New Paradigms for Spreading of Colloidal Fluids on Solid Surfaces

Surface tension gradient driven spreading of trisiloxane surfactant solution on hydrophobic solid

Association properties of two silicone surfactants based on poly(dimethylsiloxane)-graft-polyethers in aqueous solutions of 2-butoxyethanol, poly(ethylene glycol), and glucose were determined using various techniques such as surface tension, small-angle neutron scattering, and viscosity. Dilute solution phase diagrams were also constructed, and cloud points were measured for different concentrations of both the surfactants in additive aqueous solutions. The thermodynamic parameters for the micellization were obtained from the temperature-dependent data on critical micelle concentration. The influence of given additive on the micellization of silicone surfactants was monitored from the changes in the free energy of micellization values for the surfactant solutions in water and water + additives. The cloud points and the critical micelle concentration values for the surfactant solutions were found to be decreased in the presence of the selected three additives. The analysis of the changes in the relative permittivities and partial molar volumes for the surfactant solutions in the presence of water and water + additives suggests that the solvent environment around the surfactant solute molecules is different in mixed solvent systems vis-a-vis water and the micellization and surface activity of silicone surfactants were dictated predominantly by the preferential hydration of cosolute additives. The analysis of small angle neutron scattering curves for the surfactant aqueous solutions in the presence of additives showed that the micelles formed have oblate ellipsoidal shape at 30 °C with, however, increased characteristic axial ratios than those in pure water. The increase in the concentration of additives has also increased the size of the micelles. The increase in temperatures corresponding to the values close to the turbid boundaries in the phase diagrams caused a transition from the oblate to the disklike micellar shape. The changes in the hydration values of the micellar associates were monitored from the dilute solution viscosity measurements. The dehydration of the micelles in the presence of additives at 30 °C and also at elevated temperatures occur from the interior to the fringe of the core−outer shell parts and to the outer shell successively.

Aggregates of sodium hyaluronate with cationic and aminoxide surfactants in aqueous solution — light scattering study

This paper presents an experimental and theoretical study of Newtonian and non-Newtonian (Bingham plastic) emulsion drop impact on a solid non-heated surface. The utilization of different emulsifiers at a constant concentration of continuous and dispersed phases in emulsions allows the considerable variation of the surface tension at the liquid–liquid interface. Our data for the maximum spreading diameter of water, n-decane, and emulsion drops impacting on a surface are compared with that predicted from the existing models for single-phase liquid drops. All selected models underpredict the experimental data. As a result, the importance of considering the capillary effects at the internal interfaces of the emulsion drops and the careful examination of all rheological properties in the case of Bingham plastic fluids is confirmed experimentally and is taken into account theoretically. The models of Pasandideh-Fard et al. [“Capillary effects during droplet impact on a solid surface,” Phys. Fluids 8, 650 (1996)] and Ukiwe and Kwok [“On the maximum spreading diameter of impacting droplets on well-prepared solid surfaces,” Langmuir 21, 666–673 (2005)] are modified and adapted to the emulsion drop by means of including the additional surface energy term at the liquid–liquid interface of the emulsion drop in the energy conservation equation and the non-Newtonian Reynolds number. The predictions of the maximum spreading diameter give good agreement with the measured one. Several constraints and future lines of research that relate to a specific behavior of the compound liquid drops at the impact on a solid surface are highlighted.

A droplet impinging on a solid substrate can result in liquid spreading, recoil, column formation/breakup, partial or complete rebound, or splash. These outcomes are governed by liquid density, viscosity, and surface tension along with surface wettability and roughness. This chapter discusses the recent developments in modeling Newtonian drop spread-recoil dynamics on a solid surface and provides a review of post-impact drop–surface interactions for aqueous surfactant and polymeric solutions. In aqueous solutions, surfactant molecules diffuse toward interfaces and are adsorbed there. As a result, the liquid–gas interfacial tension changes with surface age and the equilibrium tension is a function of surfactant concentration. The timescale of droplet deformation is often comparable to the timescale of surface tension relaxation of surfactant solutions which affects the surface deformation, spread-recoil oscillations, and column breakup. Furthermore, physisorption of surfactant molecules on the substrate alters its wettability and affects the spread-recoil phenomena. Aqueous polymeric solutions exhibit non-Newtonian viscous behavior, where their apparent viscosity is a function of the shear rate. The complex interplay between dynamic changes in interfacial properties and liquid deformation produces drop spread-recoil dynamics that is vastly different from their pure, Newtonian counterparts. Over last two decades, high-speed videography, computational simulations, and analytical modeling have provided useful understanding of droplet impact phenomena that unfolds over timescales of milliseconds or less for these complex fluids. Current understanding of the effect of dynamic changes in interfacial properties on the outcomes of droplet impact is presented in this chapter.

A basic problem in liquid spreading is the hydrodynamic description of the viscous breaking force near the moving contact line. A solution to the problem of divergence at the triple line has been illustrated with two experimental configurations. It consists of observing that the rheological behavior of a Newtonian liquid is modified near the triple line due to high shear rates. Above a critical value of the shear rate, near the triple line and near the solid surface, the liquid becomes shear-thinning, meaning that the apparent viscosity of the liquid decreases as the shear rate increases. As a result, there is no divergence of the viscous energy dissipation and of the braking force as observed for a purely Newtonian behavior. This description of the viscous braking phenomenon in liquid spreading is well supported by spreading experiments of silicone oils on glass substrates in two different wetting configurations. The liquids used are two silicone oils (10,000 and 100,000 cSt). These liquids are Newtonian below a critical value of the shear rate. Above this critical value, the liquid viscosity decreases according to a power law of the shear rate. One series of experiments consider the spreading of silicone oil droplets on treated and untreated glass substrates. The other configuration consists of using the glass substrates as Wilhelmy plates and to determine the advancing dynamic contact angle as a function of the imposed speed of sinking of the plate into oil reservoirs. The two series of experiments satisfy the same dynamic wetting laws. The overall experimental results are compatible with the hypothesis of a Newtonian/non Newtonian transition of the rheological properties of liquids near the wetting front although the main origin of dissipation appears to result from Newtonian viscous braking. The same dynamic law applies for the drop and Wilhelmy plate geometries.

ABSTRACTThe present article reports the heat transfer characteristics of a vertical stainless steel foil of 0.15 mm thickness (SS304) by circular impinging jets of various fluids such as pure water, nano-fluids (Al2O3-water, ф = 0.15%, 0.6%), and aqueous high-alcohol surfactant (HAS, i.e., 2-ethyl-hexanol, 100–400 ppm) studied using an infrared thermal imaging camera (A655sc, FLIR System). The enhancement in the heat transfer rates for Al2O3-water nano-fluids with ф = 0.15%, ф = 0.60%, and aqueous surfactant solution (150ppm) is found to be 140%, 207%, and 117% higher compared to pure water results, respectively. The surface characteristics of the foil after jet impingement by various fluids are also studied using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and surface wettability.

Micelle formation by amine-based CO2-responsive surfactant of imidazoline type in an aqueous solution

Phoretic self-propulsion of microbubbles may contribute to surface cleaning

Unique role of ionic liquid [bmin][BF 4] during curcumin–surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

Wetting and spreading phenomena are significant in a wide variety of processes. This report discusses the results of an ASTP Science Demonstration, 'Liquid Spreading', and compares these results to theoretical predictions. On earth the initial spreading of large liquid drops on solid surfaces is always dominated by gravity; in this demonstration the effect of gravity is greatly reduced so that surface energy forces are the controlling factor.

Liquid spreading on solid surfaces and penetration into porous matrices: Coated and uncoated papers

The effect of organosilicon additives of various molecular weights—phenyltributyleneglucoxysilan (PBS) and phenyltrioligooxypropyleneglycoxysilan (KMS1052)—on the surface segregation of components of epoxyurethane adhesive compositions and their adhesive behavior is studied It is shown that the surface concentration of components differs considerably from that of the volume as a result of their selective redistribution under the influence of a solid surface. The dependence of the surface segregation of components of epoxyurethane compositions and their adhesive behavior on the concentration of the mentioned additives exhibits an extreme behavior (the effect of small additives).

Wastewater from laundry cleaning contributes to water pollution, and the amount of detergent used needs to be reduced. In the present study, water, four types of surfactants, and their microbubble mixtures were used, and washing rates were measured in swirling flows and alternating flows. The microbubble/water mixtures (average particle diameter: 25 μm; mixed with air at 1.5 vol % in water) achieved washing rates higher than those of water alone. Furthermore, microbubbles mixed with an aqueous surfactant solution had a washing rate that depended on the ionization of the surfactant: the mixtures with microbubbles and non-ionic and anionic surfactants had a washing rate that was higher than that of aqueous non-ionic and anionic surfactant solutions without microbubbles. The surface tensions of microbubble/water mixtures and mixtures of microbubbles with non-ionic and anionic surfactants were lower than those without microbubbles. These results provide evidence of an enhanced washing effect for microbubble mixtures in laundry cleaning.

Porphyrin-surfactant interactions in aqueous solutions are known to result in the selfassembly of various supramolecular structures, including pigment-surfactant complexes, J- and H-aggregates, and solubilized dye species. Detailed studies on the mechanisms of the intermolecular interactions governing the above self-assembly processes allow to predict the aggregation state and hence, the photophysical properties of the dye-surfactant assemblies in order to perform a direct synthesis of the desired porphyrin-based nanostructures at the appropriate experimental conditions. This paper describes a novel example of the surfactant-induced J-aggregate formation from the diprotonated hydrophobic tetraphenylporphyrin species in submicellar aqueous anionic surfactant solutions. The above assemblies are characterized by a rod-like morphology and possess supramolecular chirality according to the CD measurements.