Interaction between Sophorolipids and β-glucan in Aqueous Solutions

Skin disorders, including acne vulgaris, atopic dermatitis, and rosacea, are characterized by the presence of biofilms, which are communities of microorganisms. The mechanical stability of biofilms is attributed to one of their constituents-polysaccharides-which are secreted by microorganisms. Sophorolipids are biosurfactants with biofilm disruption and removal abilities and are expected to become alternatives for classical petrochemical-based surfactants in cosmetics. In this study, we investigated the influence of sophorolipids on β-glucan such as dispersion status, interaction mechanism, and configuration change as a model polysaccharide of biofilm in aqueous solution. Dynamic light scattering measurements showed that sophorolipids interfere with the aggregation of β- glucan in aqueous solutions. In contrast, sodium dodecyl sulfate (SDS), which is used as a typical surfactant reference, promotes the aggregation of β-glucan. The interaction between sophorolipids and β-glucan were investigated using surface tension measurements and isothermal titration calorimetry (ITC). Surface tension increased only near critical micelle concentration (CMC) region of sophorolipids in the presence of β-glucan. This suggests that the interaction occurred in the solution rather than at the air-liquid interface. Moreover, the results of ITC indicate that hydrophobic interactions were involved in this interaction. In addition, the results of optical rotation measurements indicate that sophorolipids did not unfold the triple helical structure of β-glucan. β-glucan dispersion was expected to be caused steric hindrance and electrostatic repulsion when sophorolipids interacted with β-glucan via hydrophobic interactions owing to the unique molecular structure of sophorolipids attributed by a bulky sugar moiety and a carboxyl functional group. These results demonstrated unique performances of sophorolipids on β-glucan and provided more insights on the efficacy of sophorolipids as good anti-biofilms.

Insights into the Characterization of the Self-Assembly of Different Types of Amphiphilic Molecules Using Dynamic Light Scattering

The self-assembly of cetyltrimethylammonium bromide, sodium dodecylsulfate, Triton X-100, and sulfobetaine surfactants in aqueous solutions was examined by dynamic light scattering, both in the presence and absence of 0.1 M NaCl salt, across various temperatures. For each surfactant, critical parameters, such as concentration and phase transition temperatures, of micelles were determined by monitoring changes in the hydrodynamic diameter with concentration and temperature. Additionally, we explored the self-assembly behavior of these surfactants when they are introduced alongside polystyrene nanoparticles. Our findings enabled the elucidation of surfactant molecule adsorption mechanisms onto polystyrene nanoparticle surfaces. Furthermore, by analyzing variations in the z-average diameter and zeta potential, we were able to establish the Krafft point, a parameter that remains imperceptible when polystyrene nanoparticles are absent from the solution.

Viscosity of Sodium Polystyrenesulfonate with Cetyltrimethylammonium Bromide in the Mixture of Methanol and Water

Viscosity of cetyltrimethylammonium bromide (CTAB) in the presence of sodium polystyrene sulfonate (NaPSS) in methanol-water mixed solvent media has been reported at 308.15 K. The results have been analyzed on the basis of a simple model based on the scaling theory of the viscosity of polyelectrolyte solutions put forward by Plucktaveesak et al. (J. Phys. Chem. B, 2003, 107, 8166-8171). The specific viscosity data obtained here for the CTAB-NaPSS couple in mixed solvent media agree very well with the predictions of the above model. It has been established that the fraction of free counterions of the polyelectrolyte can be conveniently recovered in these complex fluids.

Thermodynamics and Viscoelastic Property of Interface Unravel Combined Functions of Cationic Surfactant and Aromatic Alcohol against Gram-Negative Bacteria

Lipopolysaccharides (LPSs), the major constituents of the outer membranes of Gram-negative bacteria, play a key role in protecting bacteria against antibiotics and antibacterial agents. In this study, we investigated how a mixture of cationic surfactants and aromatic alcohols, the base materials of widely used sanitizers, synergistically act on LPSs purified from Escherichia coli using isothermal titration calorimetry (ITC), surface tension measurements, and quartz crystal microbalance with dissipation (QCM-D). ITC data measured in the absence of Ca²⁺ ions showed the coexistence of exothermic and endothermic processes. The exotherm can be interpreted as the electrostatic binding of the cationic surfactant to the negatively charged LPS membrane surface, whereas the endotherm indicates the hydrophobic interaction between the hydrocarbon chains of the surfactants and LPSs. In the presence of Ca²⁺ ions, only an exothermic reaction was observed by ITC, and no entropically driven endotherm could be detected. Surface tension experiments further revealed that the co-adsorption of surfactants and LPS was synergistic, while that of surfactants and alcohol was negatively synergistic. Moreover, the QCM-D data indicated that the LPS membrane remained intact when the alcohol alone was added to the system. Intriguingly, the LPS membrane became highly susceptible to the combination of cationic surfactants and aromatic alcohols in the absence of Ca²⁺ ions. The obtained data provide thermodynamic and mechanical insights into the synergistic function of surfactants and alcohols in sanitation, which will enable the identification of the optimal combination of small molecules for a high hygiene level for the post-pandemic society.

Polymer-Surfactant Complexes Impact the Stratification and Nanotopography of Micellar Foam Films

Freestanding films of soft matter drain via stratification due to confinement-induced structuring and layering of supramolecular structures such as micelles. Neutral polymers, added as rheology modifiers to cosmetics, foods, pharmaceuticals, and petrochemical formulations, often interact with monomers and micelles of surfactants, forming polymer-surfactant complexes. Despite many studies that explore interfacial and bulk rheological properties, the corresponding influence of polymer-surfactant complexes on foam drainage and lifetime is not well understood and motivates this study. Here, we report the discovery and evidence of drainage via stratification in foam films formed with polymer-surfactant (PEO-SDS) complexes. We show that the stratification trifecta of coexisting thick-thin regions, stepwise thinning, and nanoscopic topological features such as nanoridges and mesas can be observed using IDIOM (interferometry, digital imaging, and optical microscopy) protocols we developed for nanoscopic thickness mapping. We determine that for polymer concentrations below overlap concentration and surfactant concentrations beyond the excess micelle point, polymer-surfactant complexation impact the nanoscopic topography but not the step size, implying the amplitude of disjoining pressure changes, but periodicity remains unchanged.

Interactions between Ionic Cellulose Derivatives Recycled from Textile Wastes and Surfactants: Interfacial, Aggregation and Wettability Studies

Interactions between polymers (P) and surfactants (S) in aqueous solution lead to interfacial and aggregation phenomena that are not only of great interest in physical chemistry but also important for many industrial applications, such as the development of detergents and fabric softeners. Here, we synthesized two ionic derivatives-sodium carboxymethylcellulose (NaCMC) and quaternized cellulose (QC)-from cellulose recycled from textile wastes and then explored the interactions of these polymers with assorted surfactants-cationic (CTAB, gemini), anionic (SDS, SDBS) and nonionic (TX-100)-commonly used in the textile industry. We obtained surface tension curves of the P/S mixtures by fixing the polymer concentration and then increasing the surfactant concentration. In mixtures where polymer and surfactant are oppositely charged (P^-/S⁺ and P⁺/S^-), a strong association is observed, and from the surface tension curves, we determined the critical aggregation concentration (cac) and critical micelle concentration in the presence of polymer (cmc^p). For mixtures of similar charge (P⁺/S⁺ and P^-/S^-), virtually no interactions are observed, with the notable exception of the QC/CTAB system, which is much more surface active than the neat CTAB. We further investigated the effect of oppositely charged P/S mixtures on hydrophilicity by measuring the contact angles of aqueous droplets on a hydrophobic textile substrate. Significantly, both P^-/S⁺ and P⁺/S^- systems greatly enhance the hydrophilicity of the substrate at much lower surfactant concentrations than the surfactant alone (in particular in the QC/SDBS and QC/SDS systems).

Interfacial Structure and Electrostatics Related to Solute Activity in a Model Anionic-Surfactant/Polymer Self-Assembly

Polymer/surfactant composites are used in industry as an excipient for water-insoluble solutes. Such enhanced dissolution ability of composite media is related to the spontaneous formation of pre-micellar polymer surfactant aggregates (PS) at a magnitude of order lower than the surfactant critical micelle concentration in water. Combining electrochemical and spectroscopic studies, we investigate the microscopic interfacial structure (i.e., interface electrostatics and surface polarity) of PS formed in composite media. We establish that in a composite system, a mere change in the polymer concentration at a fixed surfactant concentration makes possible to regulate the counter-ion binding ability, surface potential, surface charge density, packing and surface polarity of the PS interface. Our study shows that the higher dissolution of water-insoluble nonionic solutes in composite media is driven by the depressing of surface charge density and polarity of the PS interface. A similar modulation of the PS interface acts as a barrier for the passive relocation of water-soluble charged solutes into the PS pseudo-phase. The time-resolved fluorescence anisotropy study allows us to underline the effect of surface charge modulation on the dynamical aspects of solutes at the PS interface.

Effect of polylactic acid on the micellization of SDS and CTAB: physicochemical studies on surfactants aggregation

This study reports the aggregation behavior of polylactic acid (PLA) with ionic surfactants e.g. sodium dodecyl sulphate (SDS) and hexadecyltrimethylammonium bromide (CTAB) at different temperatures. Surface tension and conductivity techniques were used to investigate these physicochemical properties. Surface tension measurements were carried out to find out critical micelle concentration (CMC), free energy change of micellization (ΔG m), free energy change of adsorption (ΔG ads) and surface excess concentration (Γ). Conductivity measurements were used to determine CMC, degree of ionization (α) and degree of counter ion binding (β). The values of α and β obtained for SDS were (0.389 and 0.611 respectively), while for CTAB the values of α and β were (0.239 and 0.761 respectively). This type of electrostatic interactions is very important which can be applied in various industrial applications (e.g. pharmaceutical, industrial foaming, oil recovery etc.).

Insights into Extended Structures and Their Driving Force: Influence of Salt on Polyelectrolyte/Surfactant Mixtures at the Air/Water Interface

This paper addresses the effect of polyelectrolyte stiffness on the surface structure of polyelectrolyte (P)/surfactant (S) mixtures. Therefore, two different anionic Ps with different intrinsic persistence length lP are studied while varying the salt concentration (0-10-2 M). Either monosulfonated polyphenylene sulfone (sPSO2-220, lP ∼20 nm) or sodium poly(styrenesulfonate) (PSS, lP ∼1 nm) is mixed with the cationic surfactant tetradecyltrimethylammonium bromide (C14TAB) well below its critical micelle concentration and studied with tensiometry and neutron reflectivity experiments. We kept the S concentration (10-4 M) constant, while we varied the P concentration (10-5-10-3 M of the monomer, denoted as monoM). P and S adsorb at the air/water interface for all studied mixtures. Around the bulk stoichiometric mixing point (BSMP), PSS/C14TAB mixtures lose their surface activity, whereas sPSO2-220/C14TAB mixtures form extended structures perpendicular to the surface (meaning a layer of S with attached P and additional layers of P and S underneath instead of only a monolayer of S with P). Considering the different P monomer structures as well as the impact of salt, we identified the driving force for the formation of these extended structures: compensation of all interfacial charges (P/S ratio ∼1) to maximize the gain of entropy. By increasing the flexibility of P, we can tune the interfacial structures from extended structures to monolayers. These findings may help improve applications based on the adsorption of P/S mixtures in the fields of cosmetic or oil recovery.

Comparison of the influence of cationic polysaccharides on the stability properties of montmorillonite suspensions in the presence of sodium dodecyl sulphate

The mixtures of cationic cellulose (CC) or cationic guar gum (CGG) with the anionic sodium dodecyl sulfate surfactant (SDS) were used as stabilizers for the aqueous suspensions of montmorillonite (Mt). The stabilization processes and the stabilization mechanism were investigated using the UV-VIS. The obtained results show that both polysaccharides can be used as stabilizers of the water suspensions of montmorillonite due to the effective adsorption of CC and CGG with or without SDS on the Mt. surface. To obtain complete information on the studied systems, the additional measurements of the surface tension, zeta potential, FT-IR, XRD and SEM were made. The results prove that the intermolecular complexes formed between the polysaccharides and SDS can adsorb on the Mt. surface, change the structure of the electrical double layer and the stability properties of the studied suspensions.

Responsive Material and Interfacial Properties through Remote Control of Polyelectrolyte-Surfactant Mixtures

Polyelectrolyte/surfactant (P/S) mixtures find many applications but are static in nature and cannot be reversibly reconfigured through the application of external stimuli. Using a new type of photoswitchable surfactants, we use light to trigger property changes in mixtures of an anionic polyelectrolyte with a cationic photoswitch such as electrophoretic mobilities, particle size, as well as their interfacial structure and their ability to stabilize aqueous foam. For that, we show that prevailing hydrophobic intermolecular interactions can be remotely controlled between poly(sodium styrene sulfonate) (PSS) and arylazopyrazole tetraethylammonium bromide (AAP-TB). Shifting the chemical potential for P/S binding with E/Z photoisomerization of the surfactants can reversibly disintegrate even large aggregates (>4 μm) and is accompanied by a substantial change in the net charging state of PSS/AAP-TB complexes, e.g., from negative to positive excess charges upon light irradiation. In addition to the drastic changes in the bulk solution, also at air-water interfaces, the interfacial stoichiometry and structure change drastically on the molecular level with E/Z photoisomerization, which can also drive the stability of aqueous foam on a macroscopic level.

Tuning the Stability of Liquids by Controlling the Formation of Interfacial Surfactants

Currently, the stability of liquids by nanoparticle surfactants is widely investigated, while the stability of liquids by supramolecular polymer surfactants is rarely involved. Herein, we combine small organic molecules dissolved...

Interaction of a bovine serum albumin (BSA) protein with mixed anionic-cationic surfactants and the resultant structure

The interaction of a bovine serum albumin (BSA) protein with the mixture of anionic sodium dodecyl sulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) has been investigated by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). Both SDS and DTAB as individuals interact electrostatically as well as hydrophobically with BSA and form connected protein-decorated micelle like complexes in the aqueous solution, in which the well-defined surfactant micelles are organized along the randomly distributed unfolded polypeptide chain of the protein. The protein-surfactant interaction has been tuned by adding different molar mixtures of SDS and DTAB in BSA aqueous solution. It is found that a lower molar fraction of either surfactant in the protein-mixed surfactant complexes results in the formation of a connected protein-decorated micelle structure similar to those of pure surfactants. As the molar fraction of one of the surfactants in the mixture approaches the equimolar fraction, the structure formed by the protein-mixed surfactant is very different from the connected protein-decorated micelle like structure. Different microstructures of BSA-mixed surfactant complexes are formed, mostly governed by the structure of mixed surfactants arising from the strong electrostatic interaction of oppositely charged components. In this case, unfolded proteins wrap the structures of mixed surfactants around their surface. Along with the connected protein-decorated micelle like structure, rod-like and bilayer vesicles of protein-surfactant complexes are formed at different molar fractions of mixed surfactants.

Using Molecular Simulations to Understand the Effect of Dodecyl Sulfate on the Calcium-Binding Ability of Polystyrene Sulfonate

We demonstrate the potential to tune the binding of calcium ions with polystyrene sulfonate (PSS) in the presence of dodecyl sulfate (DS). This can aid the design of surfactant-responsive water-softening agents for applications in detergency. We use molecular dynamics simulations to study the effect of the concentration of DS ions and the degree of sulfonation on the propensity of calcium ions toward PSS. We observe that the presence of DS ions increases the propensity of calcium ions toward 100% sulfonated PSS. The above phenomenon is due to the hydrophobic attraction between PSS and DS at low DS concentrations and the formation of calcium ion bridges between sulfonate and sulfate groups at moderate to high DS concentrations. We also observe the formation of calcium ion bridges between the sulfonate groups at high DS concentrations. The presence of DS ions also increases the propensity of calcium ions toward 20% sulfonated PSS. This is mainly due to the hydrophobic attraction between PSS and DS ions. The calcium ion bridges between sulfonate and sulfate groups are less prevalent than those of 100% sulfonated PSS. We do not observe calcium ion bridges between sulfonate groups of 20% sulfonated PSS. We use the above-mentioned insights to suggest potential strategies for designing an anionic polyelectrolyte having a suitable calcium-binding ability at a given concentration of the anionic surfactant. Finally, strong PSS-DS affinity is detrimental to the activity of surfactants because less surfactant ions are available for detergency. Our results also indicate the possibility of altering the PSS-DS affinity by changing the degree of sulfonation.

Dynamics and extensional rheology of polymer-surfactant association complexes

Understanding and characterizing the influence of polymers and surfactants on rheology, application, and processing is critical for designing complex fluid formulations for enhanced oil recovery, pharmaceuticals, cosmetics, foods, inks, agricultural sprays, and coatings. It is well-established that the addition of anionic surfactant like sodium dodecyl sulfate (SDS) to an aqueous solution of an oppositely-charged or uncharged polymer like poly(ethylene oxide) (PEO) can result in the formation of the polymer-surfactant association complexes (P0S-ACs) and a non-monotonic concentration-dependent variation in zero shear viscosity. However, the extensional rheology response of polymer-surfactant mixtures remains relatively poorly understood, partially due to characterization challenges that arise for low viscosity, low elasticity fluids, even though the response to strong extensional flows impacts drop formation and many processing operations. In this article, we use the recently developed dripping-onto-substrate (DoS) rheometry protocols to characterize the pinching dynamics and extensional rheology response of aqueous P0S- solutions formulated with PEO (P0) and SDS (S-), respectively. We find the PEO-SDS mixtures display a significantly weaker concentration-dependent variation in the extensional relaxation time, filament lifespan, and extensional viscosity values than anticipated by the measured shear viscosity.

Kinetic stability of the oil-in-water emulsions and dynamic interfacial properties of mixtures of sucrose esters and polysaccharides

This article presents a study of the interfacial properties of oil-in-water emulsions containing sugar esters and polysaccharides. Sucrose fatty acid esters were synthesized using immobilized Candida antarctica lipase B. A yield of 53.4% was obtained using 2-methyl-2-butanol and 1:3 M ratio of sucrose:stearic acid. Equilibrium surface tension was 45 mN/m and low critical micellar concentration (CMC) value was obtained (ca. 10 mg/mL), characteristic of non-ionic surfactant. The interfacial properties of mixtures of sucrose esters and polysaccharides, at the oil-water interface were determined using a pendant drop tensiometer. Addition of polysaccharides increased the interfacial tension. Studies of interfacial viscoelasticity showed that the films were predominantly elastic. The presence of polysaccharides in emulsions resulted in flocculated droplets. All the emulsions presented great stability along 28 days with no creaming formation.

Surface science of cosmetic substrates, cleansing actives and formulations

The development of shampoo and cleansing formulations in cosmetics is at a crossroads due to consumer demands for better performing, more natural products and also the strong commitment of cosmetic companies to improve the sustainability of cosmetic products. In order to go beyond traditional formulations, it is of great importance to clearly establish the science behind cleansing technologies and appreciate the specificity of cleansing biological surfaces such as hair and skin. In this review, we present recent advances in our knowledge of the physicochemical properties of the hair surface from both an experimental and a theoretical point of view. We discuss the opportunities and challenges that newer, sustainable formulations bring compared to petroleum-based ingredients. The inevitable evolution towards more bio-based, eco-friendly ingredients and sustainable formulations requires a complete rethink of many well-known physicochemical principles. The pivotal role of digital sciences and modelling in the understanding and conception of new ingredients and formulations is discussed. We describe recent numerical approaches that take into account the specificities of the hair surface in terms of structuration, different methods that study the adsorption of formulation ingredients and finally the success of new data-driven approaches. We conclude with practical examples on current formulation efforts incorporating bio-surfactants, controlling foaming and searching for new rheological properties.

Impact of polyelectrolyte-surfactant interactions on the rheology and wet lubrication performance of conditioning shampoo

OBJECTIVE

The purpose of this study is to understand the impact of the cationic polymer merquat on the rheological behavior of the mixed surfactant system of sodium lauryl ether sulfate (SLES) and cocamidopropyl betaine (CapB) as well as the impact of varying formulation conditions on the wet lubrication performance of the SLES-CapB-Merquat system.

METHODS

Rotation mechanical Rheometry was used to study the rheological response of the SLES-CapB-Merquat systems. Frequency sweeps were conducted to analyze the rheological properties of the system at low frequency ranges and bulk viscosity of the system was studied at high shear rates at varying salt and polymer concentrations. Wet combing tests and hair friction tests were run on the Dia-stron MTT175 flexible miniature tensile tester in order to evaluate the conditioning effects of the different formulations.

RESULTS

The SLES-CapB system on its own exhibits very little viscosity. The bulk rheology results show that the addition of Merquat enhances the viscosity and viscoelastic properties of the SLES-CapB-Merquat system indicating the presence of electrostatic interactions between the surfactant and polyelectrolyte. Addition of salt had a significant impact on the system's rheological response due to the charge screening effect of salt. Wet combing force data indicate that the charged polyelectrolyte binds to the hair substrate resulting in reduced combing force values after the product was applied. The addition of silicone oil to the formulation seemed to greatly enhance the conditioning effect of the formulation.

CONCLUSION

The charge interactions between SLES, CapB and Merquat results in the formation of an integrated gel like network, thus building the viscosity of the system. Variation of parameters like polymer and salt concentration has the potential to modify the bulk rheological properties and consequently the wet lubrication properties of the system.

Study of vitamin E microencapsulation and controlled release from chitosan/sodium lauryl ether sulfate microcapsules

Potential benefit of microencapsulation is its ability to deliver and protect incorporated ingredients such as vitamin E. Microcapsule wall properties can be changed by adding of coss-linking agents that are usually considered toxic for application. The microcapsules were prepared by a spray-drying technique using coacervation method, by depositing the coacervate formed in the mixture of chitosan and sodium lauryl ether sulfate to the oil/water interface. All obtained microcapsules suspensions had slightly lower mean diameter compared to the starting emulsion (6.85 ± 0.213 μm), which shows their good stability during the drying process. The choice and absence of cross-linking agents had influence on kinetics of vitamin E release. Encapsulation efficiency of microcapsules without cross-linking agent was 73.17 ± 0.64 %. This study avoided the use of aldehydes as cross-linking agents and found that chitosan/SLES complex can be used as wall material for the microencapsulation of hydrophobic active molecules in cosmetic industry.

Surfactant-Polymer Interactions in a Combined Enhanced Oil Recovery Flooding

The traditional Enhanced Oil Recovery (EOR) processes allow improving the performance of mature oilfields after waterflooding projects. Chemical EOR processes modify different physical properties of the fluids and/or the rock in order to mobilize the oil that remains trapped. Furthermore, combined processes have been proposed to improve the performance, using the properties and synergy of the chemical agents. This paper presents a novel simulator developed for a combined surfactant/polymer flooding in EOR processes. It studies the flow of a two-phase, five-component system (aqueous and organic phases with water, petroleum, surfactant, polymer and salt) in porous media. Polymer and surfactant together affect each other’s interfacial and rheological properties as well as the adsorption rates. This is known in the industry as Surfactant-Polymer Interaction (SPI). The simulations showed that optimum results occur when both chemical agents are injected overlapped, with the polymer in the first place. This procedure decreases the surfactant’s adsorption rates, rendering higher recovery factors. The presence of the salt as fifth component slightly modifies the adsorption rates of both polymer and surfactant, but its influence on the phase behavior allows increasing the surfactant’s sweep efficiency.

Behavior of the water/vapor interface of chitosan solutions with an anionic surfactant: effect of polymer-surfactant interactions

The adsorption of mixtures formed by chitosan and sodium lauryl ether sulfate (SLES) at the water/vapor interface has been studied on the basis of their impact on the equilibrium surface tension of the interface, and the response of such an interface to mechanical deformations. The analysis of the surfactant binding to the chitosan chains evidenced that the chitosan-SLES solutions were mixtures of polyelectrolyte-surfactant complexes and a non-negligible amount of free surfactant molecules. The interfacial properties showed two well-differentiated regions for interfacial adsorption as a function of the SLES concentration: (i) at a low surfactant concentration, co-adsorption of chitosan and SLES occurs, and (ii) at high concentrations, the surface is mostly occupied by SLES molecules. This behavior may be interpreted in terms of a complex equilibration mechanism of the interfacial layers, where different coupled dynamic processes may be involved. Furthermore, the use of the time-concentration superposition principle has confirmed the different dynamic behaviors of the chitosan-SLES adsorption as a function of the SLES concentration. This work sheds light on some of the most fundamental bases governing the physico-chemical behavior of mixtures formed by a biopolymer and a surfactant, where their complex behavior is governed by an intricate balance of bulk and interfacial interactions.

Alginic acid as a stabilizer of zirconia suspensions in the presence of cationic surfactants

The influence of hydrocarbon (CTAB), fluorocarbon (S-106-A) and silicone (C-Si) cationic surfactants: on stability, adsorption and electrokinetic properties of the alginic acid (AA)/zirconia (ZrO₂) suspensions was studied. The results obtained from the spectrophotometric measurements indicate on very high effectiveness of the surfactants in stabilization of the studied systems. This is due to the formation of multimolecular complexes between alginic acid and the surfactants. The existence of these complexes was confirmed by the surface tension and the zeta potential measurements. Presented studies also enabled the estimation of the conditions under which the complexes are effectively created and the determination of their character. These findings were also confirmed by the adsorption data. Moreover, the surface charge density measurements proved that the adsorption of AA or the AA/surfactant complexes changes the structure of the electrical double layer. The presented results may find applications in the fields of functionalized materials.

Depletion Forces Induced by Mixed Micelles of Nonionic Block Copolymers and Anionic Surfactants

Depletion forces were measured between a silica sphere and a silica plate in solutions containing nonionic Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) triblock copolymers and anionic sodium dodecyl sulfate (SDS) surfactants using colloidal probe atomic force microscopy. Prior research established synergistic depletion force enhancement in solutions containing SDS and unimeric Pluronic F108 block copolymers via formation of large pseudo-polyelectrolyte complexes. The current work addresses a more complex system where the polymer is above its critical micelle concentration, and surfactant binding alters not only the size and charge of the micelles but also the number of polymers per micelle. Force profiles were measured in 10 000 ppm P123 (1 wt %, corresponding to 1.72 mM based on average molar mass) solutions containing SDS at concentrations up to 64 mM and compared to micellar P123 solutions and to P123-free SDS solutions. Whereas force profiles in the SDS-free micellar P123 solutions were purely repulsive, P123/SDS complexation produced synergistic depletion force enhancement for SDS concentrations between 2 and 32 mM. The synergism that occurred within a finite SDS concentration range was explained by comparing the hydrodynamic size, molar mass, charge, and concentration of depletants in P123/SDS mixtures and their respective single-component solutions obtained with the aid of dynamic light scattering, static light scattering, and dodecyl sulfate ion-selective electrode measurements. These measurements showed that complexation produced effects that would be mutually counteracting with respect to depletion forces: decreasing the mixed micelle hydrodynamic diameter relative to SDS-free P123 micelles would tend to weaken depletion forces, while adding charge and decreasing the aggregation number of polymers per micelle (thereby increasing the number concentration of micellar depletants) would tend to strengthen depletion forces.

Impact of the bulk aggregation on the adsorption of oppositely charged polyelectrolyte-surfactant mixtures onto solid surfaces

The understanding of the deposition of oppositely charged polyelectrolytes-surfactant mixtures onto solid surfaces presents a high interest in current days due to the recognized impact of the obtained layers on different industrial sectors and the performance of several consumer products (e.g. formulations of shampoos and hair conditioners). This results from the broad range of structures and properties that can present the mixed layers, which in most of the cases mirror the association process occurring between the polyelectrolyte chains and the oppositely charged surfactants in the bulk. Therefore, the understanding of the adsorption processes and characteristics of the adsorbed layers can be only attained from a careful examination of the self-assembly processes occurring in the solution. This review aims to contribute to the understanding of the interaction of polyelectrolyte-surfactant mixtures with solid surfaces, which is probably one of the most underexplored aspects of these type of systems. For this purpose, a comprehensive discussion on the correlations between the aggregates formed in the solutions and the deposition of the obtained complexes upon such association onto solid surfaces will be presented. This makes it necessary to take a closer look to the most important forces driving such processes.

Counterion Condensation, the Gibbs Equation, and Surfactant Binding: An Integrated Description of the Behavior of Polyelectrolytes and Their Mixtures with Surfactants at the Air-Water Interface

By applying the Gibbs equation to the bulk binding isotherms and surface composition of the air-water (A-W) interface in polyelectrolyte-surfactant (PE-S) systems, we show that their surface behavior can be explained semiquantitatively in terms of four concentration regions, which we label as A, B, C, and D. In the lowest-concentration range A, there are no bound PE-S complexes in the bulk but there may be adsorption of PE-S complexes at the surface. When significant adsorption occurs in this region, the surface tension (ST) drops with increasing concentration like a simple surfactant solution. Region B extends from the onset of bulk PE-S binding to the end of cooperative binding, in which the slow variation of surfactant activity with cooperative binding means that the ST changes relatively little, although adsorption may be significant. This leads to an approximate plateau, which may be at high or low ST. Region C starts where the binding in the bulk complex loses its cooperativity leading to a rapid change of surfactant activity with the total concentration. This, combined with significant adsorption, often leads to a sharp drop in ST. Region D is where precipitation and redissolution of the bulk PE-S complex occur. ST peaks may arise in region D because of loss of the solution complex that matches the value of the preferred surface stoichiometry, which seems to have a well-defined value for each system. The analysis is applied to the experimental systems, sodium polystyrene sulfonate-alkyltrimethylammonium bromides and poly(diallyldimethyl chloride)-sodium alkyl sulfates, with and without the added electrolyte, and includes data from bulk binding isotherms, phase diagrams, aggregation behavior, and direct measurements of the surface excess and stoichiometry of the surface. The successful fits of the Gibbs equation to the data confirm that the surfaces in these systems are largely equilibrated.

Turning autophobic wetting on biomimetic surfaces into complete wetting by wetting additives

Autophobicity or pseudo partial wetting, a phenomenon of a liquid not spreading on its own monolayer, is characterized by an energy barrier that prevents the growth of a wetting film beyond the monolayer thickness. Applying a molecularly detailed self-consistent field theory we illustrate how autophobic wetting can be overcome by wetting additives. More specifically we use an emulsifier which keeps the interfacial tension between the wetting component and the majority solvent low, and a co-solvent additive which partitions inside the film and then destroys the molecular order in it so that the barrier for film growth is cleared. An application wherein it is believed that autophobic wetting is counteracted by such a set of wetting additives is found in an antidandruff shampoo formulation. We have experimental results that show thick deposits onto hydrophobic hair surfaces by administration of the antidandruff shampoo. The complementary modeling of such a system suggests that the active ingredient plays the role of the co-solvent additive. As significant amounts of the co-solvent additives are needed to approach the completely wet state, the formulation naturally brings large amounts of active ingredient to the root of the hair where its presence is required.