Alexander Dallinger, Paul Kindlhofer, Francesco Greco and Anna Maria Coclite
Publication Date: March 9, 2021
https://doi.org/10.1021/acsapm.0c01385

Short presentation of the multiresponsive actuators

Abstract

The method of converting insulating polymers into conducting 3D porous graphene structures, so called laser-induced graphene (LIG) with a commercially available CO₂ laser engraving system in an ambient atmosphere, resulted in several applications in sensing, actuation and energy. In this paper we demonstrate a combination of LIG and a smart hydrogel (poly(N-vinylcaprolactam) – pNVCL) for multiresponsive actuation in a humid environment. Initiated chemical vapor deposition (iCVD) was used to deposit a thin layer of smart hydrogel onto a matrix of PDMS and embedded LIG tracks. An intriguing property of smart hydrogels, such as pNVCL, is that the change of an external stimulus (temperature, pH, magnetic/electric fields) induces a reversible phase transition from a swollen to a collapsed state. While the active smart hydrogel layer had a thickness of only 300 nm (compared to the 500 times thicker actuator matrix), it was possible to induce a reversible bending of over 30° in the humid environment triggered by joule heating. The properties of each material were investigated by means of scanning electron microscope (SEM), Raman spectroscopy, tensile testing and ellipsometry. The actuation performances of single-responsive versions were investigated by creating a thermoresponsive PDMS/LIG actuator and a humidityresponsive PDMS/pNVCL actuator. These results were used to tune the properties of the multiresponsive PDMS/LIG/pNVCL actuator. Furthermore, the capabilities of self-sensing were investigated. By getting a feedback from the piezoresistive change of the PMDS/LIG composite the bending angle could be tracked by measuring the change in resistance. To highlight the possibilities of the processing techniques and the combination of materials, a demonstrator in the shape of an octopus with four independently controllable arms was produced.

Presentation @ DocDay 2021

Our contribution to the book:

Chapter 15 – Ultraconformable Organic Electronics

L. M. Ferrari, S. Taccola, J. Barsotti, V. Mattoli,  F. Greco
in Organic Flexible Electronics, Eds. P. Cosseddu, M. Caironi, Elsevier 2021, pages 437-478
Publication Date: October 5, 2020
Link to the Chapter on Science Direct – Elsevier

The Field-of-Expertise Advanced Materials Science is an interdisciplinary network of researchers at the TU Graz in chemistry, physics, architecture, mechanical engineering, civil engineering, electrical engineering and geodesy who discover, characterize and model materials, functional coatings and components.

You can listen to a short presentation of the poster in this video recorded for the virtual AMD2020.

The part of LAMPSe is the investigation of methods to create conformal conductive paths complementing the two-photon polymerization process.
Our approach is conversion of polymers to conductive carbon via laser carbonization. By investigating different laser sources and precursor materials we aim to find a method which is easy to implement in the project.

Another partner in the consortium of TU Graz is the group of Anna Maria Coclite, who will be investigating Stimuli Responsive Materials for Sensing.

On September 21st the Kick-Off meeting for the project took place. Due to the current COVID-19 situation the consortium was meeting online.

Alexander Dallinger, Kirill Keller, Harald Fitzek, Francesco Greco
ACS Appl. Mater. Interfaces, 19855-19865
Publication Date: April 6, 2020
https://doi.org/10.1021/acsami.0c03148

Abstract

The conversion of various polymer substrates into laser-induced graphene (LIG) with a CO₂ laser in ambient condition is recently emerging as a simple method for obtaining patterned porous graphene conductors, with a myriad of applications in sensing, actuation, and energy. In this paper, a method is presented for embedding porous LIG (LIG-P) or LIG fibers (LIG-F) into a thin (about 50 μm) and soft medical grade polyurethane (MPU) providing excellent conformal adhesion on skin, stretchability, and maximum breathability to boost the development of various unperceivable monitoring systems on skin. The effect of varying laser fluence and geometry of the laser scribing on the LIG micro–nanostructure morphology and on the electrical and electromechanical properties of LIG/MPU composites is investigated. A peculiar and distinct behavior is observed for either LIG-P or LIG-F. Excellent stretchability without permanent impairment of conductive properties is revealed up to 100% strain and retained after hundreds of cycles of stretching tests. A distinct piezoresistive behavior, with an average gauge factor of 40, opens the way to various potential strain/pressure sensing applications. A novel method based on laser scribing is then introduced for providing vertical interconnect access (VIA) into LIG/MPU conformable epidermal sensors. Such VIA enables stable connections to an external measurement device, as this represents a typical weakness of many epidermal devices so far. Three examples of minimally invasive LIG/MPU epidermal sensing proof of concepts are presented: as electrodes for electromyographic recording on limb and as piezoresistive sensors for touch and respiration detection on skin. Long-term wearability and functioning up to several days and under repeated stretching tests is demonstrated.