Complexation behavior of alpha-, beta-, and gamma-cyclodextrin in modulating and constructing polymer networks

A systematic study of the host-guest complexation by alpha-, beta-, and gamma-cyclodextrin (CD) in either the free state or as substituents of poly(acrylic acid) (PAA) with the hydrophobic n-octadecyl groups, C18, substituted onto PAA (HMPAA) and its effect on polymer aggregation and network formation is reported. Free alpha-CD, beta-CD, and gamma-CD mask hydrophobic associations between the C18 substituent of HMPAA in aqueous solution and form host-guest complexes with a 1:1 or CD:C18 substituent stoichiometry at 0.5 wt % polymer concentration. For alpha-CD this host-guest stoichiometry changes to 2:1 or 2alpha-CD:C18 at > or =1 wt % polymer concentrations but not for beta-CD and gamma-CD. Shear-thickening occurs when gamma-CD complexes C18 HMPAA substituents. Upon addition of sodium dodecyl sulfate, SDS (SDS:CD = 1:1), the hydrophobic associations between C18 diminished by alpha-CD masking were fully restored, were only partly restored in the case of beta-CD, and not restored for gamma-CD. When alpha- and beta-CD substituted PAA (alpha-CDPAA and beta-CDPAA) were mixed with HMPAA polymer, networks formed. As for free beta-CD, the beta-CD substituents of beta-CDPAA also formed 1:1 or beta-CD:C18 stoichiometry host-guest complexes with the C18 substituents of HMPAA. The alpha-CD substituents of alpha-CDPAA also formed 1:1 or alpha-CD:C18 stoichiometry host-guest complexes with some indication of the formation of 2:1 or 2alpha-CD:C18 stoichiometry host-guest complexes at polymer concentrations > or =1 wt %. The polymer networks formed by beta-CDPAA with HMPAA are less viscous than those formed by alpha-CDPAA, for which shear-thickening occurs at polymer concentrations > or =2 wt %. It is evident that the difference in CD annular size and its match with the C18 of HMPAA control the diversity of the interactions of alpha-CD, beta-CD, gamma-CD, alpha-CDPAA, and beta-CDPAA with HMPAA.     

Spectral properties and inclusion of 3-(4'-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one in organized media of micellar solutions, beta-cyclodextrin and viscous medium

On the line of a previous work on the spectral properties of some of heteroaryl chalcone, the absorption and fluorescence emission spectral properties of 3-(4'-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP), have been investigated in organized media of aqueous micellar and beta-cyclodextrin (beta-CD) solutions. While the absorption spectra are less sensitive to the nature of the added surfactant or beta-CD, the characteristics of the intramolecular charge transfer (ICT) fluorescence are highly sensitive to the properties of the medium. The ICT maximum is strongly blue-shifted with a great enhancement in the fluorescence quantum yield on adding micellar or beta-CD. This indicates the solubilization of DMAFP in the micellar core and formation of an inclusion complex with beta-CD. The critical micelle concentrations (CMC) as well as the polarity of the micellar core of SDS, CTAB and TX-100 have been determined. The CMC values are in good agreement with the reported values while the polarity is lower indicating that DMAFP molecules are incorporated in the micellar core not at the micellar interface. The inclusion constants of binding of DMAFP in micellar or beta-CD have been also determined. The thermodynamic parameters of formation of DMAFP:CD inclusion complex have been calculated from the temperature dependence of the fluorescence spectra of the formed complex. The highly negative value of formation entropy (DeltaS=-98.0Jmol(-1)K(-1)) reflects the high restrictions imposed on the movement of both the host and included guest molecules which is consistent with the increase of the fluorescence yield and blue shift of the fluorescence maximum.     

Inclusion complexes between beta-cyclodextrin and a Gemini surfactant in aqueous solution: an NMR study

(1)H NMR spectra, diffusion-ordered NMR (DOSY), and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY) experiments for aqueous solutions at 298 K containing the gemini surfactant, bis (dodecyl dimethylammonium)diethyl ether dibromide (12-EO(1)-12), in the absence and presence of beta-cyclodextrin (beta-CD) were used to characterize the surfactant and to determine the effects of the complexation in the micellization. For the binary system, the critical micelle concentration (cmc), the aggregation number, the stepwise micellization constant, and the size of the monomer have been obtained by studying the dependence of the chemical shifts and the self-diffusion coefficients with the concentration of surfactant. For the ternary system, the analysis of the (1)H NMR spectra and the self-diffusion coefficients reveal the formation of complexes of 1:1 and 2:1 stoichiometry (beta-CD:gemini), with a calculated stability constant for the second binding step higher than that of the first. The values of the hydrodynamic radii of the complexes were obtained from the calculated diffusion coefficients. The presence of beta-CD modifies the cmc in an extension that indicates mainly the formation of a 2:1 complex. The analysis of the chemical shifts of the surfactant indicates the nonparticipation of the complexes into the micelles. ROE enhancements depend substantially on the amount of the macrocycle added and therefore on the stoichiometry; at low concentrations of beta-CD, one of the hydrocarbon chains binds favorably with the cavity whereas the other interacts with the outer face. By contrast, at higher concentrations of beta-CD, the two hydrocarbon tails are included in two different macrocycles.     

Inhibition of the beta-cyclodextrin catalyzed dediazoniation of 4-nitrobenzenediazonium tetrafluoroborate. blocking effect of sodium dodecyl sulfate

We have investigated the effects of sodium dodecyl sulfate, SDS, on the reaction between 4-nitrobenzenediazonium, 4NBD, ions and beta-cyclodextrin, beta-CD, under acidic conditions at T = 60 degrees C by employing a combination of spectrophotometric, chromatographic, and conductometric techniques. Previous studies under acidic conditions indicate that the secondary -OH groups of beta-CD solvate 4NBD ions, which are included in the beta-CD cavity, leading to the formation of a highly unstable transient diazo ether complex that undergoes homolytic fragmentation with an observed rate constant about 1700 times higher than that in pure aqueous acid solution (t(1/2) = 6 h at T = 60 degrees C) when [beta-CD]/[4NBD] = 40. Addition of SDS to a 4NBD/beta-CD system makes the k(obs) values decrease up to its value in a SDS micellar solution, which is similar to that in aqueous acid solution. Dediazoniation product distribution is significantly affected; the reaction between 4NBD and beta-CD ([beta-CD]/[4NBD] = 40), in the absence of SDS, proceeds exclusively through a homolytic mechanism leading to the quantitative formation of nitrobenzene, ArH, but addition of SDS turns over the mechanism by promoting the heterolytic mechanism. In addition, mixtures of 4-nitrophenol, ArOH, and ArH dediazoniation products are formed; their relative yields depend on the amount of added SDS so that at very high [SDS(T)], the heterolytic mechanism becomes the predominant one. Results are consistent with conductometric measurements showing that addition of beta-CD to an aqueous surfactant solution inhibits micelle formation and elevates CMC(app) values because CD encapsulation of surfactant monomers competes with the micellization process and are interpreted in terms of SDS monomers blocking the beta-CD cavity by forming a nonreactive complex, releasing 4NBD to the bulk solution.     

Adsorption and elektrokinetic properties of the system: carboxymethylcellulose/manganese oxide/surfactant

The adsorption of carboxymethylcellulose (CMC) in the presence of the surfactants: anionic SDS, nonionic polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (Triton X-100) and their mixtures SDS/polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether with different molar ratios (1:1; 1:3 and 3:1) from the electrolyte solutions (NaCl, CaCl₂) on the manganese dioxide surface (MnO₂) was studied. In every measured system the increase of CMC adsorption in the presence of surfactants was observed. This increase was the smallest in the presence of SDS, a bit larger in the presence of polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether and the largest when the mixtures of SDS/polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether were used. Among the measured mixtures, the mixture of SDS/polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether with the molar ratio 1:3 caused the largest increase of CMC adsorption amount. These results are a consequence of formation of complexes between the carboxymethylcellulose macromolecules and the surfactant molecules. In order to determine the electrokinetic properties of the system the surface charge density of MnO₂ and the zeta potential measurements were conducted in the presence of the CMC macromolecules and the surfactants. The obtained data showed that the adsorption of CMC or CMC/surfactants complexes on the manganese dioxide surface strongly influences the structure of the electric double layer MnO₂/electrolyte solution.     

Properties of complexes and particles of gelatin with ionic surfactants

 The properties of soluble gelatinionic surfactant complexes and insoluble particles were evaluated. It was found that colloidal particles of gelatin A – cationic surfactant (dodecyltrimethyl-ammonium bromide, DTAB, and cetyltrimethylammonium bromide, CTAB) were formed. Binding isotherms showed that these particles are obtained above the CMC of each surfactant, while cooperative binding takes place. Surface tension measurements conducted for both gelatin/DTAB and gelatin/anionic surfactant, SDS (sodium dodecyl sulfate) showed a break in the curve describing surface tension vs number of bound surfactant molecules, (ν) at concentrations below the CMC of each surfactant alone. This break, which is attributed to CMC 1, is observed at the same number of bound surfactant mol ecules ν∼2 for both gelatin/surfactant couples. Contact angle measurements showed that the maximal hydro-phobicity of the gelatin-surfactant particles is obtained at the same concentration range in which the precipitation occurs. It was also found that the hydrophobicity of gelatin-SDS particles, is higher than that of the gelatin-cationic surfactants, due to a different composition of the resulting particles. The zeta potential of the particles indicated charge neutralization and even charge reversal for gelatin-CTAB at high surfactant concentration. Received: 4 April 1997 Accepted: 15 December 1997     

NMR studies on selectivity of beta-cyclodextrin to fluorinated/hydrogenated surfactant mixtures

The interactions between beta-cyclodextrin (beta-CD) and the equimolar/nonequimolar mixtures of sodium perfluorooctanoate (C(7)F(15)COONa, SPFO) and sodium alkyl sulfate (C(n)H(2n+1)SO(4)Na, C(n)SO(4), n = 8, 10, 12) were investigated by 1H and 19F NMR. It showed that beta-CD preferentially included the fluorinated surfactant when exposed to mixtures of hydrogenated (C(n)SO(4)) and fluorinated (SPFO) surfactants, notwithstanding whether the hydrogenated surfactant C(n)SO(4) was more or less hydrophobic than the SPFO. Such preferential inclusion of the fluorinated surfactant continued to a certain concentration of beta-CD at which time the C(n)SO(4) was then observed to be included. The longer the hydrocarbon chain of C(n)SO(4) the lower the concentration of beta-CD at which the hydrogenated surfactants began to show inclusion. The inclusion process can be qualitatively divided into three stages: first, formation of 1:1 beta-CD/SPFO complexes; second, formation of 1:1 beta-CD/C(n)SO(4) complexes; and finally, formation of 2:1 beta-CD/SPFO complexes upon further increase of beta-CD concentration. In the concentration range studied, during the last stage of inclusion both 2:1 beta-CD/C(12)SO(4) and 2:1 beta-CD/SPFO complexes appear to be simultaneously formed in the system of beta-CD/SPFO/C(12)SO(4) but not in either the systems of beta-CD/SPFO/C(8)SO(4) or beta-CD/SPFO/C(10)SO(4). The selective inclusion of the shorter fluorocarbon chain surfactant might be attributed to the greater rigidity and size of the fluorocarbon chains, compared to those of the hydrocarbon chains, which provide for a tighter fit and better interaction between the host and guest. This latter effect appears to dominate the increase in hydrophobic character as the carbon chain length increases in the hydrogenated series.     

Capillary electrophoretic studies on the migration behavior of cationic solutes and the influence of interactions of cationic solutes with sodium dodecyl sulfate on the formation of micelles and critical micelle concentration

The migration behavior of cationic solutes and influences of the interactions of cationic solutes with sodium dodecyl sulfate (SDS) on the formation of micelles and its critical micelle concentration (CMC) were investigated by capillary electrophoresis at neutral pH. Catecholamines and structurally related compounds, including epinephrine, norepinephrine, dopamine, norephedrine, and tyramine, which involve different extents of hydrophobic, ionic and hydrogen-bonding interactions with SDS surfactant, are selected as cationic solutes. The dependence of the effective electrophoretic mobility of cationic solutes on the concentration of surfactant monomers in the premicellar region provides direct evidence of the formation of ion-pairs between cationic solutes and anionic dodecyl sulfate monomers. Three different approaches, based on the variations of either the effective electrophoretic mobility or the retention factor as a function of surfactant concentration in the premicellar and micellar regions, and the linear relationship between the retention factor and the product of a distribution coefficient and the phase ratio, were considered to determine the CMC value of SDS micelles. The suitability of the methods used for the determination of the CMC of SDS with these cationic solutes was discussed. Depending on the structures of cationic solutes and electrophoretic conditions, the CMC value of SDS determined varies in a wide concentration range. The results indicate that, in addition to hydrophobic interaction, both ionic and hydrogen-bonding interactions have pronounced effects on the formation of SDS micelles. Ionic interaction between cationic solutes and SDS surfactant stabilizes the SDS micelles, whereas hydrogen-bonding interactions weakens the solubilization of the attractive ionic interaction. The elevation of the CMC of SDS depends heavily on hydrogen-bonding interactions between cationic solutes and SDS surfactant. Thus, the CMC value of SDS is remarkably elevated with catecholamines, such as epinephrine and norepinephrine, as compared with norephedrine. In addition, the effect of methanol content in the sample solution of these cationic solutes on the CMC of SDS was also examined.     

Decompaction of cationic gemini surfactant-induced DNA condensates by beta-cyclodextrin or anionic surfactant

Compaction of DNA by cationic gemini surfactant hexamethylene-1,6-bis-(dodecyldimethylammoniumbromide) (C12C6C12Br2) and the subsequent decompaction of the DNA-C12C6C12Br2 complexes by beta-cyclodextrin (beta-CD) or sodium dodecyl sulfate (SDS) have been studied by using zeta potential and particle size measurements, atomic force microscopy (AFM), isothermal titration microcalorimetry (ITC), and circular dichroism. The results show that C12C6C12Br2 can induce the collapse of DNA into densely packed bead-like structures with smaller size in an all-or-none manner, accompanied by the increase of zeta potential from highly negative values to highly positive values. In the decompaction of the DNA-C12C6C12Br2 complexes, beta-CD and SDS exhibit different behaviors. For beta-CD, the experimental results suggest that it can remove the outlayer hydrophobically bound C12C6C12Br2 molecules from the DNA-C12C6C12Br2 complexes by inclusion interaction, and the excess beta-CD may attach on the complexes by forming inclusion complexes with the hydrocarbon chains of the electrostatically bound C12C6C12Br2 that cannot be removed. The increase of steric hindrance due to the attachment of beta-CD molecules results in the decompaction of the DNA condensates though the true release of DNA cannot be attained. However, for SDS, the experimental results suggest that it can realize the decompaction and release of DNA from its complexes with C12C6C12Br2 due to both ion-pairing and hydrophobic interaction between SDS and C12C6C12Br2.     

Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique

The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution.     

Interaction of flavonoids within organized molecular assemblies of anionic surfactant

The interaction of various flavonoids (compounds having C6-C3-C6 configuration) with sodium dodecyl sulfate (SDS) an anionic surfactant was studied through absorption spectroscopy as a function of the concentration of surfactant above and below the critical micelle concentration (CMC) of the surfactant. A mechanism was proposed for the interaction between these flavonoids and anionic surfactants. The approximate number of additive molecules (flavonoids) incorporated per micelle was estimated at a particular concentration of SDS. Incorporation of additive in micelles shifts the UV absorption bands towards higher wavelengths of different magnitude. The spectral shift also depends upon the nature of the surfactant head group. The absorption spectra of the flavonoids in aqueous solution and in methanol are also reported.     

SDS和CTAB水溶中胶束扩散系数及第一、第二CMC测定

在无探针条件下用循环伏安法测定了不同形状SDS和CTAB胶束的扩散系数，进而得到第一CMC和第二CMC（SDS：第一CMC和第二CMC分别为8．0×10－3和5．6×10－2mol·L-1;CTAB：第一CMC和第二CMC分别为8．9×10－4和2．1×10－2mol·L－1）．此法为表面活性剂体系物理化学性质的研究，特别是为第二CMC测定提供了一个新的研究方法．     

New insights in cyclodextrin: surfactant mixed systems from the use of neutral and anionic cyclodextrin derivatives

The kinetics of the hydrolysis of 4-methoxybenzenesulfonyl chloride (MBSC) have been studied in mixed systems made up of surfactant, sodium dodecyl sulfate (SDS) or tetradecyltrimethylammonium bromide (TTABr), and cyclodextrin, beta-CD or SBE-beta-CD(Captisol). The use of SBE-beta-CD instead of beta-CD allowed us to indicate certain characteristics of the mixed cyclodextrin-surfactant system: (a) The percentage of uncomplexed cyclodextrin is higher for SBE-beta-CD than for beta-CD when we use SDS, but the opposite effect was observed when we use TTABr. This behavior can be explained by taking into account the increase in salinity when we add SBE-beta-CD, and the electrostatic forces between the SBE-beta-CD and the surfactant that have influence on the complexation. (b) The presence or even the charge of cyclodextrin has no effect on the properties of surfactant micelles once they have been formed; in particular, it does not alter K(s)(m) or k(m), parameters very sensitive to the micellar system structure. Therefore, we can conclude that for surfactants concentrations lower than the micellization point, the charge of cyclodextrin modifies the cyclodextrin-surfactant interactions but once the micelles have been formed there is no interaction between them and the cyclodextrins.     

Mixed micelles formed by SDS and a bolaamphiphile with carbohydrate headgroups

The formation of micelles in aqueous mixtures of a carbohydrate-based bolaamphiphile and sodium dodecyl sulfate (SDS) is investigated by surface tension and small-angle neutron scattering. The obtained values of critical micelle concentration (CMC) are analyzed within the framework of regular solution theory. Synergetic interactions between the bolaamphiphile and SDS are observed (parameter beta is negative; a minimum in the plot CMC vs composition). SANS data are collected for mixtures containing protonated and deuterated SDS. This gives us the possibility to conclude that mixed micelles with a homogeneous distribution of surfactant molecules within the micelle are formed. The shape of the micelles is found to be slightly oblate.     

Self-assembly of hydrophobin and hydrophobin/surfactant mixtures in aqueous solution

The self-assembly of the protein hydrophobin, HFBII, and its self-assembly with cationic, anionic, and nonionic surfactants hexadecylterimethyl ammonium bromide, CTAB, sodium dodecyl sulfate, SDS, and hexaethylene monododecyl ether, C(12)E(6), in aqueous solution have been studied by small-angle neutron scattering, SANS. HFBII self-assembles in solution as small globular aggregates, consistent with the formation of trimers or tetramers. Its self-assembly is not substantially affected by the pH or electrolytes. In the presence of CTAB, SDS, or C(12)E(6), HFBII/surfactant complexes are formed. The structure of the HFBII/surfactant complexes has been identified using contrast variation and is in the form of HFBII molecules bound to the outer surface of globular surfactant micelles. The binding of HFBII decreases the surfactant micelle aggregation number for increasing HFBII concentration in solution, and the number of hydrophobin molecules bound/micelle increases.     

Competitive adsorption in the system: carboxymethylcellulose/surfactant/electrolyte/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The adsorption of carboxymethylcellulose (CMC) in the presence or absence of the surfactants: anionic SDS, nonionic Triton X-100 and their mixture SDS/TX-100 from the electrolyte solutions (NaCl, CaCl₂) on the alumina surface (Al₂O₃) was studied. In each measured system the increase of CMC adsorption in the presence of surfactants was observed. This increase was the smallest in the presence of SDS, a bit larger in the presence of Triton X-100 and the largest when the mixture of SDS/Triton X-100 was used. These results are a consequence of formation of complexes between the CMC and the surfactant particles. Moreover, the dependence between the amount of surfactants’ adsorption and the CMC initial concentration was measured. It comes out that the surfactants’ adsorption amount is not dependent on the CMC initial concentration and moreover, it is unchanged in the whole measured concentration range. The influence of kind of electrolyte, its ionic strength as well as pH of a solution on the amount of the CMC adsorption at alumina surface was also measured. The amount of CMC adsorption is larger in the presence of NaCl than in the presence of CaCl₂ as the background electrolyte. It is a result of the complexation reaction between Ca²⁺ ions and the functional groups of CMC belonging to the same macromolecule. As far as the electrolyte ionic strength is concerned the increase of CMC adsorption amount accompanying the increase of electrolyte ionic strength is observed. The reason for that is the ability of electrolyte cations to screen every electrostatic repulsion in the adsorption system. Another observation is that the increase of pH caused the decrease of CMC adsorption. The explanation of this phenomenon is connected with the influence of pH on both dissociation degree of polyelectrolyte and kind and concentration of surface active groups of the adsorbent.     

Study of the interaction between a nonyl phenyl ether and beta-cyclodextrin: declouding nonionic surfactant solutions by complexation

Absorption and fluorescence measurements for aqueous solutions at 298 K containing pentaoxyethylene nonyl phenyl ether (NPE5), in the absence and presence of beta-cyclodextrin (beta-CD), were analyzed to determine the effect of the complexation on the aggregation of the surfactant. For the binary system, the appearance of a new emission band and the presence of an isoemissive point in the emission spectra at the time and frequency domains indicate the formation of an excimer within the micellar core. The addition of beta-CD induces the formation of an inclusion complex strong enough to break the aggregates and avoid the excimer formation. For the ternary system, the increase in fluorescence has been used to assess the binding constants of 1:1 + 2:1 stoichiometries. Static light scattering, 1H NMR diffusion-ordered spectroscopy (DOSY), and two-dimensional rotating-frame Overhauser enhancement spectroscopy (ROESY) experiments were used to characterize the cloud point of NPE5 at 298 K, and to ascertain the effects of complexation on the clouding process. In the presence of beta-CD, the analysis of the 1H NMR spectra and the self-diffusion coefficients reveal the existence of interactions between the beta-CD and the aggregates that increase the cloud-point concentration more than expected. Under conditions of excess of beta-CD, ROE enhancements point to a complex of dominant 2:1 stoichiometry (beta-CD:NPE5) in which the hydrophobic moiety of the surfactant threads two beta-CDs.     

Polymethylmethacrylate derivatives Eudragit E100 and L100: Interactions and complexation with surfactants

Precipitation or coprecipitation of polyelectrolytes has been largely investigated. However, the precipitation of polyelectrolytes via addition of charged and non‐charged surfactants has not been systematically studied and reported. Consequently, the aim of this work is to investigate the effect of different surfactants (anionic, cationic, non‐charged and zwitterionic) on the precipitation of cationic and anionic polymethylmethacrylate polymers (Eudragit). The surfactants effect has been investigated as a function of their concentration. Special attention has been dedicated to the CMC range and to the colloidal characterization of the formed dispersions. Moreover, the effect of salt (NaCl) and pH was also addressed. It is pointed out that non‐ionic and zwitterionic surfactants do not interact with charged Eudragit E100 and L100. For oppositely charged Eudragit E100/SDS and Eudragit L100/CTAB, precipitation occurs, and the obtained dispersions have been characterized in terms of particle size distribution and zeta potential. It was established that the binding of SDS molecules to Eudragit E100 polymer chains is made through the negative charges of the surfactant heads under the CMC value whereas binding of CTAB to Eudragit L100 chains is made at a CTAB concentration 5 times above its CMC. For Eudragit E100/SDS system, a more acidic medium induces aggregation. A same result was observed for the Eudragit L100/CTAB at a more basic pH. Moreover, it was observed that increasing salt concentration (higher than 100 mM) led to aggregation as generally observed for polycations/anionic surfactant systems.     

Ionic liquids as modulators of the critical micelle concentration of sodium dodecyl sulfate

Critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS), an anionic surfactant, has been investigated in aqueous solutions of a variety of room temperature ionic liquids (RTILs): 1,3-dimethylimidazolium iodide (Me2IM-I, 2), 1-butyl-3-methylimidazolium chloride (BMIM-Cl, 3), 1-hexyl-3-methylimidazolium chloride (HxMIM-Cl, 4), 1-methyl-3-octylimidazolium chloride (MOIM-Cl), 5, and 1-methyl-3-octylimidazolium tetrafluoroborate (MOIM-BF4, 6). The CMC of SDS is shown to correlate with the nature of the alkyl groups in the RTILs; SDS showed appreciably higher CMCs in presence of ionic liquids 2 and 3, whereas in the presence of ionic liquids 4, 5, and 6 much smaller CMCs were observed. The nature of the gigenions, Cl- or BF4-, has no noticeable effect on the observed CMC values.     

Investigation of the effects of cyclodextrins and organic solvents on the separation of cationic surfactants in capillary electrophoresis

The use of alpha- and beta-cyclodextrin (CD) to understand and to improve the separation of a series of cationic surfactants, homologues of alkylbenzyldimethyl ammonium compounds (ABDACs) with an alkyl chain of varying length (C10-C18), in capillary electrophoresis (CE) is reported for the first time. Similar to the effects of organic solvents, the presence of alpha- or beta-CD in the running buffer was found to reduce peak tailing/loss for the longer-chain ABDACs. Based on fluorescence measurements, it was found that formation of host-guest complexes occurred between alpha- or beta-CD and various ABDACs, with the likelihood that the hydrophobic alkyl chain including into the CD cavity and the positively charged ammonium group remaining outside the cavity. The effects of alpha- or beta-CD can be interpreted in terms of a shift away from the formation of (1) micelles in the buffer system and (2) surfactant aggregates at the fused-silica capillary walls, as a result of the formation of inclusion complexes between alpha- or beta-CD and ABDACs.