含有酰胺基或酯基的可降解阳离子Gemini表面活性剂在水溶液中的聚集行为

In the last thirty years, Gemini surfactants with various structures have been designed, synthesized, and demonstrated to show superior physicochemical properties. However, the utilization of non-degradable surfactants, including these Gemini surfactants, poses a threat to the environment; hence, degradable Gemini surfactants are desirable. Herein, biodegradable cationic Gemini surfactants with amide or ester groups in the hydrophobic chains or the spacer were synthesized. A monomeric surfactant containing an amide group and a Gemini surfactant with amide groups both in the hydrophobic chains and the spacer were synthesized for comparison. The effects of amide group location on the aggregation behavior of Gemini surfactants were studied systematically. The differences between the Gemini surfactants with amide groups and Gemini surfactants with ester groups were evaluated by comparing their aggregation behavior and hydrogen bonding formation. The Gemini surfactants with amide groups (C₁₂A-C_n-AC₁₂) in the chains showed much larger exothermic ΔH_mic and more negative ΔG_mic values than those of the corresponding monomeric surfactant C₁₂A; besides, their critical micelle concentration (cmc) was more than one order of magnitude lower than that of C₁₂A. The amide groups located in the hydrophobic alkyl chains promoted hydrogen bonding formation and self-assembly of the Gemini surfactants C₁₂A-C_n-AC₁₂. Moreover, ¹H NMR spectra revealed that the co-effect of a short spacer and hydrogen bonding leads to slow exchange of the C₁₂A-C₂-AC₁₂ molecules between the monomer and the aggregate. For the Gemini surfactant series C₁₂-AC_nA-C₁₂, the amide groups notably increased the spacer length, and largest cmc value and smallest exothermic ΔH_mic value were observed for C₁₂-AC₂A-C₁₂ instead of C₁₂-AC₆A-C₁₂. In C₁₂-AC₁₂A-C₁₂, the spacer was long and sufficiently flexible to adopt a "U"-shaped conformation above the cmc, and it acted as the hydrophobic part of the surfactant, as confirmed by ¹H NMR spectra. Among the Gemini surfactant with amide groups in both the spacer and the hydrophobic alkyl chains, C₁₂A-AC₆A-AC₁₂ had a smaller cmc and I₁/I₃ ratio as well as more exothermic ΔH_mic values than those of C₁₂A-C₆-AC₁₂ and C₁₂-AC₆A-C₁₂. ¹H NMR spectra indicated that an ester-alcohol structural equilibrium exists during aggregation for the Gemini surfactants with ester groups. In addition, the Gemini surfactants with ester groups formed water-mediated hydrogen bonds in the aggregates. This water-mediated hydrogen bonding between ester groups was weaker than the direct hydrogen bonding between amide groups. Therefore, the Gemini surfactants with ester groups, C₁₂E-C₆-EC₁₂ and C₁₂-EC₆E-C₁₂, exhibited lower surface activity, a larger micelle ionization degree, higher micropolarity, and smaller exothermic ΔH_mic and less negative ΔG_mic values than their counterparts with amide groups, C₁₂A-C₆-AC₁₂ and C₁₂-AC₆A-C₁₂.     

Self-assembling of guanidine-type surfactant

Self-assembling characteristics of dodecylguanidine hydrochloride (C 12G), a cationic surfactant with a guanidine group in its molecule, were investigated and compared with those of dodecyltrimethylammonium chloride (DTAC) and sodium dodecylsulfate (SDS). Introduction of a guanidine group into the surfactant molecule was found to increase its assembly formability more than that of the trimethylammonium group on the basis of the experimental results on the phase diagram, Kraft point, area occupied per molecule at the air-water interface, and micellar aggregation number of C 12G. Thermodynamic parameters for micelle formation suggested that an attractive force acts between guanidine groups of C 12G molecules to facilitate their assembly formation. The presence of this force was evidenced by changes in the (1)H NMR and IR spectra before and after micelle formation of the guanidine-type (G-type) surfactant, indicating that the increased assembly formability is caused by an increase in hydrogen bonding between guanidine groups of the surfactant via water molecules.     

Interaction between the water soluble poly{1,4-phenylene-[9,9-bis(4-phenoxy butylsulfonate)]fluorene-2,7-diyl} copolymer and ionic surfactants followed by spectroscopic and conductivity measurements

The interaction has been studied in aqueous solutions between a negatively charged conjugated polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer (PBS-PFP) and several cationic tetraalkylammonium surfactants with different structures (alkyl chain length, counterion, or double alkyl chain), with tetramethylammonium cations and with the anionic surfactant sodium dodecyl sulfate (SDS) by electronic absorption and emission spectroscopy and by conductivity measurements. The results are compared with those previously obtained on the interaction of the same polymer with the nonionic surfactant C12E5. The nature of the electrostatic or hydrophobic polymer-surfactant interactions leads to very different behavior. The polymer induces the aggregation with the cationic surfactants at concentrations well below the critical micelle concentration, while this is inhibited with the anionic SDS, as demonstrated from conductivity measurements. The interaction with cationic surfactants only shows a small dependence on alkyl chain length or counterion and is suggested to be dominated by electrostatic interactions. In contrast to previous studies with the nonionic C12E5, both the cationic and the anionic surfactants quench the PBS-PFP emission intensity, leading also to a decrease in the polymer emission lifetime. However, the interaction with these cationic surfactants leads to the appearance of a new emission band (approximately 525 nm), which may be due to energy hopping to defect sites due to the increase of PBS-PFP interchain interaction favored by charge neutralization of the anionic polymer by cationic surfactant and by hydrophobic interactions involving the surfactant alkyl chains, since the same green band is not observed by adding either tetramethylammonium hydroxide or chloride. This effect suggests that the cationic surfactants are changing the nature of PBS-PFP aggregates. The nature of the polymer and surfactant interactions can, thus, be used to control the spectroscopic and conductivity properties of the polymer, which may have implications in its applications.     

Synthesis and dilute aqueous solution properties of ester functionalized cationic gemini surfactants having different ethylene oxide units as spacer

New series of ester functionalized quaternary ammonium gemini surfactants having different ethylene oxide units as spacer have been synthesized and investigated for their aggregation behavior and thermodynamic properties of micellization by surface tension, conductivity, and fluorescence methods. The critical micelle concentration (cmc) of these gemini surfactants increases with the increase in the length of polar hydrophilic ethylene oxide spacer. The micellization process has been found to be entropy-driven and dependent on both the tendency of the hydrophobic group of the surfactants to transfer from aqueous environment to interior of micelle as well as the rearrangement of flexible ester-linked ethylene oxide units (hydrophilic spacer) into aqueous phase. The polar ester functional groups and pairs of nonbonding electrons on oxygen atom of ethylene oxide spacer form hydrogen bonding with water molecules enhancing their solubility in aqueous system.     

Adsorption of cationic gemini surfactants at solid surfaces studied by QCM-D and SPR: effect of the rigidity of the spacer

Two small series of cationic gemini surfactants with dodecyl tails have been synthesized and evaluated with respect to self-assembly in bulk water and at different solid surfaces. The first series contained a flexible alkane spacer and is denoted 12-n-12, with n = 2, 4, and 6. The second series had a phenylene group connected to the quaternary nitrogens in either the meta or para position and the surfactants are referred to as 12-m-Φ-12 and 12-p-Φ-12, respectively. The phenylene group is a rigid linker unit. The critical micelle concentration (cmc) was determined both by tensiometry and by conductometry, and the packing density of the surfactants at the air-water interface was calculated from the Gibbs equation. The cmc values for the geminis with a rigid spacer, 12-m-Φ-12 and 12-p-Φ-12, were of the same order of magnitude as for 12-4-12, which is the flexible surfactant that most closely matches the phenylene-based surfactants with respect to hydrophobicity, measured as log P, and distance between the positively charged nitrogen atoms. The adsorption of flexible and rigid surfactants was investigated on gold, silicon dioxide (silica), gold made hydrophobic by the self-assembly of hexadecanethiol, and gold made hydrophilic by the self-assembly of 16-hydroxyhexadecanethiol. On all of the surfaces, there was a reverse relationship between the adsorbed amount at the cmc and the length of the spacer (i.e., 12-2-12 gave the highest and 12-6-12 gave the lowest amount of adsorbed material). The adsorption pattern was similar for all of the surfactants when recorded at 25 °C. Thus, one can conclude that a rigid spacer does not render the self-assembly of a gemini surfactant difficult, neither in bulk water nor at solid surfaces. However, on one of the surfaces-untreated gold-the adsorbed amount of the geminis with a rigid spacer at 40 °C was approximately twice the values obtained at 25 °C. This is interpreted as the formation of an interdigitated bilayer at 25 °C and a regular bilayer without interpenetration of the alkyl chains at 40 °C.     

The influence of hydrophobic counterions on micellar growth of ionic surfactants

This review covers the effects of hydrophobic counterions on the phase behavior of ionic surfactants and the properties of the phases. Mixing hydrophobic counterions with ionic surfactant micellar solutions may initiate the micellar growth and transform the micellar microstructure into different morphologies. This behavior may also be achieved by mixing ionic surfactants with hydrophilic counterions, although higher counterionic concentrations are then required. First, the role of hydrophilic and hydrophobic counterions in regards to micelle growth is discussed. Second, the effect of the hydrophobic counterion on the self-assembly of cationic and anionic surfactants and their viscoelastic behavior are presented. Third, the relationships between geometry, hydrophobicity and their consequences on micellar growth for different hydrophobic counterions are reviewed. Forth, the influence of hydrophobic counterion substituents (substitution pattern) on the phase behavior is discussed. Some results we previously obtained for different isomers of hydroxy naphthaoic acids and the cationic surfactant cetyltrimethylammonium hydroxide are included. With these systems the effect that the hydrophobic counterion microenvironment has on the phase behavior, rheological behavior and the micellar microstructure is discussed. The results from other research groups are also discussed.     

Aggregation behavior of a series of anionic sulfonate gemini surfactants and their corresponding monomeric surfactant

A series of anionic sulfonate gemini surfactants with the general structure of [(Cn H2n+1)(C3H6SO(-)3) NCsN(C3H6SO(-)3)(CnH2n+1)].2Na+ have been synthesized. While the spacer group Cs represents p-xylyl or (CH2)3, the surfactants are abbreviated as CnCpxCn(SO3)2 (n=8,10,12) or C12C3C12(SO3)2(n=12), respectively. A corresponding monomeric surfactant C12H25N(CH3)(C3H6SO(-)3).Na+(C12NSO3) has also been prepared. The aggregation behavior of these surfactants has been studied at pH 9.2 and ionic strength of 30 mM. The gemini surfactants exhibit stronger aggregation tendencies and much less endothermic enthalpy changes of micellization (DeltaH mic) compared with the monomeric surfactant. The critical micelle concentrations (CMC) of the gemini surfactants decrease with the increase of the hydrophobic chain length from C8CpxC8(SO3)2 to C10CpxC10(SO3)2, but the CMC values of C10CpxC10(SO3)2 and C12CpxC12(SO3)2 are very close. The DeltaH mic values vary from endothermic for C8CpxC8(SO3)2 to almost zero for C12CpxC12(SO3)2. Besides, vesicles are observed above the CMC for all these surfactants. The water-mediated intermolecular hydrogen bonding between the tertiary nitrogen groups may assist C12NSO3 and C12C3C12(SO3)2 in their vesicle formation, while the pi-pi interaction between aromatic rings should be another additional driving force for the vesicle formation of CnCpxCn(SO3)2. Meanwhile, the hydrogen bonding, pi-pi interaction, and strong hydrophobic interaction provide the possibility of a multilayer formation for C12CpxC12(SO3)2 and C12C3C12(SO3)2 at the air/water interface, which is a possible reason for the extremely small minimum area occupied per surfactant molecule at the air/water interface for these two gemini surfactants.     

Adsorption of Gemini and Conventional Cationic Surfactants onto Montmorillonite and the Removal of Some Pollutants by the Clay

The adsorption of a series of gemini surfactants, [C(n)H(2n+1)N(+) (CH(3))(2)-CH(2)CH(2)](2).2Br(-), where n = 10, 12, 14, and 16, on clay (Na-montmorillonite) from their aqueous solution in 0.01 M KBr and the effect of this adsorption on the removal of 2-naphthol and 4-chlorophenol have been studied. Compared to those of conventional cationic surfactants with similar single hydrophilic and hydrophobic groups (C(n)H(2n+1)N(+)(CH(3))(3).Br(-), where n = 10, 12, 14, and 16), the molar adsorptions of the gemini and conventional surfactants are almost identical. This indicates that only one of the hydrophilic groups in the gemini molecule is adsorbed onto the clay and that the second hydrophilic is presumably oriented toward the aqueous phase, in contrast to the adsorption of the conventional surfactants, where the hydrophobic group is oriented toward the aqueous phase. Stability studies on dispersions of clay treated with the two types of surfactants confirm this. The slight increase in the moles of surfactant to values above the CEC of the clay with an increase in the carbon number of the hydrophobic chain indicates that adsorption through hydrophobic group interaction occurs in addition to the major ion exchange. Adsorption studies of the pollutants onto the clay treated by either the gemini or the conventional surfactants show that the former are both more efficient and more effective at removing the pollutants from the aqueous phase. Copyright 2000 Academic Press.     

Properties of mixed micelles of cationic gemini surfactants and nonionic surfactant triton X-100: effects of the surfactant composition and the spacer length

The mixed micelles of cationic gemini surfactants C12C(S)C12Br2 (S=3, 6, and 12) with the nonionic surfactant Triton X-100 (TX100) have been studied by steady-state fluorescence, time-resolved fluorescence quenching, electrophoretic light scattering, and electron spin resonance. Both the surfactant composition and the spacer length are found to influence the properties of mixed micelles markedly. The total aggregation number of alkyl chains per micelle (N(T)) goes through a minimum at X(TX100)=0.8. Meanwhile, the micropolarity of the mixed micelles decreases with increasing X(TX100), while the microviscosity increases. The presence of minimum in N(T) is explained in terms of the competition of the reduction of electrostatic repulsion between headgroups of cationic gemini surfactant with the enhancement of steric repulsion between hydrophilic headgroups of TX100 caused by the addition of TX100. The variations of micropolarity and microviscosity indicate that the incorporation of TX100 to the gemini surfactants leads to a more compact and hydrophobic micellar structure. Moreover, for the C12C3C12Br2/TX100 mixed micelle containing C12C3C12Br2 with a shorter spacer, the more pronounced decrease of N(T) at X(TX100) lower than 0.8 may be attributed to the larger steric repulsion between headgroups of TX100. Meanwhile, the increase of microviscosity and the decrease of micropolarity are more marked for the C12C12C12Br2/TX100 mixed micelle, owing to the looped conformation of the longer spacer of C12C12C12Br2.     

The Adsorption of Gemini and Conventional Surfactants onto Some Soil Solids and the Removal of 2-Naphthol by the Soil Surfaces

The adsorption of two cationic gemini surfactants, [C(n)H(2n+1) N(+)(CH(3))(2)-CH(2)CH(2)](2).2Br(-), where n=12 and 14, on limestone, sand, and clay (Na-montmorillonite) from their aqueous solution in double-distilled water and the effect of this adsorption on the removal of 2-naphthol have been studied. Compared to those of conventional cationic surfactants with similar single hydrophilic and hydrophobic groups (C(n)H(2n+1)N(+)(CH(3))(3).Br(-), where n=12 and 14), the molar adsorptions of the gemini and the conventional surfactants on Na-montmorillonite are almost identical and very close to their cation exchange capacities. On sand and limestone, the molar adsorption of the cationic gemini surfactants is much larger than that of their corresponding conventional surfactants. Adsorption studies of the pollutants onto the three kinds of solids treated by either the gemini or the conventional surfactants show that the former are both more efficient and more effective at removing 2-naphthol from the aqueous phase. On all three soil solids, the addition of KBr increases the efficiency of the adsorption of both types of cationics and for most cases increases also the maximum amount adsorbed, but decreases slightly the efficiency of removal of 2-naphthol. On limestone, the anionic gemini adsorbs with one hydrophilic group oriented toward the Ca(2+) sites on the surface and its second hydrophilic group oriented toward the aqueous phase. The conventional anionic surfactant forms a double layer. The gemini anionic is more efficient and more effective than the conventional anionic in the removal of 2-naphathol from the aqueous phase. Both anionic conventional and gemini surfactants have no adsorption on sand. The adsorption mechanisms for all the surfactants on the three soil solid surfaces are discussed. Copyright 2001 Academic Press.     

Synthesis and vesicular self-assembly of a novel asymmetric cationic and ethoxylated amphiphile

Cationic quaternary ammonium and nonionic oligo(ethylene oxide) are attractive classes of polar units for new amphiphile synthesis. However, they present distinct physical and chemical properties. We combine these two hydrophilic groups to each side of a hydrophobic segment, getting a new asymmetric cationic ethoxylated amphiphile (EO₁₂BphC₁₀NC₁₂). Different from common amphiphiles, EO₁₂BphC₁₀NC₁₂ not only connects different hydrophilic units on both ends of hydrophobic spacers but also integrates the structural characters of bola- and gemini-form amphiphiles together, which brings interesting properties to the new building block. We studied its surface activity and self-assembly behavior in aqueous solution. It turns out that EO₁₂BphC₁₀NC₁₂ can reduce the surface tension of aqueous solution and self-assembly into vesicles above the critical aggregation concentration. More importantly, the strong nuclear Overhauser effect between quaternary ammonium cation and the first oxyethylene group indicates that the two headgroups locate at the vesicle surface together randomly, other than selectively occupy inner or outer vesicle surface. The synergistic effect of molecular size and hydration of different hydrophilic groups leads to the interdigitated packing state of alky chains in the vesicle with symmetric membrane.     

Interfacial and self-assembly properties of bolaamphiphilic compounds derived from a multifunctional oil

The self-assembly characteristics in aqueous solutions of cationic bolaamphiphiles with systematic changes in their chemical structure is described with respect to their interfacial properties within water and at the air/water interface. Six cationic bolaamphiphiles were synthesized from multifunctional vernonia oil with the following variations: (a) two different alkyl chain lengths connecting the head groups, (b) polar ester or hydrogen bonding amide groups within the hydrophobic domain, and (c) an acetylcholine cationic head group with different conjugation sites to the alkyl chain. Surface tension measurements were used for determining critical aggregation concentration (CAC) values and air/water interfacial parameters such as 'effectiveness', surface excess concentration and area occupied by one molecule in the air/water interface. Fluorescent studies with pyrene were used to characterize CAC properties within the aqueous volume and transmission electron microscopy (TEM) for determining the aggregate structure's size, homogeneity and morphology. A bolaamphiphile molecular structure vs. interfacial property relationship was derived from this data which could be used to determine the molecular structure properties needed to generate interfacial forces to form either spherical vesicles or fibrous networks. The effects of the aliphatic chain length, head group orientation and functional groups within the hydrophobic domain on CAC, surface tension properties and self-aggregate morphology are described. Most bolaamphiphiles studied had CAC values in the 10-190 μM range, while two out of the six were found to assemble into MLM spherical vesicles with diameters ranging up to 120 nm suitable for drug delivery applications. Others formed a gelatinous network of fibers or multi-lamellar vesicles.     

Surfactants with an amide group "spacer": Synthesis of 3-(acylaminopropyl)trimethylammonium chlorides and their aggregation in aqueous solutions

The cationic surfactants RCONH(CH2)3N+(CH3)3Cl-, where RCO = C10, C12, C14, and C16, respectively, have been synthesized by reacting the appropriate carboxylic acids with 3-N,N-dimethylamino-1-propylamine, followed by dehydration of the ammonium salt produced. Reaction of the intermediates obtained (RCONH(CH2)3N(CH3)2) with methyl iodide, followed by chloride/iodide ion-exchange furnished the surfactants. Their adsorption and aggregation in aqueous solutions have been studied by surface tension, conductivity, EMF, static light scattering and FTIR. Additional information on the micellar structure was secured from effects of the medium on the 1H NMR chemical shifts and 2D ROESY spectra. Increasing the length of the acyl moiety increased the micelle aggregation number, and decreased the minimum area/surfactant molecule at the solution/air interface, the critical micelle concentration, and the degree of dissociation of the counter-ion. Gibbs free energies of adsorption at the solution/air interface and of micelle formation were calculated, and compared to those of 2-(acylaminoethyl)trimethylammonium chloride; alkyl trimethylammonium chloride; and benzyl(3-acylaminopropyl)dimethylammonium chloride surfactants. For both processes (adsorption and micellization), contributions of the CH2 groups in the hydrophobic tail and of the head-group to DeltaG0 were calculated. The former contribution was found to be similar to those of other cationic surfactants, whereas the latter one is more negative than those of 2-(acylaminoethyl)trimethylammonium chlorides and trimethylammonium chlorides. This is attributed to a combination of increased hydrophobicity of the head-group, and (direct- or water-mediated) intermolecular hydrogen-bonding of aggregated monomers, via the amide group. FTIR and NMR results indicated that the amide group lies at the micellar interface.     

Spectral study of Eriochrome Blue Black R in different cationic surfactant solutions

Interactions of anionic dye Eriochrome Blue Black R (EBBR) with various cationic micelles of surfactants n-alkyltrimethylammonium CnTAB (n=12; 14; 16 and 18) have been investigated spectrophotometrically at 25°C in premicellar and postmicellar region. The results have shown that with increasing the alkyl chain length of surfactants, the maximum absorbance of EBBR shifted to a higher wavelength and the binding constants of EBBR to cationic micelles (Kb) increases. This confirms that the surfactant micelle, which has a longer alkyl hydrocarbon chain, enables greater solubilization of dye. Thus, the hydrophobic interaction of the dye with micelles increases in the order: C12TAB相似文献   

Synthesis and micellar properties of surface-active ionic liquids: 1-alkyl-3-methylimidazolium chlorides

A series of surface-active ionic liquids, RMeImCl, has been synthesized by the reaction of purified 1-methylimidazole and 1-chloroalkanes, RCl, R=C(10),C(12),C(14), and C(16), respectively. Adsorption and aggregation of these surfactants in water have been studied by surface tension measurement. Additionally, solution conductivity, electromotive force, fluorescence quenching of micelle-solubilized pyrene, and static light scattering have been employed to investigate micelle formation. The following changes resulted from an increase in the length of R: an increase of micelle aggregation number; a decrease of: minimum area/surfactant molecule at solution/air interface; critical micelle concentration, and degree of counter-ion dissociation. Theoretically-calculated aggregation numbers and those based on quenching of pyrene are in good agreement. Gibbs free energies of adsorption at solution/air interface, DeltaG(ads)(0), and micelle formation in water, DeltaG(mic)(0), were calculated, and compared to those of three surfactant series, alkylpyridinium chlorides, RPyCl, alkylbenzyldimethylammonium chlorides, RBzMe(2)Cl, and benzyl(3-acylaminoethyl)dimethylammonium chlorides, R(')AEtBzMe(2)Cl, respectively. Contributions to the above-mentioned Gibbs free energies from surfactant methylene groups (in the hydrophobic tail) and the head-group were calculated. For RMeImCl, the former energy is similar to that of other cationic surfactants. The corresponding free energy contribution of the head-group to DeltaG(mic)(0) showed the following order: RPyCl approximately RBzMe(2)Cl>RMeImCl>R(')AEtBzMe(2)Cl. The head-groups of the first two surfactant series are more hydrophobic than the imidazolium ring of RMeImCl, this should favor their aggregation. Micellization of RMeImCl, however, is driven by a relatively strong hydrogen-bonding between the chloride ion and the hydrogens in the imidazolium ring, in particular the relatively acidic H2. This interaction more than compensates for the relative hydrophilic character of the diazolium ring. As indicated by the corresponding DeltaG(mic)(0), micellization of R(')AEtBzMe(2)Cl is more favorable than that of RMeImCl because the CONH group of the former surfactant series forms hydrogen bonds to both the counter-ion and the neighboring molecules in the micelle.     

Foaming and foam stability for mixed polymer-surfactant solutions: effects of surfactant type and polymer charge

Solutions of surfactant-polymer mixtures often exhibit different foaming properties, compared to the solutions of the individual components, due to the strong tendency for formation of polymer-surfactant complexes in the bulk and on the surface of the mixed solutions. A generally shared view in the literature is that electrostatic interactions govern the formation of these complexes, for example between anionic surfactants and cationic polymers. In this study we combine foam tests with model experiments to evaluate and explain the effect of several polymer-surfactant mixtures on the foaminess and foam stability of the respective solutions. Anionic, cationic, and nonionic surfactants (SDS, C(12)TAB, and C(12)EO(23)) were studied to clarify the role of surfactant charge. Highly hydrophilic cationic and nonionic polymers (polyvinylamine and polyvinylformamide, respectivey) were chosen to eliminate the (more trivial) effect of direct hydrophobic interactions between the surfactant tails and the hydrophobic regions on the polymer chains. Our experiments showed clearly that the presence of opposite charges is not a necessary condition for boosting the foaminess and foam stability in the surfactant-polymer mixtures studied. Clear foam boosting (synergistic) effects were observed in the mixtures of cationic surfactant and cationic polymer, cationic surfactant and nonionic polymer, and anionic surfactant and nonionic polymer. The mixtures of anionic surfactant and cationic polymer showed improved foam stability, however, the foaminess was strongly reduced, as compared to the surfactant solutions without polymer. No significant synergistic or antagonistic effects were observed for the mixture of nonionic surfactant (with low critical micelle concentration) and nonionic polymer. The results from the model experiments allowed us to explain the observed trends by the different adsorption dynamics and complex formation pattern in the systems studied.     

Interaction between β‐Cyclodextrin and Mixed Cationic‐Anionic Surfactants (2): Aggregation Behavior

The interactions between β‐cyclodextrin (β‐CD) and the mixtures of cationic‐anionic surfactants in the aqueous solution were investigated by surface tension, rheology, and dynamic light scattering measurements. It was shown that the key‐lock interactions between β‐CD and mixed cationic‐anionic surfactants were stronger than the electrostatic/hydrophobic interactions between cationic and anionic surfactants. The inclusion of β‐CD to surfactants could destroy the ion‐pair and aggregates of cationic‐anionic surfactants, and even inhibited the precipitation of the mixed cationic‐anionic surfactants. Furthermore, the inclusion of β‐CD to surfactants could also destroy the hydrogen bond between β‐CD molecules, inducing the disassociation of the aggregation formed by β‐CD themselves.     

Electromotive force study on interaction between a triblock copolymer and cationic surfactants in water

The interaction between a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer F127 and three cationic surfactants with varying alkyl chain length in water were investigated in detail by electromotive force (EMF) studies. The cationic surfactants investigated are hexadecyltrimethylammonium bromide (HTAB), myristytrimethylammonium bromide (MTAB), and lauryltrimethylammonium bromide (LTAB) which have carbon numbers of 16, 14, and 12 in the alkyl chain, respectively. Obvious binding was detected by EMF measurements between F127 and HTAB. For MTAB, the binding has also been detected with a weaker strength than that of HTAB. The LTAB/F127 mixed system exhibits the weakest binding, presumably due to the too short alkyl chain. This indicates that the binding between cationic surfactants and F127 is mainly dominated by the hydrophobic/hydrophobic interaction. In addition, the interaction also shows considerable dependence on the concentration of F127 and solution parameters such as the salinity.     

Polyoxyethylene alkyl ether nonionic surfactants: physicochemical properties and use for cholesterol determination in food

Polyoxyethylene alkyl ethers, C(n)E(m), are nonionic surfactants made of an alkyl chain with n methylene groups and a hydrophilic part with m oxyethylene units. C(n)E(m) nonionic surfactants are very useful in chemical analysis. The commercially available products are often a mixture of several C(n)E(m) molecules with different m values. Pure C(n)E(m) surfactants are now available. The physicochemical parameters: critical micelle concentration (c.m.c.), molar volume, density, cloud-point temperature and hydrophile-lipophile balance value for pure C(n)E(m) surfactants were collected from the literature. Regression analyses were carried out on the data. They showed that strong correlations existed between the structure of the molecule (n and m values) and its physicochemical properties. General equations linking the c.m.c., molar volume, density and cloud-point temperature of the C(n)E(m) surfactants and their structure (n and m values) are proposed and discussed. The use of these surfactants in chemical analysis is illustrated by the determination of cholesterol in egg yolk. Cholesterol was separated from the bulk yolk by cloud-point extraction using the C(12)E(10) surfactant. It was quantitated using micellar liquid chromatography. The C(12)E(23) surfactant was used to prepare the micellar mobile phase that allowed the separation of cholesterol and the use of an enzymatic detector.     

Synthesis and surface properties of semi-fluorinated gemini surfactants with two reactive bromo pendant groups

This paper presents a series of semi-fluorinated gemini surfactants with two bromo pendant groups. It reviews the effect of the number of methylene units in the spacer group between the two hydrophilic quaternary ammonium heads. Critical micelle concentration (cmc) and free energy of micellization (ΔG(M)(0)) of the title surfactants, in aqueous solution, have been investigated as a function of the number n of carbon atoms in the hydrocarbon spacer. We have pointed out a different behaviour as compared to Gemini hydrocarbon homologues. In the present study, when the number of methylene units (n) in the spacer increases, the cmc first decreases and reaches an optimum for (n=6), then it increases linearly from n≥6. Variations of cmc have been interpreted in terms of conformation changes of the surfactant ion and progressive penetration of the alkyl chain spacer in the micelle hydrophobic core. In this series, the increase of the hydrophobicity seems not to favour the micellisation process as expected, probably impacted by the mutual phobicity of the perfluorinated tails and the hydrocarbon spacer. A minimum is reached for a spacer with six methylene units which seems to be the optimal conformation. The free energy of micellization (ΔG(M)(0)) confirm this tendency.