备功能高分子材料的应用中越来越受到人们的重视。 本文详细介绍了Pickering乳液在功能性高分子材料制备中的应用研究进展,提出了Pickering乳液聚合制备功能高分子材料面临的一些问题,并结合本课题组的研究方向,对其发展前景进行了展望。     

表面活性剂-纳米粒子协同稳定Pickering乳液的双相反转实验设计

本实验以表面活性剂原位改性纳米粒子协同稳定Pickering乳液为研究对象,通过对乳液的双相反转行为研究,探究表面活性剂分子在纳米粒子表面的吸附模式,加深学生对胶体与界面化学领域相关原理的理解,培养学生综合实验能力和分析推理能力。     

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。     

Pickering乳液双相反转研究表面活性剂在纳米粒子表面的吸附研究

本实验通过制备纳米粒子和表面活性剂协同稳定的Pickering乳液,对乳液的双相反转的现象进行研究。结果表明,随表面活性剂浓度提高,乳液类型从O/W转变成W/O型,再转变成O/W型,即发生双相反转现象。基于实验现象提出了不同表面活性剂浓度条件下表面活性剂分子在纳米粒子表面的吸附模型,即单层吸附和双层吸附导致纳米粒子由偏亲水向偏疏水再到偏亲水性的转变。     

用于水性涂料的Pickering乳液包覆抗蚀活性助剂的研究进展

简述了五种包覆技术和Pickering乳液,综述了Pickering乳液包覆技术制备的复合微球,重点论述了采用Pickering乳液包覆抗蚀性活性助剂的原理以及在水性涂料中的应用,目前研究情况及应用优势,最后展望了Pickering乳液包覆技术的深入研究会对推动水性涂料行业的迅猛发展起到关键性作用。     

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.     

Bioadhesive hydrocaffeic acid modified chitosan colloidal particles using as particulate emulsifiers

A kind of bioadhesive hydrocaffeic acid modified chitosan colloidal particles (HCA-CS/TPP CPs) containing synthetic catecholamine groups was prepared via amidation reaction and ionic gelation. The formation process and property of the HCA-CS/TPP CPs were characterized by ultraviolet visible spectrophotometry and Zeta PALS instruments. The prepared HCA-CS/TPP CPs were then used as particulate emulsifier to stabilize Pickering emulsions. The stability of the Pickering emulsion droplet was characterized by digital camera and optical microscope. The results revealed that HCA-CS/TPP CPs exhibited good emulsifying property at a wide pH value range, which will endow the potential application of the Pickering emulsions stabilized by HCA-CS/TPP CPs in various fields.     

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.     

Surfactant-Free Multiple Pickering Emulsions Stabilized by Combining Hydrophobic and Hydrophilic Nanoparticles

A series of W/O/W or O/W/O emulsion stabilized solely by two different types of solid nanoparticles were prepared by a two-step method. We explored the option of particular emulsifiers for the multiple Pickering emulsions, and a variety of nanoparticles (silica, iron oxide, and clay) only differing in their wettability was used. The primary W/O emulsion was obtained by the hydrophobic nanoparticles, and then the hydrophilic nanoparticles were used as emulsifier in the secondary emulsification to prepare the W/O/W emulsion. In a similar way, the primary O/W emulsion of the O/W/O emulsion was stabilized by the hydrophilic nanoparticles, while the secondary emulsification to prepare the O/W/O emulsion was effected with the hydrophobic nanoparticles. The resultant multiple Pickering emulsion was stable to coalescence for more than 3 months, except the W/O/W emulsions of which the secondary emulsion stabilized by clay nanoparticles became a simple O/W emulsion in a day after preparation. Moreover, the temperature and pH sensitive poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAm-co-MAA)) microgels were introduced as an emulsifier for the secondary emulsification to obtain the stimulus-responsive multiple W/O/W emulsion. Such microgel-stabilized multiple emulsions could realize the efficient controlled release of water-soluble dye, Rhodamine B (RB) on demand in a multiple-emulsion delivery system.      

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.     

Biocompatible and pH‐Responsive Colloidal Surfactants with Tunable Shape for Controlled Interfacial Curvature

Molecular‐surfactant‐stabilized emulsions are susceptible to coalescence and Ostwald ripening. Amphiphilic particles, which have a much stronger anchoring strength at the interface, could effectively alleviate these problems to form stable Pickering emulsions. Herein, we describe a versatile method to fabricate biocompatible amphiphilic dimer particles through controlled coprecipitation and phase separation. The dimer particles consist of a hydrophobic PLA bulb and a hydrophilic shellac–PEG bulb, thus resembling nonionic molecular surfactants. The size and diameter ratio of the dimer particles are readily tunable, providing flexible control over the water/oil interfacial curvature and thus the type of emulsion. The particle‐stabilized emulsions were stable for a long period of time and could be destabilized through a pH‐triggered response. The biocompatible amphiphilic dimer particles with tunable morphology and functionality are thus ideal colloidal surfactants for various applications.     

Structure of microparticles in solid-stabilized emulsions

Emulsions of oil and water stabilized by adsorbed solid particles are known as solid-stabilized emulsions (often referred to as Pickering emulsions). Using confocal microscopy, we have studied the assembly of colloidal-sized polystyrene particles in poly(dimethylsiloxane)-in-water solid-stabilized emulsions. Monodisperse polystyrene particles, when included in the emulsions at low concentrations, were found to form small patches with local "hexagonal" order, separated by other particle-free domains. Polystyrene particles with different sizes (1 and 4 microm) and different wettability could simultaneously segregate to the emulsion interface; even mixtures of hydrophobic and hydrophilic solid particles were found to simultaneously segregate to the same interface.     

Size effects of discoidal PLGA nanoconstructs in Pickering emulsion stabilization

Solid particle stabilized emulsions, using unique shape defined particles, are receiving increasing research interest due to ease of formulation and interesting physiochemical characteristics. There is, however, a need to systematically investigate the effect of anisotropic discoidal microparticles, realized with top-down fabrication approaches, in emulsion stabilization. Here, the effect of poly(d ,l -lactide-co-glycolide) (PLGA) discoidal polymeric nanoconstruct (DPN) size on the formation and stability of oil-in-water emulsions is studied. Particles with a diameter of 1, 2, and 5 μm are fabricated with a lithographic templating technique, and used to stabilize medium chain triglyceride (MCT) oil emulsions. Three phase contact angles decreased from 85° ± 7° to 68° ± 12° moving from 1 to 5 μm DPN stabilized emulsions, showing a particle “hydrophilicity” increase with size. Microscopy imaging showed that the mean droplet diameter and dispersity increased with particle size, and that DPNs were present at the oil–water interface. DPN based emulsions were stable for about 24 h or less in the case of 1 and 2 μm DPNs. Emulsion stability was shorter than 12 h in case of 5 μm DPNs. Finally, calculations of DPN detachment free energies ΔG_dw and excess surface coverages C_excess demonstrated that, despite the significantly high adhesion energy of the discoidal DPN, emulsion stability was mostly affected by gravitational forces for DPN sizes above 2 μm. The use of PLGA and MCT oil in this study is relevant for future use of Pickering emulsions in pharmaceutical and drug delivery applications.