Pickering乳液的制备和应用研究进展

Pickering乳液是一种由固体粒子代替传统有机表面活性剂稳定乳液体系的新型乳液。与传统乳液相比,Pickering乳液具有强界面稳定性、减少泡沫出现、可再生、低毒、低成本等优势,在化妆品、食品、制药、石油和废水处理等行业具有广阔的应用前景,受到越来越多研究者们的关注。本文综述了近年来Pickering乳液的研究进展,先介绍Pickering乳液相对于表面活性剂乳液的特色与优势,然后介绍Pickering乳液的制备研究进展,最后介绍Pickering乳液的应用研究进展。     

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。     

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。     

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。     

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.     

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。     

碳酸钙微粒稳定的橄榄油/水乳液及其缓释性能

1907年,Pickering发现超细固体颗粒对乳液具有一定的稳定作用~([1]).此后,由固体颗粒单独稳定的乳状液也被称为Pickering乳液.Pickering乳液在新材料合成、生物活性分子保护、食品和医药等领域具有重要的应用价值~([2-7]).     

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。     

纤维素纳米晶稳定的Pickering乳液法模板制备微胶囊的研究现状

纤维素纳米晶(Cellulose Nanocrystals, CNCs)具有高结晶度、高杨氏模量、高长径比、高比表面积、纳米尺寸效应、化学可修饰以及可降解等优异性质,从而被广泛应用于Pickering乳液微胶囊的制备。本文主要回顾了CNCs的制备和改性方法,并介绍了不同条件下获得的CNCs以及CNCs衍生物的理化性质;阐述了CNCs及衍生物作为Pickering乳液稳定粒子的研究现状;最后综述了CNCs稳定的Pickering乳液为模板制备微胶囊的一些方法,并进行了展望。     

胶体颗粒在液-液界面上的吸附行为及界面组装

综述了胶体颗粒在油水界面上的吸附行为及其应用。胶体颗粒在界面上的吸附行为主要受颗粒大小、相互作用力、电性质及润湿性质等因素的影响。本文第一部分主要从作用力出发阐述了胶体颗粒在液-液吸附过程中各种影响因素的理论研究进展;第二部分主要阐述了胶体颗粒在液-液界面上的吸附能够在界面组装、乳液和具有特殊功能的新材料制备等领域中的应用。     

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.     

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.     

Recent developments in Pickering emulsions for biomedical applications

Pickering emulsions, stabilised by organic or inorganic particles, offer long-term dispersibility of liquid droplets and resistance to coalescence. The versatility of stabilising particles and their ability to encapsulate and release cargo with high internal payload capacity makes them attractive in a wide variety of applications, ranging from catalysis to the cosmetic and food industry. While these properties make them an equally promising material platform for pharmaceutical and clinical applications, the development of Pickering emulsions for healthcare is still in its infancy. Herein, we summarise and discuss recent progress in the development of Pickering emulsions for biomedical applications, probing their design for passive diffusion-based release as well as stimuli-responsive destabilisation. We further comment on challenges and future directions of this exciting and rapidly expanding area of research.     

Trends in structuring edible emulsions with Pickering fat crystals

The pace of development of edible Pickering emulsions has recently soared, as interest in their potential for texture modification, calorie reduction and bioactive compound encapsulation and delivery has risen. In the broadest sense, Pickering emulsions are defined as those stabilized by interfacially-adsorbed solid particles that retard and ideally prevent emulsion coalescence and phase separation. Numerous fat-based species have been explored for their propensity to stabilize edible emulsions, including triglyceride and surfactant-based crystals and solid lipid nanoparticles. This review explores three classes of fat-based Pickering stabilizers, and proposes a microstructure-based nomenclature to delineate them: Type I (surfactant-mediated interfacial crystallization), Type II (interfacially-adsorbed nano- or microparticles) and Type III (shear-crystallized droplet encapsulation matrices). Far from simply reporting the latest findings on these modes of stabilization, challenges associated with these are also highlighted. Finally, though emphasis is placed on food emulsions, the fundamental precepts herein described are equally applicable to non-food multicomponent emulsion systems.     

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.     

Pickering emulsions stabilized by cellulose nanocrystals grafted with thermo-responsive polymer brushes

Cellulose nanocrystals (CNCs) from ramie fibers are studied as stabilizers of oil-in-water emulsions. The phase behavior of heptane and water systems is studied, and emulsions stabilized by CNCs are analyzed by using drop sizing (light scattering) and optical, scanning, and freeze-fracture electron microscopies. Water-continuous Pickering emulsions are produced with cellulose nanocrystals (0.05-0.5 wt%) grafted with thermo-responsive poly(NIPAM) brushes (poly(NIPAM)-g-CNCs). They are observed to be stable during the time of observation of 4 months. In contrast, unmodified CNCs are unable to stabilize heptane-in-water emulsions. After emulsification, poly(NIPAM)-g-CNCs are observed to form aligned, layered structures at the oil-water interface. The emulsions stabilized by poly(NIPAM)-g-CNCs break after heating at a temperature above the LCST of poly(NIPAM), which is taken as indication of the temperature responsiveness of the brushes installed on the particles and thus the responsiveness of the Pickering emulsions. This phenomenon is further elucidated via rheological measurements, in which viscosities of the Pickering emulsions increase on approach of the low critical solution temperature of poly(NIPAM). The effect of temperature can be counterbalanced with the addition of salt which is explained by the reduction of electrostatic and steric interactions of poly(NIPAM)-g-CNCs at the oil-water interface.     

High‐Internal‐Phase Pickering Emulsions Stabilized Solely by Peanut‐Protein‐Isolate Microgel Particles with Multiple Potential Applications

High‐internal‐phase Pickering emulsions have various applications in materials science. However, the biocompatibility and biodegradability of inorganic or synthetic stabilizers limit their applications. Herein, we describe high‐internal‐phase Pickering emulsions with 87 % edible oil or 88 % n‐hexane in water stabilized by peanut‐protein‐isolate microgel particles. These dispersed phase fractions are the highest in all known food‐grade Pickering emulsions. The protein‐based microgel particles are in different aggregate states depending on the pH value. The emulsions can be utilized for multiple potential applications simply by changing the internal‐phase composition. A substitute for partially hydrogenated vegetable oils is obtained when the internal phase is an edible oil. If the internal phase is n‐hexane, the emulsion can be used as a template to produce porous materials, which are advantageous for tissue engineering.     

Pickering Interfacial Catalysis for Biphasic Systems: From Emulsion Design to Green Reactions

Pickering emulsions are surfactant‐free dispersions of two immiscible fluids that are kinetically stabilized by colloidal particles. For ecological reasons, these systems have undergone a resurgence of interest to mitigate the use of synthetic surfactants and solvents. Moreover, the use of colloidal particles as stabilizers provides emulsions with original properties compared to surfactant‐stabilized emulsions, microemulsions, and micellar systems. Despite these specific advantages, the application of Pickering emulsions to catalysis has been rarely explored. This Minireview describes very recent examples of hybrid and composite amphiphilic materials for the design of interfacial catalysts in Pickering emulsions with special emphasis on their assets and challenges for industrially relevant biphasic reactions in fine chemistry, biofuel upgrading, and depollution.