Optically Defined Modal Sensors Incorporating Spiropyran-Doped Liquid Crystals with Piezoelectric Sensors

We integrated a piezoelectric sensing layer lamina containing liquid crystals (LC) and spiropyran (SP) in a LC/SP mixture to create an optically reconfigurable modal sensor for a cantilever beam. The impedance of this LC/SP lamina was decreased by UV irradiation which constituted the underlying mechanism to modulate the voltage externally applied to the piezoelectric actuating layer. Illuminating a specific pattern onto the LC/SP lamina provided us with a way to spatially modulate the piezoelectric vibration signal. We showed that if an UV illuminated pattern matches the strain distribution of a specific mode, a piezoelectric modal sensor can be created. Since UV illumination can be changed in situ in real-time, our results confirm for the first time since the inception of smart sensors, that an optically tailored modal sensor can be created. Some potential applications of this type of sensor include energy harvesting devices, bio-chips, vibration sensing and actuating devices

Optical properties of polymers and their applications

The last decade has witnessed explosive growth in the world of photoactive polymers for a variety of applications in several sectors of the global economy. The need for efficient, reliable, and low-cost data acquisition, storage, processing, transmission, and display technologies has made it necessary for research aimed at addressing these needs. Recent accomplishments in this materials area represent exciting opportunities for major innovations in various fields. However, further work needs to be done to transfer the technology from fundamental R&D to manufacturing. The goal of this study is to provide a better understanding of the optical properties of polymers and identify the candidates that are ideal for a variety of applications. The fundamental optical properties and characteristics of several commonly used polymers are presented in this study. Mathematical simulations of signal propagation through a polymer core waveguide are examined to determine the materials that are most suitable for long range communications. Other applications such as electronic devices, temperature and pressure sensors, protective coatings and energetic materials are briefly considered. Self-healing and self-repair in polymers are examined

Supramolecular Luminescent Sensors

There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed

Sewage sludge heavy metal analysis and agricultural prospects for Fiji

Insoluble residues produced in Waste Water Treatment Plants (WWTP) as by products are known as sewage sludge (SS). Land application of SS, particularly in agricultural lands, is becoming an alternative disposal method in Fiji. However, currently there is no legislative framework governing its use. SS together with its high nutrient and organic matter contents, constitutes some undesired pollutants such as heavy metals, which may limit its extensive use. The focus of this study therefore was to determine the total concentrations of Pb, Zn, Cd, Cu, Cr, Ni and Mn in the SS produced at the Kinoya WWTP (Fiji) and in the non-fertile soil amended with the SS at 20, 40, 60, 80% application rates and in the control (100% Soil). The bioavailable heavy metals were also determined as it depicts the true extent of metal contamination. The treatment mixtures were then used to cultivate cabbage plants in which the total heavy metal uptake was investigated. Total Zn (695.6 mg/kg) was present in the highest amounts in the 100% SS (control), followed by Pb (370.9 mg/kg), Mn (35.0 mg/kg), Cu (65.5 mg/kg), Cr (20.5 mg/kg) and finally Cd (13.5 mg/kg) and hence a similar trend was seen in all treatment mixtures. The potential mobility of sludgeborne heavy metals can be classified as Ni > Cu > Cd > Zn > Mn > Cr > Pb. Total metal uptake in plant leaves and stems showed only the bioavailable metals Cu, Cd, Zn and Mn, with maximum uptake occurring in the leaves. Ni, despite being highly mobile was not detected, due to minute concentrations in the SS treatments. Optimum growth occurred in the 20 and 40% SS treatments. However maximum Cu and Mn uptake occurred in the 40% SS treatment thereby making the 20% treatment the most feasible. Furthermore the total and bioavailable metal concentrations observed were within the safe and permitted limits of the EEC and USEPA legislations

Exploring light-matter interactions with graphene

Graphene has drawn extraordinary interest from both scientists and the wider public; the idea of an atomically thin material that is staggeringly conductive while also being both strong and flexible, seems impossible. From a scientific perspective, the two dimensional nature of graphene provides an exciting playground to explore new phenomena with the potential for technical applications. The question of how light interacts with graphene underpins these devices and is often set in the context of graphene as a highly transparent material. In this thesis, results from the interaction between light and graphene will be explored across a broad frequency range and methods for manipulating the interaction between light and a graphene layer will be presented. At infrared frequencies, nanostructured graphene displays plasmonic behaviour. A layer of graphene with a periodically modulated, array-like, conductivity analogous to graphene nano-ribbons is investigated numerically. The total response of this structure was found to arise from the hybridisation between multipolar resonances supported by different areas of the array. By designing the appropriate geometric parameters the resonant absorption of the array is shown to increase by a factor of ~50%. In addition to displaying interesting linear properties, graphene is a strongly nonlinear material. To enhance a specific nonlinear optical mixing process, third harmonic generation, graphene is combined with a resonant cavity. The measurements of the third harmonic generation from this cavity structure show that integrating a graphene layer with a cavity increases the generated third harmonic power by a factor of 117. Numerical modelling of the cavity structure shows the enhancement mechanism arises from the cavity structure supporting a resonance in the electric field at the wavelengths of both the incident and third harmonic. Finally, the influence of strain in a graphene layer on the fluorescence collected from a molecule deposited on top of the graphene layer is investigated. Using Raman spectroscopy, the level of local strain was mapped across a graphene sample and confocal microscopy was used to measure the emitted luminescence. The observed correlation between the level of strain and luminescence intensity is supported by a simple model of a dipole near a graphene sheet