The properties of a family of two-headed surfactant systems: the 4-alkyl-3-sulfosuccinates 2. Surface properties of alkyl sulfosuccinate micelles (original) (raw)
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Journal of Colloid and Interface Science, 2019
The ester sulfonate anionic surfactants are a potentially valuable class of sustainable surfactants. The micellar growth, associated rheological changes, and the onset of precipitation are important consequences of the addition of electrolyte and especially multi-valent electrolytes in anionic surfactants Small angle neutron scattering, SANS, has been used to investigate the self-assembly and the impact of different valence electrolytes on the self-assembly of a range of ester sulfonate surfactants with subtly different molecular structures. The results show that in the absence of electrolyte small globular micelles form, and in the presence of NaCl, and AlCl3 relatively modest micellar growth occurs before the onset of precipitation. The micellar growth is more pronounced for the longer unbranched and branched alkyl chain lengths. Whereas changing the headgroup geometry from methyl ester to ethyl ester has in general a less profound impact. The study highlights the importance of relative counterion binding strengths and shows how the surfactant structure affects the counterion binding and hence the micelle structure. The results have important consequences for the response of such surfactants to different operational environments.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
We report on combined experimental and theoretical investigations of the water/micelle interface of cationic, anionic, zwitterionic, and non-ionic surfactants using a new hydrophobic acid-base indicator 2,6dinitro-4-n-dodecylphenol. The indices of the so-called apparent ionization constant, app a pK , of the indicator fixed in the micellar pseudophase are determined by the spectrophotometric method. The data allows estimating the Stern layer's electrostatic potential of the ionic micelles . Molecular Dynamics modeling was used to locate the dye molecule and, in particular, its ionizing group OH Owithin the micelles of the studied surfactants. The comparison of the values estimated using 2,6-dinitro-4-ndodecylphenol with both our computer simulation and literature experimental results reveals obstacles in monitoring electrical interfacial potentials. In particular, the values of the surfactant micelles with alkylammonium groups determined via 2,6-dinitro-4-n-dodecylphenol are overestimated. The reason is specific interactions of the indicator anion with the surfactant head groups. For anionic surfactants, however, this indicator is quite suitable, which is confirmed by the location of HA and Aequilibrium forms in the pseudophase.
Journal of Physical Organic Chemistry, 2007
The peculiarities of the structure of the fluorescent dye N,N'-di-n-octadecylrhodamine advantage its using as an interfacial acid-base probe in aqueous micellar solution of colloidal surfactants. Two long hydrocarbon tails of the dye provide similar orientation of both cation and zwitterion on the micelle/water interface, with the ionizing group COOH exposed to the Stern region in all the systems studied. Further, the charge type of the acid-base couple, A þ B AE , ensures similar values of the 'intrinsic' contribution, pK i a , to the 'apparent' pK a a value in micelles of different surfactants. This makes the indicator suitable for determination of electrical surface potentials, C. The pK a a s have been obtained in cationic, anionic, zwitterionic, and nonionic surfactant systems, at various salt background. In total 17 systems were studied. At bulk counterion concentration of ca. 0.05 M, the pK a a values vary from 2.14 AE 0.07 in nÀC 18 H 37 NðCH 3 Þ þ 3 Cl À micelles to 5.48 AE 0.06 in nÀC 16 H 33 OSO À 3 Na þ micelles. The C values, corresponding to the Stern region of micelles, have been evaluated as C¼ 59:16 ðpK i a À pK a a Þ for T ¼ 298.15 K. The pK i a parameter was equated to the average value of 4.23 in nonionic surfactants (4.12-4.32, depending on the surfactant type). For cetyltrimethylammonium bromide and sodium n-dodecylsulfate micelles, the C values (AE(7-11) mV) appeared to be þ118 mVand at bulk Br À concentration 0.019 M and À76 mVat bulk Na þ concentration 0.020 M, respectively. This satisfactorily agrees with the theoretical values þ111 and À84 mV, estimated using the Oshima, Healy, and White equation for these well-defined colloidal systems. Finally, not only absorption, but also fluorescence spectra display the same response to changes in bulk pH.
2013
In this paper, the different methods of estimation of the electrostatic potential, , of surfactant micelles via acid-base indicators are compared. All the methods are based on the determination of the indices of the so-called "apparent" ionization constants, app a pK. The approach developed in this Laboratory and based on using the indicator N,N /-din -octadecylrhodamine is utilized for determination of the value in the Stern layer of cetyltrimethylammonium-based micelles in the presence of tosylate ion.
Química Nova, 2011
Mixed micellization and surface properties of cationic and nonionic surfactants dimethyl decyl-, tetradecyl-and hexadecyl phosphineoxide mixtures are studied using conductivity and surface tension measurements. The models of Rubingh, Rosen, and Clint, are used to obtain the interaction parameter, minimum area per molecule, mixed micelle composition, free energies of mixing and activity coefficients. The micellar mole fractions were always higher than ideal values indicating high contributions of cationics in mixed micelles. Activity coefficients were less than unity indicating synergism in micelles. The negative free energies of mixing showed the stability of the surfactants in the mixed micelles.
HYDROPHOBICITY EFFECT ON INTERACTIONS BETWEEN ORGANIC MOLECULES IN NANOCAGES OF SURFACTANT MICELLE
Interactions between the cationic polymethine dyes 3,3′-diethyloxacarbocyanaine iodide (DiOC2), 3,3′-dioctadecyloxacarbocyanine iodide (DiOC18), and 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) in the nano-scale volume of anionic sodium dodecylsulfate (SDS) micelles have been studied using optical spectroscopy techniques. The solubilization of pairs of dye molecules (DiOC18/DiI or DiOC2/DiI) within SDS micelles was monitored by Forster resonance energy transfer (FRET) between the dyes in each pair. The influence of the hydrophobicity of the dyes DiOC2 and DiOC18 on the efficiency of their binding to SDS micelles and, consequently, on the efficiency of FRET between DiOC18 and DiI or DiOC2 and DiI fluorophors has been analyzed. It has been shown that hydrophobic interactions in addition to electrostatic interactions are of key importance for the binding between the positively charged dyes and negatively charged surfactant micelles.
Micellar and Surface Properties of Some Monomeric Surfactants and a Gemini Cationic Surfactant
Journal of Surfactants and Detergents, 2010
The physicochemical and interfacial properties of the monomeric surfactants cetyltrimethyl ammonium bromide (CTAB), cetyltriphenyl phosphonium bromide (CTPB), tetradecyl triphenyl phosphonium bromide (TTPB), cetyldiethylethanol ammonium bromide (CDEEAB), cetyltrimethyl ammonium chloride (CTACl), tetradecyltrimethyl ammonium bromide (TTAB), and a gemini surfactant (C 16-3-C 16, 2Br-) at different pH (3.1, 7.0, and 7.75) have been investigated by conductivity and surface tension measurements at 300 K. The critical micellar concentration (CMC), degree of micellar ionization (a), surface excess concentration (U max), minimum surface area per molecule of surfactant (A min), Gibbs free energy of micellization (DG m 0), surface pressure at the CMC (p CMC), and the Gibbs energy of adsorption (DG ads 0) of the monomeric surfactants have also been determined. The CMC, a and U max , increase with increasing pH whereas A min decreases.
Langmuir, 2004
The proton NMR spectra of unligated ferrous porphyrins, proposed to exist in the intermediate S = 1 spin state, have been recorded and analyzed. The dominant dipolar shifts for the phenyl protons in tetraphenylporphinatoiron(I1) result in a quantitative measure of the axial magnetic anisotropy, which, together with the average moment, yield p l = 4.9 pcg and pi 1 = 3.2 peg. The resultant contact shifts for pyrrole substituents reflect extensive a spin transfer, which originates solely from porphyriniron change transfer. The contact shift pattern indicates that dxzyz is unoccupied, confirming the spin-triplet ground state. The large a contact shifts require unpaired spins in dxr,dyr, and strongly support the ground state configuration, (d,)2(dzz)2(dxz,dyz)2r which has been previously shown to be the one favored by the average moment and Massbauer data.
Journal of Colloid and Interface Science, 2003
Alkyloxyethylene sulfates are a special class of surfactants that are unusually stable in the presence of multivalent counterions and are not as prone to precipitation as anionic surfactants without intermediate ethoxy groups in the molecule. However, formation of micelles, their structure, and the properties of monolayers of these surfactants exhibit very interesting and sometimes unexpected properties depending on the nature of the ions dissolved in the solution. This paper presents a brief overview of our recent efforts to reveal the nature of these properties, including some new results. We show that the strong binding of multivalent (and particularly trivalent counterions) triggers a sphere-to-cylinder shape transition of the micelles and facilitates their further growth, even at very low ionic strength. The properties of surfactant monolayers are coupled to those of the micelles in the bulk and are governed also by multivalent counterion binding. The effect of multivalent counterions on the aggregation and structure formation in anionic surfactant solutions has both fundamental and practical importance.