Towards Biomimetic Surfaces: Controlling Silica Nanoparticle Aggregation

Alex Wu and Robert N. Lamb

School of Chemistry, University of Melbourne

The ideal non-stick surface is one that exhibits hierarchical roughness and hydrophobic surface chemistry. The surface of a lotus leaf exhibits co-existence of macro, micro and nanoscale topography. This combination results in a perpetually clean leaf surface.

To harness this self-cleaning ability, biomimetic surfaces were fabricated synthetically using techniques such as lithography, plasma etching and most commonly, silica nanoparticle aggregation. Our group owns numerous patents to these silica-based coatings developed in the past 15 years.1-4

The next step in non-stick surface fabrication is to control the hierarchical roughness at multiple length scales. We have previously achieved micro-scale roughness control through the addition of polymer spacers5. This seemingly innocuous act of controlling roughness at the micron scale caused a dramatic change in properties. The resultant surface exhibited both optical transparency and antifouling capabilities6.

The goal of this project is to understand and control the natural aggregating behaviour of silica nanoparticles. Current technology utilizes steric hindrance and charge stability to prevent aggregation of silica nanoparticles with sizes down to ~150 nm. Our goal is to use a combination of silane chemistry combined with anionic/cationic polymerization to not only prevent aggregation, but to control the separation of adjacent silica nanoparticles through charge stabilization and in-situ oligomer synthesis. Silica nanoparticle sizes ranging from 40 nm to 7 nm will be the focus of this research.

1. Lamb, R. N., Zhang, H. & Raston, C. L. Hydrophobic Films. (1997). EP 0969934

2. Lamb, R., Norman, Jones, A., Ward & Zhang, H. Hydrophobic Material. (1999). US 6,743,467, EP 1210396

3. Lamb, R., Norman, Jones, A., Ward & Zhang, H. Hydrophobic Coating. (2004). US 2006/0263516

4. Lamb, R., Norman, Jones, A., Ward & Zhang, H. Durable Superhydrophobic Coating. Australia patent (2004). US 2007/0009657

5. Cho, K. L., Liaw, I. I., Wu, A. H. F. & Lamb, R. N. Influence of Roughness on a Transparent Superhydrophobic Coating. The Journal of Physical Chemistry C 114, 11228-11233, (2010).

6. Scardino, A. J., Zhang, H., Cookson, D. J., Lamb, R. N. & Nys, R. d. The role of nano-roughness in antifouling. Biofouling: The Journal of Bioadhesion and Biofilm Research 25, 757 – 767 (2009).