Honours Projects and Project Areas for 2011 (under construction)

My research is focussed on understanding various fundamental properties of amphiphilic compounds. These compounds are found in a very broad range of applications and technologies, thanks to their ability to self-assemble into structured phases like micelles, vesicles, liquid crystals and other complex fluids, and to form oriented, structured adsorbed films at interfaces. Honours and postraduate research projects are mainly directed at increasing our understanding of the molecular and interolecular forces, and hence the design principles that determine the structure of adsorbed films and structured phases. Several postdoctoral researchers and collaborators are engaged in more closely industry or technology-oriented projects working with commercial partners. One of our main current themes is how important dynamic factors - like reaction kinetics and flow - are in comparison with equilibrium self-assembly behaviour. This turns out to have major effects on how we can use self-assembly to design new kinds of nanostructured materials.

We use a broad range of experimental techniques including light, x-ray and neutron scattering and reflectometry, optical, electron and atomic force microscopy, calorimetry, electroacoustics, conductivity, spectroscopy, rheology and chromatography.

Simulation of the liquid structure of ethylammonium nitrate based on neutron scattering data shows an interpenetrating bicontinuous network of nonpolar (green) and ionic (yellow) functional groups. Are all ILs similarly structured?

SELF-ASSEMBLY IN IONIC LIQUIDS

Ionic liquids (ILs) are salts that melt at low temperatures. E.g. ethylammonium nitrate has a melting point of 13°C. We have recently discovered many room-temperature ionic liquids share with water the ability to promote the self-assembly of surfactants into micelles1, liquid crystals2,3 and microemulsions4. We have also discovered that many ILs themselves behave like surfactants, and organise into sponge like structures in bulk liquid5 (see figure) and oriented layers at surfaces6, 7. The unique properties of ILs such as negligible vapour pressure has led to their wide use as solvents in synthesis and catalysis. How do liquids that are nanostructured themselves affect the interactions between solutes, particles, or surfaces in chemical reactions or self-assembly processes?

In this project we will investigate how changing the structure and H-bonding capacity of IL-forming ions affects the formation, stability and structure of microemulsions. ILs are also very good glass-formers, so we will further examine how IL-microemulsions can be quenched into a solid state to create novel, porous and composite amorphous solids.

  1. M.U. Araos, G.G. Warr, Langmuir 2008, 24, 9354-9360
  2. R. Atkin, S.M.C. Bobillier, G.G. Warr J. Phys. Chem. B 2010 , 114 , 1350–1360
  3. M.U. Araos, G.G. Warr, J. Phys. Chem. B. 2005, 109, 14275-14277
  4. R. Atkin, G.G. Warr, J. Phys. Chem. B. 2008, 112, 4164-4166
  5. R. Atkin, G.G. Warr, J. Phys. Chem. B 2007, 111, 9309-9316
  6. R. Hayes; G.G. Warr; R. Atkin Phys. Chem. Chem. Phys. 2010 12 , 1709-1723.
  7. R. Atkin and G.G. Warr, J. Phys. Chem. C. 2007,111, 9309-9316

DISCOVERING THE DESIGN RULES FOR DIBLOCK OLIGOMER SELF-ASSEMBLY

In order to better understand and design new kinds of soft materials, we are working with oligomers (short polymers) containing short blocks of monomers whose lengths and chemical structure control the equilibrium and kinetics of self-assembly. These molecules are synthesised by controlled radical polymerization, pioneered at the CSIRO, and which gives exquisite control over monomer sequence. In this project we will prepare and compare the properties of new amphiphiles from a range of hydrophobic and hydrophilic monomers, and thus describe their rules of self-assembly .
  1. D.E. Ganeva, E. Sprong, H. de Bruyn, G.G. Warr, C.H. Such and B.S. Hawkett, Macromolecules 2007, 40 , 6181-6189
  2. N. Jain, Y. Wang, S.K. Jones, B.S. Hawkett, G.G. Warr , Langmuir 2010 , 26 , 4465–4472
  3. “Miniemulsion Polymerisation with Arrested Ostwald Ripening using Amphiphilic Macro-RAFT agents as Stabilisers ” B.T.T. Pham, H. Zondanos, C.H. Such, B.S. Hawkett, G.G. Warr, Macromolecules 2010 in press.

Amphiphilic RAFT agents act as copolymer stabilizers in the miniemulsion polymerization of styrene, leading to the conversion of each nanoreactor droplet into a stable polymer particle.

 

SURFACTANT-TEMPLATED MINERALIZATION

Surfactants are widely used to template the formation of mesoporous silica for diverse applications including as adsorbents and catalysts. We have recently found that biominerals like CaCO3 can also form such mesoporous materials, and this seems to depend on the existence and stability of an amorphous solid state. We will explore the use of surfactant micelles and liquid crystals as a templating agent for new nanostructured ionic solids.

Atomic force microscopy image of the surface of (amorphous) calcium carbonate showing a ridge pattern templated by cationic surfactants. Sectioning shows this structure to persist deep into the material grown on top of a calcite crystal.

 

 

DYNAMICS IN POLYMERIZABLE SURFACTANTS

Polymerizable surfactants offer a way of making new kinds of nanostructured materials. The idea is that you exploit intermolecular forces to create an equilibrium self-assembly structure – a micelle, microemulsion, or liquid crystal – then chemically lock the molecules permanently into place by initiating polymerization. Despite decades of work, this has only ever been achieved once , by carefully synthesizing a polymerizable, water-insoluble lipid.

Our recent work has shown that water-soluble surfactants change their self-assembled structure when polymerization is initiated, 1,2 and that you have to think about them as mixed solutions of surfactant and amphiphilic polymer to really understand their behaviour. It is no longer clear that the structure is ever made permanent, although the low solubility of polymerized surfactants can significantly slow the time to achieve equilibrium.

We are currently exploring two kinds of surfactants that undergo addition polymerization in the self-assembled state. Some methacrylate-containing surfactants (left) change aggregated shapes into micellar worms, and others precipitate. Using small-angle scattering we are investigating how polymerization conditions affect degree of polymerization and preferred aggregate shape. We also examine how the self-assembly of polymerized surfactants is affected by mixing with other surfactants.

While designing new polymerizable surfactants a few years ago we accidentally discovered some that polymerize in basic but not acidic solutions (right). 3 This one initially forms micelles like most simple surfactants, but inverts into a hexagonal phase. Here again the central question is how reaction conditions affect degree of polymerization, and how this determines self-assembled structure.

  1. K. Chatjaroenporn, P.A. FitzGerald, R.W. Baker and G.G. Warr Langmuir 2010 , 26 , 11715-11719
  2. K. Chatjaroenporn, P.A. FitzGerald, R.W. Baker and G.G. Warr J. Colloid Interface Sci., 2009, 336 , 449–454
  3. K.A. White and G.G. Warr J. Colloid Interface Sci, 337 2009, 304–306

Small-angle neutron scattering shows how spherical micelles grow into elongated worms during polymerization before collapsing back into globules.

Surfactants with 2- and 4- substitution undergo an unusual addition polymerization in basic solutions.