Étude de solutions micellaires par résonance magnétique nucléaire

Alexandre, Michel; Fouchet, Catherine; Rigny, Paul

doi:10.1051/jcp/1973701073

Cited by 21 publications

(7 citation statements)

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“…Above 0.6 M the relaxation rate does not follow this relation any longer and can be interpreted by an increase in the size of the aggregates and certainly by a change in their shape. Similar experiments have already been done using 1H [32,33] or 13C [34] relaxation. The lyotropic crystalline phase that appears when the solution is concentrated up to about 2 M being an hexagonal one, the micelles are assumed to be cylindrical from 0.6 M up to 2 M. We note that neither density nor 13C chemical shift measurements show this transition, indicating that the packing of the hydrocarbon chains seems to be unaffected by the micellar shape and size.…”

Section: Longitudinal Relaxation Times Of Sipmentioning

confidence: 61%

NMR investigation of the micellar properties of monoalkylphoshpates

Chevalier

Chachaty

1984

Colloid & Polymer Sci

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Abstract:The micellization of several monoalkylphoshpates with chain lenghts from 6 to 10 carbons have been investigated by 31p and "C NMR spectroscopy with some additional electrical conductivity, density and small angle neutron scattering measurements.The major part of this study was performed on sodium monooctylphosphate. The critical concentration of micellization is 0.14 M, the partial molar volume is 170 cm3/mole in the micellar state. Small angle neutron scattering measurements on a 0.5 molar solution lead to an aggregation number of 43. NMR studies over the whole concentration range show that the pseudophase model holds. The geometry around the polar head is found almost unchanged upon micellization. The frequency denpendence of the 31p longitudinal relaxation is interpreted by an isotropic fas motion (rR = 6.5 x 10 -11 s for the free monomers and by a strongly anisotropic motion with D II/D• ~ 10 and ro = (6 D) -1=1.25 x 10-9s in the micellar state.

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Section: Longitudinal Relaxation Times Of Sipmentioning

confidence: 61%

NMR investigation of the micellar properties of monoalkylphoshpates

Chevalier

Chachaty

1984

Colloid & Polymer Sci

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“…Indeed it has been demonstrated in recent years that on micelle formation there are considerable changes in both shielding and relaxation and that it is possible to characterize the effects for a large number of carbons in an alkyl chain. [1][2][3][4][5] In the present communication we wish to demonstrate that two types of significant information on the amphiphile association process may be obtained from 13C chemical shift investigations. First, it is possible by detailed studies of the concentration dependence of the chemical shift to deduce quantitative information on the amphiphile aggregation number and, secondly, the shift change on passage from the intermicellar solution to a micelle gives qualitative information on any accompanying comformational change of the alkyl chain.…”

mentioning

confidence: 92%

Amphiphile aggregation number and conformation from carbon-13 nuclear magnetic resonance chemical shifts

Persson¹,

Drakenberg²,

Lindman³

1976

J. Phys. Chem.

131

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The dependence of the l3C NMR chemical shifts from the n-nonylammonium bromide carbons on the amphiphile concentration have been used to estimate the aggregation number in the NAB micelles, resulting in 37 f 5 monomers/micelle. Furthermore, the observed downfield shift on micelle formation has been interpreted as caused by an increased proportion of the trans conformation of the alkyl chains in the micelles compared to the monomers.It could be expected that 13C NMR with its high resolution and large chemical shift range should be well suited for the study of the association of amphiphilic compounds, for example, ionic surface-active agents. Indeed it has been demonstrated in recent years that on micelle formation there are considerable changes in both shielding and relaxation and that it is possible to characterize the effects for a large number of carbons in an alkyl ~h a i n . l -~ In the present communication we wish to demonstrate that two types of significant information on the amphiphile association process may be obtained from I 3 C chemical shift investigations. First, it is possible by detailed studies of the concentration dependence of the chemical shift to deduce quantitative information on the amphiphile aggregation number and, secondly, the shift change on passage from the intermicellar solution to a micelle gives qualitative information on any accompanying comformational change of the alkyl chain.Assuming an idealized situation where the amphiphile may occur either as a monomer or in a single type of micelle with an aggregation number n the chemical shift can be written C m ct 6obsd = -6mHere C , and C t denote the concentration of micellized amphiphile and the total amphiphile concentration, respectively. 6&d is the observed chemical shift and 6 , the shift of micellized amphiphile, both taken relative to the chemical shift of the monomer. The monomer shift is obtained by extrapolation to zero amphiphile concentration. The concentrations of monomer and micelle in the equilibrium nX X, with K = [Xn]/[XIn may be expressed as [XI = ct -6obsd 6m and 6obsd 6 , n[X,] = CtThe expression for K may then be rewritten as In (Ctdobsd) = n In [Ct(6, -6,,bsd)] + In K + In n (1) Consequently, a plot of In (Ct6obsd) vs. In [Ct(6m -6obsd)l yields the aggregation number and the equilibrium constant if the simple model holds. 6 , may be estimated from plots of 6obsd -(n -1) In 6 , vs. the inverse amphiphile concentration.l Analogous procedures have bees used previously for lH and l9F chemical shifts.6,7To illustrate these principles we present variable concentration 13C chemical shift data for aqueous solutions of a cationic surfactant, n-nonylammonium bromide (NAB). Chemical shifts of the three methylenes in the center of the alkyl chain are presented in Figure 1. The critical micelle concentration obtained from the plots of Figure 1 (cf. ref 1) is 0.11 mol kg-l and thus in close agreement with results obtained by other methods.8,g A previously found* change in the NAB micellar structure at high concentrations is ve...

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“…This absence of variation of relaxation rate with n could be a cancellation of contradictory effects, but it would be a great coincidence. This slow motion is a combination of the rates of rotation of the micelles and of diffusion of the surfactant molecules at the curved interface [45]. This result suggests that the micellar size does not depend much on the intercharge distance n. On this basis, the relaxation rate variations along the intercharge polymethylene moiety are attributed to differences in the anisotropic fast motion rates and average orientation of 13C-1H bonds relative to the micellar radius.…”

Section: Nmr Relaxationmentioning

confidence: 89%

Micellar properties of zwitterionic phosphobetaine amphiphiles in aqueous solution: Influence of the intercharge distance

Chevalier

Germanaud

Perchec

1988

Colloid & Polymer Sci

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Zwitterionic amphiphiles of the general formula H(CH2)y +N(CH3)2(CH2)n PO2C6H~-, where the number of intercharge methylenes n is varied, were studied in dilute aqueous solution. Their critical micellar concentrations show a peculiar variation with n, first increasing as n varies from 1 to 4 and then slowly decreasing as methylenes are added up to 10. This behavior is interpreted as being the consequence of two opposite contributions. The first is the classical CMC lowering due to the increase of hydrophobic character with the total number of methylene groups in the surfactant molecule. The second contribution is the increase in the dipole moment of the zwitterionic headgroup with n, leading to stronger dipole-dipole repulsions between headgroups at the micellar surface. Experimental results suggest that the dipole moment does not increase linearly with n because of the polymethylene chain flexibility. This is supported by 13C NMR relaxation experiments.

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Étude de solutions micellaires par résonance magnétique nucléaire

Abstract: Des mesures de relaxation nucléaire du proton et du carbone 13 sur des solutions micellaires sont présentées.

Cited by 21 publications

References 0 publications

NMR investigation of the micellar properties of monoalkylphoshpates

NMR investigation of the micellar properties of monoalkylphoshpates

Amphiphile aggregation number and conformation from carbon-13 nuclear magnetic resonance chemical shifts

Micellar properties of zwitterionic phosphobetaine amphiphiles in aqueous solution: Influence of the intercharge distance

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