Adsorption Of Gemini Surfactants Research Articles

Adsorption dynamics of quaternary-ammonium-salt–based gemini and trimeric surfactants with different spacer structures at air/water interface

The dynamic surface tensions of gemini surfactants with spacers containing cyclic structures such as diethylene and triethylene chains, and atoms such as oxygen and nitrogen, and of linear- and star-type trimeric surfactants with spacers having propylene or hexylene chains between the quaternary ammonium groups (for the linear-type) and propylene or hexylene chains between the quaternary ammonium group and the central amino group (for the star-type) were measured using the maximum bubble pressure method. The effects of the molecular structures and surfactant concentration on the maximum rate of reduction in the surface tension as well as the diffusion coefficient were elucidated. The gemini surfactants containing cyclic structures in the spacer exhibited slower interfacial adsorption, which was ascribed to their rigid spacer structure. The longer the spacer chain length of the gemini surfactants, the greater the molecular flexibility and hence the faster the adsorption at the interface. Thus, the diffusion and adsorption of gemini surfactants are affected by the rigidity and hydrophobicity of the spacer, respectively. However, the adsorption of the trimeric surfactants at the air/water interface (which resulted in a maximum rate of reduction in the surface tension of 0.0007–0.004 mN m–1 s–1) was lower than that of the gemini surfactants (which resulted in a maximum rate of reduction in the surface tension of 0.0009–0.9 mN m–1 s–1). This was ascribed to the greater bulkiness of trimeric structures compared with those of the gemini surfactants. The star-type trimeric surfactants adsorbed faster at the air/water interface than the linear-type trimeric surfactants because the former were flexible despite their bulky spacer structure. For the linear- and star-type trimeric structures, the diffusion rate increased with the spacer chain length because of the resulting increase in the molecular flexibility. The linear-type surfactants were adsorbed faster at the air/water interface as their spacer chain length was increased, whereas the star-type surfactants were adsorbed more slowly because of their molecular bulkiness.

Study on Adsorption Behavior of a New Type Gemini Surfactant Onto Quartz Surface by a Molecular Dynamics Method

The adsorption mechanism of the branched quaternary ammonium salt Gemini surfactant (Gemini C3) at the water-surfactant-quartz interfaces for both neutral and negatively charged quartz surfaces was studied by a molecular dynamics (MD) method. Initial and final configurations, distributions of the surfactant and its interaction with surfaces, the radial distribution function (RDF) of water molecules, and the mean square displacement (MSD) of the surfactant in bulk phase have been elucidated at the molecular level. The results showed that the adsorption of Gemini surfactants onto the hydrophilic quartz surface was driven by electrostatic interaction, which increased the hydrophobicity of the solid surface when the surfactant concentration was lower than critical micelle concentration (CMC). However, the contact angle only slightly increased since the surface tension decreased simultaneously with growing concentration. Monolayers were formed during the adsorption process of Gemini C3 molecules on the quartz surface rather than a double layer when the concentration reached the CMC, indicating a gradual transformation of an extended monolayer adsorption configuration into a more compact one. The solid-liquid interfacial tension increased with the surfactant concentration and led to a significant increase of the contact angle. The simulation results were consistent with the experiments, which further revealed the microscopic adsorption mechanism of the Gemini C3 surfactant onto the quartz surface, and provided theoretical guidance for controlling the wetting properties and surface modification of the rock.

A Promising Surfactant for Enhanced Sorption and Desorption of Polycyclic Aromatic Hydrocarbons

Gemini surfactants, an innovative class of amphiphilic molecules, are of increasingly scientific interest due in part to their effectiveness in soil/water remediation. This study was carried out to investigate the overall partitioning of three representative polycyclic aromatic hydrocarbons (PAHs) in the soil-water–surfactant system which takes into consideration the soil-sorbed cationic Gemini surfactant, presence of Gemini micelles, and related developed coefficients. The results indicated that the adsorption of Gemini surfactants onto soil particles through both cation exchange and hydrophobic interaction contribute to the bi or multilayer formation. The sorbed C12–3–12 studied herein, is a highly effective partitioning media for PAHs to adsorb onto the soil phase from the aqueous phase and thus, can be considered as a good adjuvant for an enhanced sorption zone. The partitioning behavior of PAHs in the soil–water–Gemini surfactant has a strong relationship with their Kow. The experimental results from...

Adsorption of gemini surfactants at the air-water surface

We have studied the behavior of a gemini surfactant, the double chained dodecyl ammonium bromide or 12-2-12, at the surface of aqueous solutions and at room temperature. We have measured the kinetics of adsorption and the equilibrium surface tension. The surfactant has been obtained through a new synthesis method, which has the advantages of being simpler than previous ones and resulting in a product with good purity after the first crystallization. In the absence of salt, 12-2-12 behaves like other charged surfactants. The adsorption is initially diffusion limited, but as adsorption proceeds, and the surface concentration increases, the surface potential reaches large values (of around 200 mV) slowing down considerably the adsorption process. The observations are in line with existing models. The sensitivity of the gemini surfactants to salt is greater than that of single-chain surfactants, owing to their peculiar molecular structure. For single-chain nonionic surfactants or ionic surfactants, adsorption can be described by diffusion limited models. The behavior of 12-2-12 in salt solutions is very different. The very early stages of adsorption are diffusion limited, but very quickly, the behavior changes and strong deviations are observed. Such a behavior could be due to a desorption barrier, the origin of which remains to be elucidated.

Alkanediyl-α, ω-bis (dimethyl cetylammonium bromide) gemini surfactants as novel corrosion inhibitors for mild steel in formic acid

Gemini surfactants, butanediyl 1,4-bis(dimethyl cetylammonium bromide), pentanediyl 1,5 - bis (dimethyl cetylammonium bromide) and hexanediyl 1,6 - bis (dimethyl cetylammonium bromide) from Alkanediyl-α, ω-bis (dimethyl cetylammonium bromide) series were synthesized in laboratory and were characterized by using Nuclear Magnetic Resonance (NMR) spectroscopy. The surfactants were tested as corrosion inhibitors for mild steel in 20% formic acid. The influence of surfactants on mild steel corrosion inhibition was investigated by measuring the corrosion rate of mild steel in their absence and presence by weight loss measurements, solvent analysis of iron ions into the test solution and potentiodynamic polarization measurements. The surface morphology of the corroded steel samples in presence and absence of surfactants was evaluated by using Scanning Electron Microscopy (SEM). The synthesized gemini surfactants performed as excellent corrosion inhibitor, the inhibition efficiency (IE) being in the range of 76.66-97.41%. The IE of surfactants is slightly affected by the spacer length. The IE increased with increase in surfactant concentration and temperature. The adsorption of gemini surfactants on the steel surface was found to obey Langmuir adsorption isotherm. The results of the potentiodynamic polarization studies are consistent with the results of weight loss studies.

Adsorption and corrosion inhibitive properties of gemini surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl ammonium bromide) on aluminium in hydrochloric acid solution

Four new quaternary ammonium gemini surfactants in the series of hexanediyl-1,6-bis-(diethyl alkyl ammonium bromide), referred as C m C 6C m (Et)·2Br ( m = 10, 12, 14, 16), were synthesized and tested as corrosion inhibitors of aluminium in 1 mol/L HCl solution at 25 °C using gravimetric, gasometric measurements and SEM techniques. Results obtained show that the surfactants studied are efficient corrosion inhibitors for aluminium in hydrochloric acid solution. The inhibition efficiencies of C m C 6C m (Et)·2Br increase with the surfactant concentrations, and the good inhibiton efficiencies are reached near their critical micelle concentrations. In addition, the inhibition efficiency for aluminium slightly increases with increasing surfactant chain length ( m) at the same concentration since the adsorption capacity of C m C 6C m (Et)·2Br is increased with m. These gemini surfactant inhibitors adsorb at the aluminium/solution interface according the Langmuir adsorption isotherm. Thermodynamic parameters of adsorption ( b, Δ G ads) of C m C 6C m (Et)·2Br were determined and the inhibition mechanism has been discussed. The adsorption of gemini surfactants C m C 6C m (Et)·2Br at the aluminium/solution interface can be considered as a cooperative adsorption and the high absolute values of Δ G ads could be attributed to the high adsorption ability of the gemini surfactant molecules on the aluminium surface, forming a strong protective film by the synergistic effect between bromide anions and positive quaternary ammonium ions. On the basis of the variation of surface coverage rates ( θ) with the surfactant concentrations, the adsorption modes of the gemini surfactants C m C 6C m (Et)·2Br at the aluminium/solution interface were proposed.

Adsorption of Gemini Surfactants with Dodecyl Side Chains and Different Spacers, Including Partially Fluorinated Spacers, on Different Surfaces: Neutron Reflectometry Results

Neutron reflectometry has been used to study the adsorption of two symmetrical cationic (dimethyl ammonium bromide) gemini surfactants with two C(12)H(25) chains and different partially fluorinated spacers at three different surfaces: air/water, hydrophilic silica/water, and hydrophobic (octadecyltricholorosilane (OTS))/water. In addition, the adsorption of purely hydrocarbon geminis with the same side chains and spacers of different lengths has been studied at the same two solid surfaces. The limiting close-packed areas for the two fluorocarbon geminis, C(12)-C(3)fC(6)C(3)-C(12) and C(12)-C(4)fC(4)C(4)-C(12), are 92 and 72 ± 4 at the hydrophilic silica surface, 81 and 89 ± 4 at OTS, and 137 and 106 ± 4 Å(2) at the air/water interface with decreases of 38 and 24% from air/water to the average solid value, respectively. These changes suggest that the packing at the air/water interface is inefficient, and this allows the extra hydrophobicity of the chain environment at the two solid surfaces to promote much more efficient packing. At the air/water interface, the fluorocarbon spacers are on average the fragments furthest away from the underlying water, further out than in the nearest comparable hydrocarbon gemini, C(12)-C(12)-C(12). This is the probable explanation of the much lower value of the area per molecule at the air/water interface of C(12)-C(4)fC(4)C(4)-C(12) compared to that of C(12)-C(12)-C(12). It is also the probable cause of the inefficient packing of the hydrocarbon side chains. At the more hydrophobic OTS surface the situation is reversed and the fluorocarbon spacers are now the furthest from the hydrophobic surface, further out than the spacer in C(12)-C(12)-C(12). This is an unusually large structural change that must be associated with the greatly improved packing at the OTS surface. The efficiency of the packing is also high for the hydrophilic surface, no doubt because the hydrocarbon chains can interact favorably in the adsorbed bilayer core. The values of the area per molecule obtained for the series of hydrocarbon geminis at the air/water, OTS/water and silica/water interfaces are respectively 139, 104, and 98 ± 4 Å(2) for C(12)-C(12)-C(12), 114, 106, and 94 ± 4 Å(2) for C(12)-C(10)-C(12), 104, 84, and 85 ± 4 Å(2) for C(12)-C(6)-C(12), and 78, 66, and 70 ± 3 Å(2) for C(12)-C(3)-C(12). The area per molecule is also about 20% less on average at the two solid surfaces than at the air/water interface. This can also be attributed to more efficient packing caused by the more favorable hydrophobic interactions possible at these two surfaces than at the air/water interface, again showing that the packing at the air/water interface is inefficient and probably resulting from the competition between spacer and chains, which will be most pronounced for the C(12) spacer.

Adsorption of Gemini Surfactants with Partially Fluorinated Chains at Three Different Surfaces: Neutron Reflectometry Results

The adsorption of six symmetrical cationic (dimethylammonium bromide) gemini surfactants with four different partially fluorinated chains at three different surfaces--the air/water, the hydrophilic silica/water, and the hydrophobic (octadecyltricholorosilane (OTS))/water--has been investigated by neutron reflectometry. The corresponding single chain trimethylammonium bromides have also been studied at the two solid surfaces. Four of the geminis with a C(6) spacer and chains with differing amounts of fluorocarbon have identical limiting areas per molecule at the air/water interface (106 ± 5 Å(2)). This is similar to the value for the corresponding hydrocarbon gemini with a C(6) spacer and C(12) side chains, but unlike the hydrocarbon gemini, it is significantly more than twice the area per molecule of the corresponding single chain cationic. In adsorbed aggregates on hydrophilic silica the area per molecule decreases from the air/water value by an average of about 25%, indicating a substantial improvement in the packing of these geminis in the aggregate, which can be attributed to the stronger interaction between the hydrophobic chains in the interior of the aggregates. On the hydrophobic OTS surface the area per molecule in the adsorbed monolayer for three partially fluorinated geminis decreased by about 15% from the air/water value, again indicating much more favorable packing next to the hydrophobic OTS, but for one of the geminis, fC(8)C(6)-C(6)-C(6)fC(8), the change in area was reversed. This reversal is accompanied by a marked thinning of the layer, which is attributed to a shift in the balance between the interactions of the hydrocarbon spacer and fluorocarbon chain fragments and the OTS surface.

Adsorption of conventional and gemini cationic surfactants in nonswelling and swelling layer silicate

The adsorption of conventional (cetyltrimethylammonium bromide) and its corresponding gemini cationic surfactant [ethanediyl-α,β-bis(cetyldimethylammonium bromide)] in both swelling (montmorillonite) and nonswelling (kaolinite) layer silicates was investigated by adsorption isotherms and X-ray diffraction techniques. Adsorption studies showed that the adsorption of gemini surfactant was more efficient than that of the corresponding conventional surfactant on both kaolinite and montmorillonite. The adsorption amount of both surfactants on montmorillonite was much higher than on kaolinite, which was related to the nature of the clays. Although the molar adsorption amount of both surfactants on the same clay were almost identical, there existed some differences in the microstructure of adsorption layer revealed by X-ray diffraction experiments.

Understanding the effect of the spacer length on adsorption of gemini surfactants onto steel surface in acid medium

Corrosion inhibition of carbon steel in 1 M hydrochloride acid by gemini surfactants alkanediyl-α,ω-bis(dimethyl dodecylammonium bromide) with different spacer lengths (designated as 12- s-12, s = 2, 3 or 6) was studied using the weight loss method. When monolayer forms on the metal surface below or near critical micelle concentrations (CMCs) of the gemini surfactants, it can be found that gemini surfactant with long spacer (12-6-12) tends to be adsorbed with two hydrophilic ionic groups onto the metal surface site, while gemini surfactants with short spacer (12-2-12 and 12-3-12) tend to be adsorbed with one hydrophilic group onto the meta surface site and the other hydrophilic group is free in solution phase, and further increase in surfactant concentration results in the formation of multilayer. Possible adsorption mechanisms of these gemini surfactants with different spacer lengths above and below their CMCs were discussed in detail, respectively.

The adsorption and corrosion inhibition of some cationic gemini surfactants on carbon steel surface in hydrochloric acid

The adsorption and corrosion inhibition of the gemini surfactants 1,2-ethane bis(dimethyl alkyl (C n H 2 n+1 ) ammonium bromide) (designated as n−2− n, n=10, 12 and 16) on the steel surface in 1 M hydrochloride acid were studied using the weight loss method. It was found that the adsorption of the gemini surfactants on the steel surface is the main reason to cause the steel corrosion inhibition in hydrochloride acid, and the inhibition efficiency increases with the increase of surfactant concentration and reaches the maximum value near the CMC. A possible adsorption model of gemini surfactant onto the metal surface was also discussed.