ORCID Profile
0000-0001-5079-2622
Current Organisation
The University of Auckland
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Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5SM03108G
Abstract: Studies of water drop impacts on microstructured surfaces are important for understanding dynamic wetting on rough surfaces, and for developing related design principles. Here, high-speed imaging has been used to study asymmetries within the spreading phase following vertical water drop impacts at Weber numbers between 34 and 167. The eleven polydimethylsiloxane surfaces studied had micropillars arranged in square and rectangular arrays, with feature sizes ranging from ∼5 μm to ∼240 μm and various pillar cross-sections, in most cases supporting a static Cassie state. Two contrasting and apparently independent asymmetries were identified. Firstly, partial (rather than full) microstructure penetration occurred on five of the surfaces, with the edges of the penetrated profiles tending to lie parallel to the array rows and columns. These observations are best explained by considering surface energies. Secondly, the perimeter of a spreading drop tends to lie at 45° to the rows and columns. This shape is caused by movement of air from underneath the impacting drop, which generates jets and subsequent fingers in preferred directions at the edge of the drop. The area of the 'corridor' through which the air escapes is an important quantitative parameter. Experiments also demonstrate the effects of microstructures on the maximum spreading diameter, and formation of off-centre microbubble patterns.
Publisher: Elsevier BV
Date: 02-2022
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3SM00701D
Abstract: Vertical drop impacts of ferrofluids onto glass slides in a non-uniform magnetic field have been studied using high-speed photography. Side-on (left) and top-down (right) images show the dynamic evolution of instabilities.
Publisher: IOP Publishing
Date: 29-10-2008
DOI: 10.1088/0957-4484/19/47/475504
Abstract: Mechanical resizing of in idual nanopores in a thermoplastic polyurethane elastomer has been characterized. Specimen nanopores were conical, with smaller hole dimensions of the order of tens to hundreds of nanometres. Electrophoretic current measurements show that the estimated nanopore radius can be reversibly actuated over an order of magnitude by stretching and relaxing the elastomer. Within a working range of stretching, current is proportional to specimen extension to the power of a constant, n, which ranges from 0.9 to 2.3 for different specimens. The data indicate that scaling of the effective pore radius is super-affine. At strains below the working range, the pore size is relatively unresponsive to stretching. Macroscopic elastomer extension has been related to local radial strain (50-250 µm from the pore) using optical microscopy. Scanning electron microscopy and atomic force microscopy have been used to observe membrane surface features.
Publisher: Elsevier BV
Date: 04-2019
DOI: 10.1016/J.JTOS.2019.02.010
Abstract: Dry eye disease (DED) is one of the most prevalent ocular surface disorders that presents clinically. Recently, the semifluorinated alkane (SFA) perfluorohexyloctane (NovaTears Interactions of both SFAs with the corneal surface were evaluated ex vivo using high-speed photography. The in vivo influence of SFAs on tear fluid dynamics was evaluated in healthy rabbit eyes observing changes in lipid layer grade, tear evaporation rate, tear volume and tear osmolarity. Furthermore, ocular tolerability was confirmed by clinical scoring and sodium fluorescein staining. Ex vivo studies demonstrated that both SFAs rapidly spread on the ocular surface with their contact angle on the cornea being virtually zero. A significant improvement in lipid layer grade was observed immediately after instillation of both SFAs in vivo, although the improvement was more sustained upon instillation of perfluorohexyloctane with a statistically significant difference compared to saline instillation evident from day five onwards. No significant changes in tear evaporation rate, volume or osmolarity, nor any signs of ocular irritation were observed after application of either SFA over the seven-day study period. Both SFAs showed excellent spreading on the ocular surface. Perfluorohexyloctane improved the lipid layer grade significantly after topical application supporting its potential to stabilise the tear film lipid layer and thus provide symptomatic relief in evaporative DED.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B925588E
Abstract: We present a detailed experimental study of water drops coming into contact with the end of vertical polytetrafluoroethane (PTFE) capillary tubes. The drops, supported on a superhydrophobic substrate, were between 0.06 and 1.97 mm in radius, and the inner radius of the vertical tube was 0.15 mm. These experiments expand on our recent work, which demonstrated that small water droplets can spontaneously penetrate non-wetting capillaries, driven by the action of Laplace pressure within the droplet, and that the dynamics of microfluidic capillary uptake are strongly dependent on the size of the incident drop. Here we quantitatively bound the critical drop radius at which droplets can penetrate a pre-filled capillary to the narrow range between 0.43 and 0.50 mm. This value is consistent with a water-PTFE contact angle between 107.8 degrees and 110.6 degrees. Capillary uptake dynamics were not significantly affected by the initial filling height, but other experimental factors have been identified as important to the dynamics of this process. In particular, interactions between the droplet, the substrate and the tubing are unavoidable prior to and during droplet uptake in a real microfluidic system. Such interactions are classified and discussed for the experimental set-up used, and the difficulties and requirements for droplet penetration of a dry capillary are outlined. These results are relevant to research into microfluidic devices, inkjet printing, and the penetration of fluids in porous materials.
Publisher: Elsevier BV
Date: 03-2013
DOI: 10.1016/J.JCIS.2012.11.071
Abstract: Resistive pulse sensing (RPS) with tunable pores (TPs) has been used to investigate an oil-in-water emulsion stabilised with β-lactoglobulin (BLG). The mode of the droplet size distribution steadily increased over four months, from less than 150 nm to more than 200 nm. Results suggest that the dominant growth mechanism was migration of oil to relatively large droplets, as in Ostwald ripening. In contrast, the growth dynamics for salt-induced aggregation suggest flocculation and coalescence of droplets coming into contact. The charge measurement method recently developed by Vogel et al. was also applied to the emulsion. The two data analysis methods used yielded average droplet ζ-potentials of -18.9 mV and -21.8 mV, compared with -27.6 mV obtained using light scattering. Methods for measuring emulsion droplet deformation and the charge on in idual droplets are under development. Tunable pores are a useful tool for improved characterisation of submicrometre emulsions, as well as other synthetic and biological particles, as they provide better precision than light scattering for particle number distributions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0SM00574F
Publisher: American Chemical Society (ACS)
Date: 14-12-2020
Publisher: Elsevier BV
Date: 2021
Start Date: 2023
End Date: 2026
Funder: Ministry of Business, Innovation and Employment
View Funded ActivityStart Date: 2018
End Date: 2021
Funder: Marsden Fund
View Funded Activity