Dissolution Of Surfactant Research Articles

Promoting dissolution behaviors of low-carbon alcohol polyoxyethylene polyoxypropylene ether in CO2 by molecular structure optimization and adding cosolvent

The low-carbon alcohol polyoxyethylene (EO) polyoxypropylene (PO) ether surfactants have significant application potential in CO2 flooding for enhanced oil recovery (EOR) in water-bearing oil reservoirs because of their hydrophilic, lipophilic and CO2-philic properties. The dissolution of surfactants in CO2 is the important precondition for the application of the CO2 + surfactant systems injected in oil reservoir. This work combines experiments and molecular dynamics simulations to reveal the dissolution mechanism of low-carbon alcohol polyethers in CO2 at the molecular level in order to promote the dissolution behaviors of these surfactants. The results show that the appropriate adjustment of the molecular structure can promote the dissolution of surfactants in CO2 by the interactions of dispersion forces, Lewis acid–Lewis base (LA-LB) interactions, and potential hydrogen bonding. The increase of the numbers of EO groups, PO groups, and the length of the alkyl chain all lead to the increase of the cloud point pressure due to the weaken of the dispersion forces and LA-LB interactions between the surfactants and CO2 with the increase of the molecular weight of the surfactants. Under the premise of ensuring sufficient hydrophobic, lipophilic and CO2-philic properties of the surfactant molecules, decreasing the molecular weight as much as possible can increase the dissolution properties. Moreover, the distribution adjustment of EO and PO groups in surfactants has a significant impact on the dissolution behaviors. The molecules, in which EO and PO groups cross-dispersed and the terminal hydroxyl group connected to the EO group, have a better CO2-philicity than those with long EO chains and PO chains. Furthermore, ethanol can reduce the cloud point pressure of surfactants in CO2, because that the presence of ethanol can break the stronger van der Waals forces between CO2 molecules and enhance the LA-LB interactions and hydrogen bonding between the hydroxyl groups and CO2.

Methodology for the investigation of surfactant dissolution in water

Concentrated aqueous solutions of surfactants pastes are widely used in industrial productions. The dissolution phenomena of these fluids in water is difficult to optimize, given the thermodynamic complexity of the system, that adds further resistance to the mass transport efficiency. One of the most common anionic surfactants is Sodium Lauryl Ether Sulphate (SLE3S). Depending on the SLE3S-water composition, surfactant nano-molecules can assume different morphologies, such as micellar phases (<30%wt of SLE3S), hexagonal liquid crystals (>30%wt), cubic structures (~60%wt), or lamellar liquid crystals (>60%wt), which are characterized by nanoscale ordered structures. Different phases show strongly different rheological behaviour. All phases are non-Newtonian, with a shear-thinning viscosity as function of imposed shear rate. A novel methodology is here proposed to investigate the dynamic evolution of the phase changes during surfactant dissolution using Time-lapse microscopy. Samples are observed trough crossed polarizers. Differences in nano-morphology, due to molecules rearrangement during phase changes, can be easily monitored by measuring light intensity profiles.

Protein encapsulation in mesoporous silica: Influence of the mesostructured and pore wall properties

The goal of this work is to study the influence of the structured mesoporous silica (SMS), used as scaffolds for tissue engineering, on the encapsulation and on the release of a model bone morphogenetic proteins (BMP), i.e. Soybean Trypsin Inhibitor (STI). First, SBA-15 silica samples were synthesized using tetraethyl orthosilicate (TEOS) as silica precursor in the presence of P123 as the surfactant in an acidic medium. Three homemade high-pressure stainless steel reactors (with smaller Teflon reactors inside), each equipped with a temperature probe, were used for the syntheses. In addition, a swelling agent was added to increase the pore size. Indeed, the common pore size for those mesostructured materials lies between 6 nm and 8 nm, while the STI has an average radius of 4 nm. The reagent addition sequence was also investigated, by playing on the time of addition of the swelling agent. It was observed that when the swelling agent was added with TEOS, an ordered mesoporous silica was produced. On the contrary, if the swelling agent was added during the surfactant dissolution step, it resulted in an unstructured yet still mesoporous silica. Because of the high affinity of STI for hydrophobic surfaces, SMS were also produced using silica precursors containing phenylene bridging groups (1,4-bis(triethoxysilyl)benzene, BTEB). The BTEB samples exhibited two 2D-hexagonal structures with different wall thicknesses. Synthesized materials were further characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), nitrogen sorption at 77 K, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The influence of both the silica composition and structure on STI encapsulation/release was studied. For samples synthesized with TEOS, the unstructured sample showed a higher protein loading and a higher protein release, which could be explained by a difference in the pore interconnectivity within the sample. In fact, a fast release of STI was observed during the first 24 h. Afterwards, the STI release slowed down and seemed to reach a plateau. On the opposite, the structured sample showed a steady release over time. Finally, the sample synthesized with BTEB did not show a significant release over the same period of time. This led us to the conclusion that the hydrophobicity of the silica surface plays a major role on the protein encapsulation and its release rate.

The effect of hydrophobicity on the dissolution of surfactant lamellar phases

Abstract Formulated products are essential in our daily life. They are available everyway we look from toothpaste to salad dressing and from motor oil to make up. These products seem different but they share common components like oil, water, particles and surfactants. The main goal of this study is to provide further insight into surfactant dissolution process by studying the effect of changing the final concentration of surfactants and the degree of surfactant hydrophobicity. To achieve this goal dissipative particle dynamic (DPD) simulations were used. The simulated system contained surfactant molecules in solvent at 80%, which initially form a lamellar phase. The dissolution process is investigated by placing this lamellar phase of surfactant next to a box of water. Results show that the lamellar phase transforms into a micellar phase at a faster rate than the full diffusion of these micelles through the box. This two-stage dissolution process can be represented as a simple model with a transformation parameter and a diffusion parameter; both of which decrease with increasing hydrophobicity but are box size independent. Dissolution of the surfactant with higher hydrophobicity produces micelles, which are more elongated and worm-like in nature whereas lower hydrophobicity produces spherical micelles.

The influence of oil property on interfacial tension

This paper researches the oil property from three different districts in Daqing Oilfield. And then the sulfur contents in crude oil and emulsified oil is tested to explore the dissolution of surfactant into oil phase. Furthermore, the influence of oil property on the interfacial tension and oil displacement effect are studied. Results indicates that, according to the theory that similarities can be solvable easily in each other, the surfactant is likely to enter the crude oil with more heavy components. And thus few of them adsorb at the oil-water interface and the activity reduces. As a result, the interfacial tension increases, which causes the oil displacement effect to become worse.

Comparative study on the structures and properties of organo-montmorillonite and organo-palygorskite in oil-based drilling fluids

Abstract This work aims to reveal the differences of structures and properties between organo-montmorillonite (OMt) and organo-palygorskite (OPal) in oil-based drilling fluids. Organoclays are prepared in aqueous solution and characterized by XRD, SEM and TEM. Surfactants can intercalate into the interlayer space of Mt while they coat only on the palygorskite surface. OMt can form “house of cards” structure while OPal forms “haystack” structure. Temperature rising promotes network structure and rheological properties of organoclays in oil. The decline of rheological properties at high temperature is mainly caused by the dissolution of surfactants into oil, instead of thermal decomposition.

Dissolution of surfactants in supercritical CO2 with co-solvents

The dissolution of surfactant-like compounds in supercritical CO2 in presence of co-solvents was investigated. The solubility measurement was conducted using a visualized PVT cell combined with UV spectrophotometer method at different pressures and 313K. The viscosity of mixtures of CO2 and co-solvents with or without dissolved surfactants was also measured at similar conditions using a capillary tube rheometer. Nonionic surfactants (N-NP-10c, branched alkylphenol ethoxylates and APG-1214, alkyl polyglucoside) and anionic surfactants (N-NP-15c-H, sulfonated alkylphenol ethoxylates) were studied, which are good CO2 foaming agents. Experimental results showed that increasing pressure and addition of co-solvents could effectively improve solubility of surfactants in supercritical CO2. The addition of ethanol as a co-solvent could increase N-NP-10c's solubility in CO2 from 0.15g (100g)−1 to 1.76g (100g)−1 (over 11 times). APG-1214 with a mixture of ethanol and ethylene glycol as co-solvents exhibited an immediate dissolution capability in CO2, and its solubility could reach up to 1.99g (100g)−1. The solubility of N-NP-15c-H in comparison with APG-1214 was relatively low, only 0.57g (100g)−1 was obtained with the same co-solvents and at similar conditions. The addition of ethanol into CO2 could slightly increase its viscosity, while the effect of ethylene glycol and surfactants was much higher than that of ethanol, which indicates that the dissolution of surfactants in CO2 with co-solvents involves complicated interactions between molecules.

Effect of protic ionic liquid and surfactant structure on partitioning of polyoxyethylene non-ionic surfactants.

The partitioning constants and Gibbs free energies of transfer of poly(oxyethylene) n-alkyl ethers between dodecane and the protic ionic liquids (ILs) ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) are determined. EAN and PAN have a sponge-like nanostructure that consists of interpenetrating charged and apolar domains. This study reveals that the ILs solvate the hydrophobic and hydrophilic parts of the amphiphiles differently. The ethoxy groups are dissolved in the polar region of both ILs by means of hydrogen bonds. The environment is remarkably water-like and, as in water, the solubility of the ethoxy groups in EAN decreases on warming, which underscores the critical role of the IL hydrogen-bond network for solubility. In contrast, amphiphile alkyl chains are not preferentially solvated by the charged or uncharged regions of the ILs. Rather, they experience an average IL composition and, as a result, partitioning from dodecane into the IL increases as the cation alkyl chain is lengthened from ethyl to propyl, because the IL apolar volume fraction increases. Together, these results show that surfactant dissolution in ILs is related to structural compatibility between the head or tail group and the IL nanostructure. Thus, these partitioning studies reveal parameters for the effective molecular design of surfactants in ILs.

Liposomes as Vehicles for Lutein: Preparation, Stability, Liposomal Membrane Dynamics, and Structure

Lutein was loaded into liposomes, and their stability against environmental stress was investigated. Subsequently, these findings were correlated with the interactions between lutein and lipid bilayer. Results showed that the liposomes with loaded lutein at concentrations of 1 and 2% remained stable during preparation, heating, storage, and surfactant dissolution. However, with further increase in the loading concentration to 5 and 10%, the stabilization role of lutein on membrane was not pronounced or even opposite. Membrane fluidity demonstrated that at 1 and 2%, lutein displayed less fluidizing properties both in the headgroup region and in the hydrophobic core of the liposome, whereas this effect was not significant at 5 and 10%. Raman spectra demonstrated that lutein incorporation greatly affected the lateral packing order between acyl chains and longitudinal packing order of lipid acyl chains. These results may guide the potential application of liposomes as carriers for lutein in nutraceuticals and functional foods.

A new approach to sample preparation for the determination of trace metals in petroleum source rocks

The dissolution and extraction of petroleum source rocks using a nonionic surfactant to determine their trace metal (V, Ni, Co, Mn, and Mo) content with the assistance of microwave irradiation were investigated and the conditions for obtaining the optimum yield were determined. A complementary microwave-assisted acid dissolution method was also optimized. The results showed that the temperature and time have significant effects on yields of the trace metals. Factors such as surfactant concentration and sample/solvent ratio had little influence on the digestion and extraction efficiencies for these metals. The optimum temperature for microwave-assisted nonionic surfactant dissolution of petroleum source rocks for trace metal determination was 200 °C and the best yields of the metals were obtained in 40 min. The optimum temperature and time for nonionic surfactant extraction of trace metals from petroleum source rocks were 90 °C and 45 min, respectively. The microwave-assisted acid digestion gave optimum yields of the trace metals in 70 min. The new nonionic surfactant digestion and extraction methods showed efficiencies comparable to those afforded by using the acid digestion method for three out of five elements determined in this study, although the recoveries of vanadium and manganese were relatively low, but the reduction of the digestion/extraction time and environmentally friendliness of the new nonionic surfactant based methods are clear advantages. The new method showed a very good reproducibility. The results of this study also show that the microwave-assisted nonionic surfactant digestion method is a good, efficient and better alternative green analytical preparatory technique for the determination of some trace metals in petroleum source rocks.

Dissolution of Lamellar Phases

Dissolution of surfactant liquid crystals is an important process both at the manufacturing stage of surfactant based formulated products and during their use. Dissipative particle dynamics simulations were employed to study the production of surfactant-oil-water systems under both temperature and water quenches. Upon the dissolution of a high concentration lamellar phase surfactant, wormlike micelles are formed, which differ from the spherical micelles produced at the same concentration with a temperature quench. The surfactant molecules have a tendency to remain within their initially formed lamellar phase sheets and just rearrange into wormlike micelles. When a hydrophobic additive (oil) is added to the initial system, longer cylindrical micelles are formed, with the creation of some spherical micelles under dissolution. These micelles detach from the long cylinders as a result of their natural oscillations.

Experimental study of surfactant transfer in fluid systems in microgravity conditions

The paper presents the results of the space experiment studying the process of surfactant dissolution from a binary fluid drop in microgravity conditions. The experiment was performed during the flight of the space satellite “Foton M-3” in September 2007. Investigation of the surfactant diffusion was made using a new original setup based on the interferometric method. The experimental cuvette represented a thin Hele-Shaw cell filled with water, which surrounded a drop in the form of a short liquid cylinder with a free lateral surface. The drop consisted of a binary mixture, in which one of the components was the surfactant easily dissolved in water. The use of interferometry made it possible to visualize and investigate evolution of the surfactant distributions and the flow structures in the drop and the surrounding liquid. The characteristic stages of the dissolution process were identified, and the rate of the concentration front propagation was defined. It was shown that in microgravity conditions the process of surfactant diffusion through the interface did not initiate an intensive solutal Marangoni convection as contrasted to the case of terrestrial simulation. The observed phenomenon has its origins in the long-lived fields of surfactant concentration formed near the interface due to the absence of the gravitational mechanisms of motion and large characteristic time of admixture diffusion which is hundreds of times longer than the time of thermal diffusion.

Preparation and Characterization of a Novel Organic–Inorganic Nanohybrid “Cerasome” Formed with a Liposomal Membrane and Silicate Surface

A novel class of organic-inorganic hybrids, the so-called cerasomes, which have a bilayer vesicular structure and a silicate surface, has been synthesized by combination of sol-gel reaction and self-assembly of organoalkoxysilanes with a molecular structure analogous to lipids. We have synthesized two cerasome-forming organoalkoxysilanes, N-[N-(3-triethoxysilyl)propylsuccinamoyl]dihexadecylamine (1) and N,N-dihexadecyl-N (alpha)-[6-[(3-triethoxysilyl)propyldimethylammonio]hexanoyl]glycinamide bromide (2), and investigated the synthetic conditions of the cerasomes and their structural characteristics. For the proamphiphilic 1, the cerasome was obtained under restricted pH conditions where acid-catalyzed hydrolysis of the triethoxysilyl moiety proceeded without disturbing the vesicle formation. In contrast, the amphiphilic 2, additionally having a hydrophilic quaternary ammonium group, formed stable dispersions of the cerasome in a wide pH range. The hydrolysis behavior of the triethoxysilyl groups was monitored by (1)H NMR spectroscopy. Morphology of the cerasomes having the liposomal vesicular structure was confirmed by TEM observations. Extent of the development of siloxane networks through condensation among the silanol groups on the cerasome surface was evaluated by using MALDI-TOF-MS spectrometry. Formation of oligomers of the cerasome-forming lipids in the vesicle was clearly confirmed. Due to the siloxane network formation, the cerasome showed remarkably high morphological stability compared with a reference liposome, as evaluated by surfactant dissolution measurements.

Nonlinear Spontaneous Oscillations at the Liquid/Liquid Interface Produced by Surfactant Dissolution in the Bulk Phase

The results of theoretical and experimental studies of spontaneous nonlinear oscillations produced at the liquid/liquid interface by surfactant transfer from a point source situated in one of the bulk phases are presented. The theoretical analysis is based on the direct numerical simulation of the system evolution. The experiments are performed for the heptane/water interface using middle-chain aliphatic alcohols as surfactants. The results for the oil/water interface are compared with the corresponding data obtained for the air/water interface. The presented results allow the conclusion that auto-oscillations at the air/liquid and liquid/liquid interfaces are governed by very similar mechanisms but their characteristics are strongly dependent on the properties of the two contacting media, in particular, on the surfactant partition coefficient.

Effects of Dissolved Gases in Surfactant Dissolution Media

Introduction Dissolved gases,with dissolved oxygen serving as the primary marker,have been widely documented to influence dissolution experiments. The dissolved gases can cause changes in the performance of the dissolution medium by changing pH,forming bubbles on the dosage form or altering the interaction of the medium and the active pharmaceutical ingredient [1]. Extensive studies have been performed examining appropriate techniques for the removal of dissolved gases from aqueous media which include a combination of heating and vacuum filtration followed by stirring under vacuum (USP method),vacuum filtration, heating alone,sonication,helium sparging,and membrane filtration [2-6]. Regardless of technique,reaeration of the media is a concern. Reaeration can be defined as the process of gases from the atmosphere dissolving into the liquid phase raising the level of dissolved gases. Studies have shown that regardless of technique used to remove dissolved gases,reaeration will occur,and the equilibrium dissolved oxygen value will be relatively unaffected [7]. The only influence the technique will have is the amount of dissolved gas removed,and the time it will take for the media to equilibrate to atmospheric conditions. Media that have reached equilibrium do not exhibit performance changes stemming from the technique used to remove the dissolved gases. While the effect of dissolved gases on aqueous media has been studied extensively,the effect on surfactant containing media has not been addressed directly. The USP General Chapter states,“dissolved gases can cause bubbles to form, which may change the results of the test. In such cases,dissolved gases should be removed prior to testing”[8]. This statement does not specify type of media,but suggests that if dissolved gases do not affect the results,the level of dissolved gases can be largely ignored. This study investigates whether the level of dissolved gases is a source of variability that should be monitored when performing dissolution tests that utilize a surfactant-containing medium by examining the dissolution performance of oral dosage forms in media with a range of dissolved oxygen levels. Furthermore,the USP method of dissolved gases removal along with other accepted methods will be examined to determine their influence on equilibrium values of dissolved gases.

The physics of surfactant dissolution.

We have examined the early stages of surfactant dissolution and mesophase formation using a dimer-solvent model with phase behaviour representative of surfactant-water systems. We use an orientational order parameter to characterize systematically the appearance of mesophases. We find the process is diffusion controlled, and the appearance of mesophases is governed adiabatically by the equilibrium phase diagram from the earliest point at which the orientational order parameter can reliably distinguish between mesophases, when only a few repeat spacings of the mesophase microstructures are present. In real systems, such a stage would correspond to times of the order of a few microseconds after the initial contact.

Behavior of a Rising Bubble in Water with Surfactant Dissolution (1st Report, Steady Behavior)

It is well-known that a rising velocity of a nearly spherical bubble in contaminated liquid is much smaller than that of a bubble in a pure liquid and is almost the same as that of a solid particle. This phenomenon is explained by Marangoni Effect due to the variation of surface tension along the bubble surface. In the present study, this effect is analyzed both experimentally and numerically. The experiments are conducted with superpurified water. The effect of molecular structure difference is studied, using 1-pentanol, 3-pentanol and Triton X-100 as a surfactant. Although 1-pentanol and 3-pentanol have the same molecular weight, bubble behaviors with 1-pentanol solution is different from those with the 3-pentanol, due to the different characteristic of adsorption and desorption kinetics. Because the adsorption/desorption ratio is large, Triton X-100 has much stronger effect of reducing the rising velocity than pentanols under the same amount of concentration. The numerical simulations are also conducted for the motion of a single spherical bubble in water with surfactant dissolution, using a boundary-fitted grid. The results show good agreement with those of experiment and the drag coefficient varied gradually from that of purified liquid to that of solid sphere, with the slight increase of the surfactant amount.

Surfactant dissolution and mobilization of LNAPL contaminants in aquifers.

Improper disposal, accidental spills and leaks of non-aqueous phase liquids (NAPL) such as gasoline, fuel oil and creosote result in long-term persistent sources of groundwater pollution. Column and 2-D tanks experiments were conducted to evaluate the use of surfactant-enhanced recovery of light non-aqueous phase liquids (LNAPL) in groundwater aquifers. These experiments focused on the use of surfactants to promote dissolution and mobilization in addition to evaluating the increase of aqueous phase permeability as residual NAPL is recovered. Further experiments are presented that show the innovative use of surfactants during primary pumping to recover free product can potentially increase the amount of free product recovered, can potentially reduce the amount of residual NAPL remaining after primary pumping and performs better than the use of surfactants to mobilize trapped residual NAPL.

Spreading of Aqueous Trisiloxane Surfactant Solutions over Liquid Hydrophobic Substrates

Systematic studies of trisiloxane surfactant aqueous solutions spreading over hydrophobic liquids are performed by videomicroscopy. Three trisiloxane nonionic surfactants M(D‘E n)M with different ethoxy-chain lengths are investigated. In addition to surfactant concentration, the spreading rate strongly depends on surfactant solubility in the organic liquid substrate, even when the initial spreading coefficient is essentially constant. In contrast to previously studied DDAB solutions' spreading (Svitova, T.; Hill, R.; Radke, C. Langmuir 1999, 15 (21), 7392), two different spreading regimes are found. At relatively low surfactant concentrations, the spreading rate is limited by surfactant mass transport toward stretching interfaces, as in the case of DDAB solutions. At concentrations greater than 0.5 wt %, however, the maximum rate increases to a level for which viscous dissipation by the substrate starts to play an important role, along with surfactant mass transport limitations. For all liquid substrates studied, the spreading lenses of the trisiloxane surfactant solutions retract after a maximum area is reached because of surfactant dissolution into the oil phase. Intensive surfactant dissolution into the substrate leads to fast lens retraction, and it overrides the gain due to less viscous drag when the substrate liquid is of lower viscosity. The presence of surface concentration gradients and the resulting Marangoni flow is established by monitoring the movement of Teflon particles at the upper surface of the spreading lens.

Dynamics of Interface Instabilities in Nonionic Lamellar Phases

The swelling and dissolution dynamics of a soluble (small miscibility gap) and an insoluble (large miscibility gap) lamellar phase (Lα) of nonionic surfactant in water have been qualitatively and quantitatively investigated. In the case of an insoluble Lα, we observe classical myelinic instabilities at the interface. (These are absent in the soluble case.) By doping the excess water phase with colloidal tracer particles, we show that water enters at the roots, rather than through the walls, of the myelins. We estimate the mean water flux and find it to be consistent with this picture. We also study the interface between a lamellar phase and pure surfactant liquid (L2). At this interface we observe a new dynamic instability in which “onion jets” appear to be ejected from Lα into L2, where they disappear. Closer investigation shows these onions to be focal conic II defects residing near the surface of a wedge of homeotropic Lα, which is in contact with the wall of the sample holder. The defects move much faster than the wedge. We offer some theoretical discussion of how these observations shed light on the mechanism of interfacial instabilities, particularly myelin formation, in surfactant dissolution.