A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Despite its widespread use in nanocomposites, the effect of embedding graphene in highly viscoelastic polymer matrices is not well understood. We added graphene to a lightly cross-linked polysilicone, often encountered as Silly Putty, changing its electromechanical properties substantially. The resulting nanocomposites display unusual electromechanical behavior, such as postdeformation temporal relaxation of electrical resistance and nonmonotonic changes in resistivity with strain. These phenomena are associated with the mobility of the nanosheets in the low-viscosity polymer matrix. By considering both the connectivity and mobility of the nanosheets, we developed a quantitative model that completely describes the electromechanical properties. These nanocomposites are sensitive electromechanical sensors with gauge factors >500 that can measure pulse, blood pressure, and even the impact associated with the footsteps of a small spider.

/pdf/sensitive-electromechanical-sensors-using-viscoelastic-cyfjka25zb.pdf

Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites

Recent advances in carbon-based polymer nanocomposites for electromagnetic interference shielding

The electrical properties of polymer nanocomposites containing a small amount of carbon
nanotube (CNT) are remarkably superior to those of conventional electronic composites. Based on three-dimensional (3D) statistical percolation and 3D resistor network modeling, the electrical properties of CNT nanocomposites, at and after percolation, were successfully predicted in this work. The numerical analysis was also extended to investigate the effects of the aspect ratio, the electrical conductivity, the aggregation and the shape of CNTs on the electrical properties of the nanocomposites. A simple empirical model was also established based on present numerical simulations to predict the electrical conductivity in several electronic composites with various fillers. This investigation further highlighted the importance
of theoretical and numerical analyses in the exploration of basic physical phenomena, such as percolation and conductivity in novel nanocomposites.

The electrical properties of polymer nanocomposites with carbon nanotube fillers

Highly flexible and deformable electrically conductive materials are vital for the emerging field of wearable electronics. To address the challenge of flexible materials with a relatively high electrical conductivity and a high elastic limit, we report a new and facile method to prepare porous polydimethylsiloxane/carbon nanofiber composites (denoted by p-PDMS/CNF). This method involves using sugar particles coated with carbon nanofibers (CNFs) as the templates. The resulting three-dimensional porous nanocomposites, with the CNFs embedded in the PDMS pore walls, exhibit a greatly increased failure strain (up to ∼94%) compared to that of the solid, neat PDMS (∼48%). The piezoresistive response observed under cyclic tension indicates that the unique microstructure provides the new nanocomposites with excellent durability. The electrical conductivity and the gauge factor of this new nanocomposite can be tuned by changing the content of the CNFs. The electrical conductivity increases, while the gauge factor d...

Novel Electrically Conductive Porous PDMS/Carbon Nanofiber Composites for Deformable Strain Sensors and Conductors

A model for carbon nanotube (CNT)/polymer composite conductivity is developed, considering the effect of inter-tube tunnelling through the polymer. The statistical effects of inter-tube distance and alignment on the tunnelling are investigated through numerical modelling, to highlight their role in the conductance and piezoresistance of the composite film. The impact of critical parameters, including the concentration, alignment and aspect ratio of the CNTs and the tunnelling barrier height of the polymer is statistically evaluated using a large number of randomly generated CNT/polymer composite films. A numerical model is presented for the tunnelling resistance as a function of CNT concentration and polymer properties, which provides good agreement with the reported conductance in the literature. In particular, for a low concentration of CNTs close to the percolation threshold, we demonstrate how tunnelling dominates the conductance properties and leads to significant increase in the piezoresistance of the composite. This is important for gaining insight into the optimum concentration and alignment of the CNTs in the composite film for applications such as strain sensors, anisotropic conductive films, transparent electrodes and flexible electronics.

http://iopscience.iop.org/article/10.1088/0957-4484/23/5/055703/pdf

Effects of inter-tube distance and alignment on tunnelling resistance and strain sensitivity of nanotube/polymer composite films

This paper presents an analytical model of conductivity and sensitivity of passive wireless sensors for biohazard gas detection with lower computational cost and reasonable accuracy. Based on the effect of electron tunneling among the carbon nanotubes embedded in a polymer matrix, an analytical model for conductivity of the composite is presented. This model provides significantly lower computational cost as compared to the numerical resistive network models. By incorporation of electron tunneling effects, this model also provides closer approximation to experimental results in comparison to the models based on the percolation theory, which are highly relevant for filler/polymer composite applications designed around the percolation threshold. Using this conductivity model, the conductivity and sensitivity of the composite films are estimated in the presence of an organic gas. The change in the film resistance due to the absorption of the gas is investigated for different filler and gas concentrations. From the phase of the reflected radio frequency signal, the applications of the sensor for passive wireless gas sensing is estimated in a lossless transmission system terminated with a composite film as the load. This paper is useful for design and development of biohazard gas sensors for real-time remote monitoring.

Efficient Analytical Model of Conductivity of CNT/Polymer Composites for Wireless Gas Sensors

The coupled effects of varying composite film thicknesses and filler lengths on the conductivity and strain sensitivity of carbon nanotube (CNT)/polymer composite films are investigated through modeling and experiments. Change in average intertube distance is calculated statistically through the Monte Carlo simulations for samples with different CNT concentrations and film thicknesses for a given filler aspect ratio. The composite conductivity is then estimated from the intertube distance with a semi-analytical model based on a tunneling current. The dependence of conductivity on mechanical strain is investigated for varying film thickness for strain sensor applications. A partial alignment of CNTs introduced at film thicknesses less than the CNT length is observed to have a significant influence on the composite conductivity and strain sensitivity, specially at low CNT concentrations. The modeling results can explain the observed experimental results of conductivity for CNT composites, which illustrate a unique dip in conduction with increasing thickness. These results are important for understanding the composite characteristics with different filler orientations and film thicknesses for a given filler length, and useful for the design optimization of high performance composite electronic films for applications in electronic skin and sensors.

Coupled Effects of Film Thickness and Filler Length on Conductivity and Strain Sensitivity of Carbon Nanotube/Polymer Composite Thin Films

Analytical models for the transparency and sheet resistance of the SWNT thin film are developed The transparency to sheet resistance ratio is investigated for varying concentration, length and orientation angle of carbon nanotubes

Rubaiya Rahman

Papers

Effects of inter-tube distance and alignment on tunnelling resistance and strain sensitivity of nanotube/polymer composite films

Efficient Analytical Model of Conductivity of CNT/Polymer Composites for Wireless Gas Sensors

Coupled Effects of Film Thickness and Filler Length on Conductivity and Strain Sensitivity of Carbon Nanotube/Polymer Composite Thin Films

Analytical modeling of the transparency and sheet resistance of SWNT thin films

P.117: Orientation of Fillers in CNT/Polymer Composite Interfacial Layer for Enhancing Charge Transportation