Characterization and Aggregation Behaviors of Mixed DDAB/SDS Solution With and Without Poly(4-styrenesulfonic Acid-Co-Maleic Acid) Sodium

Synthetic vesicles are formed by cationic and anionic surfactants, didodecyldimethylammonium bromide (DDAB), and sodium dodecylsulfate (SDS). The morphology, size, and aqueous properties of cationic/anionic mixtures are investigated at various molar ratios between cationic and anionic surfactants. The charged vesicular dispersions made of DDAB/SDS are contacted or mixed with negatively charged polyelectrolyte, poly(4-styrenesulfonic acid-co-maleic acid) sodium (PSSAMA), to form complexes. Depending on DDAB/SDS molar ratio or PSSAMA/vesicle charge ratio, complexes flocculation or precipitation occur. Characterization of the cationic/anionic vesicles or complexes formed by the catanionic vesicles and polyelectrolytes is performed by transmission electron microscope (TEM), dynamic light scattering (DLS), conductivity, turbidity, and zeta potential measurements. The size, stability, and the surface charge on the mixed cationic/anionic vesicles or complexes are determined.     

Effect of secondary polymer on self‐precipitation of pH‐sensitive polymethylmethacrylate derivatives Eudragit E100 and Eudragit L100

Interpolyelectrolyte complexes or polyplexes can be seen as interesting alternatives in the purpose of active ingredients encapsulation. Working on polymethylmethacrylate derivatives with special focus on controlled oral drug delivery, the influence of charged polyelectrolytes (polyacrylic acid, polyethylenimine, and amino‐dextran) and noncharged ones (polyvinyl alcohol, dextran 40, and Pluronic F68) has been investigated on the precipitation of two pH‐sensitive Eudragit polymers, namely, L100 and E100. Moreover, the possibility of preparing polyplexes involving the two polymethylmethacrylate derivatives with different charged and noncharged secondary polyelectrolytes has been studied. The obtained dispersions have been characterized in terms of mean particle size, size distribution, zeta potential, and morphology. Direct precipitation of Eudragit L100 by medium acidification in a batch process and in the presence of polyethylenimine allowed the production of particles with a narrow size distribution. The mean size was around 200 nm. In this case, the zeta potential was found to be +45 mV at pH = 7 in 1mM aqueous NaCl solution, and the produced suspension was stable in time since no aggregation and sedimentation have been observed. A precipitation pH of 8.16 allows us to suggest the preparation of a polyplex based on Eudragit L100 and polyethylenimine. In contrary, polyvinyl alcohol has shown ability to induce an increase in particle mean size whereas other polyelectrolytes showed no significant effect. Moreover, it was observed that polyethylenimine and polyacrylic acid solutions were able to directly induce Eudragit E100 precipitation whereas amino‐dextran and noncharged polyelectrolytes showed no effect on its precipitation and on particle size distribution.     

Effect of Sodium Barbital on the Physico‐chemical Properties of Surfactants with Different Charges

The effects of sodium barbital (SB) on the solubility of different kinds of surfactants viz., CTAB (cationic head group), SDS (anionic head group) and Triton X‐100 (non ionic head group) in solution phase as well as their first and second critical micelle concentrations (CMC1 and CMC2), the change in Kraft temperatures (T_K) and cloud points (CP) have been studied. Furthermore, the article reports SB‐surfactant interaction study, which is application oriented and highlights the underlying physico‐chemical aspects of the system through florescence and conductivity measurements. The results show that the solubility of CTAB and Triton X‐100 increases with the addition of SB, and that of SDS increases in the presence of small amounts of SB and decreases in the presence of large amounts of SB. With the increasing SB concentration, the CMC of CTAB and CMC1 of Triton X‐100 both increase, while the CMC of SDS decreases, and the CMC2 of Triton X‐100 has no obvious change. The addition of SB decreases the T_K of CTAB sharply, but it increases the T_K of SDS and the CP of Triton X‐100. The different effects of SB on the physico‐chemical properties of differently charged surfactants may be related to its different interactions with the surfactants.     

Depletion flocculation of latex dispersion in ionic micellar systems

The flocculation behavior of anionic and cationic latex dispersions induced by addition of ionic surfactants with different polarities (SDS and cetyltrimethylammonium bromide (CTAB)) have been evaluated by rheological measurements. It was found that in identical polar surfactant systems with particle surfaces of SDS + anionic lattices and CTAB + cationic lattices, a weak and reversible flocculation has been observed in a limited concentration region of surfactant, which was analyzed as a repletion flocculation induced by the volume-restriction effect of the surfactant micelles. On the other hand, in oppositely charged surfactant systems (SDS + cationic lattices and CTAB + anionic lattices), the particles were flocculated strongly in a low surfactant concentration region, which will be based on the charge neutralization and hydrophobic effects from the adsorbed surfactant molecules. After the particles stabilized by the electrostatic repulsion of adsorbed surfactant layers, the system viscosity shows a weak maximum again in a limited concentration region. This weak maximum was influenced by the shear rate and has a complete reversible character, which means that this weak flocculation will be due to the depletion effect from the free micelles after saturated adsorption.     

Synergistic effect of mixed anionic and cationic surfactant systems on the interfacial tension of crude oil-water and enhanced oil recovery

Surfactant based enhanced oil recovery (EOR) is an interesting area of research for several petroleum researchers. In the present work, individual and mixed systems of anionic and cationic surfactants consisting of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) in different molar ratios were tested for their synergistic effect on the crude oil-water interfacial tension (IFT) and enhanced oil recovery performance. The combination of these two surfactant systems showed a higher surface activity as compared to individual surfactants. The effect of mixed surfactant systems on the IFT and critical micellar concentration (CMC) is strongly depends on molar ratios of the two surfactant. Much lower CMC values were observed in case of mixed surfactant systems prepared at different molar ratios as compared to individual surfactant systems. The lowest CMC value was found when the molar concentration of SDS was higher than the CTAB. When the individual and mixed surfacant systems were tested for EOR performance through flooding experiments, higher ultimate oil recovery was obtained from mixed surfactant flooding compared to individual surfactants. Combination of SDS and CTAB or probably other anionic-cationic surfactants show synergism with substantial ability to reduce crude oil water IFT and can be a promising EOR method.     

Interactions between polyampholytes and ionic surfactants

The interactions of two partially charged ampholytic terpolymers [consisting of acrylamide, sodium 2-acrylamido-2-methylpropanesulphonate, and 2-(methacryloyloxyethyl)trimethylammonium chloride segments with molar compositions 80/12/08 and 80/08/12] and two fully charged ampholytic copolymers (containing only the two latter comonomers with molar compositions of 80/20 and 50/50), with cationic surfactants [tetradecyl- trimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB)] and the anionic surfactant sodium dodecylsulphate (SDS), are investigated. The studies include phase behaviour (swelling, solubilisation, precipitation), viscometry, electrical conductivity, and potentiometry (bromide ion and surfactant ion-specific electrodes). The 80/08/12 and 80/12/08 polyampholytes swell in water and are solubilised in the presence of cationic or anionic surfactants above a particular surfactant concentration that is proportional to the polymer concentration. The polyampolyte 80/20 is soluble in water but precipitates in the presence of TTAB, whereas 50/50 is insoluble in water and in the presence of TTAB, but is solubilised upon addition of SDS. The results indicate that TTAB binds to 80/12/08 with little or no cooperativity. Solubilisation appears to be the result of the increasing polyelectrolyte character of the polyampholyte upon neutralisation of its charged sites by bound surfactant ions of opposite charge. The binding of TTAB by the 50/50 polyampholyte is very weak and non-cooperative. In contrast, 80/20 binds TTAB cooperatively, much like a true polyelectrolyte-surfactant system of opposing charges. In particular, the binding is characterised by the existence of a critical aggregation concentration. A partial phase diagram for this system has been determined from the TTA⁺-electrode potential data. The behaviour of true polyelectrolytes and polyampholytes, with respect to their interaction with surfactants, is discussed. Received: 22 July 1998 Accepted: 14 September 1998     

Spectrophotometric study of interaction and solubilization of procaine hydrochloride in micellar systems

The interaction of Procaine hydrochloride (PC) with cationic, anionic and non-ionic surfactants; cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and triton X-100, were investigated. The effect of ionic and non-ionic micelles on solubilization of Procaine in aqueous micellar solution of SDS, CTAB and triton X-100 were studied at pH 6.8 and 29°C using absorption spectrophotometry. By using pseudo-phase model, the partition coefficient between the bulk water and micelles, K_x, was calculated. The results showed that the micelles of CTAB enhanced the solubility of Procaine higher than SDS micelles (K_x = 96 and 166 for SDS and CTAB micelles, respectively) but triton X-100 did not enhanced the solubility of drug because of weak interaction with Procaine. From the resulting binding constant for Procaine-ionic surfactants interactions (K_b = 175 and 128 for SDS and CTAB surfactants, respectively), it was concluded that both electrostatic and hydrophobic interactions affect the interaction of surfactants with cationic procaine. Electrostatic interactions have a great role in the binding and consequently distribution of Procaine in micelle/water phases. These interactions for anionic surfactant (SDS) are higher than for cationic surfactant (CTAB). Gibbs free energy of binding and distribution of procaine between the bulk water and studied surfactant micelles were calculated.      

The Viscous Properties of Anionic/Cationic and Cationic/Nonionic Mixed Surfactant Systems

The behavior of mixed cationic/anionic and cationic/nonionic surfactants solutions have been studied by viscosimetry. The systems studied were sodium dodecyl sulfate (SDS)/cetyltrimethylammonium bromide (CTAB) and CTAB/Brij (polyoxyethylene lauryl ether, n = 10 and 23) in aqueous and sodium chloride solutions. The relative viscosity of single nonionic surfactant solutions is larger than that of SDS or CTAB solutions. It increases with the number of ethylene oxide groups. In the mixed systems, viscosity deviates from ideal behavior. The deviation results from electrostatic interactions. The surfactant mixture composition affects the self-assembled microstructure and rheology. A new mixed system that forms clear micellar solution above CMC was detected. In CTAB/Brij systems, the experimental data also deviate from ideal behavior due to mixed micelle formation and electroviscous effect. This effect is less pronounced than that of SDS/CTAB system and could be suppressed by adding an electrolyte (NaCl).     

pH‐Sensitive methacrylic acid–methyl methacrylate copolymer Eudragit L100 and dimethylaminoethyl methacrylate,butyl methacrylate,and methyl methacrylate tri‐copolymer Eudragit E100

Poly (methyl methacrylate) derivatives such as Eudragit are largely used for drug encapsulation and in controlled oral drug delivery. With special focusing on those applications, solubilization and precipitation conditions of two pH‐sensitive Eudragit polymers, namely, L100 and E100, were investigated via systematic studies. Effects of various physicochemical parameters such as pH, polymer concentration, salinity, buffer concentration, and incubation time on the solubilization and precipitation of these polymers were investigated. In addition, pH titration of both polymers was reported. Considering both macroscopic and quantitative aspects such as the final mean particle size, size distribution, morphology, and the zeta potential, it was established that the different precited parameters could not be dissociated and exert a synergic action on the solubilization and precipitation of both polymers. Titration curves revealed two equivalences that helped estimating carboxylic content of Eudragit L100 (6 mmol/g) and ammonium content of Eudragit E100 (4 mmol/g). In this study, the solubilization and the precipitation domains were for the first time clearly established by considering the above‐mentioned parameters. Moreover, it was found that Eudragit L100 and E100 cannot be considered as classic polyelectrolytes; in fact, solubilization and precipitation domains were not affected by ionic strength.     

卵清蛋白与离子型表面活性剂的相互作用

本文通过荧光光谱法、紫外-可见吸收光谱法和透射电镜并结合电导率测定分别研究了水中卵清蛋白与阴离子表面活性剂十二烷基硫酸钠（SDS）和阳离子表面活性剂十二烷基三甲基溴化铵（DTAB）和十六烷基三甲基溴化铵（CTAB）之间的相互作用。研究结果表明卵清蛋白可以增加SDS和CTAB的临界胶束浓度,但对DTAB的临界胶束浓度没有影响。阴离子表面活性剂可以使卵清蛋白构象完全伸展,而阳离子表面活性剂却不具备此种作用。表面活性剂单体与卵清蛋白的相互作用强于表面活性剂胶束与卵清蛋白的相互作用。     

Binding of ionic surfactants to purified humic acid

The binding of organic contaminants to dissolved humic acids reduces the free concentration of the contaminants in the environment and also may cause changes to the solution properties of humic acids. Surfactants are a special class of contaminants that are introduced into the environment either through wastewater or by site-specific contamination. The amphiphilic nature of both surfactants and humic acids can easily lead to their mutual attraction and consequently affect the solution behavior of the humics. Binding of an anionic surfactant (sodium dodecyl sulfate, SDS) and two cationic surfactants (dodecyl- and cetylpyridinium chloride, DPC and CPC) to purified Aldrich humic acid (PAHA) is studied at pH values of 5, 7, and 10 in solutions with a 0.025 M ionic strength (I). Monomer concentrations of the surfactants are measured with a surfactant-selective electrode. At I = 0.025 M, no significant binding is observed between the anionic surfactant (SDS) and PAHA, whereas the two cationic surfactants (DPC, CPC) bind strongly to PAHA over the pH range investigated. The binding is due both to electrostatic and hydrophobic attraction. The initial affinity increases with increasing pH (i.e., negative charge of PAHA) and tail length of the surfactant. Binding reaches a pseudo-plateau value (2-5 mmol/g) when the charge associated with PAHA is neutralized by that of the bound surfactant molecules. The pseudo-plateau values for DPC and CPC are very similar and depend on the solution pH. The cationic surfactant-PAHA complexes precipitate when the charge neutralization point is reached. This occurs at approximately 10% of the critical micelle concentration or CMC. This type of phase separation commonly occurs during surfactant binding to oppositely charged polyelectrolytes. For CPC, the precipitation is complete, but in the case of DPC, a noticeable fraction of PAHA remains in solution. At very low CPC concentrations (less than 0.1% of the CMC), CPC binding to PAHA is cooperative. The investigated range of concentrations for DPC was too limited to reach a similar conclusion. The results of this study demonstrate that the fate of humic acids will be strongly affected by the presence of low cationic surfactant concentrations in aqueous environmental systems.     

Atmospheric and electrochemical oxidation of ascorbic acid in anionic,nonionic and cationic surfactant systems

It is well known that the antioxidant activity of some species in homogenous solutions may not be the same as that in heterogeneous media. This environment dependence is the reason for investigating ascorbic acid antioxidant activity in surfactant solutions. In our study we have investigated the kinetics of atmospheric oxidation and electrochemical oxidation of ascorbic acid in aqueous solutions of the four surfactants: SDS, AOT (anionic), TRITON-100 (nonionic), and CTAB (cationic). For each surfactant the concentrations below and above CMC were investigated. As expected, a general trend in the atmospheric oxidation rate changes in the following manner: the micellar solution of nonionic surfactant shows a faster oxidation rate than that of the anionic surfactant, and the cationic surfactant an even higher one. The more subtle effects were observed with each surfactant concentration change. The influence of the surfactants on the electrochemical behavior of ascorbic acid was also studied. A general conclusion emerging from our investigation is that surfactants shift the ascorbic acid oxidation potential and change the peak current value. This phenomenon is due mainly to the surfactant film formed at the electrode/solution interface.     

Polymer-Surfactant Interactions and the Effect of Tail Size Variation on Micellization Process of Cationic ATAB Surfactants in Aqueous Medium

The interactions between oppositely charged surfactant-polymer systems have been studied using surface tension and conductivity measurements and the dependence of aggregation phenomenon over the polyelectrolyte concentration and chain length of cationic ATAB surfactants, cetyltrimethyl ammonium bromide (CTAB), tetradecyltrimethyl ammonium bromide (TTAB), and dodecyltrimethyl ammonium bromide (DTAB) have been investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolyte at critical aggregation concentration (cac). The cac values of ATAB surfactants in the presence of anionic polyelectrolyte, sodium carboxy methyl cellulose (NaCMC), are considerably lower than their critical micelle concentration (cmc). After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in polyelectrolyte aqueous solution than in pure water. Among the cationic surfactants (i.e., CTAB, TTAB, and DTAB), DTAB was found to have least interaction with NaCMC. Surfactants with longer tail size strongly favor the interaction, indicating the dependence of aggregation phenomenon on the structure, morphology, and tail length of the surfactant.      

Rheological properties of the aqueous solution for fluorocarbon‐containing hydrophobically modified sodium polyacrylic acid with various surfactants

The interaction of fluorocarbon‐ containing hydrophobically modified sodium polyacrylic acid (FMPAANa) (0.5 wt%) with various surfactants (anionic, nonionic and cationic) has been investigated by rheological measurements. Different rheological behaviors are displayed for ionic surfactants and nonionic surfactants. Fluorinated surfactants have stronger affinity with polyelectrolyte hydrophobes comparing with hydrogenated surfactants. The hydrophobic association of FMPAANa with a cationic surfactant (CTAB) and a fluorinated nonionic surfactant (FC171) is much stronger than with a nonionic surfactant (NP7. 5) and an anionic surfactant (FC143). Further investigation of the effects of temperature on solution properties shows that the dissociation energy E_m is correlated to the strength of the aggregated junctions.     

Adsorption behavior of hydrophobin and hydrophobin/surfactant mixtures at the air-water interface

The adsorption of the surface-active protein hydrophobin, HFBII, and the competitive adsorption of HFBII with the cationic, anionic, and nonionic surfactants hexadecyltrimethylammonium bromide, CTAB, sodium dodecyl sulfate, SDS, and hexaethylene monododecyl ether, C(12)E(6), has been studied using neutron reflectivity, NR. HFBII adsorbs strongly at the air-water interface to form a dense monolayer ～30 ? thick, with a mean area per molecule of ～400 ?(2) and a volume fraction of ～0.7, for concentrations greater than 0.01 g/L, and the adsorption is independent of the solution pH. In competition with the conventional surfactants CTAB, SDS, and C(12)E(6) at pH 7, the HFBII adsorption totally dominates the surface for surfactant concentrations less than the critical micellar concentration, cmc. Above the cmc of the conventional surfactants, HFBII is displaced by the surfactant (CTAB, SDS, or C(12)E(6)). For C(12)E(6) this displacement is only partial, and some HFBII remains at the surface for concentrations greater than the C(12)E(6) cmc. At low pH (pH 3) the patterns of adsorption for HFBII/SDS and HFBII/C(12)E(6) are different. At concentrations just below the surfactant cmc there is now mixed HFBII/surfactant adsorption for both SDS and C(12)E(6). For the HFBII/SDS mixture the structure of the adsorbed layer is more complex in the region immediately below the SDS cmc, resulting from the HFBII/SDS complex formation at the interface.     

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 Nonionic Surfactant Triton-X-100 with Ionic Surfactants

The interaction in two mixtures of a nonionic surfactant Triton-X-100 (TX-100) and different ionic surfactants was investigated. The two mixtures were TX-100/sodium dodecyl sulfate (SDS) and TX-100/cetyltrimethylammonium bromide (CTAB) at molar fraction of TX-100, α_TX-100 = 0.6. The surface properties of the surfactants, critical micelle concentration (CMC), effectiveness of surface tension reduction (γ_CMC), maximum surface excess concentration (Γ_max), and minimum area per molecule at the air/solution interface (A _min) were determined for both individual surfactants and their mixtures. The significant deviations from ideal behavior (attractive interactions) of the nonionic/ionic surfactant mixtures were also determined. Mixtures of both TX-100/SDS and TX-100/CTAB exhibited synergism in surface tension reduction efficiency and mixed micelle formation, but neither exhibited synergism in surface tension reduction effectiveness.     

The Interaction between High-Molecular-Weight Flocculents and Ionic Surfactants

The interaction between the anionic and cationic polyelectrolytes of various molecular masses and charges and the ionic surfactants in aqueous and salt solutions is studied by viscometry, conductometry, light scattering, and electrophoresis. Oppositely charged molecules of surfactant and polymer form strong complexes due to the forces of electrostatic attraction that is manifested in a significant decrease in the viscosity and light transmission, as well as in the relative reduction in solution conductivity. As the surfactant/polyelectrolyte ratio increases, the forming complexes precipitated and then dissolved again. In the case of strongly charged polyelectrolytes, the partial dissolution of precipitates was observed preceding the wide region of destabilization. In this region, the value of surfactant/polyelectrolyte charge ratio reaches 3–4. The interaction between the cationic surfactants and anionic polyelectrolyte increases with the lengthening of alkyl radical, thus indicating the presence of cooperative interactions between the surfactant molecules bonded to polymer and the important role of relevant hydrophobic interactions. As a result, the interaction between the high-molecular-weight anionic polyelectrolytes and anionic surfactants containing aromatic core takes place in some cases.     

THE EFFECT OF SINGLE MICELLES OF SURFACTANTS ON POLYMERIZATION OF ACRYLAMIDE

The polymerization of acrylamide in micellar solutions of cationic, anionic, zwitterionic and nonionic surfactants, initiated by NaHSO₃, has been studied at 20 and 30° C with time variable method of thermokinetics for the 1. 5-order reaction in this paper. Reaction mechanism has been suggested and rate equations have been derived. The results indicate that ionic (CTAB, TTABDTAB, SDS) and zwitterionic (SLS) surfactants catalyze the polymerization in the order SDS>SLS>DTAB ≈ TTA≈ CTAB, and nonionic surfactant (Brij35) has slight inhibition effect. These effects are mainly caused by the effect of the formation of micelle- HSO₃ complex on the step of initiator to form free radical.     

THE EFFECTS OF MIXED MICELLES OF SURFACTANTS ON POLYMERIZATION OF ACRYLAMIDE

The polymerization of acrylamide in mixed micellar solutions of surfactants, initiated by NaHSO₃ has been studied at 20 and 3Q° C with time variable method of thermokinetics for 1. 5-order reaction. The results indicate that the mixed micellar systems of cationic or anionic with zwitterionic surfactants (SLS/ CTAB, SLS/ TTAB, SLS/ SDS) and cationic with nonionic surfactants (Brij 357sol; CTAB, Bri-J35/TTAB, Brij35/ DTAB) have catalytic effect on the polymerization in the order, at 20° C. SLS/ SDS SLS/ TTAB SLS/ CTAB Brij35/ CTAB at 30° C SLS/ SDS SLS/ TTAB≈ / CTAB Bri-j35/ DTAB= sBrij35/ TTAB as Brij35/ CTAB, while Brij35/ SDS mixed micellar system has inhibition. These effects are attributed to the effect of the Stern layer of mixed micelles on the step of initiator (HSOT) to form free radical.