Explore the vast range of titles available.

The authors prove the existence and the linear stability of small amplitude time quasi-periodic standing wave solutions (i.e. periodic and even in the space variable x) of a 2-dimensional ocean with infinite depth under the action of gravity and surface tension. Such an existence result is obtained for all the values of the surface tension belonging to a Borel set of asymptotically full Lebesgue measure.

An important goal of the modern soft matter science is to discover new self-assembly modalities to precisely control the placement of small particles in space. Spatial inhomogeneity of liquid crystals offers the capability to organize colloids in certain regions such as the cores of the topological defects. Here we report two self-assembly modes of nanoparticles in linear defects-disclinations in a lyotropic colloidal cholesteric liquid crystal: a continuous helicoidal thread and a periodic array of discrete beads. The beads form one-dimensional arrays with a periodicity that matches half a pitch of the cholesteric phase. The periodic assembly is governed by the anisotropic surface tension and elasticity at the interface of beads with the liquid crystal. This mode of self-assembly of nanoparticles in disclinations expands our ability to use topological defects in liquid crystals as templates for the organization of nanocolloids.

Background Lactobacillus spp. predominantly shows its presence as a normal mucosal flora of the mouth and intestine. Therefore, the objective of our research is to investigate the in-vitro conditions for the prospective of medically valuable biosurfactants (BSs) derived from Lactobacillus spp. Biosurfactant (BS) obtained from Lactobacillus spp. exhibit antibiofilm and antiadhesive activity against broad range of microbes. In the present study we investigated the production, purification and properties of key components of the cell-associated-biosurfactant (CABS) from Lactobacillus acidophilus NCIM 2903. Results Extracted, purified, freeze-dried CABS shows reduction in surface tension (SFT) of phosphate buffer saline (PBS @pH 7.0) from 71 to 26 mN/m and had a critical micelle concentration (CMC) of 23.6 mg/mL. The CABS showed reduction in interfacial tension (IFT) against various hydrocarbons and had effective spreading capability as reflected through the decrease in contact angle (CA) on different surfaces (polydimethylsiloxane - PDMS, Teflon tape, glass surface, polystyrene film and OHP sheet). The anionic nature of CABS displayed stability at different pH and temperatures and formed stable emulsions. Thin layer chromatography (TLC) and Fourier transform infrared spectroscopy (FTIR) revealed CABS as glycolipoprotein type. The Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE) showed presence of multiple bands in a molecular range of 14.4 to 60 kDa, with prominent bands of 45 kDa. The CABS has significant antiadhesion and antibiofilm activity against tested bacterial strains. Conclusion The current challenging situation is to develop methods or search for the molecules that will prevent the formations of biofilm on medical bioimplants of PDMS based materials. These findings are supportive for the use of Lactobacilli derived BS as potential antiadhesive agent on various surfaces of biomedical devices.

The saffron composition is being widely studied for authenticity and traceability, but very few works have been carried out to investigate the relationship between the chemical and physico-chemical properties of saffron solutes and their technological functionality in colloidal systems. This study aims at evaluating the surface properties of saffron extracts obtained using solvents of different polarities to achieve extracts with different compositions in terms of the pattern and content of polar and medium polarity crocins. The air–water surface was evaluated alone and in the presence of Tween 20 at different surfactant–extract ratios. Saffron extracts were able to decrease the surface tension of the aqueous phase, indicating the presence of surface-active compounds. In the mixed saffron extract–Tween 20 systems, competitive adsorption at the air–water interface occurred when the surfactant was present at a low concentration, while at concentrations higher than the CMC, Tween 20 hindered the adsorption of the extract surface-active compounds. The results highlight the interesting technological functionality of saffron extracts for applications in colloidal systems. To better exploit their use in the design and development of formulated foods, nutraceutics and pharma products, further studies are needed to unravel the relationship between the composition of saffron extracts and corresponding surface activity.

The wettability of a liquid on a solid surface is a critical parameter in numerous fields, from microfluidics to heat transfer applications. At the microscale, it directly governs droplet mobility on engineered surfaces, with implications for phase-change heat transfer, fluid transport, and interfacial phenomena. However, the characterization of wettability, commonly quantified through contact angle measurements, is particularly challenging for many fluids employed in thermal devices. These fluids usually have low surface tension resulting in small contact angles, and their normal boiling point is below ambient temperature, which precludes contact angles measurements in open environments. Here, we present a modified optical Wilhelmy method to address these problems by measuring contact angles inside a pressure vessel under saturated conditions. Particular attention was devoted to validating the technique against the standard sessile drop method at atmospheric conditions and to provide a rigorous uncertainty estimation. Results obtained with two low Global Warming Potential refrigerants, R1234ze(E) and R1233zd(E), demonstrate that the developed technique enables accurate and reproducible contact angle measurements, even below 10°. The technique provides a robust and practical tool for screening surface treatments and identifying those most effective for specific applications, including the promotion of dropwise condensation with refrigerants.

In this paper, Stellite6 cobalt alloy is selected as the research object, and a multi-physical mesoscopic scale thermal-flow-solid coupling model is established. Using Flow-3D software, numerical simulations of the temperature and flow fields under different process parameters are performed. The laser powder layer simulation technique is utilized to simulate the laser cladding process under various parameters. The temperature distribution and morphological evolution of the molten pool are analyzed, and the flow characteristics of the molten pool are studied. The effects of two driving forces, surface tension and vapor recoil pressure, on the formation of the molten pool are also explored. The results show that increasing the scanning power leads to a rise in the maximum temperature of the molten pool and an expansion in its width and depth. On the other hand, increasing the scanning speed reduces the maximum temperature but increases the depth and length of the molten pool. As the energy density increases, the surface temperature rises, and the molten pool’s width increases, but the depth decreases. Lower surface tension enhances convection within the molten pool, particularly Marangoni convection. At higher energy densities, vapor recoil pressure becomes the main factor causing depressions in the spot region, thereby driving the flow of the molten pool.

Despite its fundamental and practical relevance, flow structure and evolution within volatile mixture drops remains largely unexplored. We study experimentally, using particle image velocimetry (PIV), the evolution of internal flow during the evaporation of ethanol–water mixture drops for different initial concentrations. The investigation revealed the existence of three stages in the evolving flow behaviour within these binary volatile drops. We propose an analysis of the nature of the flow and focus on understanding successive flow stages as well as transition from multiple vortices to a monotonic outward flow. We show that the existence of multiple vortices during the first stage is driven by local concentration gradients along the interface. When the more volatile component (in this case ethanol) is depleted, the intensity of this Marangoni flow abruptly declines. Towards the end of the first stage, ethanol is driven from the bulk of the drop to the interface to sustain weakening concentration gradients. Once these gradients are too weak, the solutal Marangoni number becomes sub-critical and the driving force for the flow switches off. The evolution of flow structure and transition between stages is found to be well correlated with the ratio of Marangoni and Reynolds numbers. Furthermore, we argue that whilst the observed vortices are driven by surface tension shear stress originating at the liquid/vapour interface, the transition in flow and its dynamics is entirely determined by viscous dissipation. The comparison between the analytical expression for vorticity decay based on viscous dissipation and the experimental data shows a very good agreement. The analysis also shows that regardless of the initial concentration, for same sized drops, the transition in flow follows exactly the same trend. This further supports the hypothesis of a viscous dissipation transition of the flow. The last stage is satisfactorily explained based on non-uniform evaporation and continuity-driven flow.

As a key physical property determining the wettability, adsorption, and structural stability of liquid materials, surface tension is of great significance in material preparation and micro-nano processing. However, traditional methods often rely on chemical composition or temperature adjustments, and how to achieve dynamic control of surface tension under pure mechanical loads remains a frontier issue in surface physics and materials science. Especially under high-frequency extreme loads, the microscopic mechanism of the surface dynamics of molten metal is still unclear, and it is necessary to establish effective theoretical models and numerical methods to reveal it. In this case, we simulated the mechanical response characteristics of the molten aluminum metal surface system to the lateral mechanical cyclic load, and analyzed the steady oscillatory behavior of the cyclic load using the dynamic surface tension of the system. This paper demonstrates that under the 50 GHz high frequency and 5% high amplitude cyclic loading conditions, the average growth rate of the dynamic surface tension of the aluminum liquid can reach approximately 5%. The peak and valley values of the instantaneous dynamic surface tension can respectively reach 30% and 15% of the equilibrium surface tension, showing a controllable trend of significant increase in surface tension with the increase of the load. We applied the previously proposed method of quantitatively adjusting the surface tension under load action to the surface system of the aluminum liquid, and obtained the conclusion that the surface tension of the aluminum liquid can also be dynamically adjusted. This verifies the reliability and universality of this regulation strategy in metal liquids, and provides strong support for the generalized intrinsic frequency and damping constant correlation theory. The analysis of liquid layering clarifies the cross-scale correlation mechanism between macroscopic mechanical response and atomic-scale dynamics, providing new insights into the microscopic mechanism of surface behavior. The research results clarify the quantitative relationship between frequency, amplitude and the rate of surface tension change. This provides direct basis for the process optimization and parameter design of liquid aluminum in precision casting, additive manufacturing and microfluidic systems. By reasonably regulating the load conditions, active control of the surface tension can be achieved. This will enhance the scientificity and process controllability of system design in applications such as wetting adjustment, interface stability improvement and flow behavior optimization.

By airway surface liquid, we mean a thin fluid continuum consisting of the airway lining layer and the alveolar lining layer, which not only serves as a protective barrier against foreign particles but also contributes to maintaining normal respiratory mechanics. In recent years, measurements of the rheological properties of airway surface liquid have attracted considerable clinical attention due to new advances in microrheology instruments and methods. This article reviews the clinical relevance of measurements of airway surface liquid viscoelasticity and surface tension from four main aspects: maintaining the stability of the airways and alveoli, preventing ventilator-induced lung injury, optimizing surfactant replacement therapy for respiratory syndrome distress, and characterizing the barrier properties of airway mucus to improve drug and gene delivery. Primary measuring techniques and methods suitable for determining the viscoelasticity and surface tension of airway surface liquid are then introduced with respect to principles, advantages and limitations. Cone and plate viscometers and particle tracking microrheometers are the most commonly used instruments for measuring the bulk viscosity and microviscosity of airway surface liquid, respectively, and pendant drop methods are particularly suitable for the measurement of airway surface liquid surface tension in vitro. Currently, in vivo and in situ measurements of the viscoelasticity and surface tension of the airway surface liquid in humans still presents many challenges.

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.