molecular self-assembled materials
We are seeking to understand how to control the structure, properties and behaviour of soft materials formed by the self-assembly of surfactants, lipids, polymers and nanoparticles into micelles, liquid crystals and other nanostructured phases. Although we focus on fundamental understanding, these materials are found almost everywhere from pharmaceutical and industrial formulations to living systems. All of the projects offered employ advanced nanoscale characterization techniques including X-ray and neutron scattering (at Australian and international facilities), electron and scanning probe microscopy, in combination with macroscopic characterization by optical microscopy, calorimetry, and rheology.
When is a micelle a micelle?
The classic cartoon picture of a surfactant micelle is a non-polar droplet coated by polar functional groups in contact with water. But this static picture hides the other main characteristic of micelles, and of all self-assembled structures. They are equilibrium structures, and therefore exist exchange molecules with solvent, break up and reform, and also stretch, bend, vibrate, and rotate about their average shape. A hydrophobic nanoparticle with hydrophilic surface groups is static. Using novel polymeric amphiphiles,1 we can vary the rate of various dynamic processes in solution, and see changes in nanostructure when components are mixed or are flowing using time-resolved neutron scattering. These processes control important applications of amphiphiles including burst release in drug delivery systems, flow behaviour of personal care or industrial formulations, and the rigidity of gels.
Emergent properties of next-generation liquids and solvents
Amphiphilic historically means made up of hydrophobic and hydrophilic parts, like a surfactant. New polymer and nanoparticle synthesis techniques now mean that there are many more kinds of amphiphilicity and self-assembly. In this project we will investigate the structure of nanoparticle-organic hybrid materials (NOHMS) – liquids made by the assembly of inorganic nanoparticles stabilized by surface-attached polymer chains. Originally developed for carbon sequestration, NOHMs contain no solvent and have no vapour pressure. What emergent structures and (optical, magnetic, conductance) properties will result when inorganic nanoparticles are combined within the same polymer matrix that guarantees mixing?
Responsive next-generation liquids and solvents
New block co- polymer synthesis techniques allow us to combine amphiphilic and responsive liquid polymers with inorganic materials to form switchable, ‘polyphilic’ nanoparticle-organic hybrid materials (NOHMS) whose surface-attached polymer chains respond to environmental changes such as temperature, humidity or pH. Here we will use external triggers to change chain conformation and simultaneously examine how the changes in nanostructure affect macroscopic properties (flow/gelation, solvent miscibility,…).
Ionic liquid miscibility and self-assembly
By altering the chemical nature of the cation and anion, salts can not only be made molten at room temperature (ionic liquids or ILs) but also miscible or immiscible with a wide range of molecular solvents. Water-miscible (hydrophilic) and immiscible (hydrophobic) ILs are common. And yet, water-immiscible ILs can still be polar solvents, readily dissolving salts, hydrophilic polymers, and allowing surfactants to form micelles and liquid crystals. In this project we will examine how amphiphilic polymers are solvated and self-assemble when dissolved into ILs different cation and anion composition in order to understand the intermolecular forces that can make an IL polar or nonpolar, hydrophilic or hydrophobic.2
Ionic liquid ‘designer’ surfactants
Until a few years ago, surfactant micelles and other self-assembled phases were only known to form in a handful of molecular solvents (water, ethylene glycol, glycerol, formic acid, formamide, hydrazine (…and liquid ammonia!)). Today, hundreds (possibly thousands) of ionic liquids (ILs) are known to be self-assembly solvents, but every surfactant known today is built for water. Properly exploiting the new properties of ILs will require us to engineer efficient self-assembly. This project will build on our recent work understanding ionic liquid structure3 to explore what polar and non-polar functionalities are best suited to detergents that will form micelles, liquid crystals and microemulsions in these unusual solvents.4
Composition of mixed vapour/surfactant monolayers (with Dr Andy Nelson, ANSTO)
Surfactant adsorption at air/water interfaces is a widespread phenomenon responsible for soap film and foam formation and stability, surface tension reduction, evaporation control, and many other phenomena. Volatile organic compounds can dissolve into adsorbed monolayers, affecting surface tension and many other properties, but this phenomenon has scarcely begun to be examined. In this project we will directly measure the composition and structure of mixed monolayers of surfactants (adsorbed from solution) and volatile organic components (adsorbed from the vapour phase) for the first time, using the PLATYPUS neutron reflectometer at ANSTO. These measurements will provide direct tests of theoretical models of adsorbed layers, and give new insights into how volatile components affect air/solution interface.
1 Ganeva, DE; Sprong, E; de Bruyn, H; Warr, GG; Such, CH and Hawkett, BS. Macromolecules, 40, 6181, 2007. DOI:10.1021/ma070442w; P.A. Fitzgerald, G.G. Warr, Adv. Colloid Interface Sci. 2012 179-182, 14–21; J.M. Heinen, A.C.M. Blom, B.S. Hawkett, G.G. Warr, J. Phys. Chem B 2013, 117, 3005-3018.
2 Atkin, R; Bobillier, SMC and Warr, GG. J. Phys. Chem. B, 114, 1350-1360, 2010. DOI: 10.1021/jp910649a.; R. Hayes, S.Imberti, G.G. Warr, R. Atkin, Angewandte Chemie Intl Ed. 2012 51, 7468–7471; M.U. Araos, G.G. Warr, Langmuir 2008, 24, 9354–9360.
3 Hayes, R; Imberti, S; Warr, GG and Atkin, R. Phys. Chem. Chem. Phys., 13, 13544, 2011. DOI: 10.1039/c1cp21080g; R. Hayes, S. Imberti, G.G. Warr, R. Atkin, Angew. Chemie Intl Ed. 2013, 52, 4623-4627.
4 S.C. Sharma, G. G. Warr, J. Phys. Chem. Lett. 2011, 2, 1937–1939; M.U. Araos, G.G. Warr, Langmuir 2008, 24, 9354–9360; R. Atkin and G.G. Warr, J. Phys. Chem. B. 2007, 111, 9309–9316
For further information, please contact:
School of Chemistry
University of Sydney NSW 2006
Phone: +61 2 9351 2106