Conductive Thermoplastic Elastomer Research Articles

3D‐Printed Soft Proprioceptive Graded Porous Actuators with Strain Estimation by System Identification

Integration of both actuation and proprioception into the robot body leads to a single integrated system that can deform and sense. Within this work, liquid rope coiling is used to 3D‐print soft graded porous actuators. By fabricating these actuators from a conductive thermoplastic elastomer, piezoresistive sensing is directly integrated. These sensor‐integrated actuators exhibit nonlinearities and hysteresis in their resistance change. To overcome this challenge, a novel approach that uses identified Wiener–Hammerstein (WH) models is proposed to estimate the strain based on the resistance change. Three actuator types were investigated, namely, a bending actuator, a contractor, and a three degrees of freedom bending segment. By using the design freedom of additive manufacturing to set the porosity, the actuation and sensing behavior of a contracting actuator can be programmed. Furthermore, the WH models can provide strain estimation with on average high fits (83%) and low root mean square (RMS) errors (6%) for all three actuators, which outperformed linear models significantly (76.2/9.4% fit/RMS error). In these results, it is indicated that combining 3D‐printed graded porous structures and system identification can realize sensor‐integrated actuators that can estimate their strain but also tailor their behavior through the porosity.

2D Printing of Piezoresistive Auxetic Silicone Sensor Structures

In this letter, we developed a piezoresistive auxetic sensor structure based on a silicone elastomer and carbon-based conductive thermoplastic elastomer fiber sensor (CTPE fiber). Liquid silicone has been used as the matrix material. In addition silicone has been mixed with silica filler to tailor the stiffness of an auxetic elastic structure that improved the sensor behavior of silicone-based CTPE fiber composites. The 2D auxetic structures with and without silica fillers have been successfully printed with the direct ink writing method. The piezoresistive fiber was integrated and the auxetic structure were embedded in the silicone matrix in a second step, via casting method. To detect the electrical signal behavior of the integrated fiber sensor, the hybrid manufactured auxetic fiber sensor composite was investigated using dynamic cycle testing between 0 and 20% strain. Using silicone with silica filler for the printing of the auxetic structure, the sensor behavior of the piezoresistive fiber elastomer composite was improved and a secondary peak of the sensor signal could be avoided at low strains. Unfortunately, a constant gauge factor between 0 and 20% strain could not be obtained by implementing the auxetic structure element inside the CTPE fiber composite. However, this structure can already be integrated into a watchband and used for gesture-controlled applications.

Conductive Thermoplastic Elastomer Composite Capacitive Strain Sensors and Their Application in a Wearable Device for Quantitative Joint Angle Prediction

Wearable devices can provide valuable information for the user when completing rehabilitation or attempting to improve athletic performance. Seamlessly incorporated soft strain sensors enable the c...

Tactile Sensing Applied to the Universal Gripper Using Conductive Thermoplastic Elastomer.

There is increasing interest in the use of soft materials in robotic applications ranging from wearable devices to soft grippers. While soft structures provide a number of favorable properties to robotic systems, sensing of large deformable soft structures is still a considerable challenge; sensors must not inhibit the mechanical properties of the soft body, and the potential infinite degree-of-freedom deformations mean that there is an intrinsically limited resolution of the sensing receptors. An approach to address these challenges using a conductive thermoplastic elastomer is proposed. This allows sensory strain information to be gained from deforming structures without disturbing the dynamics of the system enabling coverage of large soft surfaces. In this article, a theoretical framework is developed, which provides a set of design principles to optimize and characterize sensor implementation, allowing maximum information about location, posture, and shape of the object to be determined. The proposed approach has been tested experimentally for the case study of the universal gripper; investigating how a sensorized gripper can allow a robot to identify grasped objects to enable improved gripping and manipulation performance.

Liquid Metal‐Conductive Thermoplastic Elastomer Integration for Low‐Voltage Stiffness Tuning

AbstractAn electrically responsive composite is introduced that exhibits muscle‐like changes in elastic stiffness (≈1–10 MPa) when stimulated with moderate voltages (5–20 V). The stiffness‐tuning element contains an embedded layer of conductive thermoplastic elastomer (cTPE), composed of a propylene–ethylene copolymer and a percolating network of carbon black. Two opposite surfaces of the cTPE layer are coated with a ≈20 µm thin film eutectic gallium–indium (EGaIn) liquid metal alloy. When a voltage is applied to these EGaIn electrodes, electric current passes through the cTPE. This causes internal Joule heating, which induces a phase transition that changes the composite from its stiff state (E = 10.4 MPa) to its compliant state (E = 0.7 MPa). Differential scanning calorimetry is performed to show that this state change is governed by a solid–liquid transition. Voltage‐dependent activation times are demonstrated that can be reduced to below 2 s and show the ability of the composite to recover its original shape after large strains. To illustrate its applicability in robotics, the composite is incorporated into an underactuated robotic finger, providing it with two different bending modes. The ability to use the composite as a moldable stiffness‐tuning splint is also demonstrated.

Electrical conductivity and mechanical properties of carbon black modified polyolefinic blends influenced by phase inversion

ABSTRACTElectrically conductive polymer composites (CPCs) containing a carbonaceous filler and a polymeric matrix have been widely researched and utilized. Immiscible polymers are often used as the matrix of CPCs, which leads to segregated structures, hence low percolation threshold and good conductivity of a material. Polymeric blends often show low mechanical properties due to the lack of affinity of the resins. A way to improve toughness of a CPC and maintain good electrical properties is mixing two immiscible yet compatible resins. In our case one of them was polyethylene and the other was an olefinic conductive thermoplastic elastomer. In this study, a correlation between conductivity, mechanical properties, and morphology of conductive blends was analyzed. Results of tensile test, conductivity measurements, and differential scanning calorimetry were juxtaposed with information of phase morphology of the blends. A relationship of drastic changes of different properties of the blends and phase inversion point was found. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45512.

Electrically conductive thermoplastic elastomer nanocomposites at ultralow graphene loading levels for strain sensor applications

Strain sensors with high sensitivity are reported in the thermoplastic polyurethane nanocomposites with ultralow graphene loading.

A miniaturized electrolytic pump sensorized with a strain gauge based on thermoplastic nanocomposite for drug delivery systems.

In this paper we present a miniature electrolytic pump sensorized with a novel strain sensor to be used as active component of a drug delivery system. It consists of an electrolytic solution reservoir where inert electrodes are immersed. By polarizing the electrodes, the electrolytic reaction is activated and the produced gases (i.e. oxygen and hydrogen) displace an elastic membrane delimiting the electrolytic solution reservoir. In order to measure and monitor the membrane displacement, and therefore the volume of drug ejected, a strain gauge sensor has been prepared using a conductive thermoplastic nanocomposite elastomer (CTPE). The sensor has been fixed on the deformable membrane. The conductive thermoplastic elastomer is a good candidate for this application because of its high sensitivity. Furthermore, the CTPE allows to customize the resistance of the device in order to obtain low power consumption.

SVAS3: Strain Vector Aided Sensorization of Soft Structures.

Soft material structures exhibit high deformability and conformability which can be useful for many engineering applications such as robots adapting to unstructured and dynamic environments. However, the fact that they have almost infinite degrees of freedom challenges conventional sensory systems and sensorization approaches due to the difficulties in adapting to soft structure deformations. In this paper, we address this challenge by proposing a novel method which designs flexible sensor morphologies to sense soft material deformations by using a functional material called conductive thermoplastic elastomer (CTPE). This model-based design method, called Strain Vector Aided Sensorization of Soft Structures (SVAS3), provides a simulation platform which analyzes soft body deformations and automatically finds suitable locations for CTPE-based strain gauge sensors to gather strain information which best characterizes the deformation. Our chosen sensor material CTPE exhibits a set of unique behaviors in terms of strain length electrical conductivity, elasticity, and shape adaptability, allowing us to flexibly design sensor morphology that can best capture strain distributions in a given soft structure. We evaluate the performance of our approach by both simulated and real-world experiments and discuss the potential and limitations.

Piezoresistive Behavior of Electrically Conductive Carbon Fillers/Thermoplastic Elastomer Nanocomposites

Electrically conductive thermoplastic elastomer (TPE) composites consisting of polypropylene/ethylenepropylene diene-methylene (PP/EPDM), and three kinds of carbon fillers including carbon black (CB), multi-walled carbon nanotube (CNT) and hybrid (CNT-CB) were fabricated. Results showed the high pressure– resistance sensitivity at low concentration of fillers and the low pressure–resistance sensitivity at high concentration of fillers were explained. The piezoresistive properties of TPE composites with individual filler were found to be a function of filler parameters. Percolation threshold was found to be an important parameter to adjust the pressure–resistance sensitivity of TPE composites. These functional composites have potential applications in the field of pressure sensors.

Reactive processing and evaluation of butadiene–styrene copolymer/polyaniline conductive blends

AbstractBlending is an important way to obtain materials based on intrinsically conductive polymers and conventional plastics and rubber materials. Much research has been carried out to determine the best performance of materials be used for electrostatic dissipation and electromagnetic interference shielding. Mechanical mixing, codissolution, and in situ polymerization have been used to prepare these materials. The method used depends on the host polymer and its thermal stability and acid attack resistance. Homogeneity and miscibility are properties that should be controlled during blend preparation. In this study, we prepared a conductive thermoplastic elastomer material based on butadiene–styrene copolymer (SBR) and polyaniline (PANI) doped with dodecylbenzene sulfonic acid (DBSA) and poly(styrene sulfonic acid) (PSS). PSS also acted as compatibilizer between PANI and SBR. PANI was doped by reactive processing with DBSA and PSS to produce the conductive complex PANI–DBSA–PSS. This complex was mixed with 90, 70, and 50% (w/w) SBR in a counterrotatory internal mixer. Conductivity tests, swelling studies, thermal analysis, and mechanical property and reflectivity testing were done, and the results show a strong dependence on PANI concentration and the ratio between PANI–DBSA and PSS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 681–685, 2006