Effect of electrolytes on wettability of glass surface using anionic and cationic surfactant solutions

Stability of Two-Dimensional Liquid Foams under Externally Applied Electric Fields

Liquid foams are highly complex systems consisting of gas bubbles trapped within a solution of surfactant. Electroosmotic effects may be employed to induce fluid flows within the foam structure and impact its stability. The impact of external electric fields on the stability of a horizontally oriented monolayer of foam (2D foam) composed of anionic, cationic, non-ionic, and zwitterionic surfactants was investigated, probing the effects of changing the gas-liquid and solid-liquid interfaces. Time-lapse recordings were analyzed to investigate the evolution of foam over time subject to varying electric field strengths. Numerical simulations of electroosmotic flow of the same system were performed using the finite element method. Foam stability was affected by the presence of an external electric field in all cases and depended on the surfactant type, strength of the electric field, and the solid material used to construct the foam cell. For the myristyltrimethylammonium bromide (MTAB) foam in a glass cell, the time to collapse 50% of the foam was increased from ∼25 min under no electric field to ∼85 min under an electric field strength of 2000 V/m. In comparison, all other surfactants trialed exhibited faster foam collapse under external electric fields. Numerical simulations provided insight as to how different zeta potentials at the gas-liquid and solid-liquid interfaces affect fluid flow in different elements of the foam structure under external electric fields, leading to a more stable or unstable foam.

Anomalous Temperature-Controlled Concave-Convex Switching of Curved Oil-Water Menisci

While the curvature of the classical liquid surfaces exhibits only a weak temperature dependence, we demonstrate here a reversible temperature-tunable concave-convex shape switching in capillary-contained, surfactant-decorated, oil-water interfaces. The observed switching gives rise to a concave-convex shape transition, which takes place as a function of the width of the containing capillary. This apparent violation of Young's equation results from a hitherto-unreported sharp reversible hydrophobic-hydrophilic transition of the glass capillary walls. The transition is driven by the interfacial freezing effect, which controls the balance between the competing surfactants' adsorption on, and consequent hydrophobization of, the capillary walls and their incorporation into the interfacially frozen monolayer. Since capillary wetting by surfactant solutions is fundamental for a wide range of technologies and natural phenomena, the present observations have important implications in many fields, from fluid engineering to biology, and beyond.

Role of surfactants in spontaneous displacement of high viscosity oil droplets from solid surfaces in aqueous solutions

HYPOTHESIS

Displacement of oil droplets receding from solid surfaces in aqueous solutions plays a critical role in many household activities and industrial operations. Surfactants are often involved in these activities to control the displacement process. We hypothesize that the influence of surfactants on the displacement process of oil is highly dependent on the type and dosage of surfactants, with the mechanisms being elucidated by the analysis using appropriate dynamic wetting models.

EXPERIMENTS

We systematically investigated the spontaneous displacement of a high viscosity oil on curved hydrophilic glass surfaces in aqueous solutions of anionic sodium dodecylbenzene sulfonate, cationic hexadecyl trimethyl ammonium bromide, and nonionic Triton^TM X-100 over a wide range of concentrations.

FINDINGS

The rather different oil displacement behaviors were observed with different surfactant additions. The displacement dynamics of the receding oil droplet was found to be inhibited by surfactant additions and followed two distinct models quantitatively: the power-law model describing the temporal evolution of early-stage displacement, and the molecular kinetic model describing the dependence of the three-phase contact line displacement velocity on the dynamic contact angle at the late stage of oil displacement. The model-based data analysis provided insights on the role of surfactants in controlling the oil displacement dynamics.

Adsorption Behavior and Wettability of Rhodochrosite Surface: Effect of C18 Fatty Acid Unsaturation

Mineral surface wettability and its regulation by the adsorption of collectors have an important influence on the flotation performance. The adsorption behavior of C18 fatty acid with different unsaturation and its effect on rhodochrosite wettability was investigated with surface tension, contact angle, and atomic force microscopy (AFM) measurements. The results indicated that rhodochrosite hydrophobicity increased with the increasing concentration of fatty acid, along with the maximum contact angle (θmax) between hemimicelle concentration (HMC) and critical micelle concentration (CMC). Oleic acid (OA), linoleic acid (LA), and α-linolenic acid (ALA) had a higher θmax than stearic acid (SA), but the value decreased with the increase of C=C bond number. Besides, preferential adsorption of unsaturated fatty acids on the liquid-air interface can be attributed to the molecule’s steric hindrance resulting from C=C double bond, and the θ kept almost invariant with a higher value of ΓLG than ΓSL until HMC. The oriented monolayer and bilayer structure of fatty acids formed gradually on rhodochrosite surface with increasing concentration. However, the θmax may not necessarily correspond to the beginning of bilayer formation. Cylindrical monolayer and bilayer micelles of SA molecules were observed on rhodochrosite surface at HMC and CMC, respectively. While bilayer structures of unsaturated fatty acids formed before complete coverage of monolayer on rhodochrosite surface because of surface heterogeneity. This work provided a good understanding on the adsorption mechanism of fatty acid on rhodochrosite for flotation.

Adsorption behaviors of branched cationic gemini surfactants and wettability in quartz-solution-air systems

The adsorption and wetting on quartz surfaces by aqueous solutions of xylyl-substituted biquaternary ammonium salt gemini surfactants with different spacer groups (C₃ and C₆), have been investigated. The interfacial properties of surfactant solutions such as contact angle, adhesional tension (γ_LV cos θ), quartz-water interfacial tension (γ_SL) as well as adhesion work (W_A) have been estimated. The obtained results show that C₃ and C₆ have similar adsorption behavior on quartz surfaces. Before critical micelle concentration (cmc) is reached, the contact angles of gemini surfactants slowly increase with the increasing concentration, and the adsorption amount at the water-air interface is almost the same as those at a quartz-water interface. After reaching cmc, the gemini surfactant Cn molecules form a more compact adsorption film through bending the flexible spacer chain, instead of forming a bi-layer. As a result, a further increase in quartz-liquid interfacial tension (γ_SL) and a consequent increase in contact angle have been observed after cmc. Gemini C₆ shows a stronger ability towards hydrophobic modification at a quartz surface than C₃, demonstrating the contribution of the longer methylene spacer to the hydrophobic modification of the quartz surface.

Wetting of polymer surfaces by aqueous solutions of branched cationic Gemini surfactants

The adsorption of xylyl-substituted biquaternary ammonium salt Gemini surfactants with different spacer (C3 and C6) at polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) surfaces has been investigated and the different adsorption parameters such as surface tension, contact angle, adhesional tension, solid-water interfacial tension and work of adhesion have been estimated. The results show that C3 and C6 have similar adsorption behaviors at PTFE and PMMA surfaces. C3 and C6 adsorb gradually at a PFTE-water interface via hydrophobic interactions and the adsorption amounts at the water-air interface are almost three times higher than those at the PTFE-water interface due to the steric hindrance effect. However, the contact angle keeps constant throughout the experimental concentration range because the decrease in surface tension just counterbalances the decrease in PFTE-water interfacial tension. On the other hand, C3 and C6 adsorb at the PMMA surface via polar interactions between xylyl and functional groups of PMMA before CMC. Similar to PTFE, the increase in PMMA-water interfacial tension compensates the decrease in surface tension and the contact angle also shows a stationary value before the CMC. A bi-layer structure of C3 and C6 will be formed at the PMMA-water interface via hydrophobic interaction and PMMA-water interfacial tension decreases consequently after the CMC, which results in the decrease in contact angle.

Hierarchical Self-Assembly of Bile-Acid-Derived Dicationic Amphiphiles and Their Toxicity Assessment on Microbial and Mammalian Systems

A thiol-yne click chemistry approach was adopted for the first time to prepare highly water-soluble bile acid derived dicationic amphiphiles. The synthesized amphiphiles dicationic cysteamine conjugated cholic acid (DCaC), dicationic cysteamine conjugated deoxycholic acid (DCaDC), and dicationic cysteamine conjugated lithocholic acid (DCaLC) exhibited hierarchically self-assembled microstructures at various concentrations in an aqueous medium. Interestingly at below critical micellar concentration (CMC) the amphiphiles showed distinct fractal patterns such as fractal grass, microdendrites and fern leaf like fractals for DCaC, DCaDC and DCaLC respectively. The fractal dimension (Df) analysis indicated that the formation of fractal like aggregates is a diffusion limited aggregation (DLA) process. The preliminary aggregation studies such as determination of CMC, fluorescence quenching, wettability and contact angle measurements were elaborately investigated. The morphology of the aggregates were analyzed by SEM and OPM techniques. Further, we demonstrated the antimicrobial and hemolytic activity for the cationic amphiphiles. DCaC had potent antimicrobial activity and showed no toxicity on human RBCs indicating that DCaC could be used in biomedical applications, in addition to their industrial and laboratory applications such as detergency, surface cleaning, and disinfection agent.

Mobilization and micellar solubilization of NAPL contaminants in aquifer rocks

Surfactant-enhanced aquifer remediation is often performed to overcome the capillary forces that keep residual NAPL phases trapped within contaminated aquifers. The surfactant selection and displacement mechanism usually depend on the nature of NAPL constituents. For example, micellar solubilization is often used to cleanup DNAPLs from aquifers whereas mobilization is desirable in aquifers contaminated by LNAPLs. Although the majority of crude oils are LNAPLs, they often contain heavy organic macromolecules such as asphaltenes that are classified as DNAPLs. Asphaltenes contain surface-active components that tend to adsorb on rocks, altering their wettability. Previous studies revealed that surfactants that formed Winsor type III microemulsions could promote both mobilization and solubilization. However the extent by which these two mechanisms occur is still unclear, particularly in oil-contaminated aquifers. In this study we investigated the remediation of oil-contaminated aquifers using an environmentally friendly surfactant such as n-Dodecyl β-D-maltoside. Focus was given on asphaltenes to better understand the mechanisms of surfactant cleanup. Through phase behavior, spontaneous imbibition, dynamic interfacial tension and contact angle measurements, we showed that microemulsions formed by this surfactant are able to mobilize bulk NAPL (containing 9wt.% asphaltenes) in the porous rock and solubilize DNAPL (i.e., 4-6wt.% adsorbed asphaltenes) from the rock surface. Spontaneous imbibition tests, in particular, indicated that the ratio of mobilized to solubilized NAPL is about 6:1. Furthermore, aging the cores in NAPL beyond 3days allowed for more NAPL to be trapped in the large pores of the rock but did not alter the amount of asphaltenes adsorbed on the mineral surface.

Study on the synthesis and properties of an eco-friendly sugar-based anionic–nonionic surfactant

An eco-friendly surfactant (DAGA-ES) was successfully synthesized and characterized by electrospray ionization-time of flight mass spectrography (ESI-TOFMS),¹H nuclear magnetic resonance (¹HNMR) and Fourier transform infrared spectrometer (FT-IR).

Exploring the Effects of Different Types of Surfactants on Zebrafish Embryos and Larvae

Currently, surfactants are widely distributed in the environment. As organic pollutants, their toxicities have drawn extensive attention. In this study, the effects of anionic [sodium dodecyl sulphate (SDS) ], cationic [dodecyl dimethyl benzyl ammonium chloride (1227)] and non-ionic [fatty alcohol polyoxyethylene ether (AEO) ] surfactants on zebrafish larval behaviour were evaluated. Five behavioural parameters were recorded using a larval rest/wake assay, including rest total, number of rest bouts, rest bouts length, total activity and waking activity. The results revealed that 1227 and AEO at 1 μg/mL were toxic to larval locomotor activity and that SDS had no significant effects. Moreover, we tested the toxicities of the three surfactants in developing zebrafish embryos. AEO exposure resulted in smaller head size, smaller eye size and shorter body length relative to SDS and 1227. All three surfactants incurred concentration-dependent responses. Furthermore, in situ hybridisation indicated that smaller head size may be associated with a decreased expression of krox20. The altered expression of ntl demonstrated that the developmental retardation stemmed from inhibited cell migration and growth. These findings provide references for ecotoxicological assessments of different types of surfactants, and play a warning role in the application of surfactants.

Adsorption enhancement of methylene blue dye at kaolinite clay–water interface influenced by electrolyte solutions

Adsorption of methylene blue dye at kaolinite clay–water interface in the presence of electrolytes.