Pavel Riha

A Flexible Multifunctional Sensor Based on Carbon Nanotube/Polyurethane Composite

A sensor was made of a polymer composite composed of electrically-conductive carbon nanotubes embedded in elastic polyurethane. The composite was prepared using a polyurethane filter membrane, enmeshing it, and melding together with carbon nanotubes. Testing has shown that the composite can be elongated as much as 400% during which the electrical resistance is increased 270 times. The composite is also sensitive to compression and to organic solvent vapors. These properties indicate the composite could have applications as a highly-deformable strain and chemical vapors sensing element and also as flexible electromagnetic shielding or protection against lightning. As an example of the use of the composite as a strain sensor, the pressure variation between a shoe and floor during walking and knee flexion during cycling has been monitored.

Plasma-enabled sensing of urea and related amides on polyaniline

The atmospheric pressure plasma jet (APPJ) was used to enhance the sensitivity of industrially important polyaniline (PANI) for detection of organic vapors from amides. The gas sensing mechanism of PANI is operating on the basis of reversible protonation or deprotonation, whereas the driving force to improve the sensitivity after plasma modifications is unknown. Herein we manage to solve this problem and investigate the sensing mechanism of atmospheric plasma treated PANI for vapor detection of amides using urea as a model. The results from various analytical techniques indicate that the plausible mechanism responsible for the improved sensitivity after plasma treatment is operating through a cyclic transition state formed between the functional groups introduced by plasma treatment and urea. This transition state improved the sensitivity of PANI towards 15 ppm of urea by a factor of 2.4 times compared to the non-treated PANI. This plasma treated PANI is promising for the improvement of the sensitivity and selectivity towards other toxic and carcinogenic amide analytes for gas sensing applications such as improving material processing and controlling food quality.

Electromechanical properties of carbon nanotube networks under compression

The network of entangled multiwall carbon nanotubes and the composite consisting of a polystyrene filter-supported nanotube are introduced as conductors whose conductivity is sensitive to compressive stress both in the course of monotonic stress growth and when loading/unloading cycles are imposed. The testing has shown as much as a 100% network conductivity increase at the maximum applied stress. It indicates the favorable properties of the multiwall carbon nanotube network for its use as a stress-electric signal transducer. To model the conductivity–stress dependence, it is hypothesized that compression increases local contact forces between the nanotubes, which in turn leads to a decrease in the contact resistance between them. The lack of detailed knowledge of the mechanism as well as an unclear shift from individual contacts to the whole network conductance behavior is circumvented with a statistical approach. In this respect, the conductivity/compression data were fitted well using the Weibull distribution for the description of the nanotube contact resistance distribution.

Pre-Strain Stimulation of Electro-Mechanical Sensitivity of Carbon Nanotube Network/Polyurethane Composites

The change of electrical resistance of a highly extensible composite sensors consisting of a network of entangled multi-wall carbon nanotubes (CNTs) and thermoplastic polyurethane elastomer in the course of elongation was stimulated by initial tensile deformation. Though the initial deformation irreversibly changes the arrangement of CNT network, subsequent cyclic elongation and corresponding resistance change is stable. The resistance sensitivity, quantified by a gauge factor, which defines the sensitivity of strain sensor as the relative resistance change divided by the applied strain, increases nearly five times from the value of about five for not initially elongated composites. This is a substantial increase, which ranks the composites among materials with the highest electromechanical sensitivity. The observed sensitivity increase is discussed on basis of the cracking of a nanotube network with extension when the number of contacts between nanotubes decreases and thus the network has fewer interconnections that can carry an electric current.

A Kohlrausch type equation based on a simplified cooperative model

AbstractThe differential equation

Different Kinds of Carbon-Based Material for Resistive Gas Sensing

{\text{d(}}\dot n/n{\text{)/d}}t{\text{ = - }}a{\text{(}}\dot n/n{\text{) + }}b{\text{(}}\left| {\dot n} \right|/n{\text{)}}^s

Using graphene/styrene-isoprene-styrene copolymer composite thin film as a flexible microstrip antenna for the detection of heptane vapors

is analysed, with n denoting the relaxing quantity, n = dn/dt(tis time), and a, band sconstants. Equations of this type have previously been shown to describe a large variety of relaxational patterns. Especially interesting is the close relationship with Bose–Einstein (B–E) like distributions and the underlying induction mechanisms. Here, the focus is on the special case of a= 0 which yields a generalised stretched exponential and, for certain variable ranges, the Kohlrausch (KWW) function in its usual form. The relaxation time τ is shown to depend strongly on the parameters entering the underlying differential equation. Conditions for constant τ are given.

Effect of pre-strain and KMnO4 oxidation of carbon nanotubes embedded in polyurethane on strain dependent electrical resistance of the composite

The conductance properties of multi-walled carbon nanotube mats and their polystyrene composite were examined to investigate the mechanism of conduction and the specific role of the supporting polymer. By measuring the temperature dependence of the conductance, it was found that the conduction mechanism in carbon nanotube mat follows the series heterogeneous model when the conductance is described as the sum of metallic and barrier portions of the conduction path. This mechanism is affected by the polymeric portion of the composite, since the temperature dependence of the composite conductance is decreased.