Browsing by Author "Warr, GG"

Now showing 1 - 6 of 6
  • No Thumbnail Available
    Item
    Direct visualisation of mesh phases at the solid/solution interface by AFM and neutron reflectometry
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Blom, ACM; Warr, GG; Nelson, A
    Using soft-contact AFM imaging, the adsorbed layer structure of mixed solutions of single-chained dodecyltrimethylammonium bromide (DTAB) and double-chained didodecyldimethylammonium bromide (DDAB) at varying compositions has been studied. On quartz, the observed morphologies as composition was varied from DDAB-rich mixtures to DTAB-rich mixtures changed from a bilayer -> mesh -> rods -> globules. This novel mesh structure is consistent with the average curvature progression from bilayer to rods, and consists of densely branched rods. There was a narrow solution composition over which this mesh structure was observed and a fractional change in solution composition resulted in a film transformation to rods. Neutron reflectometry experiments on multiple contrasts have been performed in ISIS and at ANSTO and confirm the curvature sequence observed using AFM. The composition of the mixed film was determined as were adsorbed amounts, film thicknesses and surface coverages. Despite there being an excess of DTAB in solution, the surface was very enriched in DDAB for the two mixed films. © 2005 The Authors
  • No Thumbnail Available
    Item
    Phase behavior of amphiphilic diblock co-oligomers with nonionic and ionic hydrophilic groups
    (American Chemical Society, 2013-03-14) Heinen, JM; Blom, ACM; Hawkett, BS; Warr, GG
    The synthesis of a series of co-oligomer amphiphiles by RAFT and their self-assembly behavior in water is described. These novel amphiphiles, comprised of styrene, butyl acrylate, and alkyl hydrophobes together with ionic acrylic acid and nonionic hydroxyethylacrylate hydrophilic moieties and with a total degree of polymerization from 5 to 17, represent a new class of small-molecule surfactants that can be formed from the immense potential library of all polymerizable monomers. Examples of micellar solutions and discrete cubic, hexagonal, lamellar, and inverted hexagonal lyotropic phases, as well as vesicle dispersions and coexisting lamellar phases, are reported and characterized by small-angle scattering. The variation of self-assembly structure with co-oligomer composition, concentration, and solution conditions is interpreted by analogy with the surfactant packing parameter used for conventional small-molecule amphiphiles.© 2013, American Chemical Society.
  • No Thumbnail Available
    Item
    Phase behaviour and aggregate structures of the surface-active ionic liquid [BMIm][AOT] in water
    (Elsevier B.V., 2023-12-15) Zhang, YX; Marlow, JB; Wood, K; Wang, J; Warr, GG; Li, H; Atkin, R
    Hypothesis: The surface-active ionic liquid, 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate ([BMIm][AOT]), has a sponge-like bulk nanostructure consisting of percolating polar and apolar domains formed by the ion charge groups and alkyl chains, respectively. We hypothesise that added water will swell the polar domains and change the liquid nanostructure. Experiments: Small angle X-ray scattering (SAXS), small angle neutron scattering (SANS) and polarizing optical microscopy (POM) were used to investigate the nanostructure of [BMIm][AOT] as a function of water content. Differential scanning calorimetry (DSC) was employed to probe the thermal transitions of [BMIm][AOT]-water mixtures and the mobility of water molecules. Findings: SAXS, SANS and POM show that at lower water contents, [BMIm][AOT]-water mixtures have a sponge-like nanostructure similar to the pure SAIL, at medium water contents a lamellar phase forms, and at high water contents vesicles form. DSC results reveal that water molecules are supercooled in the lamellar phase. For the first time, results reveal a series of transitions from inverse sponge, to lamellar then to vesicles, for [BMIm][AOT] upon dilution with water. © 2023 Elsevier Inc.
  • No Thumbnail Available
    Item
    Structure of mixed DTAB/DDAB adsorbed layers on quartz: a neutron reflectometry and atomic force microscopy study
    (Elsevier, 2007-11-15) Blom, ACM; Warr, GG; Nelson, A
    The structure and composition of adsorbed layers formed by mixtures of dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB) on quartz have been determined using a combination of atomic force microscopy and neutron reflectometry. The mixed adsorbed layer was found to be substantially enriched in DDAB, stabilising the formation of a laterally unstructured bilayer even when there is only as little as 1 mol% present in the bulk mixed solute. At even higher DTAB content the adsorbed film morphology gradually transforms to globules over a very narrow composition range. DDAB was found to be significantly excluded from the mixed adsorbed film only after it was completely transformed into globular aggregates, the equilibrium adsorbed layer morphology of DTAB. © 2007, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Structure of the ethylammonium nitrate surface: an x-ray reflectivity and vibrational sum frequency spectroscopy study
    (American Chemical Society, 2010-06-01) Niga, P; Wakeham, D; Nelson, A; Warr, GG; Rutland, M; Atkin, R
    X-ray reflectivity and vibrational sum frequency spectroscopy are used to probe the structure of the ethylammonium nitrate (EAN)−air interface. X-ray reflectivity reveals that the EAN−air interface is structured and consists of alternating nonpolar and charged layers that extend 31 Å into the bulk. Vibrational sum frequency spectroscopy reveals interfacial cations have their ethyl moieties oriented toward air, with the CH3 C3 axis positioned 36.5° from interface normal. This structure is invariant between 15 and 51°C. On account of its molecular symmetry, the orientation of the nitrate anion cannot be determined with certainty. © 2010, American Chemical Society
  • No Thumbnail Available
    Item
    Temperature- and pH-responsive micelles with collapsible poly(N-isopropylacrylamide) headgroups
    (ACS Publications, 2014-06-18) FitzGerald, PA; Gupta, S; Wood, K; Perrier, S; Warr, GG
    We have studied the micelle formation and phase behavior of a series of temperature- and pH-responsive surfactants prepared by controlled radical (RAFT) polymerization. These C12NIPAMm surfactants consist of a dodecyl tail, a poly(N-isopropylacrylamide) (polyNIPAM) headgroup with average degrees of polymerization of between 7 and 96, and an ionizable carboxylate group. In the un-ionized state, these surfactants phase separate on warming toward a lower critical solution temperature (LCST), which decreases as the length of the NIPAM group is decreased. This is in agreement with the behavior of conventional nonionic poly(ethylene oxide)-based surfactants but is very different from that of polyNIPAM oligomer solutions. Small angle neutron scattering (SANS) shows that these surfactants self-assemble into micelles consisting of a nearly spherical hydrophobic core surrounded by a “hairy” polyNIPAM shell far below their LCST. Upon warming, the micelles undergo a sphere-to-rod transition induced by the collapse of the polyNIPAM shell, causing a reduction in the headgroup area. In the un-ionized state the demixing follows at the LCST, but a single charge on the free polymer end completely suppresses phase separation, allowing micelles to undergo a shape change but remain dissolved. © 2014, American Chemical Society.