Halton, B.; Cooney, M. J.; Davey, T. W.; Forman, G.S; Lu, Q.; Boese, R.; Blaser, D.; Maulitz, A. H.

Heterocyclic Substituted Methylidenecycloproparenes. J. Chem. Soc., Perkins Trans 1. 1995, 18, 2819–2827. [Download pdf - 929 K]

1H-Cyclopropa[b]naphthalene 7 is converted into a range of 6 pi 5-atom-substituted methylidene derivatives 12e-j, the pyridyl analogues 12k and l, and the phenylsulfanyl analogue 12m by way of the 1,1-disilyl compound 9 and Peterson olefination in improved procedure. The spectroscopic properties of the compounds are reported and their behaviour as possible lumophores assessed. Crystal structures of the dimethylaminophenyl 12c,d, and the thienyl 12e derivatives are presented. The permanent dipole moments of the mono-substituted 12e and k have been measured as 2.76, and 3.37 D, respectively, and that of the dithenyl 12f as 9.06 D.

Wanless, E. J.; Davey, T. W.; Ducker, W. A.

Surface Aggregate Phase Transition. Langmuir 1997, 13(16), 4223–4228. [Download pdf - 454 K]

A surface aggregate phase transition is described. Atomic force microscopy has been used to image the equilibrium association of sodium dodecyl sulfate (SDS) and 1-dodecanol molecules at the interface between graphite and aqueous solutions. In pure SDS solutions, the molecules associate into long, parallel hemicylindrical surface aggregates over a concentration range from about one-third to at least 10 times the critical micelle concentration (cmc). Above the cmc, dodecanol has little influence on the surface aggregate structure, probably because dodecanol is partitioned into the bulk micelles. Below the cmc, dodecanol causes a transition from hemicylindrical aggregates to a two-phase mixture in which flat sheets coexist with swollen hemicylindrical aggregates. In this mixture, the hemicylindrical aggregates are preferentially located at and parallel to steps on the underlying graphite substrate. Under conditions where hemicylinders and flat sheets coexist, an increase in bulk dodecanol concentration results in an increase in surface coverage by nat sheets. No bulk. solution changes were detected by NMR in the region where the surface phase transition was observed.

Davey, T. W.; Ducker, W. A.; Hayman, A. R.; Simpson, J.

Krafft Temperature Depression in Quaternary Ammonium Bromide Surfactants. Langmuir 1998, 14(12), 3210–3213. [Download pdf - 40 K]

Substitution of a triethyl for a trimethyl headgroup in alkyltrimethylammonium or (omega-hydroxyalkyl)-trimethylammonium bromide surfactants leads to a significant reduction in the Krafft temperature. This substitution allowed us to produce asymmetric bolaform surfactants that form micellar solutions at room temperature. It is reasoned that the proximity of the bromide counterion to the quaternary ammonium center stabilizes the hydrated crystal of the conventional and bolaform surfactants through Coulombic interactions. The bolaform surfactants experience further stabilization as a result of bonding between the hydroxyl functionality and the quaternary nitrogen and bromide. Substitution of ethyl for methyl groups in the headgroup increases the ion-ion and ion-dipole distances, lowering the stability of the hydrated crystal, which in turn lowers the Krafft temperature.

Davey, T. W.; Hayman, A. R.

Synthesis of Some New Quaternary Ammonium Bolaform Surfactants. Aust. J. Chem.1998, 51(7), 581–586. [Download pdf - 175 K]

Several members of a novel class of omega-substituted asymmetric bolaform surfactants have been synthesized in order to investigate their surfactant and biological properties. The omega-hydroxy trialkylammonium and pyridinium surfactants have significant antimicrobial and antifungal activity relative to their conventional analogues. For conventional quaternary ammonium alkyl surfactants, increasing the hydrocarbon chain length causes a decrease in the surfactant, monomer solubility and a corresponding decrease in the biological activity. No such trend is observed for the omega-hydroxy quaternary ammonium bromide series.

Davey, T. W.; Ducker, W. A.; Hayman, A. R.

Aggregation of omega-Hydroxy Quaternary Ammonium Bolaform Surfactants. Langmuir 2000, 16(6), 2430–2435. [Download pdf - 170 K] [Supporting information - 46 K]

Omega-Hydroxy quaternary ammonium bolaform surfactants form much smaller micelles in solution than the corresponding non-hydroxy (conventional) surfactants. Aggregation numbers for micelles formed by the omega-hydroxy surfactants, determined using ¹H NMR spectroscopy and steady-state fluorescence quenching, are very small (N = 5–18). The micelle size is consistent with aggregates of about half the diameter of a conventional surfactant. This implies that both the quaternary ammonium and the terminal hydroxyl are positioned at the micelle/water interface. The critical micelle concentrations of the bolaform surfactants, determined using ¹H NMR and the conductivity method, are between three and nine times greater than the corresponding non-hydroxy surfactants.

Sicard, L.; Frasch, J.; Soulard, M.; Lebeau, B.; Patarin, J.; Davey, T.; Zana, R.; Kolenda, F.

Investigations by fluorescence techniques of the mechanism of formation of silica and alumina MCM-41-type materials. Microporous Mesoporous Materials 2001, 44–45(0), 25–31. [Download pdf - 128 K]

Silica- and alumina-based mesostructured MCM-41-type materials were obtained at low temperature in the presence of cationic (cetyltrimethylammonium bromide (CTAB) or chloride (CTAC)) and anionic (sodium dodecylsulfate (SDS)) surfactants, respectively, by modifying the pH of the corresponding clear precursor solutions.

In situ fluorescence techniques were used to study the first steps of formation of these mesostructured solids prior to precipitation. For the silica-based system using CTAB, only a small fraction of micelle-bound bromide ions is exchanged by OH– and/or silicate ions and there is hardly any micelle growth in the presence of these additives and upon lowering the pH to a value close to that where the mesostructured solid precipitates out. A similar result was observed for the alumina-based systems. For both types of systems the micelles remain close to spherical in the precursor solution.

Davey, T. W.; Warr, G. G.; Almgren, M.; Asakawa, T.

Self-assembly of hydrocarbon and fluorocarbon surfactants and their mixtures at the mica–solution interface. Langmuir 2001, 17, 5283–5287. [Download pdf - 352 K]

The adsorbed layer structure of tetradecylpyridinium, hexadecylpyridinium, heptadecafluorodecylpyridinium and tetradecyltriethylammonium chloride and their mixtures on mica has been determined by AFM imaging. In addition, the composition of the mixed adsorbed layers has been measured, showing a significant surface enrichment of the pyridinium surfactants, particularly the partially fluorinated species. Shape transitions in the adsorbed layer are correlated with surface and bulk compositions, and explained by consideration of the adsorption mechanism.

Davey, T. W.; Warr, G. G.; Asakawa, T.

Composition of mixed hydrocarbon and fluorocarbon surfactant adsorbed layers at mica-solution interfaces. Langmuir 2003, 19, 5266–5272. [Download pdf - 136 K]

The compositions of the adsorbed aggregates at the mica-solution interface have been directly determined for mixtures of pyridinium chloride hydrocarbon and fluorocarbon surfactants by solution depletion measurements, including direct determination of the adsorbed layer composition for partially miscible surfactants. The measured adsorbed aggregate compositions are compared with predictions for bulk micelles using the group contribution method and regular solution theory. For fully miscible surfactants, there is good agreement between the models and experimental results. The group contribution method successfully predicts the existence of a miscibility gap for some mixtures, but adsorption experiments reveal some unusual features; the adsorbed layer consists of only one of the two coexisting micelle compositions, and its composition differs from that predicted. This effect is attributed to the substrate.

FitzGerald, P. A.; Carr, M. W.; Davey, T. W.; Serelis, A. K.; Such, C. H.; Warr, G. G.

Preparation And Dilute Solution Properties Of Model Gemini Nonionic Surfactants. J. Colloid Int. Sci. 2004 , 275(2), 649–658.[Download pdf - 309 K]

Dimeric poly(ethylene oxide) surfactants (or nonionic gemini surfactants) with the structure (C_n–2H_2n–3CHCH₂O(CH₂CH₂O)_mH)₂ (CH₂)₆ (or GemnEm), where n is the alkyl length and m is the average number of ethylene oxides per head group, were synthesized. Surfactants were synthesized with alkyl chain lengths n = 12, 14, and 20 and m = 5, 10, 15, 20, and 30. Water solubilities and cloud temperatures at 1 wt% were determined by measuring turbidity as a function of temperature. Cloud temperatures increase with m and decrease with n, as observed for conventional surfactants. For large m the cloud temperatures were all above 100 °C. Surfactants with small m (i.e., n = 12, 14, m = 5 and n = 20, m = 10) were insoluble at room temperature, forming two-phase mixtures. Critical micelle concentrations (CMCs) were measured using a pyrene fluorescence method and are all in the range of 10^–7 to 10^–6 M, with the lowest values from the surfactants with large n and small m. CMCs of mixtures with both anionic and nonionic conventional (monomeric) surfactants were well described by an ideal mixing model.

FitzGerald, P. A.; Davey, T. W.; Warr, G. G.

Micellar Structure in Gemini Nonionic Surfactants from Small-Angle Neutron Scattering. Langmuir 2005, 21(16), 7121–7128.

The size and shape of micelles formed by dimeric polyoxyethylene (nonionic gemini) surfactants having the structure (C_n–2H_2n–3CHCH₂O(CH₂CH₂O)_mH)₂ (CH₂)₆ with alkyl and ethoxy chain lengths ranging from n = 12-20 and m = 5-30 have been determined using small angle neutron scattering (SANS). The surfactants are polydisperse in the hydrophilic groups but otherwise analogous to the widely studied monomeric poly(oxyethylene) alkanols. We find that longer ethoxylated chains are needed to confer solubility on the gemini surfactants and that these chains in the hydrophilic corona around the alkyl core of the micelles are reasonably well described as a homogeneous random coil in a good solvent. Spherical micelles are formed by the surfactants with the longest ethoxylated chains. Shorter chains lead first to rods and ultimately a vesicle dispersion. These solutions exhibit conventional cloud point behavior, and on warming, a sphere to rod transition can be observed. For the n = 20 and m = 15 surfactant, this shape transition is accompanied by a striking increase in viscosity at low concentration and gelation at higher concentrations.

Davey, T. W.

Synthesis of some new alkylidenecycloproparenes. Honours thesis, 1993, 32 pp. Victoria University of Wellington, Wellington, New Zealand.

This project involved the multi-step synthesis of five new alkyidenecyclopropa[b]naphthalenes, starting from naphthalene. The interesting features of these molecules includes the combination of high strain with aromatic stability, their fluorescing ability and extent and direction of polarisation. These types of compounds are generally brightly coloured solids.

Davey, T. W.

Characterisation of some new bolaform surfactants. PhD thesis, 1998, 213 pp. University of Otago, Dunedin, New Zealand.

Bolaform surfactants of the omega-hydroxyalkylquaternary ammonium bromide type, N⁺(CH₂)_nOH Br^–, were prepared where N is a nitrogen-containing group (NMe₃, NHMe₂, NEt₃, Py) and n = 12–16. The aggregation behaviour of these surfactants was investigated using ¹H NMR, fluorescence quenching and conductivity. The critical micelle concentrations (cmcs) are three to nine times greater than the non-hydroxy (conventional) surfactants. The quaternary ammonium and alcohol functionalities are located on the micelle exterior, producing very small micelles (N = 5–11). The Krafft temperatures of the omega-hydroxy surfactants are at least 20 ^oC higher than for the non-hydroxy surfactants owing to ion-dipole bonding present in the crystal of the former. The Krafft temperature may be lowered by at least 32 ^oC by changing the headgroup from a trimethylammonium to a triethylammonium, producing bolaform surfactants that micellise at room temperature. This methodology was also applied to long-chain alkyltrimethylammonium bromide surfactants, producing surfactants with Krafft temperatures below room temperature that could be attractive replacements for currently used surfactants such as CTAB. S-Undecylisothiouronium bromide was investigated as a potential micellar catalyst. Following its use this surfactant could be removed from the reaction mixture in three ways: (i) by lowering the temperature below the Krafft temperature leading to precipitation of the surfactant; (ii) by deprotonation with weak base to give the insoluble thioamidine; (iii) by base hydrolysis in methanolic solution to give the thiol.