Formation Of Premicellar Aggregates Research Articles

Effects of head-group volume on the thermodynamic parameters and species distribution of ionic liquid-based surfactants in water: 1-(n-hexadecyl)-3-alkylimidazolium bromides and chlorides

The following series of ionic liquid-based surfactant halides was studied: 1-(n-hexadecyl)-3-Cm-imidazolium bromides and chlorides (C16CmImBr and C16CmImCl, respectively) where Cm = C1-C4. Using isothermal titration calorimetry, we calculated the enthalpy of micelle formation (ΔH⁰mic) at 25 °C for both halide surfactants, and from 15 to 70 °C for C16CmImCl. Values of ΔH⁰mic were then employed to calculate the entropy of micelle formation (ΔS⁰mic) from the corresponding free energy (ΔG⁰mic); the latter was calculated from the critical micelle concentration (cmc) and the degree of counter-ion dissociation (αmic). Values of ∣ΔG⁰mic∣ increase as a function of increasing Cm, although this increase is smaller than that of the previously studied series CnC1ImCl, where Cn = C10 to C16. This is attributed to the difference in dehydration of the surfactant segments that accompanies micelle formation, which is much larger for the increase in the hydrophobic chain (CnC1ImCl) than for the head-group (C16CmImCl). The calculated enthalpograms (ΔH⁰dilution versus [surfactant]) for C16C4ImBr showed deviation from ideal solution behavior, this was attributed to the formation of premicellar aggregates. The latter conclusion was corroborated by Pulsed Field Gradient (PFG)-NMR experiments of C16CmImCl in D2O. Thus, a model based on the presence of the following species in solution fitted satisfactorily the dependence of the observed surfactant diffusion coefficients on [surfactant]: free surfactant molecules; premicellar aggregates and micellized surfactant. The concentration of the premicellar aggregates increases noticeably as a function of increasing Cm, due to hydrophobic interactions between the Cm groups. The solubilization of (anionic) thymol blue indicator by C16CmImBr was studied using UV–Vis spectroscopy. The solubilization power (=moles of solubilized molecule/mole of micellized surfactant) was calculated, and compared with our previous data on the solubilization of (hydrophobic) Sudan IV dye and (less hydrophobic) drug nitrendipine by C16CmImBr. In all cases, the solubilization power decreases as a function of increasing Cm, albeit to different degrees, due to a combination of steric hindrance by the head-group, and decreased micelle size, both acting in the same direction.

Corrigendum to “Investigation on the gelatin-surfactant interaction and physiochemical characteristics of the mixture” [Journal of Molecular Liquids, 224 (2016) 900–908/MOLLIQ_2015_362

Abstract The effect of gelatin, a denatured protein on the micellization of a series of polyoxyethylated hexadecyl ethers (BC-X) were investigated through several physicochemical techniques such as surface tensiometry, contact angle measurement, fluorimetry, cyclic voltametry, zeta potential measurement, dynamic light scattering studies. The critical micellar concentrations (cmc) of BC-X increased with increase in gelatin concentration in the mixture which was also corroborated by other techniques performed. This increase in cmc was attributed to the decrease of monomeric surfactant concentration as a result of the formation of gelatin-BC-X complex. The surface excess concentration, minimum area per molecule, and surface pressure at the cmc were estimated from surface tension data. The free energies of adsorption and micellization indicated the micellization and adsorption at air/water interface to be spontaneous phenomena. Micropolarity and the aggregation numbers of the mixed systems were determined using the fluorescence behaviour of pyrene. The slanting nature of curve of polarity parameters-surfactant concentration in conjunction with appearance of pyrene excimer peak at the lower BC-X concentrations supported the stepwise growth of the micelles through the formation of pre-micellar aggregates. The entwining of the protruded chains of the surfactants around the gelatin moiety through polar and hydrophobic interactions was endorsed to be the main reason behind the formation of small sized mixed micelles. The zeta potential studies envisaged the surface of both gelatin and BC-X to have negative electrostatic potential independently. The decrease in the zeta potential of the gelatin-surfactant mixtures was attributed to the removal of fraction of the negatively charged BC-X surface as a result of casing by the hydrophobic and neutral segments of gelatin.

Interaction of alkyl chain containing pyrene derivatives with different micellar media: Synthesis and photophysical study.

The present work describes the synthesis and photophysical studies of four newly synthesized alkyl chain containing pyrene derivatives and their applications in micellization process of different types of surfactants e.g. CTAB and SDS. The fluorescent properties of these pyrene derivatives were utilized to understand the micellization process of CTAB and SDS. The length of alkyl chain affects the hydrophobicity of pyrene fluorophore which also affects the sensitivity of fluorophore towards the micellization of CTAB and SDS surfactants. The longest alkyl tail containing, PBBU showed more sensitivity whereas moderate alkyl chain containing, PABU and PBME showed moderate sensitivity and finally PAME contained smallest alkyl tail, showed no sensitivity towards the micellization of CTAB and SDS. The alkyl tail of fluorophore make it more hydrophobic and it could easily bind with the hydrophobic inner core of micelles. In both surfactants, PBBU showed LE emission at ~400 nm and aggregate emission at ~470 nm, whereas, PABU and PBME showed LE emission band at ~400 nm. Before CMC, the aggregates band of PBBU increased with increasing the surfactant concentrations, but after CMC the individual PBBU present into the water medium could binds with the inner core of micelles. Thus PBBU senses the formation of premicellar aggregates of CTAB and SDS. The LE emission of the fluorophore gradually increases while increasing the CTAB and SDS concentrations. The change in fluorescence emission of PABU, PBME and PBBU with increasing concentration of CTAB and SDS were used to calculate the CMC of CTAB and SDS surfactants.

Photophysical properties and interaction studies of Rose Bengal derivatives with biomimetic systems based in micellar aqueous solutions

Xanthene dyes are compounds extensively used in Photodynamic Therapy against infection caused by microorganisms, cancer and other diseases. In this study, structural changes in Rose Bengal (RBB) xanthene photosensitizer (PS) were performed in order to improve its interaction with biological substrates. In this way, hydrophobic RBB ester derivatives were obtained through insertion of a hydrocarbon chains containing 1, 4 and 10 carbons. The spectroscopic and photophysical properties of these compounds in homogeneous medium (water at physiological pH) and micro-heterogeneous micellar systems formed by sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB) and Pluronic™ P-123 copolymeric surfactant were evaluated. The interaction between the PS and these micelles showed that association and location are significantly dependent on PS and micelle charges, length of the inserted hydrocarbon tail (hydrophobic effects) and the micellar structure. The binding constants (Kb) for the xanthenes in SDS, P-123 and CTAB micelles follow the same trend of the partition coefficients, which reveal the influence of the hydrophobic effects on PS/micelle interaction. Resonance Light Scattering (RLS) and fluorescence anisotropy studies showed the formation of pre-micellar aggregates of PS combined with CTA+ which justifies the high Kb values in this system. Comparative analyses of Stern-Volmer constant (KSV) confirm the pKa results showing that location of each PS into the micelles depends on both, its hydrophobicity and charge. Finally, singlet oxygen quantum yield (ΦΔ1O2) of the ester derivatives presented values from 0.83 to 0.89 such shows that they exhibit high potential to be applied in future photodynamic treatments.

Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces.

The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (Kb) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.

Synthesis and aggregation behaviors of disulfonate gemini surfactant with double hexadecyl tails

Abstract Dihexadecyl diphenyl ether disulfonate (C 16 -DADS) was synthesized via three-step reactions: Friedel-Crafts alkylation, sulfonation and neutralization. 1 H NMR and ESI–MS were used to characterize the structure of target products. The aggregation behaviors of C 16 -DADS in aqueous solutions were investigated by electrical conductivity, steady–state fluorescence, dynamic light scattering, transmission electron microscopy and rheological measurements. The results show that spherical micelles, wormlike micelles, wormlike micellar gels and network of branched worms are formed with increasing the surfactant concentration. The electrical conductivity data show that C 16 -DADS possess a relatively low critical micelle concentration (0.105 mM, 30 °C) and the micellization process is primarily driven by the entropy. Transmission electron microscopy images demonstrate the existence of spherical micelles in C 16 -DADS solutions with 0.8 mM and 2 mM surfactant concentrations. The average aggregation number values of C 16 -DADS are low because of the formation of premicellar aggregates. Wormlike micelles formed by C 16 -DADS without additive are proved by rheological experiments, particularly fascinating is the formation of wormlike micellar gels and network of branched worms with the increase of C 16 -DADS concentration.

Effects of added salts on adsorbed film and premicelle formation of crown ether surfactants

Abstract Two crown ether surfactants, dodecanoyloxymethyl- (C11Φ5) and octanoyloxymethyl-15-crown-5 (C7Φ5), were synthesized and the concentration dependence of surface tension of their aqueous solutions was measured in the absence and the presence of various salts to study the effect of coexistent cation on adsorbed film and aggregation behavior of crown ether surfactants. In the absence of salt, the surface tension vs. concentration curves had two break points for both C11Φ5 and C7Φ5. The break point at the higher concentration (m0) was confirmed to be attributed to the micelle formation by the solubilization of water-insoluble dye and the concentration dependence of proton chemical shifts. Another break point at the lower concentration (mI) would be caused by the formation of premicellar aggregates. For C11Φ5 in the presence of KCl two break points were also observed. At about 0.05 mol kg−1 KCl, m0 and mI were minimized. The cause would be that the salting-out effect of KCl dominates below 0.05 mol kg−1 but above it the repulsive interaction between charged head groups of C11Φ5 complex with K+ becomes larger than it. Two break points were also observed for C11Φ5 in the presence of LiCl, NaCl, CsCl and NH4Cl of 0.22 mol kg−1. It has been found that the critical micelle concentration (m0) are the highest for Na+ having an ionic diameter comparable to the hole size of 15-crown-5 ring and decrease as an ionic diameter of added cation departs from the hole size. The aggregation number of premicelle, which was estimated from the surface excesses at mI and m0 on the assumption of two step micellization, has been about 4 in the absence of salt, about 3 for Li+ hydrated strongly and about 2 for all other cations.

Tailoring strained oxanorbornane headgroups to dimensionally controlled nanostructures through hydrogen bonding

An amphiphilic oxanorbornane skeletal frame has been efficiently organized to direct the formation of dimensionally controllable, geometry-specific nanostructures as diverse as 0-D surface/reverse micelles, 1-D nanofibers, 2-D rectangular/square sheets, and 3-D flowers. The racemate with its precise stereo-projection of the –OH groups and the ring oxygen could be used for Li+ ion sensing and aided in the formation of pre-micellar aggregates of conventional surfactants.

Synthesis and properties of novel alkyl sulfate gemini surfactants

Four anionic gemini surfactants of the sulfate type C12CnC12, where n is the spacer chain length (n = 3, 4, 6, and 10) were synthesized. The structures of these surfactants were confirmed by FT-IR, 1H NMR, ESI mass spectra (ESI-MS), and elemental analysis. The surface-active properties of these compounds were investigated by means of surface tension, electrical conductivity, and fluorescence measurements. Premicellar aggregations were found for the four gemini surfactants, as revealed by the conductivity measurement. The formation of premicellar aggregates may account for the discrepancy between the critical micelle concentration (cmc) obtained by the surface tension and conductivity measurement. The cmc values of these gemini surfactants were much lower than that of sodium dodecylsulfate (SDS) and decreased monotonously with the increase of spacer chain length from 3 to 10. The effect of spacer chain length on the performance properties like foaming, emulsion stability, and lime soap dispersing ability were also studied and discussed. Practical applications: Alkyl sulfate surfactants are one of the most widely used surfactants. The new alkyl sulfate gemini surfactants synthesized in our study are more surface-active than sodium dodecylsulfate. These gemini surfactants possess low critical micelle concentrations, high emulsion stability, and excellent lime soap dispersing ability. They have potential applications in the fields of cosmetics, detergents, etc.

Diffusion Interactions of Some Biologically Important Transition Metal Complexes on Micellar Properties of Sodium Dodecyl Sulphate

The specific conductance of aqueous solutions of sodium dodecyl sulphate (SDS) was measured from 20 to 35 ºC with an interval of 5 °C in the absence and presence of metal complexes such as [Cr(acac)2(H2O)2]Cl, K3[Fe(C2O4)3] and (NH4)4[Co(C6H5O7)2] at concentrations ranging from 2.0 × 10-4 to 8.0 x 10-4 M. The specific conductance rapidly increased at the pre-micellar region with increasing of temperature and concentration of SDS, but after critical micelle concentration (CMC) the rate of increase was slower. As the concentrations of metal complexes [Cr(acac)2(H2O)2]Cl, K3[Fe(C2O4)3] and (NH4)4[Co(C6H5O7)2] increased, the CMC of SDS decreased exponentially, which was sharp with increasing temperature. The CMC decreases due to the formation of pre-micellar aggregates of the positive counter ions of the complexes with dodecyl sulphate ions (DS-) and hydrophobic interaction between ligands of complexes and hydrophobic tail of SDS. The pre-micellar aggregate formation was essentially influenced by the counter ions binding abilities to the anionic micelle. The effect of metal complexes on lowering the CMC of SDS was found to follow the order [Cr(acac)2(H2O)2]Cl &lt; K3[Fe(C2O4)3] &lt; (NH4)4[Co(C6H5O7)2]. Thermodynamics of metal complexes with SDS and parameters of micellization ΔG°mic, ΔH°mic and TΔS°mic were calculated.Keywords: Surfactants; Sodium dodecyl sulphate; Critical micelle concentration; Pre-micellar aggregate; Hydrophobic interaction.© 2011 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i1.7989J. Sci. Res. 4 (1), 135-141 (2012)

Determination of the critical micelle concentration of surfactants and amphiphilic block copolymers using coumarin 153

We describe a method to determine the critical micelle concentration (CMC) of low molecular weight surfactants and amphiphilic diblock copolymers in water based on the use of the fluorescent dye coumarin 153 (C153). The method is based on the measurement of the fluorescence intensity, solvatochromic shift and fluorescence anisotropy of C153 and was tested with the low molecular weight surfactants SDS, CTAB and Triton X-405 in water, for which we obtained, within the experimental error, CMC values identical to those previously published. The method was further used to determine the CMC of a family of poly(N-decylacrylamide)-b-poly(N,N-diethylacrylamide) amphiphilic block copolymers synthesized by RAFT polymerization, with an equal poly(N-decylacrylamide) hydrophobic block length and increasing poly(N,N-diethylacrylamide) hydrophilic block lengths. By measuring the fluorescence anisotropy of C153 in block copolymer aqueous solutions, it is also possible to detect the formation of pre-micellar aggregates at concentrations below the CMC. The dye C153 is more appropriate than pyrene to study self-assembly in water, where pyrene forms ground and excited state aggregates at very low concentrations. Furthermore, C153 is an excellent anisotropy probe with a very high limiting anisotropy (0.375) that can be used to determine the CMC, detect the presence of pre-micellar aggregates, and evaluate the fluidity of the hydrophobic core of block copolymer micelles.

Study on premicellar and micellar aggregates of gemini surfactants with hydroxyl substituted spacers in aqueous solution using a probe showing TICT fluorescence properties

The aggregation properties of two gemini surfactants, 12-3(OH)-12,2Br − and 12-4(OH) 2-12,2Br − with hydroxyl substituted spacer group have been studied. The changes in photophysical properties of a single probe, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) showing dipolar nature in its twisted intramolecular charge transfer (TICT) excited state have been exploited rather than using multiple probes to describe various properties of micellar aggregates. Formation of a number of premicellar aggregates has been demonstrated in addition to the description of the micropolarity and the microviscosity of environment using steady-state fluorescence spectroscopy and fluorescence anisotropy of DMASBT. Conductometric measurements have been carried out to determine degree of micellar ionization ( α) and to verify critical micelle concentration (CMC) values estimated by fluorescence method. Hydroxyl substituted spacer group induces the formation of premicellar aggregates. The micropolarity of environment around probe molecules increases on going from premicellar to micellar aggregates. The growth of micellar aggregates has been demonstrated by a continuous increase in the microviscosity of environment. The micropolarity of micellar environment of 12-4(OH) 2-12 is found to be less than that of 12-3(OH)-12. The microviscosity of premicellar and micellar aggregates of 12-4(OH) 2-12 are higher than that of 12-3(OH)-12. CMC increases, whereas α decreases with increasing spacer chain length as well as number of hydroxyl substitution of a spacer group.

Introduction of Curvature in Amphipathic Oligothiophenes for Defined Aggregate Formation

In this study the possibility to control the size and shape of self-assembled structures through the local curvature of their molecular building blocks has been investigated. To this end a series of amphipathic conjugated oligothiophenes with a well-defined curvature of their backbone has been designed and synthesized. The molecular (local) curvature of these oligothiophenes resulted from a preference for cis instead of trans conformations at specific positions along the oligothiophene backbone, which can be controlled by the sequence of hydrophilic and hydrophobic groups, while their ratio was kept constant. The self-assembly of ter-, sexi-, and dodecathiophenes appeared to be a low-cooperative process, involving the formation of premicellar aggregates at sub-millimolar concentrations, which at concentrations in the millimolar regime transformed into micelles and cylindrical micelles. The aggregates display fine structures with dimensions reminiscent of the thiophene molecules. The structure-morphology relationship of the ter- and sexithiophenes could be described by conventional packing theory. However, with the dodecathiophene, the backbone curvature governed the formation of cylindrical aggregates with a well-defined diameter. These results demonstrate that it is possible to control the aggregation morphology of simple amphipathic oligothiophenes by implementation of an additional structural motif namely, the curvature.

Photophysical Changes of Pyranine Induced by Surfactants: Evidence of Premicellar Aggregates

We studied photophysical changes of pyranine in different surfactant environments using spectrophotometry, steady-state fluorescence, and time-resolved fluorescence lifetime. The effect of surfactants on such properties varied as a function of the surfactant charge. Whereas anionic surfactants did not show any kind of interaction, the nonionic surfactant Triton X-100 produced spectral changes in the dye, as a consequence of the shift of equilibrium between its excited species. In the case of fluorescence, these changes allowed the critical micellar concentration of the surfactant to be determined. However, the most important features were obtained from the interaction with cationic surfactants of the n-alkyl trimethylammonium bromides. Such interactions enabled the formation of premicellar aggregates to be determined. In addition, three or four critical concentrations could be defined, which were dependent on the length of the hydrocarbon chain. One of these was the critical micellar concentration of the surfactant. The remaining two or three were in the very dilute concentration domain from which several types of premicellar aggregates are formed. However, the interaction with dodecyltrimethylammonium bromide at submicellar concentrations evidenced a quenching effect of a different nature (either static or combined), depending on the surfactant concentration. By deconvoluting the overall pyranine fluorescence emission spectrum into a sum of overlapping Lorentzian-Gaussian functions, the principal microenvironments of the pyranine molecules can be ascertained. Fluorescence data are consistent with the location of pyranine in a variety of sites, including partitioning that may be influenced by electrostatic and pi-cation interactions in aqueous micelles.

Investigation of physico-chemical behaviour of local anaesthetics in aqueous SDS solutions

The behaviour of local anaesthetics tetracaine (TCA), procainamide (PAM) and novocaine (NOV) in aqueous sodium dodecyl sulfate (SDS) solutions has been investigated by steady-state fluorescence emission spectroscopy, electrical conductance and reaction kinetics. A sharp increase of fluorescence emission of local anaesthetics (LA) in aqueous surfactant solutions at concentrations close to the critical micelle concentration (cmc) was observed due to the formation of premicellar aggregates. Plots of the specific conductance, κ, against [SDS], measured in the presence of a fixed amount of LA, clearly had two break points. Rates of the alkaline hydrolysis of the ester function of LA were dramatically reduced in the presence of SDS at concentrations close to the cmc (∼8.3 mM). Both the increase in fluorescence emission intensity and the reduction of hydrolysis reaction rates occur within a very narrow range of SDS concentration near the cmc and then level off/down. The strongest incorporation into negatively charged micellar aggregates was observed for TCA, the anaesthetic having the strongest hydrophobicity, and the weakest incorporation was observed for PAM, the least hydrophobic molecule. This result is important in the correlation of the anaesthetic potency of LA with their hydrophobicity.

Fluorescence Investigation of Aggregation Behaviors of Novel Anionic Gemini Surfactants

Steady-state fluorescence and fluorescence quenching measurements have been carried out to investigate the aggregation behavior for four novel alkylbenzene sulfonate gemini surfactants Ib, Ic, Id, and Ie in aqueous solutions at 298.15 K. Some important micellar parameters critical micelle concentration (cmc), aggregation number (N) and micropolarity are obtained. It is found that the cmc values (cmcc) for the studied gemini surfactants determined by fluorescence quenching measurement are in agreement with the results reported previously by the surface tension measurement or the method using pinacyanol. The aggregation number of surfactant Ie is smaller than those of Ib, Ic and Id. It is explained by the formation of premicellar aggregates inhibiting the formation of micelles due to the increasing hydrophobic portion of the gemini surfactants. Furthermore, the values of I 1/I 3 for four gemini surfactants are determined. It is shown that the decreases of I 1/I 3 stretch over a range of concentrations of more than one decade. And it is given the information that the micropolarity in the four gemini surfactant micelles sensed by pyrene is relatively high.

Organization of amphiphiles, Part VIII: Role of polyoxyethylated alkylphenols in optimizing the beneficiation of hydrophilic mineral

The floatability of silica has been determined by adsorbing various concentrations of a series of polyoxyethylated nonyl and octyl alkyl phenols of varying oxyethylene units (10–40 units) to investigate the role of adsorbed layer. It is seen that the floatability of silica increases with increase in concentration till a maximum of ∼ 90% in premicellar region and then decrease to minimum of 40–45% in all cases in spite of the significant differences in adsorption densities. Zeta potential measurement reveals that a thin oxyethylene layer is formed at silica–water interface masking silica surface (Pramila K. Misra, P. Somasundaran, J. Surf. Deterg., Vol. 7, 2004, 373). This layer with oxyethylene units lying on silica surface and alkyl chain dangling to the bulk solution provides the same extent of hydrophobicity. The decrease in flotation recovery has been attributed to increase in the solvent hydrophobicity due to formation of premicellar aggregates and micelles.

The Association of Picrate Ions with Amphiphilic Cations in Water and Aqueous Solutions of Nonionic Surfactant and β-Cyclodextrin

The interaction of cetyltrimethylammonium and cetylpyridinium bromides with picrate ions in water and aqueous solutions of the nonionic surfactant Brij 35 is studied by spectrophotometry. Spectral characteristics of the associates of picrate ions with long-chain nitrogen-containing cations depend on the concentration of a cationic surfactant. When β-cyclodextrin is added, these associates decompose owing to the formation of the strong inclusion complexes of the guest-host type with amphiphilic ions of a cationic surfactant or Brij 35 molecules. The conclusion is made that the driving force for the formation of premicellar aggregates involving picrate ions is the interactions between alkyl chains of surfactant cations. It is shown that, in the presence of various surfactants, as β-cyclodextrin concentration increases, first the molecules of nonionic surfactant and then amphiphilic cations bind with the receptor cavity. It is confirmed that there is no interaction between polyethylene glycol and β-cyclodextrin in aqueous solution.

Emission Behavior of 1-Methylaminopyrene in Aqueous Solution of Anionic Surfactants

A new fluorescent probe, methylamino derivative of pyrene, has been considered to characterize the concentration dependent emission behavior of an aqueous solution of anionic surfactants, viz., SDS, DSS, and SDBS. It was found that the emission of the probe is uniquely sensitive to the changes in surfactant (anionic) concentration due to the functional group effect of the probe over the parent moiety, pyrene. Here, 1-methylaminopyrene (MAP) showed significant quenching of emission well below the critical micellar concentration (cmc) of the surfactant. Excimer emission of the probe due to the formation of premicellar aggregates of the surfactant solutions at a concentration close to but below the cmc and again an enhanced emission of the probe above the cmc were observed as a consequence of definite MAP-surfactant interactions. These observations assisted the possible quantification ofsurfactant concentrations and their chain length dependent premicellar aggregate formations. Significant monomer emission in relation to probe distribution in micelle was analytically authenticated. Dynamic light scattering (DLS) studies revealed the incorporation of the probe molecules in the micellar core. The fluorophore emission showed nonlinear behavior when the surfactant concentration was far above the cmc. Abrupt changes in the emission characteristics in relation to the micellar concentration led to the determination of the cmc of the surfactants.

Synthesis and characterization of glucosamide‐based trisiloxane gemini surfactants

AbstractA new family of glucosamide‐based trisiloxane gemini surfactants of the general formula (CH2OCH2)n (Me3SiOSiMeR1OSiMe3)2 (where R1=(CH2)3NR2(CH2)2NHCO (CHOH)4CH2OH; R2=CH2CH(OH)CH2OCH2; and n=0, 1, or 2) was prepared and characterized, both structurally and as aqueous surfactants. The monomer was prepared by amidation of the precursor amine functional trisiloxane with d‐gluconic acid δ‐lactone. Gemini surfactants were then prepared by the alkylation of the precursor secondary amine with oligoethylene glycol diglycidyl ethers. They were structurally and elemental analysis. Members of this family reduced the surface tension of water to approximately 21 mN/m at concentration levels of 10−5 mol/L. These gemini compounds showed two critical aggregation concentration values. This behavior resulted from the formation of premicellar aggregates before true micelles were formed.