Wetting of non rigid surfaces

In the world of anti-wetting surfaces, many superhydrophobic substrates comprise rigid structures on rigid substrates. The development of a thin flexible substrate would allow new avenues to be explored to fully take advantage of the non-wetting properties of superhydrophobicity. This thesis presents a novel production method and subsequent analysis of thin, conformable, superhydrophobic films based on the embedding of carbon nano-particles (CNPs) into the surface of polydimethylsiloxane (PDMS) substrates. Firstly experiments were performed to determine the effects of surface roughness on the capillary origami process. It was found that the droplet wrapping process could be controlled with the appropriate choice of liquid. Using a wetting liquid would see an enhanced wrapping state whereas use of a dewetting liquid would see a complete suppression of the wrapping process. The second set of experiments concentrated on determining whether or not it is possible to reduce the drag force experienced on cylinders in a laminar flow situation. By comparing an uncoated cylinder to a CNP PDMS coated cylinder of equivalent diameter, it was determined that it is possible to reduce the drag by a maximum of 28%

Restricting Prey Dispersal Can Overestimate the Importance of Predation in Trophic Cascades

Predators can affect prey populations and, via trophic cascades, predators can indirectly impact resource populations (2 trophic levels below the predator) through consumption of prey (density-mediated indirect effects; DMIEs) and by inducing predator-avoidance behavior in prey (trait-mediated indirect effects; TMIEs). Prey often employ multiple predator-avoidance behaviors, such as dispersal or reduced foraging activity, but estimates of TMIEs are usually on individual behaviors. We assessed direct and indirect predator effects in a mesocosm experiment using a marine food chain consisting of a predator (toadfish - Opsanus tau), prey (mud crab - Panopeus herbstii) and resource (ribbed mussel - Geukensia demissa). We measured dispersal and foraging activity of prey separately by manipulating both the presence and absence of the predator, and whether prey could or could not disperse into a predator-free area. Consumption of prey was 9 times greater when prey could not disperse, probably because mesocosm boundaries increased predator capture success. Although predator presence did not significantly affect the number of crabs that emigrated, the presence of a predator decreased resource consumption by prey, which resulted in fewer resources consumed for each prey that emigrated in the presence of a predator, and reduced the overall TMIE. When prey were unable to disperse, TMIEs on mussel survival were 3 times higher than the DMIEs. When prey were allowed to disperse, the TMIEs on resource survival increased to 11-times the DMIEs. We found that restricting the ability of prey to disperse, or focusing on only one predator-avoidance behavior, may be underestimating TMIEs. Our results indicate that the relative contribution of behavior and consumption in food chain dynamics will depend on which predator-avoidance behaviors are allowed to occur and measured. © 2013 Geraldi, Macreadie

Woven natural fibre reinforced composite materials for medical imaging

Repeatable patient positioning is key to minimising the burden on planning radiotherapy treatment. There are very few materials commercially available which are suitable for use in all common imaging and treatment modalities such as magnetic resonance imaging (MRI), X-Ray computed tomography (CT) and radiotherapy. In this article, we present several such materials based on woven natural fibres embedded in a range of different resin materials which are suitable for such applications. By investigating a range of resins and natural fibre materials in combination and evaluating their performance in terms of MRI and X-Ray imaging, we show that a woven cotton material impregnated with a two-part epoxy resin provides a 15% improvement in passage of X-Rays and has no impact on the MRI signal (unlike the 40% MRI signal attenuation from carbon fibre), whilst also retaining a flexural modulus up to 71% of that of carbon fibre. These results demonstrate that natural fibre composites produced using such materials provide desirable properties for use in patient support and positioning devices for multi-modal imaging, without the need to significantly compromise on the strength of the material

Advanced sandwich composite cores for patient support in advanced clinical imaging and oncology treatment

Ongoing advances in both imaging and treatment for oncology purposes have seen a significant rise in the use of not only the individual imaging modalities, but also their combination in single systems such as Positron Emission Tomography combined with Computed Tomography (PET–CT) and PET–MRI (Magnetic Resonance Imaging) when planning for advanced oncology treatment, the most demanding of which is proton therapy. This has identified issues in the availability of suitable materials upon which to support the patient undergoing imaging and treatment owing to the differing requirements for each of the techniques. Sandwich composites are often selected to solve this issue but there is little information regarding optimum materials for their cores. In this paper, we presented a range of materials which are suitable for such purposes and evaluated the performance for use in terms of PET signal attenuation, proton beam stopping, MRI signal shading and X-Ray CT visibility. We found that Extruded Polystyrene offers the best compromise for patient support and positioning structures across all modalities tested, allowing for significant savings in treatment planning time and delivering more efficient treatment with lower margins

Bioinspired nanoparticle spray-coating for superhydrophobic flexible materials with oil/water separation capabilities

Much of the inspiration for the creation of superhydrophobic surfaces has come from nature, from plant such as the Sacred Lotus (Nulembo nucifera), where the micro-scale papillae epidermal cells on the surfaces of the leaves are covered with nano-scale epicuticular wax crystalloids. The combination of the surface roughness and the hydrophobic wax coating produces a superhydrophobic wetting state on the leaves allowing them to self-clean and easily shed water. Here a simple scale-up carbon nanoparticle spray coating is presented that mimics the surface of the Sacred Lotus leaves and can be applied to a wide variety of materials, complex structures, and flexible substrates, rendering them super hydrophobic, with contact angles above 160°. The sprayable mixture is produced by combining toluene, polydimethylsiloxane (PDMS), And inherently hydrophobic rapeseed soot. The ability to spray the superhydrophobic coating allows for the hydrophobisation of complex structures such a metallic meshes, which allows for the production of flexible porous superhydrophobic materials that when formed into U-shape channels, can be used to direct flows. The porous meshes, whilst being superhydrophobic, are also oleophilic. Being both superhydrophobic and oleophilic allows oil to pass through the mesh, whilst water remains on the surface. The meshes were tested for their ability to separate mixtures of oil and water in a flow situation. When silicone oil/water mixtures were passed over the meshes, all meshes tested were capable of separating more than 93% of the oil from the mixture

Double-sided slippery liquid-infused porous materials using conformable mesh

Often wetting is considered from the perspective of a single surface of a rigid substrate and its topographical properties such as roughness or texture. However, many substrates, such as membranes and meshes, have two useful surfaces. Such flexible substrates also offer the potential to be formed into structures with either a double-sided surface (e.g. by joining the ends of a mesh as a tape) or a single-sided surface (e.g. by ends with a half-twist). When a substrate possesses holes, it is also possible to consider how the spaces in the substrate may be connected or disconnected. This combination of flexibility, holes and connectedness can therefore be used to introduce topological concepts, which are distinct from simple topography. Here, we present a method to create a Slippery Liquid-Infused Porous Surface (SLIPS) coating on flexible conformable doubled-sided meshes and for coating complex geometries. By considering the flexibility and connectedness of a mesh with the surface properties of SLIPS, we show it is possible to create double-sided SLIPS materials with high droplet mobility and droplet control on both faces. We also exemplify the importance of flexibility using a mesh-based SLIPS pipe capable of withstanding laminar and turbulent flows for 180 and 90 minutes, respectively. Finally, we discuss how ideas of topology introduced by the SLIPS mesh might be extended to create completely new types of SLIPS systems, such as Mobius strips and auxetic metamaterials

Projecting coral responses to intensifying marine heatwaves under ocean acidification

Over this century, coral reefs will run the gauntlet of climate change, as marine heatwaves (MHWs) become more intense and frequent, and ocean acidification (OA) progresses. However, we still lack a quantitative assessment of how, and to what degree, OA will moderate the responses of corals to MHWs as they intensify throughout this century. Here, we first projected future MHW intensities for tropical regions under three future greenhouse gas emissions scenario (representative concentration pathways, RCP2.6, RCP4.5 and RCP8.5) for the near-term (2021-2040), mid-century (2041-2060) and late-century (2081-2100). We then combined these MHW intensity projections with a global data set of 1,788 experiments to assess coral attribute performance and survival under the three emissions scenarios for the near-term, mid-century and late-century in the presence and absence of OA. Although warming and OA had predominately additive impacts on the coral responses, the contribution of OA in affecting most coral attributes was minor relative to the dominant role of intensifying MHWs. However, the addition of OA led to greater decreases in photosynthesis and survival under intermediate and unrestricted emissions scenario for the mid- and late-century than if intensifying MHWs were considered as the only driver. These results show that role of OA in modulating coral responses to intensifying MHWs depended on the focal coral attribute and extremity of the scenario examined. Specifically, intensifying MHWs and OA will cause increasing instances of coral bleaching and substantial declines in coral productivity, calcification and survival within the next two decades under the low and intermediate emissions scenario. These projections suggest that corals must rapidly adapt or acclimatize to projected ocean conditions to persist, which is far more likely under a low emissions scenario and with increasing efforts to manage reefs to enhance resilience

Low-friction self-centering droplet propulsion and transport using a Leidenfrost herringbone-ratchet structure

A fundamental limitation to the ability to transport sessile droplets is frictional forces arising from surface adhesion. This can be overcome by using the Leidenfrost effect on a heated substrate to levitate the droplet on a cushion of vapor. By structuring the surface under the droplet, the flow of vapor below the droplet can be controlled and this can be used to induce preferential droplet propulsion in a particular direction. However, while propulsion can be induced, the dramatic reduction in frictional forces leads to instability and it is difficult to control droplet motion when transporting droplets along a defined path. Here, we present a self-propulsion and self-centering concept using the principles of negative feedback to enable a droplet to be transported along a defined path. In our implementation, we use a combined herringbone and ratchet design, which provides the ability to control droplet position without compromising on speed. This intrinsic self-centering and correction via negative feedback offers the potential to design paths and tracks for droplets to follow, without the need for walls

Oyster Reefs as Natural Breakwaters Mitigate Shoreline Loss and Facilitate Fisheries

Shorelines at the interface of marine, estuarine and terrestrial biomes are among the most degraded and threatened habitats in the coastal zone because of their sensitivity to sea level rise, storms and increased human utilization. Previous efforts to protect shorelines have largely involved constructing bulkheads and seawalls which can detrimentally affect nearshore habitats. Recently, efforts have shifted towards “living shoreline” approaches that include biogenic breakwater reefs. Our study experimentally tested the efficacy of breakwater reefs constructed of oyster shell for protecting eroding coastal shorelines and their effect on nearshore fish and shellfish communities. Along two different stretches of eroding shoreline, we created replicated pairs of subtidal breakwater reefs and established unaltered reference areas as controls. At both sites we measured shoreline and bathymetric change and quantified oyster recruitment, fish and mobile macro-invertebrate abundances. Breakwater reef treatments mitigated shoreline retreat by more than 40% at one site, but overall vegetation retreat and erosion rates were high across all treatments and at both sites. Oyster settlement and subsequent survival were observed at both sites, with mean adult densities reaching more than eighty oysters m−2 at one site. We found the corridor between intertidal marsh and oyster reef breakwaters supported higher abundances and different communities of fishes than control plots without oyster reef habitat. Among the fishes and mobile invertebrates that appeared to be strongly enhanced were several economically-important species. Blue crabs (Callinectes sapidus) were the most clearly enhanced (+297%) by the presence of breakwater reefs, while red drum (Sciaenops ocellatus) (+108%), spotted seatrout (Cynoscion nebulosus) (+88%) and flounder (Paralichthys sp.) (+79%) also benefited. Although the vertical relief of the breakwater reefs was reduced over the course of our study and this compromised the shoreline protection capacity, the observed habitat value demonstrates ecological justification for future, more robust shoreline protection projects

Oyster-mediated benthic-pelagic coupling modifies nitrogen pools and processes

Removal of nitrogen through enhanced denitrification has been identified as an ecosystem service provided by oysters. In this study, we assessed the effects of an individual oyster (Crassostrea virginica) on nitrogen dynamics. Fluxes of N-2, O-2, nitrate/nitrite (NOx) and ammonium (NH4+) were measured from continuous-flow microcosms that contained a live oyster, sediment, or a live oyster + sediment. Net N-2 fluxes were indicative of nitrogen fixation in the sediment treatment and denitrification in the oyster and oyster + sediment treatments. Organic matter de position and ammonium production associated with oyster biodeposits and excretion likely decreased N limitation, and thus the demand for fixation of new nitrogen, while increasing nitrification and subsequent denitrification. Oyster-mediated denitrification accounted for 48% of the total inorganic nitrogen efflux in the oyster microcosms and 35% in the oyster + sediment microcosms. Despite high rates of ammonium production, inclusion of the eastern oyster did not increase the pool of bioavailable nitrogen but shifted the microcosms from a nitrogen source to a nitrogen sink