Showing papers in "Current Opinion in Colloid and Interface Science in 2016"
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TL;DR: In this paper, the authors reviewed DNA adsorption and desorption reactions and interactions with graphene oxide and related materials (e.g. graphene) based on the current understandings.
Abstract: Interfacing DNA oligonucleotides with graphene-based materials, especially graphene oxide, has produced many new sensors and devices. Since graphene oxide is an excellent fluorescence quencher, fluorescently labeled DNAs (probes) are nearly fully quenched upon adsorption. Addition of the complementary DNA results in probe desorption and fluorescence enhancement. Aside from its analytical applications, this system provides a fascinating topic for biointerface science. DNA can be adsorbed by graphene oxide via π–π stacking and hydrogen bonding, while it must overcome electrostatic repulsion at the same time. The mechanism of DNA-induced probe desorption has also been a topic of extensive discussion. In this article, DNA adsorption and desorption reactions and interactions with graphene oxide and related materials (e.g. graphene) are reviewed based on the current understandings. A few representative applications based on these processes are also described briefly.
198 citations
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TL;DR: Progress towards applications in environmental remediation, lab-on-a-chip microfluidics and in vivo drug delivery is highlighted, with a strong emphasis on developments that can enable autonomous applications, where colloids execute useful tasks without external interventions.
Abstract: Active colloids are small scale materials capable of producing enhanced motion within fluid environments. The field of active colloids has grown rapidly over the last ten years and is approaching maturity where viable applications are within reach. In this review, recent advances are surveyed with a strong emphasis on developments that can enable autonomous applications, where colloids execute useful tasks without external interventions. These applications are likely to prove transformative as the resulting technologies will be significantly less complex than current methods. A survey of the requirements to achieve autonomous applications is provided, considering guidance, solution compatibilities, manufacture and function; with reference to recent developments in these capacities. Following on from this, progress towards applications in environmental remediation, lab-on-a-chip microfluidics and in vivo drug delivery is highlighted.
178 citations
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TL;DR: Recent advances in understanding protein self-assembly through a soft condensed matter perspective with an emphasis on three specific systems: globular proteins, viruses and amyloid fibers are reviewed.
Abstract: Understanding protein self-assembly is important for many biological and industrial processes. Proteins can self-assemble into crystals, filaments, gels, and other amorphous aggregates. The final forms include virus capsids and condensed phases associated with diseases such as amyloid fibrils. Although seemingly different, these assemblies all originate from fundamental protein interactions and are driven by similar thermodynamic and kinetic factors. Here we review recent advances in understanding protein self-assembly through a soft condensed matter perspective with an emphasis on three specific systems: globular proteins, viruses, and amyloid fibrils. We conclude with a discussion of unanswered questions in the field.
176 citations
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TL;DR: Water-in-water (W/W) emulsions are colloidal dispersions of an aqueous solution into another anisotropic phase as mentioned in this paper, which can be formed in mixtures of at least two hydrophilic macromolecules.
Abstract: Water-in-water (W/W) emulsions are colloidal dispersions of an aqueous solution into another aqueous phase. Such dispersions can be formed in mixtures of at least two hydrophilic macromolecules, which are thermodynamically incompatible in solution, generating two immiscible aqueous phases. W/W emulsions are much less known than conventional oil-in-water or water-in-oil emulsions, despite the fact that phase separation in aqueous mixtures is highly common. The thermodynamics and the phase behavior of segregative phase separation in mixtures of hydrophilic polymers have focused a great attention, with many excellent scientific reports in the literature. However, the kinetic stability of water-in-water emulsions is generally difficult to control, since amphiphilic molecules do not adsorb on water-water interfaces. Consequently, surfactants are not good stabilizers for W/W emulsions, and until recently, only a limited number of scientific studies have dealt with the formation and stabilization of emulsions in aqueous two-phase systems. Recent advances and successful results in the stabilization of these emulsions, by alternative mechanisms, have triggered a renewed interest. Nowadays, fast progress is being made in formation and stabilization methods, and new knowledge is rapidly acquired, opening a wide range of novel possibilities for practical applications. Interestingly, highly stable water-in-water emulsions can be formulated using fully biocompatible and edible components, and consequently, these emulsions can be used in food formulations, among many other interesting applications. This review describes the general background of research in the field, and focuses on recent scientific advances, including phase behavior, formation, stability and kinetic aspects, as well as applications such as formation of microgels, encapsulation and drug delivery.
158 citations
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TL;DR: In this paper, a detailed understanding of the Hofmeister series is provided by combining results from molecular dynamics simulations, Poisson-Boltzmann theory and AFM experiments.
Abstract: Over recent years, the supposedly universal Hofmeister series has been replaced by a diverse spectrum of direct, partially altered and reversed series. This review aims to provide a detailed understanding of the full spectrum by combining results from molecular dynamics simulations, Poisson–Boltzmann theory and AFM experiments. Primary insight into the origin of the Hofmeister series and its reversal is gained from simulation-derived ion–surface interaction potentials at surfaces containing non-polar, polar and charged functional groups for halide anions and alkali cations. In a second step, the detailed microscopic interactions of ions, water and functional surface groups are incorporated into Poisson–Boltzmann theory. This allows us to quantify ion-specific binding affinities to surface groups of varying polarity and charge, and to provide a connection to the experimentally measured long-ranged electrostatic forces that stabilize colloids, proteins and other particles against precipitation. Based on the stabilizing efficiency, the direct Hofmeister series is obtained for negatively charged hydrophobic surfaces. Hofmeister series reversal is induced by changing the sign of the surface charge from negative to positive, by changing the nature of the functional surface groups from hydrophobic to hydrophilic, by increasing the salt concentration, or by changing the pH. The resulting diverse spectrum reflects that alterations of Hofmeister series are the rule rather than the exception and originate from the variation of ion-surface interactions upon changing surface properties.
153 citations
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TL;DR: In this article, the authors summarize and discuss the recent trends related to Janus droplets and particles produced through microfluidic processing and also review the parallelization technologies being developed for scaling up microfluidityic emulsification in the industry.
Abstract: Microfluidic production of multicompartmental emulsion droplets and particles has received considerable attention of late. In particular, droplets having two physically and chemically distinct segments (so-called Janus droplets) and the anisotropic particles synthesized from these droplets, are becoming increasingly popular because of their novel and promising properties, which make them suitable for use in numerous applications, including for controlled drug release, display devices, and self-assembly. So far, a range of interesting anisotropies have been accorded to Janus droplets and particles via microfluidics; these span from chromatic, magnetic, and hydrophobic–hydrophilic characteristics to selective degradation properties. Here, we summarize and discuss the recent trends related to Janus droplets and particles produced through microfluidic processing. We also review the parallelization technologies being developed for scaling up microfluidic emulsification in the industry.
130 citations
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TL;DR: In this article, the authors present a review of recent advances in the understanding of such models, including the description of the active gas and its swim pressure, the motility-induced phase separation and the high-density crystalline and glassy behavior.
Abstract: Minimal models of active Brownian colloids consisting of self-propelled spherical particles with purely repulsive interactions have recently been identified as excellent quantitative testing grounds for theories of active matter and have been the subject of extensive numerical and analytical investigation. These systems do not exhibit aligned or flocking states but do have a rich phase diagram, forming active gases, liquids, and solids with novel mechanical properties. This article reviews recent advances in the understanding of such models, including the description of the active gas and its swim pressure, the motility-induced phase separation and the high-density crystalline and glassy behavior.
126 citations
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TL;DR: In this article, the authors review recent work on active colloids or swimmers, such as self-propelled microorganisms, phoretic colloidal particles, and artificial micro-robotic systems, moving in fluid-like environments.
Abstract: We review recent work on active colloids or swimmers, such as self-propelled microorganisms, phoretic colloidal particles, and artificial micro-robotic systems, moving in fluid-like environments. These environments can be water-like and Newtonian but can frequently contain macromolecules, flexible polymers, soft cells, or hard particles, which impart complex, nonlinear rheological features to the fluid. While significant progress has been made on understanding how active colloids move and interact in Newtonian fluids, little is known on how active colloids behave in complex and non-Newtonian fluids. An emerging literature is starting to show how fluid rheology can dramatically change the gaits and speeds of individual swimmers. Simultaneously, a moving swimmer induces time dependent, three dimensional fluid flows that can modify the medium (fluid) rheological properties. This two-way, non-linear coupling at microscopic scales has profound implications at meso- and macro-scales: steady state suspension properties, emergent collective behavior, and transport of passive tracer particles. Recent exciting theoretical results and current debate on quantifying these complex active fluids highlight the need for conceptually simple experiments to guide our understanding.
122 citations
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TL;DR: In this paper, a review summarizes recent advances in understanding the colloidal behavior of nano-emulsions, and provides a unifying framework for understanding the various complex states that emerge, as well as perspective on emerging challenges and opportunities that will advance the use of nanoEMulsions in both fundamental colloid science and technological applications.
Abstract: Nanoemulsions exhibit unique behavior due to their nanoscopic dimensions, including remarkable droplet stability, interactions, and rheology. These properties are significantly enhanced by nanoscopic droplet size, as well as the selection of surfactant and other molecular species in solution. Electrostatic and polymer-induced interdroplet interactions are particularly powerful tools for fine-tuning the interdroplet interactions, and have led to stimuli-responsive nanoemulsion systems that provide deep insight into their unique properties. As such, nanoemulsions have emerged as powerful model systems for studying a number of colloidal phenomena including suspension rheology, repulsive and attractive colloidal glasses, aggregation processes, colloidal gelation and phase instability, and associative network formation in polymer–colloid mixtures. This review summarizes recent advances in understanding the colloidal behavior of nanoemulsions, and provides a unifying framework for understanding the various complex states that emerge, as well as perspective on emerging challenges and opportunities that will advance the use of nanoemulsions in both fundamental colloid science and technological applications.
94 citations
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TL;DR: In the absence of traditional surfactants, micro-emulsions can also form in a ternary system of two immiscible fluids and an amphi-solvent as discussed by the authors.
Abstract: Surfactants (or amphiphiles) are generally believed to be a necessary component of microemulsions. However, research has found that in the absence of traditional surfactants, microemulsions can also form in a ternary system of two immiscible fluids and an “amphi-solvent”. Such microemulsions are called “surfactant-free microemulsions” (SFMEs). The so-called amphi-solvent is a solvent that is completely or at least partially miscible with each of the two immiscible fluids. The structures and properties of SFMEs are similar to those of traditional surfactant-based microemulsions (SBMEs) to some extent. This review focuses on recent advances in SFMEs, including their phase behavior, structures, properties and potential applications.
86 citations
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TL;DR: In this paper, a review of recent research on the collective dynamical behavior of colloids with dipolar or multipolar interactions is presented, with an emphasis on theoretical and simulation studies.
Abstract: This article reviews recent research on the collective dynamical behavior of colloids with dipolar or multipolar interactions. Indeed, whereas equilibrium structures and static self-assembly of such systems are now rather well understood, the past years have seen an explosion of interest in understanding dynamicals aspects, from the relaxation dynamics of strongly correlated dipolar networks over systems driven by time-dependent, electric, or magnetic fields, to pattern formation and dynamical control of active, self-propelled systems. Unraveling the underlying mechanisms is crucial for a deeper understanding of self-assembly in and out of equilibrium and the use of such particles as functional devices. At the same time, the complex dynamics of dipolar colloids poses challenging physical questions and puts forward their role as model systems for nonlinear behavior in condensed matter physics. Here we attempt to give an overview of these developments, with an emphasis on theoretical and simulation studies.
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TL;DR: In this article, the authors discuss the forces that govern the motion of active Brownian microswimmers, the stress (or pressure) they generate, and the implication of these concepts on their collective behavior.
Abstract: The statistical mechanics and microhydrodynamics of active matter systems have been studied intensively during the past several years, by various soft matter physicists, chemists, engineers, and biologists around the world. Recent attention has focused on the fascinating nonequilibrium behaviors of active matter that cannot be observed in equilibrium thermodynamic systems, such as spontaneous collective motion and swarming. Even minimal kinetic models of active Brownian particles exhibit self-assembly that resembles a gas–liquid phase separation from classical equilibrium systems. Self-propulsion allows active systems to generate internal stresses that enable them to control and direct their own behavior and that of their surroundings. In this Review we discuss the forces that govern the motion of active Brownian microswimmers, the stress (or pressure) they generate, and the implication of these concepts on their collective behavior. We focus on recent work involving the unique ‘swim pressure’ exerted by active systems, and discuss how this perspective may be the basic underlying physical mechanism responsible for self-assembly and pattern formation in all active matter. We discuss the utility of the swim pressure concept to quantify the forces, stresses, and the (thermo?) dynamics of active matter.
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TL;DR: In this article, the current understanding of the utilization of different vegetable proteins as emulsifier in order to stabilize O/W multilayer emulsion systems is reviewed for improving the stability of emulsions to environmental stresses and for developing controlled or triggered release systems.
Abstract: There is great interest in the food, cosmetic and pharmaceutical industry in the use of proteins and polysaccharides as natural hydrocolloids to create novel emulsion systems with improved stability and functionality. For example, the electrostatic interaction between proteins and polysaccharides may be used to form oil-in-water (O/W) emulsions with multilayered interfacial membranes around oil droplets or multilayer emulsions. This type of emulsions have been developed using the layer-by-layer ( LbL) technique, which consists of direct adsorption of an oppositely charged polyelectrolyte layer (e.g. polysaccharides) on a primary layer of ionic emulsifiers (e.g. proteins). The polymeric structure and electrical charge of proteins make them a special class of compounds very suitable for its utilization in the LbL technique. In recent years, the utilization of proteins as emulsifiers in food and pharmaceutical industry has been turning towards plants as a preferred alternative to animal-based sources. This article reviews the current understanding of the utilization of different vegetable proteins as emulsifier in order to stabilize O/W multilayer emulsion systems. Additionally, it highlights some potential applications of the multilayer emulsion technology in the industry, for improving the stability of emulsions to environmental stresses and for developing controlled or triggered release systems.
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TL;DR: In this article, the Hofmeister series was extended by considering the inorganic anions IO 3 −, BrO 3 − and ClO 3−, which present unusual properties as compared with the ions considered in the classical HofMeister series.
Abstract: It is increasingly being accepted that solvation properties of ions and interfaces (hydration of ions, hydrophobic or hydrophilic character of interfaces) play a fundamental role in ion-surface interaction in water. However, a fundamental understanding of the precise role of solvation in ionic specificity in colloidal systems is still missing, although important progress has been made over the last years. We present in this contribution experimental evidences (including also ions not usually included in specific ion studies) together with Molecular Dynamics (MD) simulations that highlight the importance of the hydration of ions and surfaces in order to understand the origin of ionic specificity. We first show that both surface polarity and ion hydration determine the sorting of ions according to their ability to induce specific effects (the so-called Hofmeister series). We extend these classical series by considering the addition of the inorganic anions IO 3 − , BrO 3 − and ClO 3 − , which present unusual properties as compared with the ions considered in classical Hofmeister series. We also consider big hydrophobic organic ions such as tetraphenylborate anion (Ph 4 B − ) and tetraphenylarsonium cation (Ph 4 As + ) that in the context of the Hofmeister series behave as super-chaotropes ions.
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TL;DR: In this paper, the major advances to date in motor design, propulsion mechanisms and directional control, and inter-motor communication leading to collective behavior are reviewed, and the fundamental questions that remain to be addressed and new design principles required for useful applications.
Abstract: Self-propelled, active colloidal systems are of great current interest from both fundamental as well as practical standpoints, with potential applications in nanomachinery, nanoscale assembly, robotics, fluidics, and chemical/biochemical sensing. This perspective focuses on chemically powered catalytic nano- and micromotors. We review the major advances to date in motor design, propulsion mechanisms and directional control, and inter-motor communication leading to collective behavior. We conclude by discussing the next steps in going forward: the fundamental questions that remain to be addressed and new design principles required for useful applications.
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TL;DR: In this article, the authors discuss two classes of active colloids in liquid crystals (ACLCs): (i) externally driven ACLCs, in which the motion of colloidal particles is powered by an externally applied electric field, and (ii) internally driven ACLC, formed by self-propelled particles such as bacteria.
Abstract: Active colloids in liquid crystals (ACLCs) are an active matter with qualitatively new facets of behavior as compared to active matter that becomes isotropic when relaxed into an equilibrium state. We discuss two classes of ACLCs: (i) “externally driven ACLCs”, in which the motion of colloidal particles is powered by an externally applied electric field, and (ii) “internally driven ACLCs”, formed by self-propelled particles such as bacteria. The liquid crystal (LC) medium is of a thermotropic type in the first case and lyotropic (water based) in the second case. In the absence of external fields and self-propelled particles, the ACLCs are inactive, with the equilibrium LC state exhibiting long-range orientational order. The external electric field causes ACLCs of type (i) to experience translations, rotations, and orbiting, powered by mechanisms such as LC-enabled electrokinetics, Quincke rotations and entrapment at the defects of LC order. A dense system of Quincke rotators, orbiting along circularly shaped smectic defects, undergoes a transition into a collective coherent orbiting when their activity increases. An example of internally driven ACLCs of type (ii) is living liquid crystals, representing swimming bacteria placed in an otherwise passive lyotropic chromonic LC. The LC strongly affects many aspects of bacterial behavior, most notably by shaping their trajectories. As the concentration of bacteria and their activity increase, the orientational order of living liquid crystals experiences two-stage instability: first, the uniform steady equilibrium director is replaced with a periodic bend deformation, then, at higher activity, pairs of positive and negative disclinations nucleate, separate, and annihilate in dynamic patterns of topological turbulence. The ACLCs are contrasted to their isotropic counterparts.
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TL;DR: In this article, the effect of cosolutes on clouding and the behavior of related systems, non-aqueous solutions and nonionic polymers, are examined, and different aspects of surfactant self-assembly, like critical micelle concentration, micelle size and shape, intermicellar interactions and phase separation phenomena are reviewed as well as suggested underlying causes of the temperature dependence.
Abstract: Nonionic surfactants have broad applications such as cleaning and dispersion stabilization, which frequently are hampered by strong temperature sensitivities. As manifested by clouding and decreased solubility with increasing temperature, the interaction between water and the oligo(oxyethylene) head-groups is becoming less favorable. Different aspects of surfactant self-assembly, like the critical micelle concentration, micelle size and shape, intermicellar interactions and phase separation phenomena are reviewed as well as suggested underlying causes of the temperature dependence. Furthermore, the effect of cosolutes on clouding and the behavior of related systems, non-aqueous solutions and nonionic polymers, are examined.
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TL;DR: In this article, a case of collective dynamics and self-assembly of particles with externally driven torques coupled to a liquid or solid interface is considered, and the complexity of interactions in such systems is further enriched by strong hydrodynamic coupling between particles.
Abstract: Modern self-assembly techniques aiming to produce complex structural order or functional diversity often rely on non-equilibrium conditions in the system. Light, electric, or magnetic fields are predominantly used to modify interaction profiles of colloidal particles during self-assembly or induce complex out-of-equilibrium dynamic ordering. The energy injection rate, properties of the environment are important control parameters that influence the outcome of active (dynamic) self-assembly. The current review is focused on a case of collective dynamics and self-assembly of particles with externally driven torques coupled to a liquid or solid interface. The complexity of interactions in such systems is further enriched by strong hydrodynamic coupling between particles. Unconventionally ordered dynamic self-assembled patterns, spontaneous symmetry breaking phenomena, self-propulsion, and collective transport have been reported in torque-driven colloids. Some of the features of the complex collective behavior and dynamic pattern formation in those active systems have been successfully captured in simulations.
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TL;DR: Buffer specific adsorption modifies several molecular and macroscopic properties amongst which electrophoretic mobilities, and hence effective surface charges, are particularly significant.
Abstract: The aim of this work is to overview the specific effect of pH buffers in biological systems. The pH of a buffer solution changes only slightly when a small amount of a strong acid or bases is added to it. This is widely accepted and applied both in chemical and in biological (i.e. enzyme catalysis) systems. Here we show some examples – spanning from pH measurements, enzyme activities, electrophoretic mobilities, antibody aggregation, protein thermal stability – that demonstrate additional roles of buffers. They not only set pH, but also address specific ion effects, in terms of Hofmeister series, when strong electrolytes are also added. From the experimental data referred to some charged biological moieties it emerges that different buffers, at the same nominal pH, can specifically adsorb at the charged surface. Buffer specific adsorption modifies several molecular and macroscopic properties amongst which electrophoretic mobilities, and hence effective surface charges, are particularly significant. More importantly, buffers' weak electrolytes, even at low concentration, are found to compete for the adsorption at the charged surfaces with strong electrolytes, thus modulating Hofmeister effects.
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TL;DR: In this paper, a review of recent developments on the preparation of multiple emulsions and their applications as templates for material fabrication is presented, focusing on microfluidic methods for accurate control of size and morphology and on new formulations that go beyond traditional surfactant systems for increased complexity.
Abstract: We review recent developments on the preparation of multiple emulsions and their applications as templates for material fabrication. Emphasis is placed on microfluidic methods for accurate control of size and morphology and on new formulations that go beyond traditional surfactant systems for increased complexity. The straightforward applicability of multiple emulsions in the fabrication of multihollow particles or capsules of various materials is illustrated through representative examples.
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TL;DR: In this article, the authors reviewed both theory and experimental observation of the AC electrokinetic properties of conducting microparticles suspended in an aqueous electrolyte and highlighted the importance of the RC time for charging the double layer.
Abstract: This paper reviews both theory and experimental observation of the AC electrokinetic properties of conducting microparticles suspended in an aqueous electrolyte. Applied AC electric fields interact with the induced charge in the electrical double layer at the metal particle–electrolyte interface. In general, particle motion is governed by both the electric field interacting with the induced dipole on the particle and also the induced-charge electro-osmotic (ICEO) flow around the particle. The importance of the RC time for charging the double layer is highlighted. Experimental measurements of the AC electrokinetic behaviour of conducting particles (dielectrophoresis, electro-rotation and electro-orientation) are compared with theory, providing a comprehensive review of the relative importance of particle motion due to forces on the induced dipole compared with motion arising from induced-charge electro-osmotic flow. In addition, the electric-field driven assembly of conducting particles is reviewed in relation to their AC electrokinetic properties and behaviour.
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TL;DR: In this article, a review of the development of the understanding of hydrophobicity, or the hydrophobic effect, is presented, focusing on micellization and adsorption of surfactants, as well as protein unfolding.
Abstract: This review is a brief discussion on the development of the understanding of hydrophobicity, or the hydrophobic effect. The hydrophobic effect is primarily discussed in terms of partitioning of hydrocarbons between a hydrophobic environment and water as well as solubility of hydrocarbons in water. Micellization of surfactants is only briefly reviewed. It is emphasized that (i) the cause of the hydrophobic effect, e.g. the low solubility of a hydrocarbon in water, is to be found in the high internal energy of water resulting in a high energy to create a cavity in order to accommodate the hydrophobe, (ii) the “structuring” of water molecules around a hydrophobic compound increases the solubility of the hydrophobe. The “structuring” of water molecules around hydrophobic compounds is discussed in terms of recent spectroscopic findings. It is also emphasized that (iii) the lowering of entropy due to a structuring process must be accompanied by an enthalpy that is of the same order of magnitude as the TΔS for the process. Hence, there is an entropy–enthalpy compensation leading to a low free energy change for the structuring process. The assumption of a rapid decay of the entropy with temperature provides an explanation of the enthalpy–entropy compensation so often found in aqueous systems. It is also emphasized (iv) that the free energy obtained from partitioning, or solubility limits, needs to be corrected for molecular size differences between the solute and the solvent. The Flory–Huggins expression is a good first approximation for obtaining this correction. If the effect of different molecular sizes is not corrected for, this leads to erroneous conclusions regarding the thermodynamics of the hydrophobic effect. Finally, (v) micellization and adsorption of surfactants, as well as protein unfolding, are briefly discussed in terms of the hydrophobic effect.
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TL;DR: In this article, a survey of the literature on specific-ion effects in non-aqueous solvents is surveyed with a view to determining if the Hofmeister series or Lyotropic series so universally observed in aqueous systems is widely evident in nonaqueous systems.
Abstract: It is widely acknowledged that specific-ion effects are ubiquitous in aqueous systems and undoubtedly are essential to the fundamental processes of life, although a deep fundamental understanding of specific-ion effects remains an important challenge. Specific-ion effects in non-aqueous solvents are known but have attracted far less attention, yet knowledge of specific-ion effects in non-aqueous systems is likely to provide important information for guiding, evaluating and testing our theories of specific-ion effects. Here, the literature on specific-ion effects in non-aqueous solvents is surveyed with a view to determining if the Hofmeister series or lyotropic series so universally observed in aqueous systems is widely evident in non-aqueous systems. Particular attention has been applied to experiments on non-aqueous systems that are known to exhibit Hofmeister series in aqueous systems with the aim of determining if a consistent ion ordering in the strength of specific-ion effects is observed in other solvents. We find that specific-ion effects are ubiquitous in non-aqueous solvents, that both Hofmeister and lyotropic series are widely observed, although not necessarily for the same class of experiment. Moreover, we find that Hofmeister and lyotropic series are observed in non-aqueous solvents even for experiments in which these series are not observed for water. Additionally, series reversal is seen for a given experiment when the solvent is changed. All this poses significant challenges for our understanding of specific-ion effects in aqueous and non-aqueous systems and also provides guideposts for future investigations.
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TL;DR: In this article, a review summarizes some steps toward quantitative models of specific ion hydration and discusses a possible path looking forward, as well as a possible solution to the problem of ion specificity.
Abstract: Several recent developments have enhanced our understanding of specific ion hydration. These advances have included the Law of Matching Water Affinities and the realization that many-body dispersion forces and polarization can play important roles in ion specificity. Efforts have been made to partition the relevant ion free energies into their physically contributing parts in order to gain further insights into the driving forces. Yet a quantitative theory of ion specificity that links the necessary molecular-level treatment of the inner hydration shell with the many-body response of Lifshitz theory at longer range is still lacking. This review summarizes some steps toward quantitative models of specific ion hydration and discusses a possible path looking forward.
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TL;DR: In this article, a review of ionic liquid (IL) based aqueous and non-aqueous microemulsions is presented, which are quite fascinating and interesting research field for scientists.
Abstract: In the last few decades ionic liquids (ILs) have been widely considered as a “green solvents” and they are used in various fields. ILs can be used in the formation of microemulsion as a dispersed medium, polar domain and recently as a surfactant. In this particular review our discussion is about the novel IL-based aqueous and non-aqueous microemulsions which are quite fascinating and interesting research field for scientists. Synthesis of double and triple chain containing surface active ionic liquid (SAILs) and formation of microemulsion as a surfactant with ILs as a polar core have been elaborated in this review. ILs with a certain surface activity having long alkyl chain substituents can self-aggregate and form ILs microemulsion with high-temperature stability and temperature insensitivity. Characterization of these ILs in oil microemulsion and different ultrafast processes which are performed inside these characterized systems are documented very well. We have highlighted the similarities and differences between the nonaqueous microemulsions and the aqueous microemulsions. Addition of water and effect of temperature are quite important in case of the ILs containing microemulsions.
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TL;DR: In this article, a review on the theoretical basics and recent developments about the diffusiophoresis of charged particles and diffusioosmosis of electrolyte solutions driven by imposed electrolyte concentration gradients with particular emphasis on the principal analytical formulas and their physical interpretations is presented.
Abstract: A review is presented on the theoretical basics and recent developments about the diffusiophoresis of charged particles and diffusioosmosis of electrolyte solutions driven by imposed electrolyte concentration gradients with particular emphasis on the principal analytical formulas and their physical interpretations. For diffusiophoresis, migrations of particles with thin polarized electric double layers but arbitrary zeta potentials and with arbitrary double layers but relatively low surface potentials are both discussed in detail, covering not only diffusiophoresis of single particles but also their motions near solid boundaries or other particles. For diffusioosmosis, fluid flows along single plane walls, in micro/nano-channels, and in porous media are considered, in which the solid walls may have arbitrary zeta potentials or surface charge densities, and both the effect of the lateral distribution of the diffuse ions and the relaxation effect in the double layers on the tangential electric field induced by the prescribed electrolyte concentration gradient are included.
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TL;DR: In this article, the authors summarize work that has been pursued to characterize detergentless microemulsions and give a short account of their various applications, including their applications in the literature.
Abstract: Aggregation in liquid mixtures is a ubiquitous phenomenon when water and at the same time rather unpolar compounds are present. Of special interest in recent years have been systems, in which the tendency of phase separation of a binary mixture is overcome by the solubilization ability of a short-chain alcohol as a third component. In such systems, polar and nonpolar domains coexist in absence of traditional long-chain surfactants. Their microemulsion-like properties, which lead to the names “detergent-less microemulsions” and “surfactant-free microemulsions” (SFMEs), have been studied by a variety of experimental methods and by simulations. In this review we summarize work that has been pursued to characterize these systems and give a short account of their various applications.
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TL;DR: In this article, the authors focus on some more or less unconventional approaches, allowing in a direct or indirect way to design systems which show controlled motion, eventually combined with other functionalities such as light emission.
Abstract: Electric fields can be used in several ways to generate motion of objects. In this article, we focus on some more or less unconventional approaches, allowing in a direct or indirect way to design systems which show controlled motion, eventually combined with other functionalities such as light emission. We review some of the most recent results in this context with a special focus on bipolar electrochemistry as a straightforward approach for breaking symmetry, which is a necessary ingredient for any type of motion.
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TL;DR: In this article, the authors review the surviving evidence for a long-range hydrophobic force and find that there is only supporting evidence in a total of two papers, one old and one new, where net attractive forces were measured at separations greater than about 5-6nm.
Abstract: Thirty years ago there was considerable excitement over the first report of a long-ranged “hydrophobic force” between solids that were not wet by water (Israelachvili and Pashley, Nature 1982, 300 , 341–342). Many of the subsequent measurements have been reexamined and found not to support the existence of a long-range hydrophobic force. The principal difficulty was that hydrophobic solids frequently experience other forces, which obscured or were mistaken for a hydrophobic force. In this paper, we review the surviving evidence for a long-range hydrophobic force and find that there is only supporting evidence in a total of two papers, one old and one new, where net attractive forces were measured at separations greater than about 5–6 nm. Thus the evidence is scarce. In contrast there are new experiments showing no such force, thereby arguing against the universality of a measureable hydrophobic force beyond about 6 nm. Since solvent water is common to the experiments, such evidence makes it difficult to describe a universal mechanism for a long-ranged hydrophobic force based on water structure. There are also new measurements that are consistent with a hydrophobic force with a decay length in the range 0.3–1.0 nm. In particular, attractive forces have been measured on small radius surfaces (8–50 nm) consistent with a hydrophobic force with a decay length of 0.5–0.6 nm, and a variety of net repulsive measurements are consistent with an attractive hydrophobic force that has a decay length of 0.3–1.0 nm. We also discuss some new measurements, which are consistent with cavitation, and not a surface force that acts at a distance.
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TL;DR: In this article, two known mechanisms, bridging and depletion attraction, are reviewed and discussed, depending on the molecular size and interaction of the mixed solvent species, and simple theoretical considerations predict that the macromolecular state that is stabilized by each mechanism possesses unique structural properties, as well as distinct thermodynamic fingerprints.
Abstract: From colloidal dispersions to solvated polymers or proteins, solution composition is known to strongly influence the stable state of the bathing macromolecules. Mixed solvents containing species with different affinities to specific macromolecular states can shift equilibrium towards the thermodynamically preferred state with lower free energy, even when the molecular interactions with the solvent are weak. We review two known mechanisms, bridging and depletion attraction, and discuss how each can emerge, depending on the molecular size and interaction of the mixed solvent species. We show that simple theoretical considerations predict that the macromolecular state that is stabilized by each mechanism possesses unique structural properties, as well as distinct thermodynamic fingerprints. Furthermore, we demonstrate the mechanistic role of enthalpy and entropy, as seen in a simple mean field model of macromolecules in mixed solvents. These thermodynamic contributions determine the temperature dependence of cosolute induced effects. Finally, we review the possible role of fluctuations, and point to possible implications and open questions.