Jadranka Travas-Sejdic

Direct writing of conducting polymers.

Described herein is a new printing method-direct writing of conducting polymers (CPs)-based on pipette-tip localized continuous electrochemical growth. A single barrel micropipette containing a metal wire (Pt) is filled with a mixture of monomer, supporting electrolyte, and an appropriate solvent. A droplet at the tip of the pipette contacts the substrate, which becomes the working electrode of a micro-electrochemical cell confined to the tip droplet and the pipette. The metallic wire in the pipette acts as both counter and reference electrode. Electropolymerization forms the CP on the working electrode in a pattern controlled by the movement of the pipette. In this study, various width poly(pyrrole) 2D and 3D structures are extruded and characterized in terms of microcyclic voltammetry, Raman spectroscopy, and scanning electron microscopy.

Investigation of the reduction of graphene oxide by lithium triethylborohydride

The chemical reduction of a wet colloidal suspension of graphene oxide is a cost-effective and adaptable method for large scale production of quasi graphene for a wide variety of optoelectronic applications. In this study, modified Hummers procedure was used to synthesize high quality graphene oxide at 50°C. This modified protocol thus eliminates the potentially hazardous second high-temperature step in Hummers method for the production of GO. Furthermore, the reduction of graphene oxide by lithium triethyl-borohydride is demonstrated for the first time. According to FT-IR, UV-Vis, TGA, Raman, SEM/EDS, and AFM results, the reduced graphene oxide (LiEt3BH-RGO) has properties comparable to other reduced graphene oxide products reported in the literature.

Bio-inspired flow sensor from printed PEDOT:PSS micro-hairs

This paper reports on the creation of a low-cost, disposable sensor for low flow velocities, constructed from extruded micro-sized hair of conducting polymer PEDOT. These microstructures are inspired by hair strands found in many arthropods and chordates, which play a prime role in sensing air flows. The paper describes the fabrication techniques and the initial prototype testing results toward employing this sensing mechanism in applications requiring sensing of low flow rates such as a flow sensor in neonatal resuscitators. The fabricated 1000 μm long, 6 μm diameter micro-hairs mimic the bending movement of tactile hair strands to sense the velocity of air flow. The prototype sensor developed is a four-level direct digital-output sensor and is capable of detecting flow velocities of up to 0.97 m s(-1).

A novel air flow sensor from printed PEDOT micro-hairs

We report the creation of a low flow rate sensor from PEDOT micro-hairs. The hairs are printed as pipette-defined depositions using a nanopositioning system. The printing technique was developed for fabricating structures in 2D and 3D. Here micro-hairs with diameters of 4:4 m were repeatedly extruded with constant heights. These hairs were then applied to produce a prototype flow rate sensor, which was shown to detect flows of 3:5 l min 1 . Structural analysis was performed to demonstrate that the design can be modified to potentially observe flows as low as 0:5 l min 1 . The results are extended to propose a practical digital flow rate sensor. (Some figures may appear in colour only in the online journal)

Computational design of mixers and pumps for microfluidic systems, based on electrochemically-active conducting polymers

We present a theoretical description of the propagation of composition waves along a strip of electrochemically-active conducting polymer, upon electrochemical stimulation. We develop an efficient solution of the electro-neutral Nernst-Plank equations in 2-D for electromigration and diffusional transport in the solution based on an extension of the methods of Scharfetter and Gummel [D. L. Scharfetter and H. K. Gummel, IEEE Trans. Electron Devices, 1969, ED16, 64-77.] and of Cohen and Cooley [H. Cohen and J. W. Cooley, Biophys. J., 1965, 5, 145-162.], and demonstrate important effects of the geometry of the cell. Under some circumstances, waves reflecting back from the end of the strip are predicted. We then demonstrate theoretically how such waves, associated as they are with expansion of the polymer, could be employed to enhance mixing or induce pumping in microfluidic systems.

Flammability and Thermal Properties of Zeolite-Filled High-Impact Polystyrene Composites

Effect of zeolite and organically modified montmorillonite (MMT) clay on flammability of high-impact polystyrene (HIPS) with ammonium polyphosphate (APP) flame retardant was investigated. Composites were prepared by melt blending in a twin-screw extruder, and it was found that zeolite and APP improve fire performance of HIPS with optimal concentration of 4 mass % of zeolite. Samples with MMT/APP and zeolite/APP have similar results of flammability, yet combination MMT/zeolite/APP had no additional improvement of thermal and fire properties. Mechanical properties were degraded with increasing concentration of zeolite, and improvement was visible when only MMT clay was used in combination with APP.

Electrochemically switchable surfaces using polymer brush-grafted conducting polymer films

We demonstrate an electrochemical switching of conformation of surface-bound polymer brushes, by grafting environmentally sensitive polymer brushes from an electrochemically-active conducting polymer (ECP). Using atom transfer radical polymerization (ATRP), we grafted zwitterionic polymer brushes, poly(3-(methacryloylamino)propyl)- dimethyl(3-sulfopropyl)ammonium hydroxide) (MPDSAH), from a surface initiated poly(pyrrole-co-pyrrolyl butyric acid) film. The changes in ionic solution composition in electrical double layer at the surface resulting from oxidation and reduction of the ECP trigger a switch in conformation of surface-bound poly(MPDSAH), demonstrated here by electrochemical impedance spectroscopy (EIS). The switch is also dependent upon temperature. We speculate that the synergistic combination of properties embodied in these smart materials may find application in electrochemical control of surface wetting and of interaction with biomolecules and living cells.

Water Structure Change-Induced Expansion and Collapse of Zwitterionic Polymers Surface-Grafted onto Carbon Black

We demonstrate the expansion and collapse of surface-grafted zwitterionic polymer brushes in water caused by the addition of urea. We hypothesize that at low urea concentrations, this is an effect of an ion–dipole interaction between urea and the polymer, and at high urea concentrations, an effect of a change in water structure causing change in solvation of the brushes and hence a change in the dipole–dipole interaction, and that it is analogous to the effects of urea on protein stability.