Adsorption Properties Of Surfactants Research Articles

New Insights into Surfactant Adsorption Estimation in Carbonates under Harsh Conditions Using Surface Complexation Modeling

Summary Several laboratory experiments demonstrated that the use of sodium hydroxide could increase the solution pH and reduce the adsorption of anionic surfactants. However, a better understanding of rock-oil-brine interactions and their effect on surfactant adsorption during alkaline-surfactantpolymer (ASP) flooding is needed for realistic and representative estimations of surfactant adsorption levels. Therefore, this study presents a novel approach to capture these interactions and better predict their effect on surfactant adsorption as well as effluent concentrations of surfactant and various aqueous species using the Phreeqc simulator. Currently, surface complexation models (SCMs) consider rock-brine, oil-brine, and surfactant-brine reactions. In this work, four new surface complexation reactions with intrinsic stability constants that honor oil-surfactant interactions have been proposed for the first time and then validated against experimental data reported in the literature. In addition, we analyzed the effect of various parameters on surface adsorption under harsh conditions of high temperature and high salinity using the proposed SCM. The results showed that the developed surfactant-based SCM is capable of estimating surfactant adsorption and its concentration in the effluent during chemical floods. The model was validated against two sets of ASP corefloods from the literature including single-phase and two-phase dynamic surfactant adsorption studies. The findings highlighted that oil-surfactant surface complexation reactions are important and should be captured for a more representative and accurate estimation of surfactant adsorption during chemical flooding. Moreover, the detailed and comprehensive analysis showed that surfactant adsorption increased and its concentration in the effluent decreased with the increase in temperature of the chemical flood. The latter shows that the adsorption process is endothermic and it is more of chemisorption as opposed to physio-adsorption. It was also showed that a decrease in water total salinity decreases the surfactant adsorption on the rock surface, which is related to the increase in the repulsive forces between the rock surface and adsorbed species. Additionally, with the increase in surfactant concentration in the chemical flood, surfactant concentration in the effluent increases, with a slight increase in surfactant adsorption. This slight increase in adsorption can be neglected compared with the injected and produced masses of the surfactant that are proportional. Moreover, the effect of sulfate spiking is significant where the increase in sulfate concentration reduces the surfactant adsorption. Furthermore, it is worth highlighting that the lowest surfactant adsorption levels were achieved through injected water dilution; less than 0.1 mg/g of rock. This is the first study to test a novel formulation of SCM considering the oil-surfactant effect on surfactant adsorption properties. The proposed framework to estimate surfactant adsorption is conducted for high-temperature and high-salinity reservoir conditions. Thus, it could be used in numerical reservoir simulators to estimate oil recovery due to wettability alteration by chemical flooding in carbonates, which will be investigated in our future work. The surfactant adsorption mechanisms during chemical flooding are very case-dependent and hence, the findings of this study cannot be generalized.

The Influence of Monolayer Morphology and Dynamics on Lung Stability

For the past 100 years, surfactant monolayers have been studied on the planar interface of Langmuir trough, even though most physiological interfaces are curved at the micron to millimeter scale. Here we show that as a lung surfactant monolayer-covered bubble approaches a critical radius, the equilibrium morphology changes from dispersed circular solid domains in a continuous liquid to a continuous solid phase linear mesh separating discontinuous liquid phase domains. Monolayer dynamics and surfactant adsorption properties are also strongly influenced by the interfacial curvature. The phase morphology transition phenomena cannot be readily explained by current theories based on isotropic domains but rather on the anisotropic properties of the semi-crystalline solid phase. The changes in morphology and dynamics may have important physiological consequences for lung stability and function as the morphological transition occurs at alveolar dimensions. The anisotropy of the condensed-phase monolayers of the primary lipid component of lung surfactant, dipalmitoylphosphatidylcholine, DPPC is shown in its rheological properties that differ between monolayers sheared clockwise (C) or counter-clockwise (CC). The nonlinear elastic modulus and yield stress of R-DPPC monolayers are greater when sheared clockwise, i.e. against the natural CC winding of individual DPPC domains than when sheared counter-clockwise. These differences disappear for racemic mixtures. Direct visualization of the deforming domains shows a different evolution of defect structures for shear in the C or CC directions. We argue that the coupling between the tilt grain boundaries and applied shear can give rise to the chiral rheology we observed. The long-time, macroscopic consequences of the underlying molecular chirality are remarkable given the single-component, non-cross-linked nature of DPPC monolayers.

Electrostatic binding of oppositely charged surfactants to spherical polyelectrolyte brushes

We use Brownian dynamics (BD) simulations to investigate the formation and structural characteristics of the complex between a spherical polyelectrolyte brush (SPB) and oppositely charged surfactants. Increasing the amount of added surfactants leads to a collapsed conformation of the SPB and the number of adsorbed surfactants exhibits a linear dependence. Nevertheless, the surfactant uptake into the SPB does not increase with further addition of surfactants. It is found that the surfactant length has a strong influence on the SPB conformation and the adsorption properties of surfactant. Upon changing the surfactant length from 3 to 11, the SPB undergoes a swelling-deswelling-reswelling conformational transition. The brush deswelling is due to the increase in the surfactant uptake. The increasing size of adsorbed aggregates is a main reason for reswelling of the SPB. A non-linear relationship between the brush thickness and the grafting density is observed. Especially at intermediate grafting densities, increasing the number of grafted chains has a weak effect on the brush thickness. We also find that a completely collapsed brush conformation occurs at high surfactant/SPB charge ratios or large surfactant lengths, while the brush layer is in a partly collapsed or extended state at an intermediate charge ratio and surfactant length.

Advancement of high power ultrasound technology for the destruction of surface active waterborne contaminants

The current paper explores recent advances in sonochemical techniques to improve the ultrasound-mediated degradation efficiency of surface active, waterborne contaminants. Sonochemical degradation efficiency of surface active contaminants generally has a strong dependence on the concentration of contaminant at the gas/solution surface of cavitation bubbles. This in turn depends on the thermodynamic and diffusion/kinetic-controlled adsorption properties of the surfactant at the rapidly pulsating gas/solution surface of acoustic cavitation bubbles. The adsorption properties of surfactants can be exploited to enhance their sonochemical decomposition by varying ultrasound exposure parameters such that changes in the nature of the bubble population (especially the bubble life-time and rate of pulsations) cause changes in the amount of surfactant that adsorbs to the gas/solution interface of cavitation bubbles. Herein we describe recent results on the effect of ultrasound frequency and pulsing mode on sonochemical degradation of surfactants in aqueous solutions and show how the exposure parameters can be adjusted in ways to produce more efficient decomposition of contaminants, even under exposure conditions where seemingly poor sonochemical activity is detected in the bulk solution. The relevance of these results to scale-up of ultrasound decontamination processes is discussed.

Surfactant and Protein Interactions on Wettability Gradient Surfaces

Surfaces with a gradient in wettability were made by diffusion of dichlorodimethylsilane along silicon dioxide surfaces. Interaction of surfactants and fibrinogen was then studied at the solid/liquid interface with the use of ellipsometry. Adsorption properties of surfactants like cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and pentaethyleneglycol mono n-dodecyl ether (C 12E 5) were investigated at different pH. All of the surfactants adsorbed at the hydrophobic (SiCH 3) part of the gradient and the adsorption was found to be essentially independent of pH in solution. At the hydrophilic (SiOH) part, on the other hand, adsorption was strongly influenced by pH, in a way that partly can be explained by electrostatic attraction or repulsion between the surfactants and the surface. In addition, there were also effects within the gradient region that provide new information about the role of the chemical groups on the solid surface and their interactions with surfactants. All surfactant adsorption was reversible upon rinsing with distilled water. A variety of detergents were used to desorb fibrinogen adsorbed to the gradient surfaces. All the surfactants were effective in desorbing proteins from the far hydrophobic part of the gradient, probably through competition with the protein on the surface. There were also transient effects of desorption in the gradient region as well as desorption effects at the hydrophilic part of the gradient that can mainly be explained in terms of interactions between the surfactants and the proteins.

Effect of new surfactants on zinc extraction with liquid surfactant membranes

Using newly synthesized surfactants, extraction of zinc ion with liquid surfactant membranes (LSMs) containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester ( PC-88A) as a carrier was carried out in a stirred cell. The adsorption properties of surfactants were clarified and the effects of new surfactants on zinc extraction by LSMs were studied. New surfactants having two oleyl chains form stable emulsions in an even lower concentration range than the commercial surfactants. The extraction rate of zinc by LSMs was explained by an interfacial reaction model between the carrier and zinc ion taking into account the adsorption of a surfactant at the interface. Additionally, it is found that the new cationic surfactants appeared to accelerate the extraction rate due to an electrostatic interaction with the carrier.