Surfactant Monomers Research Articles

Enhancing the emulsification and demulsification efficiency of switchable surfactants through molecular dynamics simulation: The roles of surfactant concentration, salinity, and structure

This study aims to investigate the impacts of a surfactant structure, surfactant concentration, and salt content on switchable emulsification processes through molecular dynamics (MD) simulations. Specifically, we focus on assessing the properties and behaviors of water/tetradecane systems containing CO2-switchable acetamidine surfactant N’-dodecyl-N, N-dimethylacetamidine (C12DMAA) and C18 naphthalene sulfonate (C18PS), both of which are relevant to enhanced oil recovery processes. Utilizing MD simulations, we comprehensively explore the influence of the molecular composition of switchable surfactants, salinity, and surfactant concentration on the reversible processes of emulsification and demulsification in a complex oil/water/C18PS/C12DMAA system. This system can be activated through the injection of CO2 or N2 gas. Various analyses, including molecule mobility, hydration behavior, void volume analysis, a solvent accessible surface area (SASA), a diffusion coefficient, and relative concentration profiles, are employed to gain insights into the emulsification and demulsification processes. Our study reveals that lower surfactant concentrations result in the formation of partial emulsions, while the presence of salt disrupts surfactant hydration and weakens emulsification properties. Additionally, we observe that the impact of hydrogen bonding interactions is less pronounced at lower surfactant concentrations. Furthermore, the MD simulations provided insights into the interplay of a surfactant monomer number and alkyl phenyl introduction with a solvent-accessible surface area (SASA) and a void volume. Understanding these factors is crucial for designing and optimizing emulsion systems, particularly in oil recovery processes. The findings advance our understanding of CO2/N2-switchable surfactants, offering insights into their potential for sustainable development in the petroleum industry. This research contributes to the optimization of switchable surfactants, providing a foundation for improved emulsification processes in enhanced oil recovery applications.

Ellipsoidal micelle formation of quaternary ammonium salt-based gemini surfactants: structural analysis through small-angle X-ray scattering.

Gemini surfactants exhibit better adsorption and aggregation properties than those of monomeric surfactants. However, to enhance the functional properties of gemini surfactants, the effect of spacer structures on their aggregation behavior must be elucidated. Small-angle X-ray scattering (SAXS) has been performed to study the aggregate structures of monomeric surfactants, but its application has not been expanded to the analysis of gemini surfactants. Therefore, in this study, we performed a structural analysis of aggregates formed by quaternary ammonium salt-based gemini surfactants with different spacer structures in aqueous solutions through viscosity, dynamic light scattering (DLS), and SAXS measurements. We also investigated the effects of the spacer structure and surfactant concentration on the aggregation behavior. The DLS results indicated that gemini surfactants with spacers containing cyclic structures, such as diethylene and triethylene chains, formed small micelles (several nanometers in size) at the limiting concentration for dissolution in water. In contrast, gemini surfactants with nitrogen and oxygen atoms at the center of the spacer formed ellipsoidal micelles at low concentrations, as shown by SAXS results. The core and overall radii of the minor and major axes of the ellipsoidal micelles decreased with increasing surfactant concentration and were larger for spacers with two ethylene chains connected to central nitrogen and oxygen atoms than for spacers with rigid diethylene and ethylene chains connected to a central nitrogen atom.

Cationic Gemini surfactants: a review on synthesis and their applications

Abstract The molecules of Gemini surfactants are dimeric and consist of two monomeric surfactant units linked by a spacer. Among them, cationic Gemini surfactants have a wide range of application in various industrial sectors such as pharmaceuticals, home and personal care, corrosion inhibition, etc. Various methods of synthesis have been investigated and tested for the synthesis of cationic Gemini surfactants. The surface properties of Gemini surfactants are highly dependent on various factors like spacer, headgroups, counterions, etc. The cationic Gemini surfactants have lower CMC values as compared to their monomeric analogues. This review highlights the different methods for the synthesis of cationic Gemini surfactants and the applications of these surfactants in different fields are presented.

An Investigation of the Effect of pH on Micelle Formation by a Glutamic Acid-Based Biosurfactant

NMR spectroscopy, molecular modeling, and conductivity experiments were used to investigate micelle formation by the amino acid-based surfactant tridecanoic L-glutamic acid. Amino acid-based biosurfactants are green alternatives to surfactants derived from petroleum. NMR titrations were used to measure the monomeric surfactant’s primary and gamma (γ) carboxylic acid pKa values. Intramolecular hydrogen bonding within the surfactant’s headgroup caused the primary carboxylic acid to be less acidic than the corresponding functional group in free L-glutamic acid. Likewise, intermolecular hydrogen bonding caused the micellar surfactant’s γ carboxylic functional group to be less acidic than the corresponding monomer value. The binding of four positive counterions to the anionic micelles was also investigated. At pH levels below 7.0 when the surfactant headgroup charge was −1, the micelle hydrodynamic radii were larger (~30 Å) and the mole fraction of micelle-bound counterions was in the 0.4–0.7 range. In the pH range of 7.0–10.5, the micelle radii decreased with increasing pH and the mole fraction of micelle bound counterions increased. These observations were attributed to changes in the surfactant headgroup charge with pH. Above pH 10.5, the counterions deprotonated and the mole fraction of micelle-bound counterions decreased further. Finally, critical micelle concentration measurements showed that the micelles formed at lower concentrations at pH 6 when the headgroup charge was predominately −1 and at higher concentrations at pH 7 where headgroups had a mixture of −1 and −2 charges in solution.

New long tail gemini surfactant in aqueous solution: Self-assembly, rheological properties and responsiveness to hydrocarbon

Gemini surfactants are promising to replace conventional monomeric surfactants in various applications. In this paper, a new gemini surfactant with long unsaturated oleyl tails and bis(hydroxyethyl) ammonium head groups linked by butyl spacer was synthesized. Its critical micelle concentration in salt-free water (12 µM) is much lower than for its monomeric analog (220 µM). Without any additives this surfactant can form viscoelastic solutions with the viscosity of up to 1 kPa·s and elastic modulus of 15 Pa at the conditions, when the viscosity of the single-chained monomeric analog is close to that of pure water. These are one of the highest values reported so far for C18-tailed gemini surfactants without additives. The structure of the gemini surfactant solutions was studied by cryo-TEM and SAXS. Cryo-TEM revealed the presence of closed-looped micelles coexisting with linear wormlike micelles as well as the regular spacing between the micelles arising from strong electrostatic repulsion between them. The SAXS curves were well-fitted by a form-factor of core–shell cylinder, which yielded the radius of the core and the thickness of the shell equal to 1.4 nm each. Addition of n-decane induced the drop of viscosity by 6 orders of magnitude accompanied by the transformation of wormlike micelles into microemulsion droplets with 4.4 nm radius. Such gemini surfactants providing high viscoelasticity to aqueous solution that is responsive to added hydrocarbon are promising for the application in oil recovery as thickeners of fracturing fluids that can be cleaned up without any breakers at the backflow of oil.

Newly synthesized surfactants as antimicrobial and anti-adhesion agents

Quaternary ammonium salts (QAS) are widely used in medicine, industry and agriculture as disinfectants, biocides, and fungicides. QAS have the ability to coat various surfaces, prevent adhesion of microorganisms to them and inhibit the formation of biofilm. A group of surfactants derived from benzoic acid with different chemical structures was tested: monomeric QAS with different alkyl chain lengths (C12, C14, C16), gemini QAS containing 12-carbon alkyl chains and linkers of various lengths (3,4,6 methylene groups), as well as multifunctional QAS. Among the tested surfactants, monomeric QAS showed the highest bactericidal and fungicidal activity. All three groups of tested compounds inhibited the filamentation of C. albicans. The best antimicrobial activity was demonstrated by the monomeric surfactant C12AA, while the multifunctional equivalent (2xC12AA) was characterized by good anti-adhesive activity. All tested compounds are non-mutagenic and cause low hemolysis of sheep erythrocytes. Multifunctional and gemini surfactants are also non-toxic.

Exploring the Impact of Cationic Surfactant Ctab on Bleu Brilliant G 250 De Cosmassie: Implications for Health Management and Environmental Sustainability

Background: Surfactants are ubiquitous in both natural and industrial processes due to their unique ability to reduce surface tension and facilitate interactions between hydrophilic and hydrophobic substances. Cationic surfactants like cetyltrimethylammonium bromide (CTAB) are of particular interest because of their widespread applications in areas such as healthcare and environmental management. The interaction between surfactants and dyes, such as Bleu Brilliant G 250 de Cosmassie, is critical in industrial processes, especially in the textile industry where wastewater treatment poses significant environmental challenges. Objective: The aim of this study was to explore the thermodynamic behavior of CTAB when combined with Bleu Brilliant G 250 de Cosmassie in aqueous solutions at room temperature. It sought to determine the critical micelle concentration (CMC) and the degree of counter-ion dissociation (α), and to calculate the changes in Gibbs free energy (ΔGm), enthalpy (ΔHm), and entropy (ΔSm) of the system. Methods: The study employed conductometric and spectrophotometric techniques to analyze the CTAB-dye interactions. Solutions were prepared with varying concentrations of CTAB and Bleu Brilliant G 250 de Cosmassie in deionized water, ensuring solvent purity through stringent conductivity and pH monitoring. Electrical conductance was measured at different temperatures to determine the CMC, while absorbance spectra were recorded to observe changes in the interaction between the surfactant and dye. The degree of counter-ion dissociation was calculated by the slope ratio method, and thermodynamic parameters were computed using established equations. Results: The conductometric studies revealed an increase in CMC with temperature, indicating a stabilization of surfactant monomers at higher temperatures. For CTAB and Bleu Brilliant system 1, the CMC was found to be 0.8 with α valued at 0.83. For system 2, the CMC values were 1.55 and 1.6 with α values of 1.01 and 0.91, respectively. Thermodynamically, the system displayed a Gibbs free energy of micellization of -33.09 KJ/mol, an enthalpy change of -6.53, and an entropy change of 0.1325 JK^-1 mol^-1. Conclusion: The study concluded that the interaction between CTAB and Bleu Brilliant G 250 de Cosmassie is influenced significantly by temperature, which affects the micellization behavior and thermodynamic properties. The findings contribute to a better understanding of the fundamental thermodynamic parameters influencing surfactant-dye interactions, providing insights that may improve industrial processes and environmental sustainability.

Refolding SDS-mediated partially-unfolded proteins: A distinguishing role of tetraalkylammonium ionic liquids via mixed micellar aggregation

The current study reports a new strategy for ionic liquid (ILs) assisted refolding of sodium dodecyl sulfate (SDS)-induced partially unfolded protein via mixed micellar aggregate formation between SDS and the ionic liquid. This approach can indeed be utilized to keep many essential and sensitive proteins as active and prolong their shelf life. For SDS-induced partially unfolded proteins, the ionic liquid has been identified to function as a refolding agent. The phenomenon has been observed by us for the first time and we have thoroughly investigated the same utilizing a variety of spectroscopic, microscopic approaches, and attempted to rationalize from computational techniques as well. The steady-state fluorescence emission spectra and time-resolved fluorescence decay show that both the intrinsic emission intensity and the average lifetime, respectively, of the surfactant-induced partially-unfolded protein increase in the presence of ionic liquid, indicating a possible reversal of unfolding (refolding) of the protein (up to ∼95 % revival of luminescence intensity and average lifetime with respect to the native protein). The CD and FTIR results also confirmed that the α-helical content of the pre-unfolded protein reverts substantially and is very close to that of the native protein. To understand the refolding process of SDS-induced partially-unfolded protein, we have further studied the structural recovery of urea-induced pre-denatured protein utilizing the same ionic liquid. Interestingly, no such refolding was observed in this case. From the experimental results, it appears that ionic liquid is involved in scavenging the unfolding surfactant monomers by forming mixed-micellar aggregates where the ion-ion attachment is likely to have impact on the said process.

Experimental study on the impact of “IDS + JFCS” complex wetting agent on the characteristics of coal bodies

As China's coal mines have transitioned to deep mining, the ground stress within the coal seams has progressively increased, resulting in reduced permeability and poor wetting ability of conventional wetting agents. Consequently, these agents have become inadequate in fulfilling the requirements for preventing washouts during deep mining operations. In response to the aforementioned challenges, a solution was proposed to address the issues by formulating a composite wetting agent. This composite wetting agent combines a conventional surfactant with a chelating agent called tetrasodium iminodisuccinate (IDS). By conducting a meticulous screening of surfactant monomer solutions, the ideal formulation for the composite wetting agent was determined by combining the monomer surfactant with IDS. Extensive testing, encompassing evaluations of the composite solution's apparent strain, contact angle measurements, and alterations in the oxygenated functional groups on the coal surface, led to the identification of the optimal composition. This composition consisted of IDS serving as the chelating agent and fatty alcohol polyoxyethylene ether (JFCS).Subsequent assessment of the physical and mechanical performance of the coal briquettes treated with the composite wetting agent revealed notable enhancements. These findings signify significant advancements in the field and hold promising implications. Following the application of the composite wetting agent, notable reductions were observed in the dry basis ash and dry basis full sulfur of coal. Additionally, the water content within the coal mass increased significantly, leading to a substantial enhancement in the wetting effect of the coal body. This enhanced wetting effect effectively mitigated the coal body’s inclination towards impact, thereby offering technical support for optimizing water injection into coal seams and preventing as well as treating impact ground pressure.

Synthesis and application of novel Gemini esterquats in fabric softeners: Role of spacer chain length on surfactant properties

AbstractGemini surfactants are dimeric molecules having two monomeric units connected by a spacer. Gemini surfactants, owing to their molecular structure have better surfactant properties than other monomeric surfactants. Esterquat class gemini surfactants can be synthesized using a spacer containing ester linkages. In the current study, the synthesis of novel esterquat gemini surfactants was carried out with spacers of varying chain lengths and was characterized using sophisticated instrumental methods. Various surfactant properties including foaming, emulsification, CMC, surface excess, antimicrobial activity and wetting potential using contact angle were analyzed and compared with benzalkonium chloride. It was observed that the CMC as low as 24.79 × 10−3 mM of the synthesized surfactants is potentially lower than that of conventional monomeric surfactants and was found to increase with an increase in spacer chain length. Further, the applicability and evaluation of performance properties of the synthesized surfactants were studied in fabric softener formulation. The water absorbency and whiteness retention of the formulation prepared using 12‐6‐12 GS was the highest due to its better wettability amongst other synthesized surfactants owing to its higher spacer chain length. To summarize, the surface and anti‐microbial properties of the synthesized surfactants vary greatly with the alteration in spacer chain length.

Synthesis, self-assembly and surface-active properties of alkyl halide mediated imidazolium monomeric surfactants

Two imidazolium monomeric surfactants, that is, 1-tetradecyl-1H-imidazole [14IM] and 1-hexadecyl-1H-imidazole [16IM] has been synthesized and characterized by 1H NMR,13C NMR, FTIR, HRMS spectroscopies and thermogravimetric analysis (TGA) for number and types of protons and carbon, functional groups, estimation of molecular weight and thermal stability of these compounds. The conductivity was measured in double distilled water at four different temperatures, 288, 293, 298, and 303 K. The results showed that these surfactants behave as weak electrolytes. The density and viscosity data have shown the existence of strong interactions between imidazolium surfactants and solvent (water) molecules. The results obtained from Root’s equation indicate that surfactant–solvent interactions are important than surfactant–surfactant interactions in dilute solutions, that is, below critical micellar concentration. The values of constants obtained from Einstein and Moulik equations have revealed that there was stronger and significant interaction between imidazolium surfactants and water molecules below critical micellar region. The surface tension parameters have indicated that these surfactants are good contenders to lower the surface tension of air/water interface. The results obtained from surface tension data have shown that standard change in free energy of micellization (ΔG°mic) and adsorption (ΔG°ads) were negative, indicating that these surfactants molecules have spontaneous tendencies to form micelles in solution at higher concentration and to get adsorb at the air/water interface at lower concentration. The TGA has indicated good thermally stability and activation energy for thermal decomposition was found in the range of 37.26.26–98.20.20 kJ/mol.

Rheology of high-temperature resistant fracturing fluids formed by VES, acids and oxidants for enhancing CO2 injection in deep coal seams

To address the low efficiency of CO2 injection into deep coal seams due to coal adsorption-induced swelling and low permeability, this study proposes the use of a CO2 injection enhancement fracturing fluid (IEFF) to increase injection efficiency, which is composed of viscoelastic surfactant (quaternary ammonium Gemini surfactant, 18-3-18), organic acids (acetic acid, C2H4O2) and oxidants (hydrogen peroxide, H2O2). The rheology and micelle morphology of the IEFF were investigated in terms of temperature and substance ratios. In addition, comparative study was conducted with monomeric surfactants (STAB). The results demonstrated that compared to STAB, 18-3-18 exhibited a two orders of magnitude lower critical micelle concentration (CMC), a lower surface tension (γCMC), and formed a system with favorable rheology at lower concentrations. Moreover, the viscosity of the IEFFs increased as the substance ratio of C2H4O2 to H2O2 decreased. Inflection points in the IEFFs were observed at 313.15 K, 323.15 K, and 333.15 K, where the viscosity exceeded 25 mPa·s. At 323.15 K, a shear rate of 170 s−1, and a substance ratio of 1:1.5, the IEFF reached its maximum viscosity of 40.390 mPa·s, with a micelle size of 109.56 nm, and the intertwined wormlike micelles formed a robust network structure. The results can provide a reference for optimizing fracturing fluid and promoting the efficiency of CO2 injection into deep coal seams.

Effect of Solute on Interfacial Properties and Micelle Structure of Dodecylbenzenesulfonate (DBS): Experimental and Molecular Dynamics Studies.

A combined experimental and molecular dynamic simulation approach was used to examine the structure and interfacial properties of solute-saturated micelles. The properties of dodecylbenzenesulfonate (DBS) micelles were examined in dodecane and benzene hydrocarbon systems. Pyrene fluorescence was used to determine the aggregation number of surfactant monomers in the micelle systems. Molecular dynamic (MD) simulations using energy minimization applying the CHARMm force field with the TIP3P model for water. Comparison of the DBS/benzene and DBS/Dodecane micelles equilibrium structures via radial distribution function (RDF) and probability distribution function (PDF) analysis indicates that the area per head group for the DBS/Benzene micelle interface is significantly larger than that of the DBS/Dodecane at the interface. It was also determined that benzene molecules can move freely within the micelle while dodecane is strictly confined in the core of the micelle. The increased interfacial area per monomer caused by the insertion of benzene also reduces the effectiveness of the surfactant, which has implications for use in various environmental applications. However, the DBS/benzene micelle can solubilize many more hydrocarbon molecules in one micelle with less surfactant monomer (i.e., lower aggregation number) per micelle due to the increased available packing positions within the micelle. This, in turn, increases the efficiency of the surfactant in real-world applications which is consistent with previous laboratory results. Understanding the differing solubilization characteristics of surfactants against various classes of hydrocarbons in single solute systems is a necessary step to beginning to understand their solubilization properties in the mixed waste systems prevalent in most surfactant enhanced remediation (SEAR) strategies.

Vesicle-to-micelle transition in a double chain quaternary ammonium surfactant system: Interfacial behavior and molecular insights

Vesicles have emerged as promising drug carriers with excellent compatibility with cell membranes, holding immense potential for biomedical applications. While most reported micelle-to-vesicle transitions involve increasing surfactant or additive concentrations, the reverse vesicle-to-micelle transition remains less explored. In this study, we investigate the vesicle-to-micelle transition of hexyldimethyloctylammonium bromide (C6C8Br) using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy. Tetradecyltrimethylammonium bromide (TTABr), a single-chain tetraalkylammonium surfactant with the same chain-length, is studied for comparison. Through the chemical trapping (CT) method, we explore the interfacial composition changes during the vesicle-to-micelle transition. Notably, C6C8Br exhibits a unique characteristic setting it apart from TTABr and other cationic surfactants. At lower concentration ranges, there is a simultaneous increase in interfacial molarities of water and bromide ions, signifying a decrease in interfacial headgroup molarity and surfactant molecule packing. Moreover, our dissipative particle dynamics (DPD) simulation results show that, as the surfactant concentration rises, the interior angle between surfactant chains widens, and the molecular configuration of C6C8Br approaches a straight line. These combined CT and DPD findings underscore the prominent role of steric effects arising from the rigidity of the double-chain. These effects become more pronounced at higher C6C8Br concentrations, leading to looser interfacial packing of surfactant monomers and driving the transition from vesicles to micelles. Interestingly, the breakage of vesicles was not observed when replacing the counterion of C6C8Br with acetate in C6C8Ac solutions. CT results suggest that the elevated interfacial acetate molarity may faciliate the compact packing of surfactant monomers and hinder vesicle-to-micelle transformation. Our study provides a molecular-level understanding of the vesicle-to-micelle transitions in C6C8Br solutions and establishes a theoretical basis for morphological control of surfactant aggregates.

Polymerization Behavior and Rheological Properties of a Surfactant-Modified Reactive Hydrophobic Monomer

The structures and properties of hydrophobic association polymers can be controlled using micelles. In this work, we synthesize a reactive hydrophobic surfactant monomer, KS-3, from oleic acid, N,N-dimethylpropylenediamine, and allyl chloride. A strong synergistic effect between KS-3 and cocamidopropyl betaine in aqueous solution enhances the hydrophilic dispersibility of KS-3, thereby transforming spherical micelles into cylindrical micelles. KS-3 was grafted onto a polyacrylamide chain via aqueous free-radical polymerization to obtain RES, a hydrophobic association polymer. Structural analysis revealed that the RES polymers assembled in wormlike micelles were more tightly arranged than those assembled in spherical micelles, resulting in a compact network structure in water, smooth surface, and high thermal stability. Rheological tests revealed that the synthesized polymers with wormlike and spherical micelles exhibited shear-thinning properties along with different structural strengths and viscoelasticities. Therefore, controlling the micellar state can effectively regulate the polymer properties. The polymers obtained through wormlike micelle polymerization have potential applications in fields with high demands, such as drug release, water purification, and oilfield development.

The use of polyoxyethylene (20) cetyl ether in assessing the hydrophobicity of compounds of biomedical importance and in the process of drug release from microemulsions

Abstract The creation and study of artificial membranes based on microemulsions is an important direction due to the similarity of the structure of both direct and reverse microemulsions with cell membranes. A microemulsion mobile phase prepared with a non-ionic surfactant in combination with a C18 type stationary phase creates a similar image of the cell membrane in a chromatographic column. In addition, the use of microemulsion systems to transport drugs with low bioavailability into the body can increase their bioavailability. The chromatographic behaviour of model substances of biomedical importance was investigated using micellar mobile phases containing polyoxyethylene (20) cetyl ether in biopartitioning micellar chromatography (BMC) in the concentration range of 1–5 %. Cholic acid was introduced into the polyoxyethylene (20) cetyl ether micellar mobile phase to approximate the structure of the cell membrane. The hydrophobicity of the model compounds was evaluated. Hydrophobicity indices in the micellar mobile phase with and without addition of cholic acid were compared. The release profile of promethazine hydrochloride from microemulsion systems with monomeric and polymeric surfactants was investigated. The kinetic properties of the release of promethazine hydrochloride from microemulsion systems were calculated. It was found that a microemulsion of polyoxyethylene (20) cetyl ether mixed with polyoxyethylene (4) lauryl ether reduced the release of promethazine hydrochloride in weight percent. The release of promethazine hydrochloride from microemulsions does not obey Fick’s diffusion but follows a non-Fick’s transport mechanism, as evidenced by the high values of the diffusion exponent (n > 0.5).

Preparation of Cubosomes with Improved Colloidal and Structural Stability Using a Gemini Surfactant.

Cubosomes are nanoparticles with bicontinuous cubic internal nanostructures that have been considered for use in drug delivery systems (DDS). However, their low structural stability is a crucial concern for medical applications. Herein, we investigated the use of a gemini surfactant, sodium dilauramidoglutamide lysine (DLGL), which is composed of two monomeric surfactants linked with a spacer to improve the structural stability of cubosomes prepared with phytantriol (PHY). Uniform nanosuspensions comprising a specific mixing ratio of DLGL and PHY in water prepared via ultrasonication were confirmed by using dynamic light scattering. Small-angle X-ray scattering and cryo-transmission electron microscopy revealed the formation of Pn3̅m cubosomes in a range of DLGL/PHY solid ratios between 1 and 3% w/w. By contrast, cubosome formation was not observed at DLGL/PHY solid ratios of 5% w/w or higher, suggesting that excess DLGL interfered with cubosome formation and caused them to transform into small unilamellar vesicles. The addition of phosphate-buffered saline to the nanosuspension caused aggregation when the solid ratio of DLGL/PHY was less than 5% w/w. However, Im3̅m cubosomes were obtained at solid ratios of DLGL/PHY of 6, 7.5, and 10% w/w. The lattice parameters of the Pn3̅m and Im3̅m cubosomes were approximately 7 and 11-13 nm, respectively. The lattice parameters of Im3̅m cubosomes were affected by the concentration of DLGL. Pn3̅m cubosomes were surprisingly stable for 4 weeks at both 25 and 5 °C. In conclusion, DLGL, a gemini surfactant, was found to act as a new stabilizer for PHY cubosomes at specific concentrations. Cubosomes composed of DLGL are stable under low-temperature storage conditions, such as in refrigerators, making them a viable option for heat-sensitive DDS.

Oppositely charged surfactants and nanoparticles at the air-water interface: Influence of surfactant to nanoparticle ratio

HypothesisThe interactions between oppositely charged nanoparticles and surfactants can significantly influence the interfacial properties of the system. Traditionally, in the study of such systems, the nanoparticle concentration is varied while the surfactant concentration is kept constant, or vice versa. However, we believe that a defined variation of both components' concentration is necessary to accurately assess their effects on the interfacial properties of the system. We argue that the effect of nanoparticle-surfactant complexes can only be properly evaluated by keeping the surfactant to nanoparticle ratio constant. ExperimentsZeta potential, dynamic light scattering, high amplitude surface pressure and surface tension measurements are employed synergistically to characterize the interfacial properties of the nanoparticle-surfactant system. Interferometric experiments are performed to highlight the effect of surface concentration on the stability of thin liquid films. FindingsThe interfacial properties of surfactant/nanoparticle mixtures are primarily determined by the surfactant/nanoparticle ratio. Below a certain ratio, free surfactant molecules are removed from the solution by the formation of surfactant-nanoparticle complexes. Surprisingly, even though the concentration and hydrophobicity of these complexes do not seem to have a noticeable impact on the surface tension, they do significantly affect the rheological properties of the interface. Above this ratio, free surfactant monomers and nanoparticle-surfactant complexes coexist and can co-adsorb at the interface, changing both the interfacial tension and the interfacial rheology, and thus, for example, the foamability and foam stability of the system.

Thermal and Dielectric Investigations of Polystyrene Nanoparticles as a Viable Platform-Toward the Next Generation of Fillers for Nanocomposites.

Nanoparticles are often used as fillers for enhancing various properties of polymer composites such as mechanical, electrical, or dielectric. Among them, polymer nanoparticles are considered ideal contenders because of their compatibility with a polymer matrix. For this reason, it is important that they are synthesized in a surfactant-free form, to obtain predictable surface and structural properties. Here, we synthesized a series of polystyrene nanoparticles (PS NPs), by emulsion polymerization of styrene, using varying amounts of divinylbenzene as a crosslinking agent and sodium 4-vinylbenzenesulfonate as a copolymerizing monomer surfactant-"surfmer". Using "surfmers" we obtained surfactant-free nanoparticles that are monodisperse, with a high degree of thermal stability, as observed by scanning electron microscopy and thermogravimetric investigations. The prepared series of NPs were investigated by means of broadband dielectric spectroscopy and we demonstrate that by fine-tuning their chemical composition, fine changes in their dielectric and thermal properties are obtained. Further, we demonstrate that the physical transformations in the nanoparticles, such as the glass transition, can be predicted by performing the first derivative of dielectric permittivity for all investigated samples. The glass transition temperature of PS NPs appears to be inversely correlated with the dielectric permittivity and the average diameter of NPs.

Fracturing Fluid Polymer Thickener with Superior Temperature, Salt and Shear Resistance Properties from the Synergistic Effect of Double-Tail Hydrophobic Monomer and Nonionic Polymerizable Surfactant

To develop high-salinity, high-temperature reservoirs, two hydrophobically associating polymers as fracturing fluid thickener were respectively synthesized through aqueous solution polymerization with acrylamide (AM), acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), nonionic polymerizable surfactant (NPS) and double-tail hydrophobic monomer (DHM). The thickener ASDM (AM/AA/AMPS/NPS/DHM) and thickener ASD (AM/AA/AMPS/DHM) were compared in terms of properties of water dissolution, thickening ability, rheological behavior and sand-carrying. The results showed that ASDM could be quickly diluted in water within 6 min, 66.7% less than that of ASD. ASDM exhibited salt-thickening performance, and the apparent viscosity of 0.5 wt% ASDM reached 175.9 mPa·s in 100,000 mg/L brine, 100.6% higher than that of ASD. The viscosity of 0.5 wt% ASDM was 85.9 mPa·s after shearing for 120 min at 120 °C and at 170 s−1, 46.6% higher than that of ASD. ASDM exhibited better performance in thickening ability, viscoelasticity, shear recovery, thixotropy and sand-carrying than ASD. The synergistic effect of hydrophobic association and linear entanglement greatly enhancing the performance of ASDM and the compactness of the spatial network structure of the ASDM was enhanced. In general, ASDM exhibited great potential for application in extreme environmental conditions with high salt and high temperatures.