Arousian Arshak

Review on State-of-the-art in Polymer Based pH Sensors

This paper reviews current state-of-the-art methods of measuring pH levels that are based on polymer materials. These include polymer-coated fibre optic sensors, devices with electrodes modified with pH-sensitive polymers, fluorescent pH indicators, potentiometric pH sensors as well as sensors that use combinatory approach for ion concentration monitoring.

Review Paper: Materials and Techniques for In Vivo pH Monitoring

Advances in semiconductor sensor technology, medical diagnostics, and health care needs a rapid boost in research into novel miniaturized pH sensors, which can be used in vivo for continuous patient monitoring. Requirements for the in vivo sensor are materials biocompatibility, high measurement precision, a response time of an order of less than seconds, and the possibility of continuous 24-h monitoring. Monitoring of the pH values is important in the study of tissue metabolism, in neurophysiology, cancer diagnostics, and so forth. Muscle pH can be used to triage and help treat trauma victims as well as to indicate poor peripheral blood flow in diabetic patients. Clearly, to avoid infection and spread of diseases, all in vivo monitoring devices should be single-use/disposable, which puts strict requirement on their price. This paper reviews the wide range of methods and materials used for in vivo measurement of pH levels, such as using the optical fibers, pH-sensitive polymers, ion-sensitive field effect transistors, near infrared spectroscopy, nuclear magnetic resonance, and fluorescent pH indicators.

pH Sensitivity of Novel PANI/PVB/PS3 Composite Films.

This paper reports on the results from the investigation into the pH sensitivity of novel PANI/PVB/PS3 composite films. The conductimetric sensing mode was chosen as it is one of the most promising alternatives to the mainstream pH-sensing methods and it is the least investigated due to the popularity of other approaches. The films were deposited using both screen-printing and a drop-coating method. It was found that the best response to pH was obtained from the screen-printed thick films, which demonstrated a change in conductance by as much as three orders of magnitude over the pH range pH2-pH11. The devices exhibited a stable response over 96 hours of operation. Several films were immersed in buffer solutions of different pH values for 96 hours and these were then investigated using XPS. The resulting N 1s spectra for the various films confirmed that the change in conductance was due to deprotonation of the PANI polymer backbone. SEM and Profilometry were also undertaken and showed that no considerable changes in the morphology of the films took place and that the films did not swell or contract due to exposure to test solutions.

Pattern formation induced by an electric field in a polymer-air-polymer thin film system†

Strong electric fields produce forces that can overcome the surface tension in thin liquid polymer films and in this way induce an instability of the free surface of the film, that triggers the formation of structures on a micrometer length scale. Here, we study experimentally a polymer–air–polymer system for several combinations of polymer films. These results are accompanied by theoretical considerations based on coupled long-wave time evolution equations for the two free surface profiles. The linear stability and nonlinear time evolution are investigated and compared to the experimental findings. The prediction that the instability always evolves through a mirror mode that couples the two surfaces in an anti-phase manner agrees well with the experimental results. The model describes well the linear (early stage) evolution of the instability. In the non-linear (later stage) evolution, topographical differences in the instability pattern occur if the mobilities of the two layers significantly differ and an unpredicted acceleration of growth is seen in thinner less mobile films. Possible reasons for the mismatch are discussed.

Stability of Ultrathin Nanocomposite Polymer Films Controlled by the Embedding of Gold Nanoparticles

Thin and ultrathin polymer films combined with nanoparticles (NPs) are of significant interest as they are used in a host of industrial applications. In this paper we describe the stability of such films (hpoly ≤ 30 nm) to dewetting, specifically, how the development of a spinodal instability in a composite NP-polymer layer is controlled by the embedding of Au NPs. At working temperatures (T = 170 °C) above the polymer glass transition temperature (Tg ≈ 100 °C) the absence of Au NPs leads to film rupture by nucleation dewetting, while their presence over a large surface area enhances the development of a spinodal instability without destroying the film continuity. When the NPs embed, the surface undulations are suppressed. The dynamics change from an unstable to a stable state, and the thin composite NP-polymer layer returns to a flat configuration, while the wavelength of the pattern remains constant. Moreover, we demonstrate from a thermodynamic perspective that NPs will remain on the surface or embed in the polymer film depending on their free energy, which is determined by the NP interactions with the underlying polymer, the native SiOx layer, and the Si substrate.

Thin and thick films of metal oxides and metal phthalocyanines as gamma radiation dosimeters

Numerous efforts were devoted to investigating the influence of radiation on metal oxides and polymer materials for dosimetry applications. Metal oxides, such as NiO, LaFeO/sub 3/, CeO/sub 2/, TeO/sub 2/, In/sub 2/O/sub 3/, SiO and MnO, and polymers, such as CuPc, NiPc, MnPc and CoPc, were used as the active constituents in the fabrication of /spl gamma/-radiation sensors. Thin and thick film devices were made in various topologies to form resistors, capacitors, pn-junctions and transistors. It was found that the properties of the active films (and, hence, their sensitivity to radiation) could be controlled by doping their constituent materials with carbon and mixing them in different proportions. The /sup 60/Co and /sup 137/Cs sources were used to expose the samples to /spl gamma/-radiation. Current-voltage characteristics, optical absorption spectra, Raman spectra, SEM and XRD measurements were recorded for the samples after each exposure procedure and values of radiation damage were estimated. Thin film devices were found to be more sensitive to radiation than their thick film counterparts. Annealing was used to restore the properties of thick film devices after they were damaged with radiation. Thick films could be therefore reused on a repeatable basis, but thin film devices could not, as the heat treatments necessary for annealing were found to cause diffusion of the electrode materials. In this work, the possibility of fabricating a device that would satisfy the requirement of a particular application, such as sensitivity to /spl gamma/-radiation and working dose region, was experimentally demonstrated. Based on the findings, these devices were found to provide a cost-effective alternative for room temperature real time /spl gamma/-radiation dosimeter applications.

Effect of Au nanoparticle spatial distribution on the stability of thin polymer films.

The stability of thin poly(methyl-methacrylate) (PMMA) films of low molecular weight on a solid substrate is controlled by the areal coverage of gold nanoparticles (NPs) present at the air-polymer interface. As the polymer becomes liquid the Au NPs are free to diffuse, coalesce, and aggregate while the polymer film can change its morphology through viscous flow. These processes lead at the same time to the formation of a fractal network of Au NPs and to the development of spinodal instabilities of the free surface of the polymer films. For thinner films a single wavelength is observed, while for thicker films two wavelengths compete. With continued heating the aggregation process results in a decrease in coverage, the networks evolve into disordered particle assemblies, while the polymer films flatten again. The disordering occurs first on the smallest scales and coincides (in thicker films) with the disappearance of the smaller wavelength. The subsequent disordering on larger scales causes the films to flatten.

Development of a Wireless Pressure Measurement System Using Interdigitated Capacitors

Remote pressure monitoring is of particular importance in medical and environmental applications as it is less labour intensive, safer and offers peace of mind to the general public. To meet this demand, a prototype system has been developed and used to evaluate thick-film pressure sensors with an oxide dielectric layer. The circuit is based on the principle of capacitance-frequency-voltage conversion and has been designed to minimize power consumption. Each device was tested under hydrostatic pressure in the range 0-17 kPa and assessed in terms of sensitivity, hysteresis, repeatability, creep and temperature effects. The results show that this approach may be used for the fabrication of cost effective, reliable devices for wireless pressure sensing applications

Investigation of Thick-Film Polyaniline-Based Conductimetric pH Sensors for Medical Applications

This paper reports on the development and testing of a polyaniline-based conductimetric pH sensor. The sensor functions successfully in both the pH range for stomach acid (pH1.0-pH2.0) and for human blood (pH7.0-pH8.0). Experiments were performed by exposing the sensors to buffer solutions with pH values in the ranges identified. The sensors demonstrated reproducible and repeatable results with little hysteresis being recorded between experiments, along with a response time of approximately 1 min in acidic solutions and 2 min in buffers with pH values in the blood pH range. In the case of measurements made in the blood pH range, a novel memory effect was observed, which corresponds to a permanent ldquorecordingrdquo of the pH measurement into the electrical characteristics of the film. This memory effect only applies to measurements made in alkaline pH ranges and is due to the deprotonation of the polyaniline material in the sensing layer. The sensor reported in this paper has the potential to be a more economically viable option when compared to other approaches being used for commercial applications.

The stability of thin polymer films as controlled by changes in uniformly sputtered gold

The stability of polystyrene thin films of low molecular weight on a solid substrate is shown to be controlled by the presence of uniformly distributed gold sputtered at the air–polymer interface. Continuous gold coverage causes the formation of wrinkles. High coverage and Au nanoparticle (NP) density leads to the development of a spinodal instability while low coverage and NP density retards the nucleation dewetting mechanism that beads up the thin polymer film into drops when no coverage is present. Heating at temperature larger than the polymer glass transition temperature for extended periods allows the gold NPs to coalesce and rearrange. The area of polymer surface covered by NPs decreases as a result and this drives the films from unstable to metastable states. When the gold NPs are interconnected by polymer chains a theoretically predicted spinodal instability that patterns the film surface is experimentally observed. Suppression of the instability and a return to a flat film occurs when the polymer interconnections between particles are broken. While the polymer films maintain their physical continuity changes in their chemical surface composition and thickness are observed. The observed film metastability is nevertheless in agreement with theoretical prediction that includes these surface changes.