Trevor Lewis

Electrofunctional polymers: their role in the development of new analytical systems

The overall analytical process involves a number of steps: sample collection, transportation and storage, analysis, data collection, processing and evaluation. Most of these essential steps commonly involve the use of polymeric materials in one form or another. Inert polymers are the usual materials of choice for sample collection, transportation and storage, and are indirectly involved in the form of engineering polymers in the other steps.

Conducting Polmers as a Basis for Responsive Materials Systems

Conducting polymers such as polypyrrole and polyaniline are being extensively studied for their use in a wide range of new products. These materials are unique in that they have switchable properties due to their 2 or more mechanically stable oxidation states. Thus, films or coatings can be easily switched by the application of small voltages and currents to change the mechanical and electrical properties, the density, light absorbance and even to emit light in a diode arrangement. This paper reviews the factors that influence the performance of conducting polymers in four applications being developed at the Intelligent Polymer Research Institute: actuators, membranes, sensors and corrosion resistant coatings.

Manufacturing and application of a fully polymeric electrophoresis chip with integrated polyaniline electrodes

This work describes the development of a fully polymeric microchip with integrated polymeric electrodes suitable for performing microchip electrophoresis. The polymer electrodes were fabricated in a thin film of the conducting polymer, polyaniline (PANI), by flash lithography using a studio camera flash and a transparency mask. During flash welding, exposed regions welded into non-conducting regions forming a conducting polymer circuit in the non-exposed regions. Using a structured layer of dry film photoresist for sealing, a polydimethylsiloxane (PDMS) substrate containing channels and reservoirs was bound to the PANI film to form an integrated microfluidic device. The conducting regions of the PANI film were shown to be capable of carrying the high voltages of up to 2000 V required for chip electrophoresis, and were stable for up to 30 minutes under these conditions. The PANI electrodes were used for the electrophoretic separation of three sugars labelled with 8-amino-1,3,6-pyrenetrisulfonic acid (APTS) in the dry film resist-PDMS hybrid device. Highly efficient separations comparable to those achieved in similar microchips using platinum electrodes confirm the potential of polyaniline as a new material suitable for high voltage electrodes in Lab-on-a-chip devices.

Lab-on-a-Chip device with laser-patterned polymer electrodes for high voltage application and contactless conductivity detection

A laser-patterned microchip electrophoresis device with integrated polymer electrodes for DC high voltages and AC capacitively-coupled contactless conductivity detection was developed. Electrophoresis separations comparable to devices with metal electrodes were obtained, at approximately 20 times lower cost.

Calcium-phosphorus interactions at a nano-structured silicate surface.

Nano-structured calcium silicate (NCS), a highly porous material synthesized by controlled precipitation from geothermal fluids or sodium silicate solution, was developed as filler for use in paper manufacture. NCS has been shown to chemisorb orthophosphate from an aqueous solution probably obeying a Freundlich isotherm with high selectivity compared to other common environmental anions. Microanalysis of the products of chemisorption indicated there was significant change from the porous and nano-structured morphology of pristine NCS to fibrous and crystalline morphologies and non-porous detritus. X-ray diffraction analysis of the crystalline products showed it to be brushite, CaHPO42H2O, while the largely X-ray amorphous component was a mixture of calcium phosphates. A two-step mechanism was proposed for the chemisorption of phosphate from an aqueous solution by NCS. The first step, which was highly dependent on pH, was thought to be desorption of hydroxide ions from the NCS surface. This was kinetically favoured at lower initial pH, where the predominant form of phosphate present was H2PO(-)4, and led to decreased phosphorus uptake with increasing pH. The second step was thought to be a continuing chemisorption process after stabilization of the pH-value. The formation of brushite as the primary chemisorption product was found to be consistent with the proposed mechanism.

Structure of wood extract colloids and effect of CaCl2 on the molecular mobility

Electron paramagnetic resonance (EPR) was used to study the colloidal structure of model wood extractive colloids composed of a resin acid (abietic acid), a fatty acid (oleic acid) and a triglyceride (triolein). Two nitroxides were chosen as EPR probes to gain a greater understanding of the different regions of the colloid in order to assess the current proposed models of the structure of the wood extractive colloid. A non-polar nitroxide probed non-polar regions of the colloid, such as triglycerides, while a surfactant-type nitroxide probed regions occupied by fatty acids. The effect of varying the amounts of each of the model colloid components on the structure of the colloid and its interaction with the probe was investigated. Results of the EPR study confirm the existence of a hydrophobic core. However, surface tension and EPR results suggest that the outer layer of the colloid is composed of mostly resin acids. It is proposed that a fatty acid layer exists between the resin acids and triglycerides and is sufficiently mobile to move between them. The addition of salt (CaCl2) was found to

Enhanced physicochemical properties of polydimethylsiloxane based microfluidic devices and thin films by incorporating synthetic micro-diamond

Synthetic micro-diamond-polydimethylsiloxane (PDMS) composite microfluidic chips and thin films were produced using indirect 3D printing and spin coating fabrication techniques. Microfluidic chips containing up to 60 wt% micro-diamond were successfully cast and bonded. Physicochemical properties, including the dispersion pattern, hydrophobicity, chemical structure, elasticity and thermal characteristics of both chip and films were investigated. Scanning electron microscopy indicated that the micro-diamond particles were embedded and interconnected within the bulk material of the cast microfluidic chip, whereas in the case of thin films their increased presence at the polymer surface resulted in a reduced hydrophobicity of the composite. The elastic modulus increased from 1.28 for a PDMS control, to 4.42 MPa for the 60 wt% composite, along with a three-fold increase in thermal conductivity, from 0.15 to 0.45 W m−1 K−1. Within the fluidic chips, micro-diamond incorporation enhanced heat dissipation by efficient transfer of heat from within the channels to the surrounding substrate. At a flow rate of 1000 μL/min, the gradient achieved for the 60 wt% composite chip equalled a 9.8 °C drop across a 3 cm long channel, more than twice that observed with the PDMS control chip.

Effect of copper and other trace metal addition to pulp and paper wastewater

Porous pots were used to mimic, on a laboratory scale, an industrial activated sludge plant from a thermomechanical pulp and news print paper mill. Trace metal additions of Ca, Co, Cu, Fe(III), and Mg were found to improve chemical oxygen demand removal from 82% to 86 to 87%. Copper (0.1 to 1.0 mg/L) was also found to be beneficial in significantly inhibiting the growth of filamentous bacteria, contributing to a reduction of 20 to 45% in sludge volume index (SVI) with improved settle ability and decreased bulking. However, at levels of 1.0 mg/L and higher, the concentration of Cu in the porous pot effluent would potentially exceed guidelines for receiving waters. The fate and impact of Cu was affected by the presence of other trace metals, in particular Mg and Ca. The addition of Mg or Ca along with 0.5 mg/L Cu increased the amount of Cu in the aqueous phase to levels that would potentially exceed government environmental guidelines. Calcium addition was also found to inhibit the effect of Cu in reducing filamentous bacteria and SVI.