Colloidal stability of bare and polymer-grafted silica nanoparticles in ionic liquids

The colloidal stability of bare and poly(methyl methacrylate) (PMMA)-grafted silica nanoparticles was studied in 1-alkyl-3-methylimidazolium ([C(n)mim])-based ionic liquids (ILs) with different anionic structures. The theoretical estimation of the colloidal interaction between monodispersed bare silica particles by using the Derjaguin-Landau-Verwey-Overbeek theory indicates that bare silica particles cannot be stabilized and they rapidly form aggregates in all the ILs used in this study. The instability of bare silica particles was experimentally confirmed by dynamic light scattering measurement and in situ transmission electron microscopy observations by utilizing the negligible vapor pressure of ILs. This evidence suggests that electrostatic stabilization is inefficient in ILs because of the high ionic atmosphere and the resulting surface-charge screening. The PMMA-grafted silica particles exhibited long-term colloidal stability in [C(4)mim][PF(6)] and [C(n)mim][NTf(2)], which are compatible with the grafted PMMA. On the other hand, the PMMA-grafted particles could not be stabilized in [C 4mim][BF 4] due to the poor solubility of the grafted PMMA in the IL. Effective steric stabilization is important for obtaining stable colloidal particles in ILs.     

Ionogels, ionic liquid based hybrid materials

The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).     

离子液体表/界面性质与结构

离子液体与气体、溶剂等物质组成的多相体系为吸收、萃取、两相催化等技术的发展提供了新的平台。离子液体的表/界面性质与结构是含离子液体多相体系的重要科学问题,可在介观尺度下显著影响多相体系反应和分离过程的效率。近年来,离子液体表/界面性质和结构的研究得到了广泛的关注。本文综述了离子液体及其与水、有机溶剂组成的混合物的表/界面张力及结构研究进展,介绍了现有的研究方法、研究对象与研究成果,归纳了离子液体及其混合物表/界面张力及结构的变化规律,分析了表/界面结构与表/界面张力之间的关系,探讨了离子液体表/界面研究存在的问题和未来的发展方向。     

离子液体功能化金属/共价-有机框架材料在催化反应中应用

离子液体（ILs）功能化的金属有机框架（MOFs）和共价有机框架（COFs）材料兼具离子液体和MOFs/COFs的优点，是一种极具潜力的复合催化材料。MOFs和COFs材料固定的孔结构及较大的比表面积为负载高分散催化中心提供了天然的物理空间；多孔结构促使催化剂与反应物充分接触；丰富的孔道有利于运输催化反应底物和产物，进而实现催化反应的高效进行。特别是离子液体片段的引入，可以作为催化活性中心的配体（稳定剂）或分散剂，同时能够有效改善MOFs和COFs材料孔道和活性中心周围的微环境。此外，还可以充分利用离子液体片段在适当的反应条件下转化为氮杂环卡宾配体的特点，在MOFs和COFs材料中引入氮杂环卡宾有机金属配合物。因此，我们对近几年来离子液体功能化的MOFs或COFs催化体系在CO2环加成、CO2还原、C-C偶联、羰基化以及其它有机转化反应中的研究应用进行简要综述。并对复合材料在催化领域的发展进行总结和展望。     

Influences of colloidal stability and electrokinetic property on electrodialysis performance in the presence of silica sol

Negatively charged silica sol is known to lead to fouling of anion exchange membranes during electrodialysis (ED) as a result of its deposition on the membrane surface. It is known that the fouling potential is related to the physical and electrochemical properties of the silica particles as well as those of the anion exchange membranes. In this study, the properties of the silica sol were characterized in terms of its particle size, turbidity, and zeta potential in order to predict their effects on the electrodialysis performance. In the stability of colloidal particles, the critical coagulation concentrations of silica sol were determined as functions of ionic strength, cation species, and solution pH. In the electrodialysis of NaCl solution containing silica sol with various concentrations of CaCl(2), the colloidal behavior related to deposition and transport was examined during and after electrodialysis. The electrodialysis experiments clearly showed that the deposition and transport of silica sol during electrodialysis were related to the colloidal stability of dispersion.     

Protein–polysaccharide associative interactions in the design of tailor-made colloidal particles

This article reviews some recent advances in the use of diverse protein–polysaccharide associative interactions in the design of colloidal particles having potential to be used for both fortification of food colloids with health-promoting bioactive compounds with better control of their physical stability and breakdown within the gastrointestinal tract. Protein–polysaccharide associative interactions are discussed in the following aspects: (i) the formation of micro- and nanoparticles for the delivery of health promoting ingredients (nutraceuticals); (ii) the controlled gastrointestinal fate of colloidal particles; (iii) the formation of biopolymer-based particles as fat replacers; and (iv) the behavior of colloidal particles as stabilizers of emulsions and foams. The first aspect concerns soluble protein–polysaccharide complex particles (electrostatic nanocomplexes, complex coacervates, covalent conjugates), mixed hydrogel particles, and nanoemulsion-based delivery systems.     

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.     

Stimuli-responsive liquid foams: From design to applications

Stimuli-responsive liquid foams and bubbles are systems for which the stability, structure, shape, and movement can be controlled by the application of stimuli. The foam stability can be modified by a stimulus which can change solution condition (pH, temperature, and ionic strength) or with the application of an external field (light and magnetic). Different foam stabilizers have been described in the literature to design these responsive foams systems ranging from surfactants, peptides, polymers, soft polymer particles, surfactants self-assembly, crystalline particles, emulsion droplets, and solid particles. This review aims to cover the recent advances of the design of stimuli-responsive liquid foams and their applications. Responsive liquid foams are attractive in textile coloring process, biomedical application, washing, and material recovery processes.     

Analysis of colloidal particles V. size-exclusion chromatography of colloidal semiconductor particles

An HPLC technique for the size determination of colloidal cadmium sulphide and zinc sulphide in a diameter range from 20 down to 2 nm using silica with pore sizes from 30 to 100 nm is described. The growth of the particles during the run was suppressed by the addition of stabilizers to the eluent and by the use of reversed-phase silica as the stationary phase for inorganic stabilizers. The calibration of the column sets by electron microscopy resulted in a linear relationship between the logarithm of the particle diameter and the elution time. The analysis was carried out within 4–10 min. The lateral resolution lay between 1.3% for larger particles and 1.9% for smaller particles. Below a diameter of 13 nm these values were better than those found from electron microscopy. From the comparison of the calibration lines for various colloidal materials, the differences in their electrical double layers could be estimated. The limitations of the method are discussed and the size-exclusion chromatographic and electron microscopic methods are compared.     

Preparation of novel fluoroalkyl end-capped oligomers/silica hybrid nanoparticles-encapsulation of a variety of guest molecules into fluorinated nanoparticles

Fluoroalkyl end-capped oligomers reacted with tetraethoxysilane and silica/nanoparticles under alkaline conditions to afford fluoroalkyl end-capped oligomers/silica nanoparticles (mean diameters: 31–54 nm) with a good dispersibility and stability in organic media. Interestingly, the isolated fluorinated particle powders were found to afford nanometer size-controlled colloidal particles with a good redispersibility and stability in these media. In addition, fluoroalkyl end-capped oligomers/silica nanoparticles-encapsulated guest molecules such as stable organic radicals and ionic liquids were prepared under similar conditions. These fluorinated nanoparticles-encapsulated guest molecules were applied to a new type of surface-modification agent, and these particles were able to disperse well above the poly (methyl methacrylate) films.     

聚醚型氨酯酰亚胺/二氧化硅杂化材料的合成与性能研究

利用Sol Gel共聚合反应制备出聚醚型氨酯酰亚胺 (PUI) /二氧化硅 (SiO2 )杂化材料 .利用NMR、FTIR、TG、DSC及SEM等测试手段对性能进行了基本表征 .FTIR研究结果发现在 10 0℃下能同时完成有机相PUI的亚胺化和无机相SiO2 凝胶网络的Sol Gel转变 .TG及SEM发现SiO2 含量为 9wt%时SiO2 聚集相粒径在 0 2～1 0 μm之间 ,耐热性明显提高并达到最佳 ;发现SiO2 含量的增加其颗粒粒径不断增大 ,并不断聚集成大粒径SiO2 相 ,有机和无机相分离明显 .DSC研究显示 ,SiO2 相的引入 ,对杂化材料聚醚软段富集相的Tg 不产生明显影响 .     

Surface functionalization of silica nanoparticles supports colloidal stability in physiological media and facilitates internalization in cells

The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.     

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.     

Advances in Enzyme and Ionic Liquid Immobilization for Enhanced in MOFs for Biodiesel Production

Biodiesel is a promising candidate for sustainable and renewable energy and extensive research is being conducted worldwide to optimize its production process. The employed catalyst is an important parameter in biodiesel production. Metal–organic frameworks (MOFs), which are a set of highly porous materials comprising coordinated bonds between metals and organic ligands, have recently been proposed as catalysts. MOFs exhibit high tunability, possess high crystallinity and surface area, and their order can vary from the atomic to the microscale level. However, their catalytic sites are confined inside their porous structure, limiting their accessibility for biodiesel production. Modification of MOF structure by immobilizing enzymes or ionic liquids (ILs) could be a solution to this challenge and can lead to better performance and provide catalytic systems with higher activities. This review compiles the recent advances in catalytic transesterification for biodiesel production using enzymes or ILs. The available literature clearly indicates that MOFs are the most suitable immobilization supports, leading to higher biodiesel production without affecting the catalytic activity while increasing the catalyst stability and reusability in several cycles.     

Recent developments of task-specific ionic liquids in organic synthesis

Abstract

Task-specific ionic liquids (TSILs) have received increased attention over the past few years as it is possible to form any specific ionic liquid (IL) composition depending upon user's need of the desired physical, chemical, and biological properties. These fascinating materials have shown promising results in various areas such as organic synthesis, catalysis, and specially recent emerging trend of use as functionalized ILs for chiral and nanoparticle synthesis. Present review gives an update of recent developments in the field of TSILs with emphasis on their applications in organic synthesis.     

Ionic Liquids Made with Dimethyl Carbonate: Solvents as well as Boosted Basic Catalysts for the Michael Reaction

This article describes 1) a methodology for the green synthesis of a class of methylammonium and methylphosphonium ionic liquids (ILs), 2) how to tune their acid–base properties by anion exchange, 3) complete neat‐phase NMR spectroscopic characterisation of these materials and 4) their application as active organocatalysts for base‐promoted carbon–carbon bond‐forming reactions. Methylation of tertiary amines or phosphines with dimethyl carbonate leads to the formation of the halogen‐free methyl‐onium methyl carbonate salts, and these can be easily anion‐exchanged to yield a range of derivatives with different melting points, solubility, acid–base properties, stability and viscosity. Treatment with water, in particular, yields bicarbonate‐exchanged liquid onium salts. These proved strongly basic, enough to efficiently catalyse the Michael reaction; experiments suggest that in these systems the bicarbonate basicity is boosted by two orders of magnitude with respect to inorganic bicarbonate salts. These basic ionic liquids used in catalytic amounts are better even than traditional strong organic bases. The present work also introduces neat NMR spectroscopy of the ionic liquids as a probe for solute–solvent interactions as well as a tool for characterisation. Our studies show that high catalytic efficacy of functional ionic liquids can be achieved by integrating their green synthesis, along with a fine‐tuning of their structure. Demonstrating that ionic liquid solvents can be made by a truly green procedure, and that their properties and reactivity can be tailored to the point of bridging the gap between their use as solvents and as catalysts.     

Light Scattering Probes of Viscoelastic Fluids and Solids

In this article, we discuss recent advances in static and dynamic light scattering applied to soft materials. Special emphasis is given to light scattering methods that allow access to turbid and solid‐like systems, such as colloidal suspensions, emulsions, glasses, or gels. Based on a combination of single‐ and multispeckle detection schemes, it is now possible to cover an extended range of relaxation times from a few nanoseconds to minutes or hours and length scales below 1 nm up to several microns. The corresponding elastic properties of viscoelastic fluids or solid materials range roughly from below 1 Pa to several 100 kPa. Different applications are discussed such as light scattering from suspensions of highly charged colloidal particles, colloid and protein gels, as well as dense surfactant solutions.     

Amphiphilic micro- and nanogels: Combining properties from internal hydrogel networks,solid particles,and micellar aggregates

Polymeric micro- and nanogels are defined by their water-swollen hydrophilic networks that can often impart outstanding biocompatibility and high-colloidal stability. Unfortunately, this highly hydrophilic nature limits their potential in areas where hydrophobic or amphiphilic interactions are required, for example, the delivery of hydrophobic cargoes or tailored interactions with amphipathic (bio-)surfaces. To overcome this limitation, amphiphilic micro−/nanogels are emerging as new colloidal materials that combine properties from hydrogel networks with hydrophobic segments, known from solid hydrophobic polymer particles or micellar cores. The ability to accurately adjust the balance of hydrophobic and hydrophilic components in such amphiphilic colloidal systems enables new tailored properties. This opens up new applications ranging from the controlled and sustained delivery of hydrophobic drugs, over carriers for catalytic moieties, to their assembly at hydrophilic/hydrophobic interfaces, for example, as advanced stabilizers in Pickering emulsions. While promising, the synthetic realization of such amphiphilic materials remains challenging since hydrophobic and hydrophilic moieties need to be combined in a single colloidal system. As a result, adjusting the micro−/nanogel amphiphilicity often changes the colloidal features too. To overcome these limitations, various strategies have been reported. The aim of this review is to give a brief overview of important synthetic tools, considering both advantages and disadvantages, thus critically evaluating their potential in different research fields.     

Intercalation synthesis of functional hybrid materials based on layered simple hydroxide hosts and ionic liquid guests--a pathway towards multifunctional ionogels without a silica matrix?

Functional hybrid materials on the basis of inorganic hosts and ionic liquids (ILs) as guests hold promise for a virtually unlimited number of applications. In particular, the interaction and the combination of properties of a defined inorganic matrix and a specific IL could lead to synergistic effects in property selection and tuning. Such hybrid materials, generally termed ionogels, are thus an emerging topic in hybrid materials research. The current article addresses some of the recent developments and focuses on the question why silica is currently the dominating matrix used for (inorganic) ionogel fabrication. In comparison to silica, matrix materials such as layered simple hydroxides, layered double hydroxides, clay-type substances, magnetic or catalytically active solids, and many other compounds could be much more interesting because they themselves may carry useful functionalities, which could also be exploited for multifunctional hybrid materials synthesis. The current article combines experimental results with some arguments as to how new, advanced functional hybrid materials can be generated and which obstacles will need to be overcome to successfully achieve the synthesis of a desired target material.