Nanotextured surfaces with anti-fouling and liquid-repellent properties

Liquid-repellent surfaces have many applications such as self-cleaning, anti-fouling and anti-bacterial coatings. We pioneered a technique involving nanoscale wrinkles to create nanotextured surfaces and infused them with a viscous lubricant to fabricate slippery liquid-infused surfaces. The wrinkled surfaces can be fabricated to be superhydrophobic in air, superoleophobic underwater and superhydrophobic under oil. Our technique allows patterning at length-scales from a few hundred nanometers to several tens of micrometers in a manner that is simple, cost-effective, and rapid.

SEM and AFM (insets) images of (a) Teflon wrinkles on Polyshrink and (b) Teflon wrinkles on shrink w
SEM and AFM (insets) images of (a) Teflon wrinkles on Polyshrink and (b) Teflon wrinkles on shrink wrap

Bioinspired anti-fouling surfaces

Using our nanotextured wrinkled polymer surface, we mimic the lubricating mechanism of the pitcher plant. When infused with lubricant, our wrinkled surface traps the lubricant and becomes slippery; thereby functioning as a bioinspired anti-fouling surface with demonstrated ability to inhibit the attachment of bacteria in vitro and marine fouling in the ocean for up to 7 weeks.

2 photos

References:

  1. Ware, C. S.; Smith-Palmer, T.; Peppou-Chapman, S.; Scarratt, L. R. J.; Humphries, E. M.; Balzer, D.; Neto, C. Marine antifouling behavior of lubricant-infused nanowrinkled polymeric surfaces. ACS Applied Materials & Interfaces 2018, 10 (4), 4173-4182. https://pubs.acs.org/doi/10.1021/acsami.7b14736
  2. Peppou-Chapman, S.; Neto, C. Mapping depletion of lubricant films on anti-biofouling wrinkled slippery surfaces. ACS Applied Materials & Interfaces 2018https://pubs.acs.org/doi/10.1021/acsami.8b11768
  3. Owais, A.; Smith-Palmer, T.; Gentle, A.; Neto, C. Influence of long-range forces and capillarity on the function of underwater superoleophobic wrinkled surfaces. Soft Matter 2018, 14 (32), 6627-6634. https://pubs.rsc.org/en/content/articlehtml/2018/sm/c8sm00709h
  4. Scarratt, L. R.; Hoatson, B. S.; Wood, E. S.; Hawkett, B. S.; Neto, C. Durable superhydrophobic surfaces via spontaneous wrinkling of teflon AF. ACS applied materials & interfaces 2016, 8 (10), 6743-6750. https://pubs.acs.org/doi/abs/10.1021/acsami.5b12165

Pattern formation via thin film dewetting

The Neto group pioneered a spontaneous patterning technique via dewetting of thin liquid films, particularly dewetting of polymer bilayers. This is based on the understanding of the intermolecular forces and spreading parameter that make thin liquid films stable.

Thin polymer film dewetting has many advantages over other patterning techniques such as micro-contact printing, photolithography and patterned plasma deposition as it is

  1. Simple
  2. Cost effective – the polymers that can be used to produce functional patterns are many, low cost and easily (often commercially) available
  3. Versatile – no restriction on the choice of polymers used to fabricate the bilayers
  4. Scalable and easy control on the dimension of the patterns
Optical micrographs illustrating the main stages of dewetting of a thin polystyrene film (PS, 110 nm
Optical micrographs illustrating the main stages of dewetting of a thin polystyrene film (PS, 110 nm thick) on a hydrophobized silicon substrate by thermal annealing. (a) Holes nucleate at random locations in the film (b) Holes grow and start to coalesce with neighboring holes and producing cylinders of liquids (c) which further decay into isolated droplets on the substrate.

Patterns are formed by dewetting a bilayer system formed by poly(4-vinylpyridine) (P4VP) thin film (
Patterns are formed by dewetting a bilayer system formed by poly(4-vinylpyridine) (P4VP) thin film (80 nm) on a polystyrene (PS) thin film (100 nm) prepared by spin-coating

Passive atmospheric water capture

We harness our polymer dewetting technique to create micro- and nano-patterns that passively capture water from the atmosphere. Our pattern generation approach is intrinsically up-scalable, and it could be applied to three dimensional large objects as shown in the image. This technology could lead to the delocalised, large scale capture of water for use for drinking, irrigation and for animals. More details on this multidisciplinary project at https://nano-acwa.sydney.edu.au/

Micropatterned polymer surfaces, possessing both topographical and chemical characteristics, were pr
Micropatterned polymer surfaces, possessing both topographical and chemical characteristics, were prepared on three-dimensional copper tubes and used to capture atmospheric water.

References:

  1. Chiu, M.; Wood, J. A.; Widmer-Cooper, A.; Neto, C. Aligned droplet patterns by dewetting of polymer bilayers. Macromolecules 2018, 51 (15), 5485-5493. https://pubs.acs.org/doi/10.1021/acs.macromol.8b00620
  2. Telford, A. M.; Thickett, S. C.; Neto, C. Functional patterned coatings by thin polymer film dewetting. J. Colloid Interface Sci. 2017, 507, 453-469. https://www.sciencedirect.com/science/article/pii/S0021979717307749
  3. Al-Khayat, O.; Hong, J. K.; Beck, D. M.; Minett, A. I.; Neto, C. Patterned polymer coatings increase the efficiency of dew harvesting. ACS applied materials & interfaces 2017, 9 (15), 13676-13684. https://pubs.acs.org/doi/abs/10.1021/acsami.6b16248
  4. Al-Khayat, O.; Geraghty, K.; Shou, K.; Nelson, A.; Neto, C. Chain collapse and interfacial slip of polystyrene films in good/nonsolvent vapor mixtures. Macromolecules 2016, 49 (4), 1344-1352. https://pubs.acs.org/doi/abs/10.1021/acs.macromol.5b02253

Drag-reducing surfaces

We are interested in identifying the interfacial properties that make surfaces slippery.

To study this at a nanoscale, we quantify liquid slip at a solid surface with high reliability and accuracy by squeezing a nanoscale thin films out of a gap between a microsphere and a flat surface in an atomic force microscope (AFM) measurement.

To study this at a microscale, we test our lubricant-infused surfaces in microfluidics channels to study their drag-reducing properties.

Interfacial slip has important consequences for liquid flow in confined geometries, such as in microfluidics devices, porous media and in biological flows.

Lubricant-infused surfaces have drag reducing properties

References:

  1. Lee, T.; Charrault, E.; Neto, C. Interfacial slip on rough, patterned and soft surfaces: A review of experiments and simulations. Adv. Colloid Interface Sci. 2014, 210, 21-38. https://www.sciencedirect.com/science/article/pii/S0001868614000724?via%3Dihub
  2. Zhu, L.; Neto, C.; Attard, P. Reliable measurements of interfacial slip by colloid probe atomic force microscopy. III. Shear-rate-dependent slip. Langmuir 2012, 28 (7), 3465-3473. https://pubs.acs.org/doi/abs/10.1021/la204566h
  3. Zhu, L.; Attard, P.; Neto, C. Reliable measurements of interfacial slip by colloid probe atomic force microscopy. II. Hydrodynamic force measurements. Langmuir 2011, 27 (11), 6712-6719. https://pubs.acs.org/doi/abs/10.1021/la104597dZhu, L.; Attard, P.; Neto, C. Reliable measurements of interfacial slip by colloid probe atomic force microscopy. I. Mathematical modeling. Langmuir 2011, 27 (11), 6701-6711. https://pubs.acs.org/doi/abs/10.1021/la2007809

Self-assembled monolayer of perfluorinated molecules

Self-assembled monolayer of perfluorinated molecules
Halogen bonding is the attractive, non-covalent interaction that can form between an electrophilic region of a halogen atom in a molecule and a nucleophilic region of a molecule.

 

Our group has recently utilised halogen bonding for nanoscale surface modification; more specifically to develop a new family of self-assembled monolayers (SAM). The self-assembly of halogen-bond driven perfluorocarbon monolayers offers a convenient, flexible and simple method to functionalise silicon and other oxide substrates. Our method can be used as a platform for numerous applications, ranging from biosensing to electronics, photovoltaic cells and microfluidics.

References:

  1. Abate, A.; Dehmel, R.; Sepe, A.; Nguyen, N. L.; Roose, B.; Marzari, N.; Hong, J. K.; Hook, J. M.; Steiner, U.; Neto, C. Halogen-bond driven self-assembly of perfluorocarbon monolayers. arXiv preprint arXiv:1803.05672 2018. https://arxiv.org/abs/1803.05672