Research & Publications
1) Self Assembly of Hydrophobic Amphiphiles
From the double helix of DNA to thickening agents in food, the self-assembly of molecules governs many aspects of our daily life and is fundamental to many scientific fields. Ordered structures form through the cumulative effect of multiple non-covalent interactions between adjacent molecules. In water, amphiphiles with hydrophilic and hydrophobic sections (e.g. detergents) also assemble through multiple non-covalent interactions. However, in this case solution parameters such as concentration and solvent type additionally influence the self-assembly process, as well as the balance of hydrophilic and hydrophobic content within the amphiphile. Consequently, an amphiphile can be made to form several different complex structures, such as those shown in the image below (from wikipedia, http://en.wikipedia.org/wiki/Lyotropic_liquid_crystal), simply by changing the solution parameters.
One area in which research into self-assembly is crucial is the creation of carbon-based electronic components, known as “organic electronics”. These materials can be produced more cheaply than silicon and allow for flexible handheld devices. The use of self-assembled molecules will permit desirable macroscopic properties to be targeted simply by optimizing the way the individual molecules interact and align with one another. Unfortunately, the ability to control molecular organization remains difficult.
To address this issue, we’re developing a new mode of self-assembly. The aim is to significantly extend the amphiphilic assembly concept mentioned above to include fully hydrophobic amphiphiles. These are asymmetric molecules comprising mutually immiscible alkyl (e.g. long, branched) and π-conjugated parts (common ones include C60, C70, azobenzene or pyrene). As with conventional amphiphiles, the introduction of additives or solvents with a selective affinity towards either part of the hydrophobic amphiphile provokes self-assembly.By changing solution parameters, several structures can be formed with a single hydrophobic amphiphile, permitting a level of control over the self-assembly of the π-conjugated units not currently accessible by other means.
2) The application of small-angle neutron scattering to investigate the structure and kinetics of self-assembly and colloidal growth.
Small-angle neutron scattering (SANS) is a powerful way to analyse samples containing objects with diameters of 1 ‒ 100 nm (1 nm = 10-9 m). In a SANS experiment, the neutron beam is scattered by nuclei within these nanoscale objects and the intensity of the scattered beam is measured as a function of the angle at which it deviates from its original course. The amount of scattering is determined by factors including the shape, size and number density of the objects in the sample. As such, SANS can be used to build up detailed pictures of the nanoscale constituents of a sample. For this reason, it is regularly used to study a variety of practical materials, ranging from the precipitates in metals that influence strength, flexibility and hardness to the self-assembled molecular structures responsible for the cleaning action of shampoos laundry detergents.
So what sort of experiments do we do using SANS? As noted above, much of our research is focused on the organization of organic molecules into larger assemblies. These typically have dimensions in the region of 1 ‒ 100 nm, and are therefore suited to analysis by SANS. To gain more insight, we use a SANS-specific technique known as contrast variation to selectively highlight different parts of the assembly. Basically, this is done by exchanging deuterium (2H) for hydrogen in one or more of the system components. For example, a 2-component system comprising an alkylated-C60 hydrophobic amphiphile and n-hexane (H14) will highlight the contribution to the overall scattering from just the C60 parts, while using an 84:16 vol:vol mixture of D14 and H14 n-hexane will highlight the contribution from the alkyl chains in the hydrophobic amphiphile only (see image below).
In addition to using SANS to determine the structure of samples, we also use it to study phase transitions (for example, going from micelles to gels or lyotropic phases) and mechanisms in materials chemistry (for example, the growth of mesoporous silcia spheres – see http://pubs.acs.org/doi/abs/10.1021/la203097x). Much of this work is currently in progress: I’m fitting a rather large dataset that we took on SANS2D later last year at the moment. Watch this space for the results.
3) Mesoporous nanoparticle synthesis
Previously, we’ve investigated and developed systems based on porous silica nanoparticles for anti-corrosion coatings (for example, see Chem. Commun. 2012, 48, 115-117 and Adv. Mater. 2011, 23 (11), 1361-1365). Now, we’re interested in developing complex silica-alumina particles. This project is just starting out, but one or two project students will begin work on it in September 2014. Watch this space for results.
Links to my research profile:
Full publication list (last updated – October 2014)
27) Hollamby, M. J.; Karny, M.; Bomans, P. H. H.; Sommerdijk, N. A. J. M.;Saeki, A.; Seki, S.; Minamikawa, H.; Grillo, I.; Pauw, B. R.; Brown, P.; Eastoe, J.; Möhwald, H.; Nakanishi, T. “Directed assembly of optoelectronically active alkyl–π-conjugated molecules by adding n-alkanes or π-conjugated species” Nat. Chem. 2014, 6, 690–696
23) Babu, S. S.; Hollamby, M. J.; Aimi, J.; Ozawa, H.; Saeki, A.; Seki, S.; Kobayashi, K.; Hagiwara, K.; Yoshizawa, M.; Möhwald, H.; Nakanishi, T. “Nonvolatile liquid anthracenes for facile full-colour luminescence tuning at single blue-light excitation” Nat. Commun. 2013, 4, 1969
22) Li, H.; Babu, S. S.; Turner, S. T.; Neher, D.; Hollamby, M. J.; Seki, T.; Yagai, S.; Deguchi, Y.; Möhwald, H.; Nakanishi, T. “Alkylated-C60 Based Soft Materials: Regulation of Self-Assembly and Optoelectronic Property by Chain Branching” J. Mater. Chem. C, 2013, 1, 1943-1951
21) Hollamby, M. J.; Nakanishi, T. “Self-Assembly Properties of Fullerenes” in “Handbook on Fullerene: Synthesis, Properties and Applications”, Eds. Verner, R. F.; Benvegnu, C. Nova Science Publishers, 2012.
20) Hollamby, M. J.*; Borisova, D.; Möhwald, H.; Shchukin, D. “Porous ‘Ouzo-effect’ silica-ceria composite colloids and their application to aluminum corrosion protection” Chem. Commun. 2012, 48, 115-117
19) Hollamby, M. J.*; Borisova, D.; Brown, P.; Eastoe, J.; Grillo, I.; Shchukin, D. “Growth of mesoporous silica nanoparticles monitored by time resolved small-angle neutron scattering.” Langmuir 2012, 28(9), 4425-4433
18) Schnepp, Z.; Hollamby, M.; Tanaka, M.; Katsuya, Y.; Matsushita, Y.; Sakka, Y. “One-step route to a hybrid TiO2/TixW1-xN nanocomposite by in situ selective carbothermal nitridation” Sci. Technol. Adv. Mater. 2012, 13, 035001
16) Hollamby, M. J.*; Fix, D.; Doench, I.; Borisova, D.; Möhwald, H.; Shchukin, D. “Hybrid Polyester Coating Incorporating Functionalized Mesoporous Carriers for the Holistic Protection of Steel Surfaces” Adv. Mater. 2011, 23 (11), 1361-1365
15) Li, H.; Hollamby, M. J.; Seki, T.; Yagai, S.; Möhwald, H.; Nakanishi, T. “Multifunctional, polymorphic, ionic fullerene supramolecular materials: Self-assembly and thermotropic properties” Langmuir 2011, 27 (12), 7493-7501
11) Trickett, K.; Xing, D.; Eastoe, J.; Enick, R. M.; Mohamed, A.; Hollamby, M. J.; Cummings, S.; Rogers, S. E.; Heenan, R. K. “Hydrocarbon Metallosurfactants for CO2” Langmuir 2010, 26 (7), 4732-4737
10) Myakonkaya, O.; Deniau, D.; Eastoe, J.; Rogers, S. E.; Ghigo, A.; Hollamby, M. J.; Vesperinas, A.; Sankar, M.; Taylor, S. H.; Bartley, J. K.; Hutchings, G. J. “Recovery and Reuse of Nanoparticles by Tuning Solvent Quality” ChemSusChem 2010, 3 (3), 339-341
9) Myakonkaya, O.; Deniau, B.; Eastoe, J.; Rogers, S. E.; Ghigo, A.; Hollamby, M. J.; Vesperinas, A.; Sankar, M.; Taylor, S. H.; Bartley, J. K.; Hutchings, G. J. “Recycling nanocatalysts by tuning solvent quality” J. Colloid Interface Sci. 2010, 350(2), 443-446
8) Hollamby, M. J.; Trickett, K. J.; Mohamed, A.; Cummings, S.; Tabor, R. F.; Myakonkaya, O.; Gold, S.; Rogers, S.; Heenan, R. K.; Eastoe, J. “Tri-Chain Hydrocarbon Surfactants as Designed Micellar Modifiers for Supercritical CO2” Angew. Chem. Int. Ed. 2009, 48 (27), 4993-4995
5) Hollamby, M. J.; Tabor, R.; Mutch, K. J.; Trickett, K.; Eastoe, J.; Heenan, R. K.; Grillo, I. “Effect of Solvent Quality on Aggregate Structures of Common Surfactants” Langmuir 2008, 24 (21), 12235-12240
4) Hollamby, M. J.; Trickett, K.; Vesperinas, A.; Rivett, C.; Steytler, D. C.; Schnepp, Z.; Jones, J.; Heenan, R. K.; Richardson, R. M.; Glatter O.; Eastoe, J. “Stabilization of CeO2 nanoparticles in a CO2 rich solvent” Chem. Commun. 2008, (43), 5628-5630