Forces between glass surfaces in mixed cationic-zwitterionic surfactant systems

We report atomic force microscopy (AFM) measurements of the forces between borosilicate glass solids in aqueous mixtures of cationic and zwitterionic surfactants. These forces are used to determine the adsorption of the surfactant as a function of the separation between the interfaces (proximal adsorption) through the application of a Maxwell relation. In the absence of cationic surfactant, the zwitterionic surfactant N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) undergoes little adsorption to glass at concentrations up to about 2/3 critical micelle concentration (cmc). In addition, DDAPS does not have much effect on the forces over the same concentration range. In contrast, the cationic surfactant dodecylpyridinium chloride (DPC) does adsorb to glass and does affect the force between glass surfaces at concentrations much lower than the cmc. In the presence of a small amount of DPC (0.05 mM = cmc/300), the net force between the glass surfaces is quite sensitive to the solution concentration of DDAPS. A model-independent thermodynamic argument is used to show that the surface excess of DDAPS depends on the separation between the glass interfaces when the cationic surfactant is present and that the surface excess of the cationic surfactant is more sensitive to interfacial separation in the presence of the zwitterionic surfactant. The change in adsorption of the zwitterionic surfactant is explained in terms of an intermolecular coupling between the long-range electrostatic force acting on the cationic surfactant and the short-range hydrophobic interaction between the alkyl chains on the cationic and zwitterionic surfactants. The adsorptions of cationic and zwitterionic surfactants in mixtures were measured independently and simultaneously by attenuated total internal reflection infrared spectroscopy (ATR-IR). The adsorption of the zwitterionic surfactant is enhanced by the presence of a small amount of cationic surfactant.     

Effect of surfactants on the chemiluminescence of acridinium dimethylphenyl ester labels and their conjugates

Chemiluminescent acridinium dimethylphenyl esters, containing two methyl groups flanking the phenolic ester bond, display excellent chemiluminescence stability and are used as labels in automated immunoassays for clinical diagnostics. Light emission from these labels is triggered with alkaline peroxide in the presence of the cationic surfactant cetyltrimethylammonium chloride. Under these conditions, light emission is rapid and is complete in <5 s. In the present study we examined the effect of various surfactants on light emission from acridinium dimethylphenyl ester labels and their conjugates containing hydrophilic linkers derived either from hexa(ethylene)glycol or a sulfobetaine zwitterion. Sulfobetaine zwitterions are very polar and incorporation of these functional groups in acridinium dimethyphenyl esters and their conjugates represents a new approach to improving the aqueous solubility of these chemiluminescent labels. Our results indicate that in general, surfactants affect light emission from these labels and their conjugates by two discrete mechanisms. Cationic surfactants, but not anionic or non-ionic surfactants, accelerate overall light emission kinetics and a more modest effect is observed with zwitterionic surfactants. Surfactants also enhance total light output and the magnitude of this enhancement is maximal for cationic surfactants and a sulfobetaine zwitterionic surfactant. These observations are the first to clearly delineate the role of the surfactant on the chemiluminescence reaction pathway of acridinium esters and can be rationalized based on known effects of surfactant aggregates on bimolecular and unimolecular reactions.     

Alpha-Lactalbumin is unfolded by all classes of surfactants but by different mechanisms

We show that all four classes of surfactants (anionic, cationic, non-ionic, and zwitterionic) denature alpha-lactalbumin (alphaLA), making alphaLA an excellent model system to compare their denaturation mechanisms. This involves at least two steps in all surfactants but is more complex in charged surfactants due to their strong binding properties. At very low concentrations, charged surfactants bind specifically as monomers, but the first denaturation process only sets in when 4-10 surfactant molecules are bound to form clusters on the protein surface and is followed by a second loss of structure as 20-25 surfactant molecules are bound. Sub-micellar interactions can be modeled as simple independent binding at multiple sites which does not achieve saturation before micelle formation sets in. In contrast, no specific sub-micellar surfactant binding is detected by calorimetry in the presence of zwitterionic and non-ionic surfactants, and denaturation only occurs around the cmc. Unfolding rates are very rapid in charged surfactants and reach a similar plateau level around the cmc, indicating that monomers and micelles operate on a mutually exclusive basis. In contrast, unfolding occurs slowly in zwitterionic and non-ionic surfactants and the rate increases with the cmc, suggesting that monomers cooperate with micelles in denaturation.     

Determination of zwitterionic and cationic surfactants by high-performance liquid chromatography with chemiluminescenscent nitrogen detection

The use of chemiluminescent nitrogen specific detection (CLND) combined with an HPLC separation allows for the identification and quantification of cationic and zwitterionic surfactants. The CLND provides equimolar responses, based on the amount of nitrogen within any compound. This allows for the detection of any nitrogen containing surfactant. Reversed-phase separation methods using cyano columns are developed for cationic and zwitterionic (sulfobetaine) surfactant mixtures. The limits of detection for these surfactants are in the single micromolar range (1 ng N). A linear response was obtained (R2=0.9981) between 50 microM and 5 mM. The methodology was then applied to the determination of an industrial zwitterionic surfactant, Rewoteric AM CAS U [coco(amidopropyl)hydroxyldimethylsulfobetaine].     

Kinetics of alkaline fading of methyl violet in micellar solutions of surfactants: Comparing Piszkiewicz's,Berezin's,and pseudophase ion-exchange models

The micellar effect of surfactants of various types on the rate of the reaction between methyl violet and hydroxide ion is studied. The absorption spectra show that the cation of methyl violet is bound by micelles of all types at proper concentrations of surfactants. The observed rate constant in micellar systems containing nonionic Brij-35, zwitterionic 3-(dimethyldodecylammonio)-propanesulfonate, cationic cetyltrimethylammonium bromide and hydroxide surfactants is higher, whereas in solutions of the anionic surfactant sodium dodecylsulfate is lower than that one in the surfactant-free system. Piszkiewicz's, Berezin's, and pseudophase ion-exchange models of the kinetic micellar effect are used for the treatment of the dependences of the above-mentioned constants on the surfactant concentration. The values of the corresponding kinetic parameters are compared and discussed. The influence of nonionic, zwitterionic, and anionic micelles on the reaction rate is discussed on the basis of medium and concentration kinetic effects. The character of the cationic micelles effect is somewhat paradoxical. Although the observed pseudo–first-order reaction rate constant substantially increases in the presence of such micelles, the second order-rate constant in these micelles is lower than the corresponding value in surfactant-free aqueous solution. As a possible explanation, the decrease in the reactivity of the HO^– ions is proposed, owing to their electrostatic association with the cationic headgroups (“diverting effect”).     

Observations of the effect of anionic, cationic, neutral, and zwitterionic surfactants on the Belousov-Zhabotinsky reaction

In this paper we report the experimental observations of the effects of various surfactants on the oscillations of the ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction. The oscillations are followed by observing the change in absorbance at 510 nm due to ferroin in a well-stirred closed BZ reacting system. We have used sodium dodecyl sulfate (SDS) as the anionic surfactant, cetyl trimethylammonium bromide (CTAB) as the cationic surfactant, Triton X-100 as the neutral surfactant, and 3-[(3-cholamidopropyl)dimethylammonio)]-1-propanesulfonate (CHAPS) as the zwitterionic surfactant. In general, we observed that there is a change in the oscillation behavior in the presence of each of these surfactants above their critical micellar concentrations. For different surfactants, the time-dependent evolution of the oscillations is found to be characteristic of the surfactant. The results of our study suggest that the evolution of oscillations is most regular in the presence of micelles of SDS.     

Interaction of surfactants and aminoindophenol dye

The interaction of dye and surfactants was studied by their spectroscopic and surface properties. Large bathochromic shift (15 nm) in the absorption spectrum was found for aminoindophenol dye at high pH in cationic surfactant, while there is no significant shift in anionic, zwitterionic and nonionic surfactant solutions. The static and dynamic surface properties show there is strong interaction in mixture of cationic surfactant and aminoindophenol dye. Interaction of dye and surfactants on surface and in solution is correlated to the intensity of dye deposition on fiber. The charge complex formation between cationic surfactant and aminoindophenolic dye delays the dye diffusion into keratin fiber. The stronger is the dye/surfactant interaction, the lower dye deposition and diffusion become.     

Raman spectroscopic study on the structure of water in aqueous solution of zwitterionic surfactants

The structure and hydrogen bonding of water in aqueous solutions of various surfactants were analyzed using the contours of the O-H stretching in the polarized Raman spectra. From the relative intensity of the collective band (C value) corresponding to a long-range coupling of the O-H stretching in the aqueous surfactant solutions, the number of hydrogen bonds disrupted due to the presence of one surfactant molecule (N(corr) value) was evaluated. The N(corr) value for decylsulfobetaine was slightly negative, whereas those for ordinary ionic surfactants such as sodium dodecylsulfate and dodecyltrimethylammonium chloride were large positive values. Furthermore, the N(corr) for carboxybetaine surfactant was a small positive value. These results suggest that zwitterionic surfactants do not disturb the hydrogen-bonded network structure of water significantly, probably due to the counteraction of the electrostriction effect by the proximity between the anionic and cationic groups.     

Capillary Electrophoresis of Cationic Surfactants

Surfactants are important additives in many chemical processes and products. A wide range of surfactants exists, including anionic, cationic, nonionic and zwitterionic. Benzalkonium chloride (BAC) is a widely used cationic surfactant in pharmaceutical and health-care products since it possesses antiseptic and antibacterial properties.     

阳离子和两性表面活性剂在聚甲基丙烯酸甲酯表面的吸附行为

利用座滴法研究了阳离子表面活性剂十六烷基醚羟丙基季铵盐(C₁₆PC)、十六烷基聚氧乙烯醚羟丙基季铵盐(C₁₆(EO)₃PC)和两性离子表面活性剂十六烷基醚羟丙基羧酸甜菜碱(C₁₆PB)、十六烷基聚氧乙烯醚羟丙基羧酸甜菜碱(C₁₆(EO)₃PB)溶液在聚甲基丙烯酸甲酯(PMMA)表面上的润湿性质, 考察了表面活性剂类型及浓度对接触角的影响趋势. 研究发现: 低浓度条件下表面活性剂分子可能以平躺的方式吸附到固体界面, 且亲水基团靠近固体界面, PMMA表面被轻微疏水化; 在高浓度时则通过Lifshitz-van der Waals 作用吸附, 亲水基团在外, PMMA表面被亲水改性. 聚氧乙烯基团(EO基团)的引入对阳离子表面活性剂的接触角影响不大; 而含有聚氧乙烯基团的两性离子表面活性剂在PMMA界面上以类似半胶束的聚集体吸附, 大幅度降低接触角.     

Effect of Cationic and Zwitterionic Surfactants on Contact Angle of Quartz–Water–Crude Oil System

The influences of four cationic surfactants hexadecyl glycidyl ether ammonium chloride and four zwitterionic surfactants hexadecyl glycidyl ether glycine Betaine solutions on contact angle of crude oil on a quartz surface were investigated using a captive drop method. The effects of surfactant type, structure, and concentration on contact angle were expounded. From obtained results it appears that the adsorbed surfactant at oil–water interface reduces the interfacial tension and the adsorption at quartz–water interface improves interfacial free energy, which results in reducing the stable value of contact angle and weakening dynamic behavior. At high concentration, the zwitterionic surfactant with branched-chain may form semi-micelle at quartz surface. As a result, the stable value of contact angle passes through a sharp minimum with the increasing concentration.     

正负离子表面活性剂与两性表面活性剂的相互作用

本文研究正负离子表面活性剂与两性表面活性剂混合水溶液的表面性质, 以及两性表面活性剂对正负离子裘面活性剂溶解度的影响。结果表明: (1) 两性表面活性剂的加溶作用,有助于正负离子表面活性剂的溶解; (2) 加入两性表面活性剂的量适当, 混合溶液基本保持原正负离子表面活性剂的表面活性; (3) 正负离子表面活性剂与两性表面活性剂在表面层和胶团中分子间的相互作用比正负离子表面活性剂与非离子表面活性剂分子间的相互作用稍强HC-FC正负; 离子表面活性剂与两性表面活性剂混合体系在表面层中有可能形成双分子或多分子层结构。     

Effects of Surfactants on Hydride Transfer from Methylene Blue Leucodye to 2,5-Dihydroxyl-1,4-benzoquinone in Aqueous Solution

The effects of monomeric surfactants on the hydride transfer from (one electron oxidation of) methylene blue leucodye to (by) 2,5-dihydroxy-1,4-benzoquinone in aqueous solution were investigated at 25°C using a stopped-flow spectrometer. The results indicated that cationic, anionic, and zwitterionic surfactants inhibited the reaction while nonionic surfactant showed no appreciable effect on the reaction. These observations are rationalized by electrostatic factors between surfactant monomer (or micelle) and reactant with charge or the charge transfer complex of the hydride transfer reaction. Above the cmc, the effects are treated quantitatively using a kinetic model.     

Synthesis and aqueous solution properties of homologous gemini surfactants with different head groups

A series of homologous gemini surfactants possessing identical hydrophobic chains but different ionic head groups (cationic, anionic, zwitterionic) were synthesized, and their aqueous solution properties were examined. The results showed that the surface activities of gemini surfactants are superior to those of corresponding conventional monomeric surfactants, and molecular arrangements of gemini surfactants at the air-water interface are tighter than those of corresponding conventional surfactants. It was also found that zwitterionic gemini surfactant possesses the highest surface activity among the three surfactants. The behavior at the air-water interface is closely related to the molecular structural features of surfactants, which provide an indication for synthesizing highly-efficient surfactants.      

Studies of Interfacial Activities of Four Kinds of Surfactants at Oil/Water Interface

This article aims to compare the interfacial activities of different kinds of surfactants in the same oil/water system. The anionic surfactants of alkylbenzene sulfonates, the polyoxyethylenated nonionic surfactants, the cationic surfactants of alkyl trimethyl ammonium chlorides, and the zwitterionic surfactants of alkyl hydroxyl sulfobetaines were used, and the interfacial tensions of the surfactant solutions against kerosene at different NaCl concentrations were measured. It is found that the interfacial activities of the alkylbenzene sulfonates are high and ultralow interfacial tensions (<0.01 mN/m) can be obtained at proper salinities. While, the nonionic surfactants have relatively low interfacial activities and the minimum tensions are around 0.01 mN/ms. The salinity scanning curves of the alkylbenzene sulfonates and nonionic surfactants decrease first, then increase, showing their interfacial activities can be changed by the salinity effectively. The cationic and zwitterionic surfactants have very low interfacial activities, of which all the tensions are higher than 0.1 mN/ms and are hard to be changed by the salinity. The experimental results may have important reference values for enhanced oil recovery.     

Effect of surfactants on the kinetics of nickel(II) extraction by 2-hydroxy-5-nonylacetophenone oxime (LIX 84) in an n-heptane/water system

The initial reaction rates of the extraction of nickel(II) by 2-hydroxy-5-nonylacetophenone oxime (HNAPO) in a two-phase oil/water system was measured using a total internal reflectance static transfer cell. A two-step reaction mechanism between nickel(II) and HNAPO was found to satisfactorily explain the observed initial reaction rate (R(int)). The addition of neutral surfactants, nonionic octaethylene glycol mono-n-dodecyl ether and zwitterionic n-dodecyldimethyl-3-ammonio-1-propanesulfonate, decreased R(int), which could be accounted for with a competitive surface adsorption model. The presence of the anionic surfactant sodium dodecyl sulfate accelerated and then decelerated R(int), while the cationic surfactant dodecyltrimethylammonium chloride caused a decrease. The effects of these charged surfactants were accounted for using a combination of a competitive surface adsorption model and the Boltzmann distribution of charged species.     

Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: the pH and spacer effect

Mixed micelle formation of binary cationic gemini (12-s-12, s=4, 6) and zwitterionic (N-dodecyl-N,N-dimethylglycine, EBB) surfactants has been investigated by measuring the surface tension of aqueous solution as a function of total concentration at various pH values from acidic to basic, under conditions of 298.15 K and atmospheric pressure. The results were analyzed by applying regular solution theory (RST), and Motomura's theory, which allows for the calculation of the excess Gibbs energy of micellization purely on the basis of thermodynamic equations. The synergistic interactions of all the investigated cationic gemini + zwitterionic surfactants mixtures were found to be dependent upon the pH of the solution and the length of hydrophobic spacer of gemini surfactant. The evaluated excess Gibbs free energy is negative for all the systems.     

Stability and Adsorption Properties of Suspensions of Finely Dispersed Silica in the Presence of Cationic Surfactants

Interrelation between the coagulation rate, adsorption and electrokinetic properties of silica polydisperse suspensions in the presence of cationic surfactants is studied. The highest coagulation rate is observed in a certain concentration range of the cationic surfactants. When pH values increases, an increasing amount of cationic surfactant is required to achieve maximal coagulation rate. For bisquaternary cationic surfactants, ethonium and decamethoxine, maximal coagulation rate is observed at concentrations by an order of magnitude lower than for monoquaternary cetyltrimethylammonium bromide. It is concluded that the suspensions lost their stability as a result of both neutralization of particle surface charge and flocculating effect of the cationic surfactants. Moreover, the flocculation mechanism depends on the cationic surfactant nature and physicochemical parameters of the medium, ionic strength and pH.     

Thermodynamic characterization of 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) micellization using isothermal titration calorimetry: temperature, salt, and pH dependence

A systematic investigation of the micellization process of a biocompatible zwitterionic surfactant 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) has been carried out by isothermal titration calorimetry (ITC) at temperatures between 278.15 K and 328.15 K in water, aqueous NaCl (0.1, 0.5, and 1 M), and buffer solutions (pH = 3.0, 6.8, and 7.8). The effect of different cations and anions on the micellization of CHAPS surfactant has been also examined in LiCl, CsCl, NaBr, and NaI solutions at 308.15 K. It turned out that the critical micelle concentration, cmc, is only slightly shifted toward lower values in salt solutions, whereas in buffer media it remains similar to its value in water. From the results obtained, it could be assumed that CHAPS behaves as a weakly charged cationic surfactant in salt solutions and as a nonionic surfactant in water and buffer medium. Conventional surfactants alike, CHAPS micellization is endothermic at low and exothermic at high temperatures, but the estimated enthalpy of micellization, ΔHM0, is considerably lower in comparison with that obtained for ionic surfactants in water and NaCl solutions. The standard Gibbs free energy, ΔGM0, and entropy, ΔSM0, of micellization were estimated by fitting the model equation based on the mass action model to the experimental data. The aggregation numbers of CHAPS surfactant around cmc, obtained by the fitting procedure also, are considerably low (nagg ≈ 5 ± 1). Furthermore, some predictions about the hydration of the micelle interior based on the correlation between heat capacity change, Δcp,M0, and changes in solvent-accessible surface upon micelle formation were made. CHAPS molecules are believed to stay in contact with water upon aggregation, which is somehow similar to the micellization process of short alkyl chain cationic surfactants.     

Effect of cationic surfactants on enhancement of firefly bioluminescence in the presence of liposomes

Firefly bioluminescence (BL) was greatly affected by cationic surfactants coexisting with liposomes containing phosphatidylcholine and cholesterol. In this study, the effects of the type and concentration of cationic surfactants on BL were studied in the presence of the liposomes. Three types of cationic surfactant: benzalkonium chloride (BAC), n-dodecyltrimethylammonium bromide (DTAB), and benzethonium chloride (BZC), were used. As a common effect in these surfactants, BL intensity was increased and then drastically decreased with increasing surfactant concentration. This can be explained by the formation of cationic liposomes as BL enhancers at low concentration of the surfactant, and by the transformation into cationic (mixed) micelles as inhibitors at high concentration. The maximal BL intensity and the concentration for the maximal BL were dependent on the type of the surfactants. To explain the differences in these parameters in the enhanced BL, we determined the distribution coefficient, K, of the surfactants to the liposomal membrane. The result indicated that the surfactant with higher K value gives the maximal BL intensity at lower concentration.