Mixed Adsorbed Films Research Articles

Interaction of novel anionic gemini surfactants with cetyltrimethylammonium bromide

This study describes the synthesis of three novel anionic gemini surfactants via a convenient and easily controllable method, sodium 2,2′-(6,6′-(ethane-1,2-diylbis(azanediyl) bis(4-(octylamino)-1,3,5-triazine -6,2-diyl) bis(azanediyl)diethanesulfonate (C 8-2-C 8), sodium 2,2′-(6,6′-(propane-1,3-diylbis(azanediyl) bis(4-(octylamino)-1,3,5-triazine-6,2-diyl) bis(azanediyl)diethanesulfonate (C 8-3-C 8), sodium 2,2′-(6,6′-(butane-1,4-diylbis(azanediyl) bis(4-(octylamino)-1,3,5-triazine-6,2-diyl) bis(azanediyl)diethanesulfonate (C 8-4-C 8). The interactions of these new anionic gemini surfactants with the conventional cationic cetyltrimethylammonium bromide (CTAB) are investigated in 0.1 mol/L NaCl aqueous solutions. The mixed systems are C 8-2-C 8/CTAB, C 8-3-C 8/CTAB, and C 8-4-C 8/CTAB, and the mole factions ( α G ) of C 8- n-C 8 ( n = 2, 3, 4) were 0.5, 0.7, and 0.9 respectively. These mixtures exhibit synergism in both surface tension reduction effectiveness and surface tension reduction efficiency. When α G = 0.5 the three systems exhibit synergism in mixed micelle formation, whereas the other surfactant mixtures do not show this synergism. The interactions in mixed adsorbed films are stronger than those involved in mixed micelles for all mixtures.

The characterisation of polygalacturonic acid-based layer-by-layer deposited films using a quartz crystal microbalance with dissipation monitoring, a dual polarization interferometer and a Fourier-transform infrared spectrometer in attenuated total reflectance mode

The rational design of layer-by-layer deposited biopolymer films is underpinned by measurements of their growth characteristics and functional properties. In this study we compare measurements of the hydrated mass, polymer mass and concentration, density and composition of the films measured using a quartz crystal microbalance with dissipation monitoring (QCMD), a dual polarization interferometer (DPI) and a Fourier-transform infrared spectrometer in attenuated total reflectance mode (FTIR-ATR). The biopolyanion used for the deposition was polygalacturonic acid (PGA) and the biopolycations were poly-L-lysine (PLL), chitosan (Chi) and lysozyme (Lys). A 10 step deposition of PGA–PLL and PGA–Chi from 10 mM pH 7.0 phosphate buffer with 30 mM NaCl led to 18.3 nm and 32 nm thick multilayer films, respectively, and the PGA–Lys deposition to a 3.2 nm thick mixed adsorbed film. The PGA–PLL multilayer assembled with a relatively small polycation showed exponential growth and QCMD showed its material properties remained constant during assembly. The PGA–Chi multilayer also showed exponential growth and, despite some stripping of Chi when PGA was deposited, grew more rapidly than the PGA–PLL multilayer. The QCMD showed that the multilayer was more viscous when the Chi was uppermost and more elastic when PGA was uppermost. The PGA–Lys deposition showed a cyclical behaviour corresponding to repeated deposition and stripping with little net growth after the first 3–4 deposition cycles. Further analysis of the PGA–Chi acoustic and optical hydrated mass measurements suggested that the refractive index of the film was relatively high in the region close to the adsorbing surface, and an extensive lower refractive index region stretched out from the surface. The polymer mass measured by FTIR-ATR was up to 1.5 times greater than that measured by DPI, a discrepancy which could be explained in terms of the known sensitivity of the FTIR-ATR amide I band to conformational changes of these polycations which change upon deposition. The strength of the FTIR-ATR method was that it yielded film compositions which indicated that the polymers in the multilayer films carried an excess of negative charge, evidence for extrinsic charge balance within the multilayer films.

水性２成分混合の界面活性剤系に関する最近の研究の総覧

Recent studies on mixed surfactant systems were systematically overviewed, paying special attention to synergism observed in micellization as well as adsorbed film formation upon mixing of a few nonionic surfactants with a variety of surfactants (such as anionics including bile salts and a hybrid type surfactant, cationics including a Gemini type surfactant, different types of nonionics and a zwitterionic surfactant used as a membrane solubilizer) in addition to various combinations of anionics. Through the text, it was shown for each given binary mixed system composed of surfactants 1 and 2 how to estimate not only the composition of mixed micelles (Y(2)) equilibrated with singly dispersed surfactant species in bulk solution phase, where the mole fraction of 2 in the surfactant mixture is denoted as X(2), but also the composition of adsorbed film phase (Z(2)). Almost all combinations were discussed in terms of the respective interaction parameters, omega(R) and omega(A), in mixed micelles (3-D phase) and in mixed adsorbed film (2-D phase), respectively, surface excess concentration (Gamma), partial molecular area (PMA), minimum surface Gibbs energy (G(s)min), and such defined measures as pC(20), CMC/C(20) etc. for evaluation of synergism.

Structure and Composition of Cationic−Nonionic Surfactant Mixed Adsorbed Layers on Mica

The composition and morphology of mixed adsorbed layers comprising one of several poly(oxyethylene) alkyl ether nonionic surfactants, C(i)E(j), and two cationic surfactants-dodecyltrimethylammonium bromide (DTAB) and tetradecyltriethylammonium bromide (TTeAB)-at the mica/solution interface have been studied using depletion adsorption and atomic force microscopy. The nonionic surfactants do not themselves adsorb onto mica, but can coadsorb with a cationic surfactant. The extent of their hydrophobic association with the adsorbed cationic surfactant depends on alkyl chain length, while the adsorbed layer morphologies are sensitive to the number of ethoxy groups. Nonionic surfactants with headgroups containing less than eight ethylene oxide units decrease the adsorbed aggregate curvature, gradually transforming globular TTeAB or cylindrical DTAB adsorbed aggregates into a rod, mesh, or bilayer structure. Those with larger headgroups favor globular aggregates. The mechanism by which the nonionic surfactant modifies the adsorbed morphology is the formation of defects in the form of cylinder end-caps or branch-points, leading to adsorbed layer compositions that differ from ideal mixing predictions. All mixed adsorbed films become saturated with the nonionic component when the capacity of the aqueous side of the adsorbed layer is reached.

Surface properties of mixtures of surface-active sugar derivatives with ionic surfactants: Theoretical and experimental investigations

Surface properties of systems that are mixtures of ionic surfactants and sugar derivatives—anionic surfactant sodium dodecyl sulfate and n-dodecyl- β-D-maltoside (SDS/DM) and cationic surfactant dodecyltrimethylammonium bromide and n-dodecyl- β-D-glucoside (DTABr/DG)—were investigated. The experimental results obtained from measurements of surface tension of mixtures with various ratio of ionic to nonionic components were analyzed by two independent theories. First is Motomura theory, derived from the Gibbs–Duhem equation, allowing for indirect evaluation of the composition of mixed monolayers and the Gibbs energies of adsorption, corresponding to mutual interaction between surfactants in mixed adsorbed film. As second theory we used our newly developed theoretical model of adsorption of ionic–nonionic surfactant mixtures. Using this approach, we were able to describe the experimental surface tension isotherms for mixtures of surface-active sugar derivatives and ionic surfactants. We obtained a good agreement with experimental data using the same set of model parameters for a whole range of studied compositions of a given surfactant mixture. The values of surface excess calculated from both theories agreed with each other with a reasonable accuracy. However, the newly developed model of adsorption of ionic–nonionic surfactant mixtures has the advantage of straightforward determination of surface layer composition. By the solution of equations of adsorption, one can obtain directly the values of surface excess of all components (surfactant ions, counterions, and nonionic surfactants molecules), which are present in the investigated system.

Adsorptive and stripping behavior of methylene blue at gold electrodes in the presence of cationic gemini surfactants

The adsorptive and stripping behavior of methylene blue (i.e. methylene blue chloride, MB) at a gold electrode has been studied with voltammetry, alternating current impedance spectra (ACIS) and quartz crystal microbalance (QCM). MB exhibits a pair of cyclic voltammetry peaks at about −0.3 V (versus SCE) in 0.05 M pH 6.9 phosphate buffer solutions. In the presence of cationic gemini surfactants such as C 16H 33N(CH 3) 2–C 4H 8–N(CH 3) 2C 16H 33Br 2 (C 16–C 4–C 16), C 16H 33N(CH 3) 2–C 4H 7OH–N(CH 3) 2C 16H 33Br 2 (C 16–C 4OH–C 16), C 16H 33N(CH 3) 2–CH 2–C 6H 4–CH 2–N(CH 3) 2C 16H 33Br 2 (C 16–ph–C 16) and C 16H 33N(CH 3) 2–C 12H 24–N(CH 3) 2C 16H 33Br 2 (C 16–C 12–C 16), the anodic peak grows rapidly and moves in positive direction, but the cathodic peak gradually decreases, due to the association adsorption and electrostatic interaction of the geminis with MB and its reduced product (i.e. leuko methylene blue, LMB). With the aid of geminis the adsorption amount of MB increases under open-circuit, but the impedance of the mixed adsorption film to Fe(CN) 6 3−/4− almost keeps unchanged, compared with either bare gold electrodes or MB film, while the adsorption film of geminis exhibits greater impedance. This probably is due to the electron medium action of MB in the film. Gemini surfactants with same alkyl-chain (i.e. –(CH 2) 15CH 3) but different molecular structure, exhibit different influence. The enhancing action of geminis studied follows such order as: C 16–ph–C 16 > C 16–C 4–C 16 > C 16–C 4OH–C 16 > C 16–C 12–C 16. The change of peak potential was ascribed to the interaction between MB and surfactants, as well as the blocking action of surfactant film. For comparison, the influence of dihexadecyldimethylammonium bromide (DCAB) and cetyltrimethylammonium bromide (CTAB) was studied, and the influence of other factors is discussed as well.

A study of the interaction of dodecyl sulfobetaine with cationic and anionic surfactant in mixed micelles and monolayers at the air/water interface

The miscibility and interactions between components in mixed adsorbed films and micelles containing zwitterionic (dodecyl sulfobetaine—DSB) and cationic (dodecyltrimethylammonium bromide) or anionic (sodium dodecyl sulfonate) surfactant, respectively, have been investigated. The molecular interactions have been quantified by the values of the excess free energy of adsorption ( Δ G S , Exc ) and micelle formation ( Δ G M , Exc ). The obtained results indicate nonideal behavior of the investigated mixtures since the values of Δ G S , Exc and Δ G M , Exc are negative. Moreover, it has been found that DSB interact more strongly with anionic surfactant as compared to cationic surfactant owing to different structure of mixed monolayers and micelles.

Surface properties of cationic–nonionic mixed surfactant systems

Surface properties of the binary cationic–nonionic mixed systems (dodecyltrimethylammonium bromide + n-dodecyl-β-d-maltoside and dodecyltrimethylammonium bromide + n-dodecyl-β-d-glucoside) have been investigated by measuring the surface tension of aqueous solutions as a function of the total concentration and mole fraction of surfactants.The experimental results were analysed thermodynamically applying the Motamura theory, which allows for calculation of the composition of mixed monolayers and micelles as well as the excess free energy of adsorption and micelle formation, corresponding to mutual interactions between surfactants in mixed adsorbed film and micelle. Phase diagrams of adsorption and micelle formation and values of the excess Gibbs energy for both of the investigated systems were compared.The obtained results indicate that dodecyltrimethylammonium bromide mixes nonidealy with each of the investigated surfactants in both adsorbed film and micelle and proved that the size of hydrophilic group influences on the interactions between components in formed aggregates.

Surface properties of the binary mixed systems of alkylpyridinium halides and sodium alkylsulfonates

Surface properties of the binary mixed systems of decyl- and dodecylpyridinium chloride or bromide and sodium pentyl- and heptylsulfonate have been investigated. The surface tension of solutions of equimolar mixtures of surfactants and individual surfactants was measured, and the composition of mixed monolayers and surface interaction parameter β were calculated with the regular solution theory. Our results indicate that the properties of mixed films depend on both ionic strength and the kind of added inorganic electrolyte. With the increase of inorganic electrolyte concentration, the content of more surface active ions in the adsorption films enhances and is the highest in the presence of NaI and the smallest when solutions contain NaCl. Mutual interactions in mixed adsorbed films were found to be attractive. However, the strength of interaction weakens with the increase of ionic strength and depends on the kind of inorganic ions in the order: Cl−>Br−>I−.

The interaction of an anionic gemini surfactant with conventional anionic surfactants

The interaction in two mixtures of an anionic gemini surfactant having N, N-dialkylamide and carboxylate groups in a molecule, (CH 2) 2[N(COC 11H 23)CH(CO 2H)CH 2(CO 2H)] 2 ·2NaOH (GA), and conventional anionic surfactants have been investigated in 0.1 M NaCl at pH 5.0. The two mixtures are GA/sodium dodecylsulfate (SDS) and GA/sodium N-dodecanoylglutamate (AGS) at a molar fraction of GA, α GA =0.25 . Mixtures of both GA/SDS and GA/AGS exhibit synergism in surface tension reduction effectiveness. The GA/SDS mixture also exhibits synergism in surface tension reduction efficiency and mixed micelle formation, whereas the GA/AGS mixture does not. The interaction in mixed adsorption film formation is stronger than that in mixed micelle formation for the two mixtures. The interaction in the formation of the mixed adsorption film and the mixed micelle for the GA/SDS mixture is stronger in both formations than that for the GA/AGS mixture. The stronger interaction for the GA/SDS mixture may be caused by the combination of the smaller minimum area per molecule at the air/water interface ( A min ) of the head groups in the GA molecule and the larger A min in the SDS molecule.

Do Mixtures of Proteins Phase Separate at Interfaces?

Recent microscopy experiments have investigated the structure of mixed adsorbed protein films. These studies have provided conflicting messages about the extent of miscibility of different proteins at fluid interfaces. We address this problem here using a Brownian dynamics simulation approach. We find that formation of bonds between model protein molecules can lead to either phase-separated or homogeneous mixed film structures, depending on the attributes of the bonds. We compare the behavior with that for a simulated case where an effective repulsion between unlike species can lead to phase separation, and we discuss the overall relevance of the model to protein mixtures.

Adsorption and Micelle Formation of Mixed Surfactant Systems in Water II: A Combination of Cationic Gemini-type Surfactant with MEGA-10

Mixed micellization and mixed adsorbed film formation were investigated for the combination of a Gemini type cationic and a nonionic surfactants mixture: Bis-trimethyl ammonium Gemini derived from tartaric acid bromide (BAGTB) and n-Decanoyl-N-methylglucamide (MEGA-10). The surface tension of the aqueous mixed surfactant solution was measured at every 0.1 mole fraction of MEGA10 in the surfactant mixture applying a drop volume method at 30°C. From the curves of surface tension (γ) vs logarithmic concentration in molality (ln m ), critical micellization concentration (CMC), minimum surface tension at CMC (γCMC), surface excess (Γ), mean surface area occupied by a molecule (A m) and parameters related to synergism in surface activity such as pC20 and CMC / C20 were determined. Based on the regular solution theory, the relation of compositions of the singly dispersed phase (X MEGA10) and the micellar phase (Y MEGA10), and the relation of X MEGA10 with the composition in adsorbed film phase (Z 2) were estimated, and along with these, the interaction parameters in micelles (ωR) and in adsorbed film (ωA ) were calculated. Both the CMC-X MEGA-10 and CMC-Y MEGA-10 curves showed a negative deviation from ideal mixing and even the curve of Z MEGA10-m t (bulk phase concentration) produced a slightly negative ωA . However, the synergism in surface tension reduction was found to be rather weak from examination of partial molecular area (PMA) and the minimum free energy at surface G min(S) = (γCMC·A m·L ). As for the adsorbed film, the interaction mode between molecules, as well as two dimensional molecular packing, was observed to be separated into three regions; i. e. at X STDS = 0.45 and at X STDS = 0.75 different properties changed discontinuously.

Properties of anionic–cationic adsorption films:: Part 2

The composition and mutual interactions of the components in anionic–cationic adsorption films have been determined by using a regular solution model for the mixed monolayers. Equimolar mixtures containing sodium nonylsulfonate and decyl- or dodecylpyridinium chloride or bromide have been investigated. The ionic strength of the solutions has been fixed by addition of appropriate amount of inorganic electrolyte (NaCl, NaBr, NaI). It has been found that an increase of the ionic strength and change of the inorganic electrolyte from sodium chloride through bromide to iodide results in a weakness of mutual attraction of the adsorbed components which indicates that these interactions have a mainly electrostatic character. The ionic strength of the solution and the kind of the inorganic electrolyte also distinctly influence the composition of mixed adsorption films. This effect is greater the more different the surface activity is of the mixture components.

Properties of mixed adsorption films of aniline– p-fluoroaniline at the water/air interface

The paper presents the properties of mixed adsorption films of aniline– p-fluoroaniline at the aqueous solutions/air interface. These properties were studied by surface tension and surface potential measurements carried out as a function of total molarity of solution of both components at a constant mole fraction of p-fluoroaniline. The mixed adsorbed film composition, the interaction between adsorbed molecules, the effective dipole moment of adsorbed molecules and the angles of surface orientation of molecules were determined.

Properties of Anionic–Cationic Adsorption Films in the Presence of Inorganic Electrolytes, 2

The composition and mutual interaction of the components in anionic–cationic adsorption films have been determined by using a regular solution model for the mixed monolayers. Equimolar mixtures of surfactants that differ markedly in their surface activity (decylpyridinium chloride and sodium butylsulfonate) have been investigated. A marked asymmetry of the composition of mixed adsorption films, as well as mutual attraction of the adsorbed components (negative values of surface interaction parameter β) have been found in these systems. The effect of the ionic strength and kind of the inorganic electrolyte on the surface interactions is similar, as in the case of mixtures of decylpyridinium chloride and sodium alkylsulfonates with hydrocarbon chains longer than the butyl ones that were previously investigated.

Properties of anionic–cationic adsorption films

The regular solution model for mixed monolayers was used to calculate the composition of the anionic–cationic adsorption films and parameters characterizing the mutual interactions between their components. The surfactants forming the mixed monolayers were decylpyridinium chloride and sodium hexylsulfonate. The monolayers under investigation were all adsorbed from equimolar solutions of surfactants. The results obtained show that the composition of the anionic–cationic adsorption films is dependent on the concentration and the kind of inorganic electrolyte present in the solution. The values of surface interaction parameter β, being all negative, show that the adsorbed components attract mutually. It has been observed that the strength of the attraction mentioned is also dependent on the factors given above for the composition of mixed adsorption films. It has also been established that the system examined here behaves, both qualitatively and quantitatively, in very similar manner to the previously investigated mixture of decylpyridinium chloride and sodium octylsulfonate, i.e. of surfactants with the same difference in length of the hydrocarbon chains as examined in this work.

Surface mixed adsorption films of 2,4,6- trimethylphenol-2,4,6-trichlorophenol at aqueous solution/air interface

The results of experimental studies of the adsorption at the solution/air interface from an aqueous mixture: 2,4,6-trimethylphenol–2,4,6-trichlorophenol are presented. The surface properties of the above-mentioned mixture were studied by surface potential and surface tension measurements. These measurements were carried out as a function of the concentration of 2,4,6-trimethylphenol aqueous solution at a constant concentration of 2,4,6-trichlorophenol.

Influence of Inorganic Electrolyte Concentration on Properties of Anionic–Cationic Adsorption Films

The composition and mutual interaction of the components in mixed adsorption films have been determined on the basis of the results of surface tension measurements obtained for solutions of single anionic and cationic surfactants with hydrocarbon chains of the same length (sodium decylsulfonate and decylpyridinium chloride) and their mixtures. An equation analogous to one derived on the basis of a regular solution model, however without the controversial assumption that the excess entropy of mixing is zero, has been used in calculations. Investigations have been made for mixtures of different compositions and for different concentrations of added inorganic electrolyte (NaCl).

Properties of Mixed Adsorption Films of 2,2,2-Trichloroethanol–Ethanol at the Water/Air Interface

The properties of aqueous 2,2,2-trichloroethanol–ethanol mixtures were studied by surface potential and surface tension measurements. Based on the Gibbs equation and Motomura's method the relative surface excesses of adsorbed substances, molar fractions of solutes, surface orientation angles of molecules at the interface, and miscibility of adsorbed films were determined. The effective dipole moment of 2,2,2-trichloroethanol was obtained on the basis of surface excess values and surface potential changes, using the Helmholtz equation.

Adsorption Behavior of Propylammonium Chloride and Hexylammonium Chloride Mixture at Water/Air Interface

The adsorption behavior of a mixture of propylammonium chloride (PAC) and hexylammonium chloride (HAC) at the water/air interface was investigated by measuring the surface tension of the aqueous solution as a function of the total molality of PAC and HAC and the mole fraction of HAC in the total salt at 298.15 K under atmospheric pressure. The total surface density of the mixture and the composition of HAC in the adsorbed film were evaluated by using thermodynamic equations derived previously. The HAC molecules were seen to be adsorbed predominantly by the water/air interface. The composition of HAC in the adsorbed film was observed to have a larger value than unity in a region where the mole fraction of HAC in the aqueous solution was large. It was proved that such peculiar behavior is attributable to the negative adsorption of PAC in the adsorbed film, that is, the expulsion of the PAC molecules from the interface by the HAC molecules adsorbed. Further, the thermodynamic equations of mixed adsorbed films were concluded to be applicable not only to the mixed systems of surfactants but to those of various kinds of substances.