Current Opinion in Colloid & Interface Science最新文献

Microgels stand out as compelling alternatives to traditional emulsifiers in Pickering emulsions, owing to their unique deformability and responsiveness, distinguishing them from rigid particles and conventional surfactants. In this review, we provide an overview of recent advancements and breakthroughs in microgel synthesis and the stabilization of Pickering emulsions using microgels. Additionally, we discuss the underlying stabilization mechanisms of microgel-stabilized emulsions, elucidating the influencing factors such as microgel properties, environmental conditions, and interfacial structures that significantly impact emulsion stability. Given these recent achievements, we summarize and highlight the promising applications associated with diverse Pickering emulsion systems stabilized by tailored microgels, including interfacial catalysis, functional foods, vaccine adjuvants, stimuli-responsive colloidosomes, and droplet manipulation. Conclusively, we identify the existing research gaps in microgel studies and propose future directions, emphasizing the need for the rational design of microgels, comprehensive mechanism studies of microgel-stabilized emulsions, and the formation of next-generation Pickering emulsions.

Microfluidic techniques have emerged as powerful tools to unveil dynamic processes occurring during foam and emulsion production, and instabilities during their lifetime (coalescence and digestion), and to gain detailed insights in interfacial effects at (sub)millisecond time scales, including but not limited to, interfacial adsorption (i.e. dynamic interfacial/surface tension) and interfacial rheology. These insights are pivotal in connecting the interfacial effects to dynamic processes as they would occur during emulsion/foam production. We highlight the importance of conducting research at relevant time scales.

Soft, light, and aesthetically captivating, yet often enigmatic, liquid foams represent highly complex and intriguing systems. Their intrinsic multiscale structure requires the integration of multiple techniques to fully unveil their properties. This review provides a concise introduction to neutron and x-ray scattering experiments on liquid foams, focusing on their structural characterization at the submicrometer scale. In particular, small-angle scattering experiments for foam characterization are experiencing a renaissance in recent years, with emphasis placed on the breadth of information attainable through these methods. Additionally, it highlights recent advancements in the field and identifies several open challenges that could be addressed using neutron and synchrotron radiation.

This paper reviews the literature on various biosurfactant mixtures used to obtain foams. The interactions between different biosurfactants, biosurfactants, and synthetic surfactants, biosurfactants' interactions with various additives (as non-surface-active macromolecules or particles), and the impact of pH and ionic strength variations on adsorption processes, foamability, foam stability, and rheology are discussed. Biosurfactants are natural and synthetic compounds that can facilitate the process of foam formation and stabilisation; they are an alternative to classical surfactants. Research on such materials will allow the development of innovative foaming technologies that minimise the negative environmental effects of foaming compounds without losing the properties of the final product.

The primary objective of this review is to consolidate our current understanding of the factors controlling the foamability of surfactant solutions under hydrodynamic conditions realized in various laboratory tests. In particular, two regimes of foam generation are considered: at low surfactant concentrations where the coalescence between the bubbles plays a crucial role, and a high surfactant concentration range where the hydrodynamic conditions are much more important for the final outcome of foaming. The review discusses the role of surfactant concentration, dynamic surface coverage, and surface forces acting between film surfaces for the foam generated in the surfactant-poor regime. Additionally, the interplay between the hydrodynamic conditions and the viscosity of the formed foams in the surfactant-rich regime is also discussed.

Ordered porous materials (OPMs) are defined according to pore size, where ordered macropores (>50 nm) govern transport of fluids and mesopores (>2 nm, <50 nm) and micropores (<2 nm, IUPAC definitions) control molecular or ionic interactions. The growing importance of sustainable materials has incentivized the development of biobased OPMs (bioOPMs) with pore sizes ranging from 0.3 nm–9 nm and 1 μm–500 μm. Synthesizing bioOPMs typically involves aqueous solutions and suspensions which require a thorough understanding of biobased precursor-water interactions. Emerging approaches in templating based on liquid foams, breath-figure, and micelles are pivotal for achieving ordered assemblies, with solidity and consolidation occurring through water removal. This review describes recent advances in the design and utilization of bioOPMs, particularly those produced by water-based templating. It also highlights notable exceptions to water-based synthesis and identifies gaps in the science and technology of bioOPMs, offering perspectives on future developments in the field.

This paper reviews the literature on various natural and synthetic biosurfactants, which can facilitate the process of foam formation and stabilisation. Biosurfactants are an alternative to classical surfactants. For example, proteins, through their stabilising properties, can be used both in the food industry and in cosmetics, and this confirms their versatile properties and application in many areas of industry. Sugar-based foaming agents, on the other hand, are characterised by their ability to maintain high foam stability, and their natural origin and biodegradability are attractive substitutes for classical compounds of this type. This review aims to compare the effects of various compounds on the properties and stability of foams. Research on such materials will allow the development of innovative foaming technologies that minimise the negative environmental impacts of foaming compounds without losing the properties of the final product.

Predicting the behavior and fate of redox-sensitive trace elements (TEs; e.g. As, U, Cu, Cr) in natural systems is challenging. Colloids have been reported to control TEs speciation and catalyze TEs redox reactions in many aquatic environments. We hypothesize that the lack of accurate thermodynamic models that account for the role of colloids in TEs speciation explains our inability to predict their redox state distribution in the environment. The slow evolution of the colloidal compartment in response to the prevailing bio/hydro/pedo/climatological conditions need to be decoupled from the fast TEs redox reactions promoted by colloidal surfaces. Further progress is hampered by experimental and theoretical challenges associated with capturing the extreme physical and chemical heterogeneity of colloids, their metastable structures, and their dynamic transformation behavior.

Compared to conventional mesoporous silica nanoparticles (MSNs) with ordered porous structures, hierarchical MSNs (HMSNs) have attracted increasing research interests in biological fields, owing to their highly porous structures with multiple distinct interfaces, which create more possibilities to explore complex biological realms. However, due to the structural complexity, the controllable assembly of HMSNs with desired nanostructures and well-defined particle properties is challenging. Herein, we review the advances of engineering HMSNs via control over surfactant nanoarchitectonics and discuss the synthesis-guiding principles and formation mechanisms. Based on the structural features of HMSNs, the corresponding bio-applications (e.g., macromolecule encapsulation, drug release, biointerface adhesion, immune cell activation and stimuli-responsive target motion) are summarized, highlighting the importance of structure–activity relationship. Challenges and future perspectives are also proposed for characterizations and extended applications of HMSNs.

All personal and industrial cleaning sectors search for environmentally friendly methods to clean contaminated solid surfaces. Having relied for a long time on chemical and physico-chemical means with non-negligible environmental impact, these sectors are increasingly exploring the use of physical phenomena to improve cleaning efficiency. We summarise here recent progress in the area of cleaning methods that exploit the physical properties of liquid interfaces created by liquid menisci, bubbles, drops or foams. The high energy of these interfaces leads to a complex interplay between (1) interfacial forces, (2) viscous stresses created by flow fields under confinement, and (3) the capacity to adsorb solid and liquid contaminations. In appropriately designed cleaning processes, this interplay can reach an astounding efficiency, in many cases even with pure water, i.e. in the absence of any detergent. We will also show that whilst foams have always been assumed to be a mere side product of cleaning processes, recent research puts in evidence that they can actually be highly efficient cleaning agents, provided that their physical properties are properly chosen. We discuss a wide range of examples in which different interface-based cleaning methods have been investigated, including solid and liquid contaminations, or biological contaminations (bacteria, biofilms and biofouling).