The effect of surfactants on adsorbed layers of a cationic polyelectrolyte

A comparative study of the influence of anionic (sodium dodecyl sulfate, SDS), cationic (tetradecyltrimethylammonium bromide, TTAB) and non-ionic (penta-ethyleneglycol mono n-dodecyl ether, C₁₂E₅) surfactants on the structure and composition of adsorbed layers of cationic hydrophobically modified hydroxyethylcellulose (Quatrisoft LM 200) on hydrophilic surfaces (mica and silica) was carried out using surface force apparatus andin situ null ellipsometry. It is shown that a complex interplay of electrostatic, hydrophobic, and steric effect govern polymer/surfactant/surface interactions and that the effect of surfactant addition strongly depends on its nature and concentration.Both anionic and non-ionic surfactants exhibit aggregation on the polymer hydrophobes. SDS has the most profound influence on Quatrisoft interfacial behavior due to the changes in electrostatics accompanying formation of the polymer/surfactant complex. In the case of C₁₂E₅, large surfactant clusters bound to the polymer affect the macromolecules' conformation in the adsorbed layer via steric effects. In contrast to SDS and C₁₂E₅, no evidence of interaction between the polycation and a like-charged surfactant, TTAB, was obtained. At the same time, TTAB adsorbs on the surface in competition with the polyelectrolyte. This results in partial displacement of the latter and its looser attachment to the surface.     

Light and host-guest inclusion mediated salmon sperm DNA/surfactant interactions

DNA/cationic surfactant interaction is relevant from the viewpoint of gene therapy, where the complexation and resulting compaction are essential to protect DNA from nuclease, and to allow entry of DNA into cells. In this work, light input and host-guest inclusion controlled DNA complexation by a novel cationic surfactant 1-[6-(4-phenylazo-phenoxy)-hexyl]-3-methylimidazolium bromide (AzoC6Mim) is reported. The surfactant is covalently attached with an azobenzene group, which undergoes reversible photoisomerizations by changing light input. Under visible light, trans-AzoC6Mim can bind to salmon sperm DNA through electrostatic attraction and hydrophobic interaction, resulting into DNA compaction. Under UV light, although cis-AzoC6Mim still binds to DNA chain, DNA/surfactant complex is decompacted owing to the decrease of surfactant hydrophobicity. On the other hand, azobenzene group can form an inclusion complex with α-CD through host-guest interaction, which removes AzoC6Mim from DNA chain and decompacts the DNA/surfactant complex.     

Surfactant effect on the lower critical solution temperature of poly(organophosphazenes) with methoxy-poly(ethylene glycol) and amino acid esters as side groups

 The surfactant effect on the lower critical solution temperature (LCST) of thermosensitive poly(organophosphazenes) with methoxy-poly(ethylene glycol) and amino acid esters as side groups was examined in terms of molecular interactions between the polyphosphazenes and surfactants including various anionic, cationic, and nonionic surfactants in aqueous solution. Most of the anionic and cationic surfactants increased the LCST of the polymers: the LCST increased more sharply with increasing length and hydrophobicity of the hydrophobic part of the surfactant molecule. The ΔLCSTs (T _0.03M− T _0M), the change in the LCST by addition of 0 and 0.03 M sodium dodecyl sulfate (SDS), were found to be 7.0 and 14.5 °C for the polymers bearing ethyl esters of glycine and aspartic acid, respectively. The LCST increase of poly(organophosphazene) having a more hydrophobic aspartic acid ethyl ester was 2 times larger compared with that of the polymer having glycine ethyl ester as a side group. The binding behavior of SDS to the polymer bearing glycine ethyl ester as a hydrophobic group was explained from the results of titration of the polymer solutions containing SDS with tetrapropylammonium bromide. Graphic models for the molecular interactions of polymer/surfactant and polymer/surfactant/salt in aqueous solutions were proposed. Received: 17 February 2000/Accepted: 25 April 2000     

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     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Growth of poly(methyl methacrylate) particles in three-component cationic microemulsions

Polymerization of methyl methacrylate (MMA) has been studied in ternary microemulsions which were stabilized by tetradecyltrimethylammonium bromide (TTAB) or stearyltrimethylammonium chloride (STAC). The sizes of MMA-swollen polymer particles (R_h) increased continuously during polymerization. This is in contrast to that of the styrene system, where R_h increased very rapidly to a maximum and then decreased continuously towards a constant value. The continuous growth of PMMA particles at 60°C are discussed. The stability of PMMA latexes increased with increasing the hydrophobic chain length of the cationic surfactant used. Traces of the coagulations of PMMA particles in the TTAB system can be seen from TEM. © 1995 John Wiley & Sons, Inc.     

丙烯酰胺和表面活性大单体共聚物的合成及其性能研究

首先合成表面活性大分子单体丙烯酸聚氧乙烯（２３）－十二烷基酯（ＡＡ－ＰＯＥＬＥ）,再通过与丙烯酰胺共聚合的方法得到在水溶性聚合物聚丙烯酰胺分子结构中引入疏水基团的共聚物改性ＰＡＭ。因ＡＡ－ＯＰＥＬＥ单体具有表面活性,所以共聚合时无需添加乳化剂。当改性ＰＡＭ中疏水基团含量为１．１０ｍｏｌ％时,其水溶液表现出独特的流变性和增稠性,着重讨论了改性ＰＡＭ作为乳胶增稠剂的性能。     

Adsorptive modification of hydrophobic solid surfaces by mixed surfactant solutions

We studied the reciprocal influence of a nonionic surfactant (triton X-305) and a cationic surfactant (tetradecyltrimethylammonium bromide; TTAB) on their adsorption from aqueous solution on hydrophobic glass, interfacial tension at the solution/solid interface, composition of the mixed adsorption layer, and interaction parameters between surfactant molecules in mixed adsorption layers.     

Capillary zone electrophoretic separation of neutral species of chloro-s-triazines in the presence of cationic surfactant monomers

Chloro-s-triazines are difficult to separate by capillary zone electrophoresis (CZE), due to their low pKa values. However, these analytes can be effectively separated by CZE in the presence of cationic surfactant monomers, such as tetradecylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DTAB). The separation mechanism based on a 1:1 binding of analytes to cationic surfactant monomers is proposed. The binding constants of chloro-s-triazines to cationic surfactant monomers are estimated. The results show that the strength of the interactions of these analytes with TTAB monomers is considerably strong, whereas that of the corresponding analyte with DTAB monomers is about 12- to 14-fold weaker. A linear correlation of binding constants with log P(ow) (the logarithm of the partition coefficient of analytes between 1-octanol and aqueous phases) indicates that the migration order of these chloro-s-triazines depends primarily on their hydrophobicity. Moreover, the skewed peaks of chloro-s-triazines observed may reveal the occurrence of adsolubilization of these analytes in the adsorbed cationic surfactant layer on the capillary surface.     

Surfactant fouling of nanofiltration membranes: measurements and mechanisms.

Fouling of nanofiltration membranes is studied during filtration of aqueous surfactant solutions under different conditions. To this purpose, four typical nanofiltration membranes (Desal51HL, NF270, NTR7450 and NFPES10) and three typical surfactants (nonionic neodol, anionic SDBS and cationic cetrimide) are selected. Fouling is studied as a function of the surfactant concentration, with and without addition of an electrolyte (NaCl), at different pH and when filtering a mixture of surfactants. Adsorption experiments and hydrophobicity measurements (to study the orientation of the surfactants on the membrane surface) are also performed under the different conditions. The least membrane fouling is found for the anionic surfactant SDBS, while for the cationic surfactant cetrimide very low relative fluxes are observed. Neodol shows an intermediate degree of fouling. Both hydrophobic and electrostatic interactions (in the case of ionic surfactants) between the membrane surface and the surfactant explain the degree of adsorption and hence fouling, as membrane fouling is correlated with the amount of adsorbed surfactant. The difference between cetrimide and SDBS becomes especially visible when changing the pH: increasing the pH leads not only to an opposite orientation of the adsorbed surfactants, but also to an opposite trend in adsorbed amount and membrane fouling. This study permits selection of an optimal nanofiltration membrane to recycle wastewater containing surfactants in the carwash industry. The optimal choice would be a hydrophilic membrane with a low molecular weight cut-off and a small negative surface charge at neutral pH. Cationic surfactants in the wastewater should also be avoided as much as possible.     

Influence of sodium sulfate or sodium sulfite on the solubilization of benzylalcohol in cationic micellar solutions

The enthalpy of benzylalcohol (BzOH) solution has been determined as a function of alcohol concentration in aqueous trimethyltetradecylammonium bromide (TTAB) solutions in the presence of sodium sulfite or sodium sulfate up to high salt concentration. The electrolytes studied do not seem to induce TTAB sphere-torod transition at least up to 0.6 mol/kg of salt. Comparison with the enthalpic behavior of BzOH in sodium dodecylsulfate solutions and with that of 1-pentanol in both cationic and anionic micellar solutions suggests that the solubilization of BzOH in TTAB solutions is specifically favored by intramolecular interactions between alcohol molecules within the cationic micelles. The replacement of the bromide counterions by the sulfite or sulfate ions has been studied using potentiometry with an ionselective electrode in the case of trimethylhexadecylammonium bromide (CTAB). No difference could be detected between the effects of either divalent anions on the rate of change of the bromide ion-condensation with the salt/surfactant concentration ratioR. The degree of counter-ion condensation on micellar surface depends not only on theR values, but also on the total surfactant concentration.     

Determination of the Critical Micelle Concentration of Cationic Surfactants by Capillary Electrophoresis

The determination of the critical micelle concentration (CMC) of cationic surfactants by capillary electrophoresis was demonstrated. In this study, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium bromide (DoTAB) were selected as cationic surfactants and propazine was chosen as test solute. In the evolution of the effective electrophoretic mobility of propazine as a function of surfactant concentration, a dramatic change in slope at a particular concentration is a good indication of the CMC of this surfactant. The CMC values determined experimentally were further confirmed by a curve-fitting approach. Simulation of the electrophoretic mobility curves as a function of surfactant concentration in both micellar electrokinetic chromatography and capillary zone electrophoresis using cationic surfactants as an electrolyte modifier was performed for propazine, and the intersection of these two mobility curves allowed us to precisely predict the CMC of the surfactant. The CMC values determined for TTAB and DoTAB are 1.6 ± 0.1 and 11.0 ± 0.1 mM, respectively, in the case of an electrolytic solution consisting of 70 mM phosphate buffer at pH 6.0. Moreover, the applicability of the electroosmotic mobility as a parameter for the determination of the CMC was examined.     

The interaction between a nonionic surfactant and acid dyes studied by measurements of cloud point

In order to clarify the interaction behaviors between a nonionic surfactant (S) and an acid dye (D), the cloud points (CP) were measured for the solution containing S and D with increasing amounts of electrolytes and are plotted as a function of the electrolyte concentration. A clear transition point Z was observed in the CP curve. The value of C^z, the electrolyte concentration at Z, depends upon the valence number of the cation of the added electrolyte rather than that of the anion. While the value of T^z, the temperature at Z, is independent of the kind of electrolyte and dye, but depends on the molar ratio of S to D in the solution. On the basis of the phase rule, the existence of Z was interpreted in terms of a triple point of three types of mixed micelles which are formed of S and D.     

Effect of Short Chain Alcohols upon Viscosity of TTAB Solution

The effect of ethanol (C2H5OH), propanol (C3H7OH), and butanol (C4H9OH) upon the viscosity of tetradecyltrimethylammonium bromide (TTAB) solution in the presence or absence of KBr at 30 o C was investigated, where the surfactant concentration CS is kept constant. In the absence of KBr, the relative viscosity ηr of TTAB solution increases linearly with the alcohol concentration CA, indicating that the alcohols do not promote micelle formation of TTAB. In the presence of KBr, ′r linearly decreases with CA for C2H5OH, but it exhibits a maximum with increasing CA for C3H7OH or C4H9OH. The facts reveal that C2H5OH or C4H9OH promotes the micelle formation of TTAB. A possible explanation is that the hydrophobicity of the micellar interior is enhanced by KBr, so that C2H5OH or C4H9OH can dissolve in micelle and promotes micelle formation. In the presence of KCl, which is less efficient in promoting the micelle formation of cationic surfactant, both C3H7OH and C4H9OH have only a slight effect on the micelle formation. In contrast, due to the hydrophilicity, C2H5OH cannot dissolve in micelles in the presence of KBr or KCl.     

Adsorption of ethoxylated cationic surfactants on self-assembled monolayers of alkanethiols on gold using surface plasmon resonance detection

Adsorption of a series of ethoxylated cationic surfactants at model surfaces of alkanethiol self-assembled monolayers was studied by the surface plasmon resonance technique. Model surfaces were tailor-made by choosing alkanethiols or mixtures of alkanethiols with methyl, hydroxyl, carboxyl, and trimethylammonium groups in terminal position. The ethoxylated and quaternized cationic surfactants having from 2 to 18 oxyethylene units, showed a decrease in adsorbed amount with increasing oxyethylene chain length for both hydrophobic and hydrophilic surfaces. On a negatively charged surface, containing carboxylate groups, the surfactant with only two oxyethylene groups adsorbed strongly due to electrostatic attraction and the adsorption increased with increasing amount of surface carboxylate groups. This work shows the usefulness of self-assembled alkanethiols on gold as a tool for performing surfactant adsorption studies on surfaces with variable hydrophobicity and charge.     

Interaction of surfactant with antistatic polymer thin layers

Thin layers made from three kinds of hydrophilic polymer were coated onto poly(ethylene terephthalate)(PET) fibers to study the interaction of an anionic surfactant, sodiumn-dodecyl benzenesulfonate, with the polymer layers. The coated layers include a) poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde [nonionic], b) crosslinked, sulfated PVA [anionic], and c) polyethyleneimine crosslinked with poly(ethyleneglycol diglycidylether) [cationic]. All of these coatings were found to reduce the electrostatic charging of the PET cloths, indicating that they were effectively coated with the hydrophilic polymers. The PET cloth coated with the thin layers was immersed in the aqueous solution of surfactant at 40°C for different durations and the electrostatic voltage as well as the weight change were determined after drying. When the cloth coated with the nonionic or the anionic layer was brought into contact with the surfactant, neither the electrostatic voltage nor the weight of PET changed. On the contrary, immersion in the surfactant solution brought about an increase in both the electrostatic voltage and the weight for the PET coated with the cationic layer. This suggested that the surfactant molecules were bound to the cationic layer, in contrast to the nonionic and the anionic layer. It was concluded that the binding was due to ion complexing between the cationic groups in the polymeric layer and the sulfate groups in the surfactant molecules.     

纳米SiO2与阳离子表面活性剂的相互作用及其诱导的正辛烷-水乳状液的双重相转变

研究了3种不同结构的水溶性阳离子表面活性剂对纳米二氧化硅颗粒的原位表面活性化作用, 它们分别是单头单尾的十六烷基三甲基溴化铵(CTAB)、单头双尾的双十二烷基二甲基溴化铵(di-C12DMAB)和双头双尾的Gemini型阳离子三亚甲基-二(十四酰氧乙基溴化铵)(II-14-3), 并通过测定Zeta电位、吸附等温线及接触角等参数对相关机理进行了阐述. 结果表明, 阳离子表面活性剂吸附到颗粒/水界面形成以疏水基朝向水的单分子层, 从而增强了颗粒表面的疏水性是原位表面活性化的基础. 通过吸附CTAB和II-14-3, 颗粒的疏水性适当增强, 能吸附到正辛烷/水界面稳定O/W(1)型乳状液; 而通过吸附di-C12DMAB所形成的单分子层更加致密, 颗粒的疏水性进一步增强, 进而使乳状液从O/W(1)型转变为W/O型; 当表面活性剂浓度较高时, 由于链-链相互作用, 表面活性剂分子将在颗粒/水界面形成双层吸附, 使颗粒表面变得亲水而失去活性, 但此时体系中游离表面活性剂的浓度已增加到足以单独稳定O/W(2)型乳状液的程度. 因此当采用纳米二氧化硅和di-C12DMAB的混合物作乳化剂时, 通过增加di-C12DMAB的浓度即可诱导乳状液发生O/W(1)→W/O→O/W(2)双重相转变.     

Effect of Molecular Weight on the Interfacial Dilational Viscoelasticity of Anionic Polyelectrolyte/Surfactant Systems

In this article, the effect of molecular weight on the interfacial tension and interfacial dilational viscoelasticity of polystyrene sulfonate/surfactant adsorption films at the water-octane interface have been studied by spinning drop method and oscillating barriers method respectively. The experimental results show that different interfacial behaviors can be observed in different type of polyelectrolyte/surfactant systems. PSS/cationic surfactant CTAB systems show the classical behavior of oppositely charged polyelectrolyte/surfactant systems and can be well explained by electrostatic interaction. Molecular weight of PSS plays a crucial role in the nature of adsorption film. The complex formed by CTAB and higher molecular weight PSS, which has larger dimension and stronger interaction, results in higher dilational modulus at lower surfactant bulk concentration. In the case of PSS/anionic surfactant SDS systems, the co-adsorption of PSS at interface through hydrophobic interaction with alkyl chain of SDS leads to the increase of interfacial tension and the decrease of dilational modulus at lower surfactant bulk concentration. For PSS/nonionic surfactant T × 100 systems, PSS may form a sublayer contiguous to the aqueous phase, which has little effect on interfacial tension but slightly decreases dilational modulus.     

Viscosity-Temperature Behavior of Hydroxypropyl Cellulose Solution in Presence of an Electrolyte or a Surfactant: A Convenient Method to Determine the Cloud Point of Polymer Solutions

The viscosity of hydroxypropyl cellulose (HPC) solution with or without an additive has been measured continuously as a function of temperature with the help of a vibro-viscometer. The viscosity of the polymer solution showed a gradual decrease initially with increase in temperature until a particular point beyond which there was a sharp decrease in the viscosity, which coincided with the clouding of the solution. The cloud point temperature (CP) of the polymer solution was determined from the first derivative plot of viscosity vs. temperature. Effect of addition of an electrolyte or a surfactant on the CP of HPC solution has also been studied. While a decrease in CP of HPC solution in presence of fluoride, chloride, or bromide ions was observed, presence of iodide or thiocyanide ions led to an increase in the CP. However, presence of an ionic surfactant initially lowered the CP but beyond a particular surfactant concentration a sharp increase in cloud point was observed due to interaction of the surfactant with the polymer. The results suggest that surfactants with longer hydrophobic tail or more hydrophobic groups have more affinity for HPC.     

Role of surfactants in clouding phenomenon of imipramine hydrochloride

The clouding behavior of tricyclic antidepressant drug imipramine hydrochloride (IMP) in aqueous solution has been studied in presence of surfactants. A pH increase in the presence as well as in the absence of surfactants decreased the CP. Drug molecules become neutral at high pH and therefore head–head repulsion decreases which lead to CP decrease. Addition of non-ionic and cationic surfactants increased the CP whereas anionic surfactants showed a peaked profile. Effect of CTAB/TX-100 at different fixed drug concentrations showed that at all surfactant concentrations the CP value was higher for higher drug concentrations. However, variation of pH produced opposite effect: CP at all CTAB/TX-100 concentrations decreased with increasing pH. All results are interpreted in terms of increase in hydrophobicity or hydrophilicity of micelles on addition of surfactants.