Intrinsic conducting polymer current limiting device

This thesis investigates the development of novel intrinsic conducting polymer current limiting devices (CLDs), which are small self-resettable components used to protect circuitry in portable electronic appliances during situations of overcurrent. There are many existing solutions that enable the interruption and limitation of current surges in devices. A simple and common device is the use of a hybrid system of small metallic/semiconducting particles embedded in a thermally responsive polymeric material. During an overcurrent situation the positive temperature coefficient resistance (PTCR) of the polymeric material expands due to joule heating, which causes the percolating current pathways in the device to break which in turn causes the device to become temporarily non conducting. Although commonly used in the electronics industry today there are some limitations in the conductive fillers such as fretting and degradation that cause unwanted shifts in the percolation threshold, which can result in faulty operation. There is also increasing demand for faster operating devices as well as cheaper and more convenient methods of fabrication. One possibility that has emerged is the use of intrinsic conducting polymers as current limiting materials. There are several benefits of this for commercialization, such as cheap starting materials, simple chemical or electrochemical solution-based methods for device fabrication and potentially very fast device operation if the mechanism is electronic rather than mechanical in nature. Although preliminary measurements in these materials have shown evidence of switching to a non-conducting state at high currents, which is resettable upon cooling, the mechanism that causes the switching has not been established and no studies on this effect have been reported in the literature.This motivates further work into developing current limiting devices based on these materials. The intention of this research is (1) to develop current limiting devices based on the intrinsic conducting polymer polyaniline (PANI), (2) to improve the electronic properties of the device, ideally we desire to have low resistance at low current level (normal operating conditions) and saturated or limited conductivity at high current level (overcurrent/short-circuit conditions), (3) elucidate the switching mechanism of the devices and (4) investigate the devices stability and resetability characteristics in different environmental conditions.The results of this thesis show that the presence of moisture in the conducting polymer plays an important role in the current limiting performance. Our results indicate that the electronic switching of the devices is a result of a partial de-doping/re-doping effect caused by water diffusing into and out of the polymer film during joule heating/ cooling of the devices. We speculate that the polymer/metal interface region plays an important role in this and as such significant improvement in the electrical properties were made using self-assembled monolayer (SAM) modified electrodes.Studies were also performed to understand the temperature dependent electrical resistivity of the polymer material, shown to be variable range hopping in three dimensions, and as well, investigations were made to understand device performance in different environmental conditions (varying from vacuum to 100% relative humidity). Stability and degradation testing was performed in order to find the best operational and stable conditions for the current limiting devices. Results showed that devices were very stable in low to medium voltage values. In an effort to understand the effect of dopant type on the moisture content in the polymer film, thermal analyses (thermogravimetric and differential scanning calorimetry) of samples with different dopants were investigated. Polyaniline doped with methanesulfonic acid was found to be among the samples with the highest moisture content

The Role of Institutional Pressures in Driving Internal and External Green Supply Chain Practices and Environmental Performance

The contribution of the present investigation is also extended to determine the impact of green supply chain practices in influencing organizational performance. Hence, the understanding drive from such comprehensive approach will aid the manufacturing sector of Malaysia to identify the contribution of local and international institutions’ pressures in affecting the success of Malaysian green supply chain methods. In this current research, we applied of Exploratory Factor Analysis (EFA) to discover the four factors are extracted by total twenty-nine items in which all items factor loadings are more noteworthy than 0.70. The results of structural equation modelling confirm that internal green supply chain practice and external green supply chain practice have significantly and positively influenced by institutional pressure. Furthermore, the outcomes of structural equation modelling also certify that, institutional pressure has a positive and significant impact on environmental performance. Finally, the outcomes more explained that internal green supply chain practices and external green supply chain practices have a positive and significant effect on environmental performance in manufacturing firms of Malaysia

Debt maturity and Shari’ah compliance : evidence from Malaysian panel data

This paper investigates the effect of firm-specific characteristics on debt maturity in Malaysia. We examine the impact of Shari’ah compliance on debt maturity structure by grouping companies based on compliance status as governed by the Securities Commission of Malaysia over the sample period of 2007 to 2016. The results indicate that Shari’ah compliant firms tend to have longer debt maturity structure indicating that the nature of compliance determines the maturity structure of companies in Malaysia as managers of these firms tend to focus on mitigating liquidity risks potentially faced. In addition, Shari’ah compliant firms also tend to have lower bankruptcy costs. Contrary to their non-compliant counterparts, managers of Shari’ah compliant firms tend to change debt maturity structure as a signaling tool whilst opting for longer structures in periods of positive share price performance. We also find that Shar’iah compliance has no impact on firms’ strategy of matching debt to asset maturity structure.peer-reviewe

Novel conducting polymer current limiting devices for low cost surge protection applications

We report on the development of novel intrinsic conducting polymer two terminal surge protection devices. These resettable current limiting devices consist of polyaniline nanofibres doped with methane sulphonic acid electrochemically deposited between two 55 μm spaced gold electrodes. At normal applied voltages, the low resistance devices act as passive circuit elements, not affecting the current flow. However during a current surge the devices switch from ohmic to non-ohmic behaviour, limiting current through the device. After the current surge has passed, the devices reset back to their original state. Our studies show that a partial de-doping/re-doping process caused by the rapid diffusion of moisture out of or into the polymer film during joule heating/cooling is the underlying mechanism responsible

The impact of Sharia compliance on the adjustment to target debt maturity of Malaysian firms

This paper investigates the speed of adjustment to target debt maturity for a sample of Malaysian firms based on the sample period of 2007 to 2016. We examine the impact of Sharia compliance on the speed of adjustment to target debt maturity structure by grouping companies based on nature of compliance to Sharia requirements which is categorised by the Securities Commission of Malaysia. In line with our expectations, the analysis shows that firms classified as Sharia compliant tend to adjust at more rapid rates to target debt maturity when below target levels suggesting that compliant firms are able to issue long-term debt at cheaper levels relative to non-compliant counterparts. In addition, the reverse is observed when evaluating firms above target levels where non-compliant firms adjust at more rapid rates. Our findings indicate that compliant firms are able to raise long-term debt at cheaper rates relative to non-compliant firms given the captive market situation observed in the Islamic capital markets in Malaysia. This does however indicate the potential for higher agency costs as well as greater levels of information asymmetry for compliant firms relative to non-compliant firms given that non-compliant firms are more willing to reduce maturity structures to reach target levels when above target levels.peer-reviewe

Non Linear Speed of Adjustment to Lead Leverage Levels and the Timing Element in Equity Issues: Empirical Evidence from the UK

The dynamic trade-off view of capital structure is based on partial adjustment models that find that firms adjust towards target levels. In this paper, we estimate the speed of adjustment based on the first difference of the lead leverage levels (actual lead) and lag leverage levels (actual lag) to the first difference of simulated lead (target) leverage levels and lag levels (actual lag leverage) for UK firms. Consistent with the literature we find that firms adjust the lag (current) leverage levels faster to lead levels when they are above lead levels relative to periods when they are below lead levels. This is due to managerial actions in minimizing present value of bankruptcy costs when firms are over-levered. Bringing in the market timing view of capital structure, we measure deviation of market prices to predicted theoretical values, and find that speed of adjustment is influenced by equity mispricing. We find that firms adjust faster to lead levels when lag levels are above lead levels and the extent of deviation above theoretical values is not excessive relative to when deviations of prices from theoretical levels are too high. Furthermore, looking at firms below lead levels, we find that firms adjust faster to lead levels when equities prices below theoretical values severely deviate; suggesting that firms increase debt issues when equity prices are acutely suppressed. This indicates managers are consistently looking at windows of opportunities when issuing or repurchasing to ensure successful timing attempts. Thus, our findings suggest that although market timing could also work within a trade-off framework where managers are timing based on the deviation from theoretical prices as well as moving towards simulated lead levels, the extent of the integration of both explanations of capital structure remains puzzling

Large dopant dependence of the current limiting properties of intrinsic conducting polymer surge protection devices

New two terminal surge protection devices based on intrinsic conducting polymers are demonstrated to be strongly affected by the dopant molecule type. Thermogravimetric analysis combined with current–voltage studies show a causal link between the dopant molecule, moisture content and the current limiting capability of the devices. Polyaniline thin-films with high moisture content produce devices with current saturation and foldback effects at high applied voltages while low moisture content films exhibit no current rectification and instead demonstrate decreasing resistivity with increasing voltage. Polyaniline doped with sulfuric acid (H2SO4) exhibited the largest moisture content and surge protection devices built with this material produced for the first time negative differential resistance under ambient conditions. A further improvement was made upon this through surface engineering of the interface between the polymer and electrodes using self-assembled monolayers

Super hydrophobic SAM modified electrodes for enhanced current limiting properties in intrinsic conducting polymer surge protection devices

Surface interface engineering using superhydrophobic gold electrodes made with 1-dodecanethiol self-assembled monolayer (SAM) has been used to enhance the current limiting properties of novel surge protection devices based on the intrinsic conducting polymer, polyaniline doped with methanesulfonic acid. The resulting devices show significantly enhanced current limiting characteristics, including current saturation, foldback, and negative differential effects. We show how SAM modification changes the morphology of the polymer film directly adjacent to the electrodes, leading to the formation of an interfacial compact thin film that lowers the contact resistance at the Au−polymer interface. We attribute the enhanced current limiting properties of the devices to a combination of lower contact resistance and increased Joule heating within this interface region which during a current surge produces a current blocking resistive barrier due to a thermally induced dedoping effect caused by the rapid diffusion of moisture away from this region. The effect is exacerbated at higher applied voltages as the higher temperature leads to stronger depletion of charge carriers in this region, resulting in a negative differential resistance effec

Speed of Adjustment and Financial Constraints: Evidence from the UK

Our paper estimates the speed of moment adjustment based on the first difference of the lead (t+1) leverage levels (actual lead) and lag (t-1) leverage levels (actual lag) to the first difference of simulated lead (target) leverage levels and lag levels (actual lag leverage) for firm level data. We introduce an intrinsic limitation (financial constraints) to the model to test the impact on speed of adjustment and distance reduction. We find that financial constraints have a statistically and economically significant impact on rate of adjustment and distance reduction to target leverage levels