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The ability to manipulate droplets on a substrate using electric signals 1 —known as digital microfluidics—is used in optical 2 , 3 , biomedical 4 , 5 , thermal 6 and electronic 7 applications and has led to commercially available liquid lenses 8 and diagnostics kits 9 , 10 . Such electrical actuation is mainly achieved by electrowetting, with droplets attracted towards and spreading on a conductive substrate in response to an applied voltage. To ensure strong and practical actuation, the substrate is covered with a dielectric layer and a hydrophobic topcoat for electrowetting-on-dielectric (EWOD) 11-13 ; this increases the actuation voltage (to about 100 volts) and can compromise reliability owing to dielectric breakdown 14 , electric charging 15 and biofouling 16 . Here we demonstrate droplet manipulation that uses electrical signals to induce the liquid to dewet, rather than wet, a hydrophilic conductive substrate without the need for added layers. In this electrodewetting mechanism, which is phenomenologically opposite to electrowetting, the liquid–substrate interaction is not controlled directly by electric field but instead by field-induced attachment and detachment of ionic surfactants to the substrate. We show that this actuation mechanism can perform all the basic fluidic operations of digital microfluidics using water on doped silicon wafers in air, with only ±2.5 volts of driving voltage, a few microamperes of current and about 0.015 times the critical micelle concentration of an ionic surfactant. The system can also handle common buffers and organic solvents, promising a simple and reliable microfluidic platform for a broad range of applications. A method of droplet manipulation is described that uses electrical signals to induce the liquid to dewet, rather than wet, a hydrophilic conductive surface.

Micelles are of increasing importance as versatile carriers for hydrophobic substances and nanoprobes for a wide range of pharmaceutical, diagnostic, medical, and therapeutic applications. A key parameter indicating the formation and stability of micelles is the critical micelle concentration (CMC). In this respect, we determined the CMC of common anionic, cationic, and non-ionic surfactants fluorometrically using different fluorescent probes and fluorescence parameters for signal detection and compared the results with conductometric and surface tension measurements. Based upon these results, requirements, advantages, and pitfalls of each method are discussed. Our study underlines the versatility of fluorometric methods that do not impose specific requirements on surfactants and are especially suited for the quantification of very low CMC values. Conductivity and surface tension measurements yield smaller uncertainties particularly for high CMC values, yet are more time- and substance consuming and not suitable for every surfactant.

A delicate balance of noncovalent interactions directs the hierarchical self-assembly of molecular amphiphiles into spherical micelles that pack into three-dimensional periodic arrays, which mimic inter-metallic crystals. Herein, we report the discovery that adding water to a mixture of an ionic surfactant and n-decane induces aperiodic ordering of oil-swollen spherical micelles into previously unrecognized, aqueous lyotropic dodecagonal quasicrystals (DDQCs), which exhibit local 12-fold rotational symmetry and no long-range translational order. The emergence of these DDQCs at the nexus of dynamically arrested micellar glasses and a periodic Frank–Kasper (FK) σ phase approximant sensitively depends on the mixing order of molecular constituents in the assembly process and on sample thermal history. Addition of n-decane to mixtures of surfactant and water instead leads only to periodic FK A15 and σ approximants with no evidence for aperiodic order, while extended ambient temperature annealing of the DDQC also reveals its transformation into a σ phase. Thus, these lyotropic DDQCs are long-lived metastable morphologies, which nucleate and grow from a stochastic distribution of micelle sizes formed by abrupt segregation of varied amounts of oil into surfactant micelles on hydration. These findings indicate that molecular building block complexity is not a prerequisite for the formation of aperiodic supramolecular order, while also establishing the generic nature of quasicrystalline states across metal alloys and self-assembled micellar materials.

In this paper, the mechanism of ionic surfactants synergistically changing the surface wettability of bituminous coal dust was investigated using various macroscopic and microscopic means, and the interactions of anionic and nonionic surfactants were explored. The study showed that: the surface tension of the three surfactants decreased with the increase of concentration at low concentrations and stabilised when the mass concentration was greater than 0.05%; the anionic-nonionic complex had the strongest synergistic ability; and the best wetting effect was achieved when the volume ratio of 0.05% SDS and 0.05% OP- 10 was 3:2. The related research ideas and results can provide reference for the application of dust reduction technology in underground coal mines.

In order to study surfactants suitable for a heavy oil reservoir and further improve the degree of heavy oil reservoir production, this paper provides a concentration optimization and compound study on anionic surfactant, nonionic surfactant, and zwitterionic surfactant based on the three major mechanisms of surfactant oil dispersing: reduced interface tension, oil-water emulsification and wetting reversal. Combined with the characteristics of a heavy oil reservoir, the concentration optimization and complex study of anionic surfactant, nonionic surfactant, and zwitterionic surfactant are conducted, respectively. Through the performance test of different ionic surfactants and composite systems, the best oil displacement system is preferred. The results show that the oil-repellent system formed by the zwitterionic surfactant cocoa aminobetaine (CB) is combined with alkali, polymer, and nanomaterial at a concentration of 0.5 wt%. It has high viscosity and low interfacial tension, oil-repellent properties. After the on-site test of a heavy oil reservoir, the daily oil production of the well group in the test area increased from 35.2 t to 68.5 t, and the moisture content decreased from 54.2% to 38.6%, achieving a good oil-increasing and precipitation effect. At the same time, the production liquid was analyzed, and a large amount of emulsions were observed, which confirmed that the compound system had a good emulsification effect. The research results are of great guiding significance for improving the recovery rate of heavy oil reservoirs.

Sea spray is the largest contributor to atmospheric aerosol by mass and contains mixtures of inorganic salts and organics. The chemically complex organic fraction can contain soluble, highly surface-active organics, and field studies commonly identify ionic surfactants in aerosol samples. In macroscopic solutions, divalent cations present in sea spray can alter the partitioning of ionic surfactants. Furthermore, the high surface area-to-volume (SA / V) ratio of aerosol droplets may lead to depletion of surfactant from the bulk, requiring more surfactant, relative to its volume, to lower the surface tension of a droplet compared to a macroscopic solution. Here, we investigate the partitioning of model ionic surfactants (sodium dodecyl sulfate, an anionic surfactant, and cetrimonium bromide, a cationic surfactant) in 6–10 µm radius droplets containing glutaric acid, NaCl, or sea spray mimic cosolutes. Surface tension measurements are compared to two independent partitioning models accounting for the SA / V ratio of the droplets. Salting out of the ionic surfactants leads to strong bulk depletion in 6–10 µm radius droplets, with no observable difference in droplet surface tension between NaCl and sea spray mimic cosolutes. The total ionic surfactant concentration required to reach the minimum surface tension for these droplets was 2.0 ± 0.5 mM, consistent with previous observations in droplets containing strong surfactants. Modeling results suggest that surfactant concentrations on the order of tens to hundreds of millimolar are required to significantly reduce surface tension in 100 nm droplets. These results have implications for cloud droplet activation and chemistry occurring at the interface of sea spray aerosol.

Surfactants adsorb at interfaces and reduce the interfacial tension. In technical applications, they are typically used as complex mixtures rather than monodisperse systems. These mixtures often include ionic and non‐ionic surfactants, with the non‐ionic components comprising various monodisperse species. Such complexity influences adsorption behavior significantly. In this study, we therefore investigated how different monodisperse components within a technical surfactant system affect adsorption kinetics, characterized through dynamic interfacial tension measurements. We focused on blends of the anionic biosurfactant di‐rhamnolipid and technical alkyl ethoxylates. Our results show that increasing the di‐rhamnolipid ratio enhances the adsorption rate at interfaces logarithmically compared to ethoxylates, which is especially relevant for applications requiring rapid adsorption. Moreover, we observed partitioning effects of the ethoxylates’ hydrophobic moieties when comparing adsorption at the oil/water and air/water interfaces. These differences explain why more hydrophilic ethoxylates are often preferred in practice. Overall, our findings deepen the understanding of adsorption behavior in mixed surfactant systems and provide a basis for tailoring formulations by adjusting the component ratio for specific application needs.

A library of alkyl galactosides was synthesized to provide the “polar head” of sugar fatty acid esters to be tested as non‐ionic surfactants. The enzymatic transglycosylation of lactose resulted in alkyl β‐D‐galactopyranosides, whereas the Fischer glycosylation of galactose afforded isomeric mixtures of α‐ and β‐galactopyranosides and α‐ and β‐galactofuranosides. n‐Butyl galactosides from either routes were enzymatically esterified with palmitic acid, used as the fatty acid “tail” of the surfactant, giving the corresponding n‐butyl 6‐O‐palmitoyl‐galactosides. Measurements of interfacial tension and emulsifying properties of n‐butyl 6‐O‐palmitoyl‐galactosides revealed that the esters of galactopyranosides are superior to those of galactofuranosides, and that the enantiopure n‐butyl 6‐O‐palmitoyl‐β‐D‐galactoside, prepared by the fully enzymatic route, leads to the most stable emulsion. These results pave the way to the use of lactose‐rich cheese whey as raw material for the obtainment of bio‐based surfactants. (Bio)Surfing the wave of lactose upcycling. Sugar fatty acid esters were prepared starting either from lactose through a two‐step enzymatic approach catalyzed by immobilized β‐galactosidase from Aspergillus oryzae and immobilized CalB (Novozym® 435), or from galactose through a two‐step chemoenzymatic strategy. n‐Butyl galactoside fatty acid esters were shown to possess good interfacial features, being the pure β‐anomer prepared by the fully enzymatic route the best emulsifier.

The manuscript presents research focusing on the adsorption and emulsion properties of starch hydrolysates modified through acetylation, oxidation, and cross-linking. The techniques used in this study included measurements of equilibrium surface tension (du Noüy ring) dynamic surface tension (drop shape analysis), and the preparation and evaluation of emulsion stability (TURBISCAN). The surface activity of the acetylated starch hydrolysates is affected by the degree of acetylation. The acetylated starch 0.02Ac-H exhibited higher surface activity than the more highly substituted derivative 0.1Ac-H. Furthermore, it was shown that the surface activity of the components increased as the acetylated oxidized starch underwent hydrolysis. The fractions collected after 180 min using a membrane with a low separation capability (8 kDa) revealed the highest capacity for reducing surface tension. In binary systems consisting of starch derivatives and surfactants, synergistic effects in reducing surface tension were particularly noticeable in systems containing ionic surfactants. The addition of a cationic surfactant to the modified starch hydrolysate solution (1:6 mol/mol) resulted in a significantly more efficient saturation of the air/water interface. This study demonstrated that emulsions stabilized with modified starch hydrolysates remained stable over time, even when these hydrolysates constituted up to 60% of the emulsifier mixture.

Boron nitride nanotubes (BNNTs) have attracted significant attention due to their outstanding properties such as high thermal stability, high tensile strength, and light weight. The use of BNNTs to generate macroscopic materials and composites, as well as their use in biological and electronic applications require their effective dispersion in a variety of solvents. In this review, we explore the work generated in the area of BNNT dispersions, highlighting the different approaches that have been taken. Topics that will be covered in this review include covalent functionalization, acids and bases, polymers, biomolecules, aromatic molecules, ionic surfactants, and solvents without additives. The properties of these dispersions will be discussed in light of the dispersion obtained, properties and/or materials made, and will culminate with an outlook of the field, outstanding challenges, and future directions. Graphical abstract