Limitations in the use of surface tension and the Gibbs equation to determine surface excesses of cationic surfactants. by Li, P, Thomas, R, Penfold, J

“…Neutron reflection (NR) and surface tension (ST) are used to show that there are serious limitations in applying the Gibbs equation accurately to ST data of cationic surfactants to obtain the limiting surface excess, Γ(CMC), at the critical micelle concentration (CMC). …”

Surface behavior, aggregation and phase separation of aqueous mixtures of dodecyl trimethylammonium bromide and sodium oligoarene sulfonates: the transition to polyelectrolyte/surf... by Jiang, L, Huang, J, Bahramian, A, Li, P, Thomas, R, Penfold, J

“…These systems exhibit a single critical micelle concentration (CMC) at which the surface tension reaches the usual plateau. This is contrary to a recent report which suggests that the onset of the surface tension plateau does not coincide with the CMC. …”

Surface behavior, aggregation and phase separation of aqueous mixtures of dodecyl trimethylammonium bromide and sodium oligoarene sulfonates: The transition to polyelectrolyte/surf... by Jiang, L, Huang, J, Bahramian, A, Li, P, Thomas, R, Penfold, J

“…These systems exhibit a single critical micelle concentration (CMC) at which the surface tension reaches the usual plateau. This is contrary to a recent report which suggests that the onset of the surface tension plateau does not coincide with the CMC. …”

Neutron reflectometry of quaternary gemini surfactants as a function of alkyl chain length: anomalies arising from ion association and premicellar aggregation. by Li, P, Dong, C, Thomas, R, Penfold, J, Wang, Y

“…The structures of the surface layers, which were determined by neutron reflectometry, indicate that the anomalous behavior of the surface tension and area are probably caused by poor packing of the gemini side chains between adjacent molecules. …”

Adsorption of oppositely charged polyelectrolyte/surfactant mixtures. Neutron reflection from alkyl trimethylammonium bromides and sodium poly(styrenesulfonate) at the air/water in... by Taylor, D, Thomas, R, Li, P, Penfold, J

“…The surface tension and neutron reflection results were explained in terms of a model in which there were three kinds of polymer/surfactant complex.…”

Structure of Partially Fluorinated Surfactant Monolayers at the Air-Water Interface (dagger). by Jackson, A, Li, P, Dong, C, Thomas, R, Penfold, J

“…Partially fluorinated cationic surfactants of the form C(n)F(2n+1)C(m)H(2m)N(CH(3))Br have been prepared, and their behavior at the air-water interface has been studied using surface tension measurements and neutron reflectometry. …”

Limitations in the application of the Gibbs equation to anionic surfactants at the air/water surface: sodium dodecylsulfate and sodium dodecylmonooxyethylenesulfate above and below... by Xu, H, Li, P, Ma, K, Thomas, R, Penfold, J, Lu, JR

“…The NR results for SDS are compared to the definitive surface tension (ST) measurements of EM, and the surface excesses agree over the range where they can safely be compared, from 2 to 6 mM. …”

Impact of biogenic amine molecular weight and structure on surfactant adsorption at the air–water interface by Penfold, J, Thomas, R, Li, P

“…In the neutron reflectivity, NR, and surface tension, ST, results presented here the role of the oligoamine structure on the adsorption of SDS is investigated more fully using a range of different biogenic amines. …”

The impact of electrolyte on the adsorption of the anionic surfactant methyl ester sulfonate at the air-solution interface: Surface multilayer formation by Xu, H, Thomas, RK, Penfold, J, Li, P, Ma, K, Welbourne, RJL, Roberts, DW, Petkov, JT

“…Neutron reflectivity and surface tension have been used to characterise the adsorption at the air-aqueous solution interface of the anionic surfactant sodium tetradecanoic 2-sulfo 1-methyl ester, C14MES, in the absence of electrolyte and in the presence of mono, di, and tri-valent counterions, Na+, Ca2+, and Al3+. …”

Tuning Polyelectrolyte-Surfactant Interactions: Modification of Poly(ethylenimine) with Propylene Oxide and Blocks of Ethylene Oxide by Penfold, J, Thomas, R, Li, P, Batchelor, S, Tucker, I, Burley, A

“…Neutron reflectivity and surface tension data are presented here which show how the polyelectrolyte-surfactant interaction can be manipulated by tuning the PEI structure. …”

Adsorption of DNA and dodecyl trimethylammonium bromide mixtures at the air/water interface: a neutron reflectometry study. by Zhang, J, Taylor, D, Li, P, Thomas, R, Wang, J, Penfold, J

“…The interactions between dodecyl trimethylammonium bromide (C12TAB) and two samples of DNA with widely differing molecular weights have been studied using surface tension and neutron reflectometry. Neutron reflection data show that the surfactant and polymer are adsorbed together in a highly cooperative fashion over a 1000-fold change in surfactant concentration. …”

Adsorption of methyl ester sulfonate at the air-water interface: can limitations in the application of the Gibbs equation be overcome by computer purification? by Xu, H, Li, P, Ma, K, Welbourn, R, Penfold, J, Roberts, D, Thomas, R, Petkov, J

“…The neutron-measured surface excesses were combined with the integrated Gibbs equation to fit the variation in surface tension with concentration (σ-ln C curve). The fit was exact provided that we used a prefactor consistent with the counterion at the surface being an impurity divalent ion, as has previously been found for sodium diethylhexylsulfosuccinate (aerosol OT or AOT) and various perfluorooctanoates. …”

Interaction of a Cationic Gemini Surfactant with DNA and with Sodium Poly(styrene sulphonate) at the Air/Water Interface: A Neutron Reflectometry Study (dagger). by Vongsetskul, T, Taylor, D, Zhang, J, Li, P, Thomas, R, Penfold, J

“…The interactions between a dicationic gemini surfactant with a six-hydrocarbon spacer (1,2-bis(dodecyldimethylammonio)hexane dibromide, C(12)C(6)C(12)Br(2)) and anionic polyelectrolyte DNA or sodium(polystyrene sulfonate) (NaPSS) at the air/solution interface have been studied and compared using neutron reflectometry together with surface tension. In the presence of the dichained cationic gemini surfactant, DNA and NaPSS display very different adsorption behaviors. …”

Application of the Gibbs equation to the adsorption of nonionic surfactants and polymers at the air-water interface: comparison with surface excesses determined directly using neut... by Li, P, Li, Z, Shen, H, Thomas, R, Penfold, J, Lu, JR

“…Four recent papers by Menger et al. have questioned methods of analysis of surface tension (ST) data that use the Gibbs equation to obtain the surface excess (Γ) of a surfactant at the air-water interface. …”

Multivalent electrolyte induced surface ordering and solution self-assembly in anionic surfactant mixtures: Sodium dodecyl sulfate and sodium diethylene glycol monododecyl sulfate by Li, P, Wang, Z, Ma, K, Chen, Y, Yan, Z, Penfold, J, Thomas, RK, Campana, M, Webster, JRP, Washington, A

“…In this paper the impact of sodium dodecyl sulfate, SDS, an anionic surfactant more susceptible to precipitation in the presence of multivalent counterions, on the surface multilayer formation and solution self-assembly of sodium diethylene glycol monododecyl sulfate, SLES, is explored using surface tension, neutron reflectivity and small angle neutron scattering.…”

Analysis of the asymmetric synergy in the adsorption of zwitterionic–ionic surfactant mixtures at the air–water interface below and above the critical micelle concentration by Li, P, Ma, K, Thomas, R, Penfold, J

“…Surface tension (ST) and neutron reflection (NR) measurements have been made on a series of mixtures of two ionic surfactants, one anionic (SDS) and one cationic (C12TAB), with the two zwitterionic surfactants dodecyldimethylammonium propanesulfonate (C12SB) and dodecyldimethylammonium acetate C12CB. …”