Macroscopic and Microscopic Properties of Some Surfactants and Biosurfactants

SERS imaging investigation of the removal efficiency of pesticide on vegetable leaves by using different surfactants

Pesticide residues on vegetables could be removed by commercial detergents to guarantee food safety, but the removal efficiencies of different formulations of detergents need to be further investigated. In this work, surface enhanced Raman scattering (SERS) imaging method due to its good space resolution as well as high sensitivity is used to track the thiram residue, and evaluate the pesticide removing efficiencies by mixtures of several surfactants at different ratios. Sodium linear alkylbenzene sulphonate-alkyl glycoside (LAS-APG) with the ratio at 5:5 and the concentration at 0.2 % show the best removing effect. In addition, HPLC method is employed to validate the results of SERS imaging. Furthermore, LAS-APG mixture could be efficiently washed out from the leaves through simple household cleaning, meaning no secondary contamination. It is perspective that SERS imaging is an effective technique to explore the effect of fruit and vegetable detergents in removing pesticide residues.

Surface-Active Ionic Liquids and Surface-Active Quaternary Ammonium Salts from Synthesis, Characterization to Antimicrobial Properties

The present work provides new evidence of the ongoing potential of surface-active ionic liquids (SAILs) and surface-active quaternary ammonium salts (surface-active QASs). To achieve this, a series of compounds were synthesized with a yield of ≥85%, and their thermal analyses were studied. Additionally, antimicrobial activity against both human pathogenic and soil microorganisms was investigated. Subsequently, their surface properties were explored with the aim of utilizing SAILs and surface-active QASs as alternatives to commercial amphiphilic compounds. Finally, we analyzed the wettability of the leaves' surface of plants occurring in agricultural fields at different temperatures (from 5 to 25 °C) and the model plant membrane of leaves. Our results show that the synthesized compounds exhibit higher activity than their commercial analogues such as, i.e., didecyldimethylammonium chloride (DDAC) and dodecyltrimethylammonium bromide (C12TAB), for which the CMC values are 2 mM and 15 mM. The effectiveness of the antimicrobial properties of synthesized compounds relies on their hydrophobic nature accompanied by a cut-off effect. Moreover, the best wettability of the leaves' surface was observed at 25 °C. Our research has yielded valuable insights into the potential effectiveness of SAILs and surface-active QASs as versatile compounds, offering a promising alternative to established antimicrobials and crop protection agents, all the while preserving substantial surface activity.

Surfactants as biodegradable sustainable inhibitors for corrosion control in diverse media and conditions: A comprehensive review

BACKGROUND

Corrosion is a challenging and potentially harmful process that involves the continuing, impulsive deterioration of metallic structures via reactions involving environmental components and electro- or chemical processes. To inhibit corrosion, various additives are added. Traditional additives, on the other hand, contain environmentally hazardous substances. Surfactants are less expensive, easier to manufacture, and have high inhibitory efficacy and low toxicity compared to standard corrosion inhibitors. They are often employed as corrosion inhibitors to protect metallic materials against corrosion.

METHODS

Surfactant molecules' amphiphilic nature promotes adsorption at surfaces such as the metal/metal oxide-water interface. Surfactant adsorption on metals and metal oxides forms a barrier that can prevent corrosion.

SIGNIFICANT FINDINGS

This review of surfactants as corrosion inhibitors aims to offer a systemic evaluation of various surfactant physical and chemical properties, surfactant influence in corrosion inhibition, and surfactant used in corrosion inhibition that can be used to enhance the efficacy of surfactant use as corrosion inhibitors in a variety of environments. The effect of several parameters on the potential to suppress corrosion of surfactant molecule series is also discussed here.

Thermodynamic Consideration of the Solid Saponin Extract Drop-Air System

The aim of this research was to elucidate the surface active properties of Saponaria officinalis (soapwort) extract containing the plant surfactants saponins. To this end, the advancing contact angle (θ) of water, formamide and diiodomethane on the glass, as well as θ of the aqueous solution of S. officinalis extract fractions on PTFE, PMMA and glass, were studied. Based on the obtained results, the wetting behaviour of saponins was considered with regard to the surface tension components and parameters of the solutions and solids. The investigations also involved the description of the θ isotherms, the dependences between the cosine of contact angle and/or the adhesion of the solution to the solid surfaces and solution surface tension, as well as the critical surface tension of PTFE, PMMA and glass wetting. These dependences were studied based on the saponin adsorption at the different interfaces, which was deduced from the dependence between the adhesion and surface tension of the solution, as well as using the Gibbs and Frumkin isotherm equations. This proved that the saponins are poor wetting agents and that the contact angle isotherm can be described by the exponential function of the second order as well as the Szyszkowski equation, but only for PTFE.

Corn Silk Flavonoids Ameliorate Hyperuricemia via PI3K/AKT/NF-κB Pathway

Hyperuricemia (HUA) is a widespread metabolic disease marked by an elevated level of uric acid, and is a risk factor for premature death. The protective effect of corn silk flavonoids (CSF) against HUA and its potential mechanisms were explored. Five important apoptosis and inflammation-related signaling pathways were identified by network pharmacological analysis. The CSF exhibited significant uric acid (UA)-lowering activity in vitro by decreasing xanthine oxidase (XOD) and increasing hypoxanthine-guanine phosphoribosyl transferase levels. In a potassium oxonate-induced HUA in vivo, CSF treatment effectively inhibited XOD activity and promoted UA excretion. Furthermore, it decreased the levels of TNF-α and IL-6 and restored pathological damage. In summary, CSF is a functional food component to improve HUA by reducing inflammation and apoptosis through the down-regulating PI3K/AKT/NF-κB pathway.

Adsorption and volumetric properties of some nonionic surfactants and their mixtures with quercetin and rutin

The adsorption and volumetric properties of the Triton X-114 (TX114), Tween 80 (T80), quercetin (Q) and rutin (Ru) at the different temperatures in relation to above properties of the TX114 and T80 mixtures with quercetin and rutin in the absence and presence of alcohol were discussed based on the studies reported in the literature. The adsorption isotherms of the mixtures of the nonionic surfactants with flavonoids in the presence and absence of alcohol were analyzed based on the isotherms of the surface tension of the particular mixture components and thermodynamic parameters of the adsorption of these components at the water-air interface. The surface tension isotherms of the particular component of the mixtures were taken into account while considering the surface tension isotherms of the mixtures and the composition of the mixed surface layer at the water-air interface. Different ways of the mixed surface layer composition determination were shown. The values of the surface tension and composition of the mixed surface layers obtained using different methods were discussed in the light of the intermolecular interactions and their contribution to the surface tension of the surfactants mixture with flavonoids and alcohol. The composition of the mixed monolayer and the bulk phase were compared and the differences between them were explained. The behaviour of the nonionic surfactants and flavonoids in the presence and absence of alcohol was analyzed in relation to the micelle formations and molar volumes of the mixtures and their components. Moreover, the micelles composition and their size as well as the thermodynamic parameters of the micellization process were analyzed.

Biofouling in Membrane Bioreactors: Mechanism, Interactions and Possible Mitigation Using Biosurfactants

Biofouling roots damage to membrane bioreactors (MBRs), such as physical, functional and organisational changes and even therefore clogging of the membrane pores and successive microbial degradation. Further, it blocks the pores, results into a biomass cake and in due course reduces the membrane flux and leads to an increase in the operational costs. MBR fouling contributed to the rise in transmembrane pressure (TMP) and decrease in permeate flux (in case of constant pressure operation mode). Chemical surfactants adopted for the cleaning of membrane surfaces have certain disadvantages such as toxicity manifestations, damage to the membranes and high CMC concentrations. Biosurfactant surfactants have attained increasing interest due to their low toxicity, biodegradability, stability to extreme environmental conditions such as temperatures, pH and tolerance to salinity. The biosurfactants trapped the foulants via micelle formation, which distresses hydrophobic interactions amongst bacteria and the surface. Rhamnolipids as an anionic biosurfactant pose a significant interfacial potential and have affinity to bind organic matter. The present review discusses the problem of biofouling in MBRs, type and interactions of foulants involved and also highlights the mechanisms of biosurfactant cleaning, effect of different parameters, effect of concentration, TMP, flux recovery, permeability, mitigation practices and challenges.

Bacterial-derived surfactants: an update on general aspects and forthcoming applications

The search for sustainable alternatives to the production of chemicals using renewable substrates and natural processes has been widely encouraged. Microbial surfactants or biosurfactants are surface-active compounds synthesized by fungi, yeasts, and bacteria. Due to their great metabolic versatility, bacteria are the most traditional and well-known microbial surfactant producers, being Bacillus and Pseudomonas species their typical representatives. To be successfully applied in industry, surfactants need to maintain stability under the harsh environmental conditions present in manufacturing processes; thus, the prospection of biosurfactants derived from extremophiles is a promising strategy to the discovery of novel and useful molecules. Bacterial surfactants show interesting properties suitable for a range of applications in the oil industry, food, agriculture, pharmaceuticals, cosmetics, bioremediation, and more recently, nanotechnology. In addition, they can be synthesized using renewable resources as substrates, contributing to the circular economy and sustainability. The article presents a general and updated review of bacterial-derived biosurfactants, focusing on the potential of some groups that are still underexploited, as well as, recent trends and contributions of these versatile biomolecules to circular bioeconomy and nanotechnology.

Green surfactants for corrosion control: Design, performance and applications

Surfactants enjoy an augmented share of hydrophilicity and hydrophobicity and are well-known for their anticorrosive potential. The use of non-toxic surfactants is gaining growing interest because of the scaling demands of green chemistry. Green surfactants have successfully replaced traditional toxic surfactant-based corrosion inhibitors. Recently, many reports described the corrosion inhibition potential of green surfactants. The present article aims to describe the recent advancements in using green surfactants in corrosion mitigation. They create a charge transfer barrier through their adsorption at the interface of the metal and the environment. Their adsorption is well explained by the Langmuir adsorption isotherm. In the adsorbed layer, their hydrophilic polar heads orient toward the metal side and their hydrophobic tails orient toward the solution side. They block the active sites and retard the anodic and cathodic and act as mixed-type inhibitors. Their adsorption and bonding nature are fruitfully supported by surface analyses. They can form mono- or multilayers depending upon the nature of the metal, electrolyte and experimental conditions. The challenges and opportunities of using green surfactants as corrosion inhibitors have also been described.

Rhamnolipid Micellization and Adsorption Properties

Biosurfactants are naturally occurring amphiphiles that are being actively pursued as alternatives to synthetic surfactants in cleaning, personal care, and cosmetic products. On the basis of their ability to mobilize and disperse hydrocarbons, biosurfactants are also involved in the bioremediation of oil spills. Rhamnolipids are low molecular weight glycolipid biosurfactants that consist of a mono- or di-rhamnose head group and a hydrocarbon fatty acid chain. We examine here the micellization of purified mono-rhamnolipids and di-rhamnolipids in aqueous solutions and their adsorption on model solid surfaces. Rhamnolipid micellization in water is endothermic; the CMC (critical micellization concentration) of di-rhamnolipid is lower than that of mono-rhamnolipid, and both CMCs decrease upon NaCl addition. Rhamnolipid adsorption on gold surface is mostly reversible and the adsorbed layer is rigid. A better understanding of biosurfactant self-assembly and adsorption properties is important for their utilization in consumer products and environmental applications.

Wetting Properties of Rhamnolipid and Surfactin Mixtures with Triton X-165

The wetting properties of the rhamnolipid and surfactin mixtures with Triton X-165 were considered based on the contact angle measurements of their aqueous solution on the polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA) and quartz (Q) surfaces. The obtained contact angle isotherms were described by the exponential function of the second order as well as by Szyszkowski equation in some cases. Using the contact angle isotherms of individual biosurfactants and TX165 as well as the earlier obtained isotherms of their surface tension the contact angle isotherms of the biosurfactants mixtures with TX165 were deduced. As follows the presence of the maxima on the contact angle isotherms of the biosurfactants mixtures with TX165 is justified. They do not prove negative adsorption of the biosurfactant and TX165 at the interfaces. However, the mutual exchange of the biosurfactant and TX165 molecules is observed in the layers at the interfaces. The concentration of the studied mixtures at the PTFE-solution interface was established to be close to that at the solution-air one but that at the PTFE-air is equal to zero. However, the concentration of the studied mixtures at the PMMA-solution and quartz-solution is greater than zero. The concentration at the PMMA(quartz)-air and PMMA(quartz)-solution interfaces is smaller than that at the solution-air one.

Mutual Influence of Some Flavonoids and Classical Nonionic Surfactants on Their Adsorption and Volumetric Properties at Different Temperatures

Due to the increasing practical use of mixtures of flavonoids with nonionic surfactants the presented studies were based on the measurements of surface tension and conductivity of aqueous solution of the quercetin (Q) and rutin (Ru) in the mixtures with Triton X-114 (TX114) and Tween 80 (T80) as well as the contact angle of model liquids on the PTFE surface covered by the quercetin and rutin layers. Based on the obtained results components and parameters of the quercetin and rutin surface tension were determined and the mutual influence of Q and Ru in the mixtures with TX114 and T80 on their adsorption and volumetric properties were considered. It was found, among others, that based on the surface tension isotherms of the aqueous solution of the single flavonoid and nonionic surfactant, the surface tension isotherms of the aqueous solution of their mixture, the composition of the mixed monolayer at the water-air interface as well as the CMC of flavonoid + nonionic surfactant mixture can be predicted. The standard Gibbs energy, enthalpy and entropy of the adsorption and aggregation of the studied mixtures were also found, showing the mechanism of the adsorption and aggregation processes of the flavonoid + nonionic surfactant mixture.

Adsorption Properties and Composition of Binary Kolliphor Mixtures at the Water-Air Interface at Different Temperatures

The studies on the adsorption properties and composition of the adsorbed monolayer at the water–air interface of the binary Kolliphor^® ELP (ELP) and Kolliphor^® RH 40 (RH40) mixtures based on the measurements of the surface tension (γ_LV) of their aqueous solution in the temperature range from 293 to 318 K were carried out. The γ_LV isotherms were described by the exponential function of the second order and the Szyszkowski equation as well as predicted by Fainerman and Miller equation. The obtained γ_LV isotherms were analyzed using the exponential function of the second order, the Szyszkowski, Fainerman and Miller as well as independent adsorption equations. The γ_LV isotherms were also used for determination of the Gibbs surface excess concentration of RH40, ELP and their mixture (Γ) at the water–air interface as well as the mixed monolayer composition. Based on Γ and the constant a in the Szyszkowski equation, the standard thermodynamic functions of adsorption were considered. From the consideration dealing with the γ_LV isotherms obtained by us, it results, among others, that these isotherms for the non-ideal solution of macromolecular surfactants mixture can be predicted using the Fainerman and Miller equation. From this consideration, it also results that a simple method proposed by us, based on the isotherms of RH40 and ELP, allows us to predict the composition of their mixed monolayer in the whole concentration range of RH40 and ELP in the bulk phase.

Effect of Spontaneous and Water-Based Passivation on Components and Parameters of Ti6Al4V (ELI Grade) Surface Tension and Its Wettability by an Aqueous Solution of Sucrose Ester Surfactants

Solid wettability is especially important for biomaterials and implants in the context of microbial adhesion to their surfaces. This adhesion can be inhibited by changes in biomaterial surface roughness and/or its hydrophilic–hydrophobic balance. The surface hydrophilic–hydrophobic balance can be changed by the specifics of the surface treatment (proper conditions of surface preparation) or adsorption of different substances. From the practical point of view, in systems that include biomaterials and implants, the adsorption of compounds characterized by bacteriostatic or bactericidal properties is especially desirable. Substances that are able to change the surface properties of a given solid as a result of their adsorption and possess at least bacteriostatic properties include sucrose ester surfactants. Thus, in our studies the analysis of a specific surface treatment effect (proper passivation conditions) on a biomaterial alloy’s (Ti6Al4V ELI, Grade 23) properties was performed based on measurements of the contact angles of water, formamide and diiodomethane. In addition, the changes in the studied solid surface’s properties resulting from the sucrose monodecanoate (SMD) and sucrose monolaurate (SML) molecules’ adsorption at the solid–water interface were also analyzed. For the analysis, the values of the contact angles of aqueous solutions of SMD and SML were measured at 293 K, and the surface tensions of the aqueous solutions of studied surfactants measured earlier were tested. From the above-mentioned tests, it was found that water environment significantly influences the components and parameters of Ti6Al4V ELI’s surface tension. It also occurred that the addition of both SMD and SML to water (separately) caused a drop in the water contact angle on Ti6Al4V ELI’s surface. However, the sucrose monolaurate surfactant is characterized by a slightly better tendency towards adsorption at the solid–water interface in the studied system compared to sucrose monodecanoate. Additionally, based on the components and parameters of Ti6Al4V ELI’s surface tension calculated from the proper values of components and parameters of model liquids, it was possible to predict the wettability of Ti6Al4V ELI using the aqueous solutions of SMD and SML at various concentrations in the solution.

Polyethylene-water partition coefficients for polychlorinated biphenyls: Application of QSPR predictions models with experimental validation

The water environmental recalcitrance and ecotoxicity caused by polychlorinated biphenyls (PCBs) are international issues of common concern. The partition coefficients with PCBs between low-density polyethylene (LDPE) and water (K_PE-w) are significant to assess their environmental transport and/or fate in aquatic environment. Even moderately hydrophobic PCBs, however, possess large K_PE-w values, which makes directly experimental measurement labored. Here, based on the combination of quantitative structure-property relationships (QSPRs) and machine-learning algorithms, 10 in-silico models are developed to provide a quick estimate of K_PE-w. These models exhibit good goodness-of-fit (R²_adj: 0.919-0.975), robustness (Q²_LOO: 0.870-0.954) and external prediction performances (Q²_ext: 0.880-0.971), providing a speedy feasibility to close data gaps for limited or absent experimental information, especially the RF-2 model. Particularly, an additional experimental verification is performed for models by a rapid and accurate three-phase system (aqueous phase, surfactant micelles and LDPE). The results of the experiments for 16 PCBs show the modeling results agree well with experimental values, within or approaching the residuals of ± 0.3 log unit. Mechanism interpretations imply that the number of chlorine atoms and ortho-substituted chlorines are the great effect parameters for K_PE-w. This result also heightens interest in measuring and predicting the K_PE-w values of chemicals containing halogen atoms in water.

Nanoemulsions as Ophthalmic Drug Delivery Systems

Nanoemulsions are liquid-in-liquid dispersion with a droplet size of about 100 nm. They have a transparent appearance, high rate of bioavailability, and increased shelf life. Nanoemulsions mainly consist of oil, water, surfactant, and cosurfactant and can be prepared by high- and low-energy methods. Diluted nanoemulsions are utilized for the delivery of ophthalmic drugs due to their capability to penetrate the deep layers of the ocular structure, provide a sustained release effect, and reduce the frequency of administration and side effects. These nanoemulsions are subjected to certain tests, such as safety, stability, pH profile, rheological studies, and so on. Cationic nanoemulsions are prepared for topical ophthalmic delivery of active ingredients from cationic agents to increase the drug residence time on the ocular surface, reducing their clearance from the ocular surface and improving drug bioavailability. This review article summarizes the main characteristics of nanoemulsions, ophthalmic nanoemulsions, and cationic nanoemulsions and their components, methods of preparation, and the evaluation parameters for ophthalmic nanoemulsions.

Adsorption Properties of Hydrocarbon and Fluorocarbon Surfactants Ternary Mixture at the Water-Air Interface

Measurements were made of the surface tension of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl) phenoxypoly(ethylene glycols) having 10 oxyethylene groups in the molecule (Triton X-100, TX100) and cetyltrimethylammonium bromide (CTAB) with Zonyl FSN-100 (FC6EO14, FC1) as well as with Zonyl FSO-100 (FC5EO10, FC2) ternary mixtures. The obtained results were compared to those provided by the Fainerman and Miller equation and to the values of the solution surface tension calculated, based on the contribution of a particular surfactant in the mixture to the reduction of water surface tension. The changes of the aqueous solution ternary surfactants mixture surface tension at the constant concentration of TX100 and CTAB mixture at which the water surface tension was reduced to 60 and 50 mN/m as a function of fluorocarbon surfactant concentration, were considered with regard to the composition of the mixed monolayer at the water-air interface. Next, this composition was applied for the calculation of the concentration of the particular surfactants in the monolayer using the Frumkin equation. On the other hand, the Gibbs surface excess concentration was determined only for the fluorocarbon surfactants. The tendency of the particular surfactants to adsorb at the water-air interface was discussed, based on the Gibbs standard free energy of adsorption which was determined using different methods. This energy was also deduced, based on the surfactant tail surface tension and tail-water interface tension.

Simultaneous removal of organics and heavy metals from industrial wastewater: A review

The co-existence of heavy metals and organics in industrial effluents is a prevalent problem. These pollutants usually have dissimilar compositions and properties, making their complete removal very tedious even with the use of conventional methods. In some cases, organics and heavy metals usually exist in a mixed matrix in industrial wastes. This poses harmful health risks to humans, aquatic lives and the entire ecosystem, because majority of these mixed pollutants amass in water in concentrations which are more than the permissible discharge limits in the environment. Therefore, it is necessary to remove these pollutants in order to prevent them from contaminating both the surface and ground water. Although, the removal of organic compounds and heavy metals (such as Hg, Pb, Cd, As and Cr) could be easily achieved individually, however, these pollutants exist together in many industrial effluents and even in surface waters. Hence the complete removal of these pollutants concurrently in a polluted system is the focus of this study. Several technologies have been used for the simultaneous removal of organics and heavy metal pollutants from water, which includes adsorption, ion exchange, photocatalysis, and coagulation. The success of these techniques depends on the water matrices and the choice of water treatment media such as adsorbents, resins, photocatalysts, and coagulants. The advantages and limitations of these technologies together with their respective mathematical modelling is critically examined in this review. Finally, the effect of joint existence of organic pollutants and heavy metals on the removal efficiency were examined in addition to the mathematical models that discusses the mechanisms of their combine elimination.

Thermodynamic Analysis of Trisiloxane Surfactant Adsorption and Aggregation Processes

The trisiloxane polyether surfactant (3-[3-(hydroxy)(polyethoxy)propyl]-1,1,1,3,5,5,5 -heptamethyltrisiloxane) (TS-EO12) was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt catalyst. The structural analysis of the surfactant was done by ¹H-NMR, ¹³C-NMR, ²⁹Si-NMR and FT-IR analysis. In addition the thermal stability of TS-EO12 was studied by the thermogravimetric measurements. On the one hand the surface properties of TS-EO12 at the water-air interface were investigated by surfactant aqueous solutions surface tension measurements carried out at 293 K, 303 K and 313 K, and on the other the aggregation properties were analyzed based on the solubilization properties of TS-EO12 aggregates at different temperatures. On the basis of the obtained thermodynamic parameters of adsorption and micellization of studied surfactant the temperature impact on its surface and volume properties were deduced. It was proved that the tendency of the studied surfactant molecules to adsorb at the water-air interface and to form micelles weakens with decreasing temperature. It was also concluded that the structure of the adsorption layer changes with temperature. Optical microscopy measurements were used for the TS-EO12 micelle morphology determination.

Modification of adsorption, aggregation and wetting properties of surfactants by short chain alcohols

The adsorption of methanol, ethanol and propan-1-ol at the solution-air and solid-solution interfaces, their aggregation in the aqueous media as well as wetting properties regarding their applications as additives or co-surfactants in the surfactants aqueous solution were discussed based on the literature data. Mutual influence of alcohols and surfactants on the solution-air and solid-solution interface tension was considered. For this purpose there were used different methods allowing to describe or predict changes of water surface tension as a function of alcohols concentration. These, in turn, as a function of alcohol and/or surfactant concentration were also analyzed by means of the methods applied for prediction of surface tension of aqueous solution of the classical surfactants mixture. The same considerations related to the behaviour of alcohol and surfactant at the solid-solution and solution-air interfaces were made. To explain the behaviour of alcohols and surfactants mixture at the solution-air and solid-solution interfaces the components and parameters of water, alcohols, surfactants and solids surface tension as well as the Gibbs free energy changes during the adsorption process were taken into account. It was proved that wettability of some solids can be predicted based on alcohol and surfactants adsorption as well as surface tension components and parameters. As follows the mutual influence of alcohol and surfactant on their adsorption at the solution-air and solid-solution interfaces as well as on the wetting properties at the alcohol concentration from zero to its critical aggregation concentration (CAC) is different from that at its concentration higher than CAC.