The structure of aqueous tetramethylammonium dodecylsulphate solutions at the air-water interface studied by the specular reflection of neutrons

Penfold, J.; Lee, E.M.; Thomas, Robert K.

doi:10.1080/00268978900101951

Cited by 19 publications

(10 citation statements)

References 7 publications

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“…The basic parameters of the various fragments in the system used in the calculation are given in Table . These results are in reasonable agreement with the earlier study of ref .…”

Section: Resultssupporting

confidence: 94%

Neutron Reflection from Counterions at the Surface of a Soluble Surfactant Solution

Wu¹,

Lu²,

Thomas³

et al. 1997

J. Phys. Chem. B

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The distribution of counterions at a charged surface has been measured directly using neutron specular reflection with isotopic labeling being used to highlight the scattering from the counterions. The system investigated was the soluble surfactant tetramethylammonium dodecyl sulfate with and without added tetramethylammonium chloride. Depending on the conditions a fraction of ions were found to penetrate the surfactant head-group region. The majority of the counterions observed formed a layer adjacent to the head-group layer which must be part of the diffuse layer. These two layers did not, however, account for all the counterions, and the remainder of the diffuse layer could not be observed with certainty. The reason for this is not understood, although it is probably associated with the roughness of the diffuse layer. Using the measured charge density and surface coverage as parameters, the counterion distribution calculated from the Stern−Gouy−Chapman model of the electrical double layer appears to account quite well for the shape of the distribution, although the effect of the “missing” ions made a detailed quantitative comparison impossible.

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“…The basic parameters of the various fragments in the system used in the calculation are given in Table . These results are in reasonable agreement with the earlier study of ref .…”

Section: Resultssupporting

confidence: 94%

Neutron Reflection from Counterions at the Surface of a Soluble Surfactant Solution

Wu¹,

Lu²,

Thomas³

et al. 1997

J. Phys. Chem. B

Self Cite

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“…We showed in an early paper using the neutron reflection technique that in certain circumstances it is possible to observe neutron reflection from just the ion layer adsorbed at a charged surface by using suitable isotopic labeling. 4 More recently, we have been able to show that such a signal has contributions from both a bound Stern layer and a more diffuse layer. 5 The experiments were done on a soluble surfactant monolayer where the surface charge is determined by the system itself and cannot be controlled in such a way as to make it possible to follow systematically the effects of, for example, changes in ionic strength at a fixed surface charge or changes in surface charge at a fixed ionic strength.…”

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Neutron Reflection from Counterions at the Surface Formed by a Charged Insoluble Monolayer

Wu¹,

Thomas²,

Penfold

1997

Langmuir

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Isotopic substitution has been used in conjunction with neutron reflection to make a selective study of the counterion layer beneath a charged insoluble monolayer spread on water. The insoluble monolayer consisted of a mixture of sodium docosyl (C 22) sulfonate and docosanol, and its charge was adjusted by varying the relative amounts of anionic and neutral species in the layer. The counterion was the tetramethylammonium ion, TMA + . The counterion distribution was determined at three surface charge densities, corresponding to areas per negative charge of about 30, 60, and 85 Å 2 , and at three bulk electrolyte (TMACl) concentrations, 0.1, 0.01, and 0.001 M. There was found to be significant penetration of the counterions into the headgroup region of the amphiphile to form a well defined "Stern" layer, and there was also a thicker layer corresponding to part of the diffuse layer. The changes in the behavior of the counterions with changes in surface charge density and bulk electrolyte concentration were qualitatively consistent with double-layer theory. However, a complication in applying theory to the diffuse part of the double layer was that not all the counterions could be observed by the neutrons. This may have been because of preferential adsorption of Na + present in the original spreading solution or because of roughness of the counterion distribution. The obervation by neutron reflection of penetration of the amphiphilic layer by the counterions was consistent with the unusual behavior of the π-A isotherms on addition of TMACl.

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“…The kinetics of the film formation necessitated relatively short counting times, and each data set was therefore acquired in 30 min. A flat background has been shown to be appropriate for studies of this kind and was subsequently included as a parameter in the modeling of the data. The observed background is predominantly due to incoherent scattering from the sample.…”

Section: Methodsmentioning

confidence: 99%

Growth of Highly Ordered Thin Silicate Films at the Air−Water Interface

et al. 1998

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The growth of thin silicate−organic films at the air−water interface of surfactant solutions has been studied in situ by X-ray and neutron reflectivity to a resolution of ca. 5 Å. Surfactant in the solution and the air−water interface itself are involved in directing the growth and final structure of the films. Hexadecyltrimethylammonium chloride (C16TAC) and bromide (C16TAB) have been used as the templating surfactants, and the film structure is independent of the anions under the conditions used. In situ X-ray and neutron reflectivity measurements at an early stage of film growth show a slow development of structure in the top 100 Å of the solution, which is consistent with a monolayer of tilted surfactant molecules at the air−water interface, a layer of partly silicated material, and an interdigitated surfactant bilayer or layer of cylindrical micelles oriented with their long axes parallel to the surface. Following this induction period a rapid crystallization occurs to give a structure with a crystallographic repeat distance of 45 Å perpendicular to the surface and composed of alternating surfactant layers and silicate material. The very narrow observed diffraction peaks indicate that the final silicate film is highly ordered.

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The structure of aqueous tetramethylammonium dodecylsulphate solutions at the air-water interface studied by the specular reflection of neutrons

Cited by 19 publications

References 7 publications

Neutron Reflection from Counterions at the Surface of a Soluble Surfactant Solution

Neutron Reflection from Counterions at the Surface of a Soluble Surfactant Solution

Neutron Reflection from Counterions at the Surface Formed by a Charged Insoluble Monolayer

Growth of Highly Ordered Thin Silicate Films at the Air−Water Interface

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