NOVEL ELECTROACTIVE SOFT ACTUATORS BASED ON IONIC GEL/GOLD NANOCOMPOSITES PRODUCED BY SUPERSONIC CLUSTER BEAM IMPLANTATION

Ionic electro-active polymers (IEAPs) constitute a promising solution for developing self-regulating, flexible and adaptive mechanical actuators in the area of soft robotics, micromanipulation and rehabilitation. These smart materials have the ability to undergo large bending deformations as a function of a low applied voltage (1 to 5 V), as a result of the ions migration through their inner structure when the network is liquid filled. Among this broad family of materials, ionic-polymer-metal composites (IPMC) based on DuPont\u2019s Nafion\uae have attracted an increasing interest for the production of light weight controllable soft machines due to their easiness to be metalized (e.g. by mean of electroless plating), fast response and capability of working exposed to air. However, the high cost of the material, its relatively low working density (i.e. the maximum mechanical work output per unit volume of active material that drives the actuation) and weak force output, as well as the considerable fatigue effects endured by the surface electrodes upon cycling, is limiting the performance of these IPMC actuators and hindering their implementation in traditional mechatronic and robotic systems. On the other hand, ionic hydrogels, such as poly(acrylic acid) (PAA) and poly-styrene sulfonate (PSS) based polymers, exhibit controllable mechanical properties and porosity and have shown to be excellent candidates to be used as electrically triggered artificial muscles and miniaturized robots operating in aqueous environments. Although the relatively low cost of these materials render them appealing for mass production scale up, the applicability of these polymeric actuators is limited to a liquid environment, which is intrinsically facilitating the solvent evaporation when the hydrogels are exposed to air. Furthermore, because of the difficulty encountered in fabricating stable and anchored metal structures on these polymer surfaces, these smart soft systems operate in a non-contact configuration with respect to the pilot electrodes, therefore increasing the actuators response time up to few tenths of seconds. In order to achieve an efficient electromechanical transduction along with a stable and durable performance for electro-active actuators operating in air, two main interplaying characteristics must be tailored when designing the system. On one hand side, the need of electrodes that are physically interpenetrating with the polymeric basis is of absolute priority, since the intercalation of ions into the electrode layers and the resulting material volumetric change are fundamental for strain generation. On the other hand, the formulation and engineering of new low cost materials able to merge highly elastic properties and efficient ionic transport features is of crucial importance. The present thesis work deals with the formulation, synthesis and manufacturing of a novel ionic gel/metal nanocomposite (IGMN) that was designed and developed to merge the advantageous properties of both IPMCs and ionic hydrogel actuators and to contextually overcome many of the above mentioned drawbacks characteristic of these two families of polymers. These composites were obtained by mean of Supersonic Cluster Beam Implantation (SCBI). This technique, developed in-house, relies on the use of supersonically accelerated gas-phase metal cluster beams directed onto a polymeric substrate in order to generate thin conductive layers (few tenths to few hundreds of nanometers thick) anchored to the polymer. This scalable approach already proved to be suitable for the manufacturing of elastomer/metal functional nanocomposites, and, as described in this work, it enabled the production of cluster-assembled gold electrodes (100 nm thick) interpenetrating with an engineered ionic gel matrix. This novel approach led to the fabrication of highly conductive metal nanostructures, large surface area for ions storage and providing minimal interfacial stresses between the metal layer and the polymeric basis upon deformation. The key features of this novel system comprise the control on the polymer elasticity, bending actuation in air from 0.1V to 5V, fast response time ( 5 cm), high work density ( >10 J/cm3), minimal electrodes fatigue upon cycling and low manufacturing costs. A bottom-up approach was firstly adopted to engineer and produce Uv photo-cross-linked ionic co-polymers (iongel) with tailored mechanical properties and provided with inorganic nano-structures embedded in the macromolecular matrix which show excellent long-term performance. The polymer is based on poly(acrylic acid)-co-poly(acrylonitrile) (PAA-co-PAN) co-polymers, which are chemically cross-linked in a hydrogel-like fashion and swollen with suitable imidazolium-based ionic liquid. The materials are produced as 100 um freestanding layers using a one-pot synthesis and a simple molding process. Due to the incommensurably low vapor pressure of the ionic liquid, issues concerning the shrinkage of traditional water swollen gels operating exposed to air could be avoided. An organic cation (tetraethyl ammonium, TEA+) is stably coordinated to the carboxyl groups of the PAA and free to move in the polymer sieve-like structure when a small voltage is applied at the electrodes. PAN was introduced to enhance the elastic properties of whole polymer. In the bulk polymer, halloysite nanoclays (HNC) are physically embedded into the gel in order to both improve the toughness of the gel and to improve the ionic conductivity of the system. In fact, the nanostructures interacts with the imidazolium cation of the ionic liquid through an oxygen reduction reaction, and therefore the latter is able to contribute to the charge transport phenomena induced by the electric field due to the solvent partial dissociation. Furthermore, the porosity of the polymer, tailored by the cross-linker, creates physical channels to favor the mobility of positive ions when an electric field is applied. The contribution of both the positive charged species (TEA+ and cations of ionic liquid) that accumulates at the nanostructured electrode in a double layer capacitance regime generates a differential swelling at the opposite sides of the actuator, which bends towards the anode. As it will be shown in the next sections, the actuation mechanism of the IGMN could be modeled according to both the material structure and design, as well as to the experimental data on its electrochemical and electro-mechanical properties.Comparing with traditional soft polymers incompatibility with current metallization processes, like electroless plating or surface silver laminated electrodes fabrication, which are not suitable to guarantee long-term actuation of the components, SCBI demonstrated to be a suitable technique for the production of next generation electro-active soft actuators. The IGMN-based actuators showed superior performance, such as large bending displacement, fast response time, long durability in a low voltage regime during the actuation process. The combination of the SCBI fabrication technology with the ionic gel synthesis and fabrication renders the manufacturing of these systems time-saving and costs-effective, and the unique properties of these actuators render them good candidates for potential scale up and for applications in micro-electromechanical systems, microfluidics, soft robotics, and rehabilitation

MICROFABRICATION AND MODELLING OF DIELECTRIC ELASTOMER ACTUATORS

Dielectric elastomer actuators (DEAs) are a class of polymeric actuators that have gained prominence over the last decade. A DEA is comprised of a polymer sandwiched between two compliant electrodes. When voltage is applied between the two electrodes, electrostatic attraction between the electrodes compresses the elastomer in that direction and stretches it in the other two directions. DEAs produce dimensional changes (strains) up to 300% upon application of an electric field. DEAs have tremendous potential for applications requiring large displacements and have been demonstrated for many macro-scale (centimeter and larger) applications such as robots, loudspeakers, and motors. There are potentially many useful applications for micro-scale DEAs (less than millimeter-sized devices with micron-sized actuators) in the fields of micro-robotics, micro-optics, and micro-fluidics. However, miniaturization of DEAs is challenging because many of the materials and DEA fabrication methods used on the macro-scale cannot be adapted for micro-scale fabrication of DEAs. This thesis explores the feasibility of developing fabrication strategies for micro-scale DEAs by adapting micro-electromechanical systems (MEMS) technology. In addition, fabrication protocols for micro-scale DEAs have been developed. The other aspect of this thesis is the design of bending DEAs. Benders are useful because for a given actuation strain, greater deflection can be observed by controlling the stiffnesses and thicknesses of different layers. A general guideline for designing bending DEA configurations such as unimorph, bimorph, and multilayer stacks was developed using a multilayer analytical model. The design optimization is based on the effect of thickness and stiffness of different layers on curvature, blocked force, and work. Complaint electrodes and their design are important for DEAs to enable the elastomer to stretch unrestricted. Thus, design criteria for the fabrication of crenellated electrodes and crenellated elastomers with electrodes were investigated. This guideline enabled design of structures with appropriate axial or bending stiffnesses based on the amplitude, angle, length, and thickness. Simple analytical equations for axial and bending stiffness for crenellated electrodes with different shapes were derived. In addition, numerical simulations of crenellated elastomer with stiff electrode were performe

Formation of Advanced Nanomaterials by Gas-Phase Aggregation

The book represents a collection of papers from Special Issue “Formation of Advanced Nanomaterials by Gas-Phase Aggregation” published in journal Applied Nano. It contains review and original articles covering a range of topics on the growth of clusters/nanoparticles using gas-phase aggregation approaches, the application of cluster beams for the formation of nanomaterials with advanced properties and specific nanostructures as well as providing new fundamental insights on nanoscale properties of materials

DEVELOPMENT OF FUNCTIONAL NANOCOMPOSITE MATERIALS TOWARDS BIODEGRADABLE SOFT ROBOTICS AND FLEXIBLE ELECTRONICS

World population is continuously growing, as well as the influence we have on the ecosystem\u2019s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity\u2019s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today\u2019s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices

Computational Intelligence in Electromyography Analysis

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG may be used clinically for the diagnosis of neuromuscular problems and for assessing biomechanical and motor control deficits and other functional disorders. Furthermore, it can be used as a control signal for interfacing with orthotic and/or prosthetic devices or other rehabilitation assists. This book presents an updated overview of signal processing applications and recent developments in EMG from a number of diverse aspects and various applications in clinical and experimental research. It will provide readers with a detailed introduction to EMG signal processing techniques and applications, while presenting several new results and explanation of existing algorithms. This book is organized into 18 chapters, covering the current theoretical and practical approaches of EMG research

Designing a New Tactile Display Technology and its Disability Interactions

People with visual impairments have a strong desire for a refreshable tactile interface that can provide immediate access to full page of Braille and tactile graphics. Regrettably, existing devices come at a considerable expense and remain out of reach for many. The exorbitant costs associated with current tactile displays stem from their intricate design and the multitude of components needed for their construction. This underscores the pressing need for technological innovation that can enhance tactile displays, making them more accessible and available to individuals with visual impairments. This research thesis delves into the development of a novel tactile display technology known as Tacilia. This technology's necessity and prerequisites are informed by in-depth qualitative engagements with students who have visual impairments, alongside a systematic analysis of the prevailing architectures underpinning existing tactile display technologies. The evolution of Tacilia unfolds through iterative processes encompassing conceptualisation, prototyping, and evaluation. With Tacilia, three distinct products and interactive experiences are explored, empowering individuals to manually draw tactile graphics, generate digitally designed media through printing, and display these creations on a dynamic pin array display. This innovation underscores Tacilia's capability to streamline the creation of refreshable tactile displays, rendering them more fitting, usable, and economically viable for people with visual impairments

Design and fabrication of flexible tactile sensing and feedback interface for communication by deafblind people

Humans generally interact and communicate using five basic sensory modalities and mainly through vision, touch and audio. However, this does not work for deafblind people as they have both impaired hearing and vision modalities, and hence rely on touch-sensing. This necessitates the development of alternative means that allows them to independently interact and communicate. To do this requires a solution which has the capability for tactile sensing and feedback. Therefore, tactile interface becomes a critical component of any assistive device usable by deafblind people for interaction and communication. Given that existing solutions mainly use rigid and commercial components, there is a need to tap into the advancements in flexible electronics in order develop more effective and conformable solutions. This research involves the development of flexible tactile communication interface usable in assistive communication devices for deafblind people. First, commercial sensors and actuators were utilised as a proof-of-concept and then four novel tactile interfaces were explored which include two similar touch-sensitive electromagnetic actuators, one capacitive tactile sensing array, and a facile flexible inductance-based pressure sensor. The two fabricated touch-sensitive electromagnetic actuators (Type 1 and 2) are both based on electromagnetic principle and capable of simultaneous tactile sensing and feedback. Each comprises of a tandem combination of two main modules - the touch-sensing and the actuation module, with both modules integrated as a single device in each case. The actuation module employs a flexible planar spiral coil and a Neodymium magnet assembled in a soft Polydimethylsiloxane (PDMS) structure, while the touch-sensing module is a planar capacitive metal- insulator-metal structure of copper. The flexible coil (~17µm thick and with 45 turns) was fabricated on a Polyimide sheet using Lithographie Galvanoformung Abformung (LIGA) process. The results of characterisation of these actuators at frequencies ranging from 10Hz to 200Hz, shows a maximum displacement (~ 190µm) around 40Hz. Evaluation of this by 40 (20 deafblind and 20 sighted and hearing) participants show that they can feel vibration at this range. Another tactile interface fabricated is an 8 x 8 capacitive tactile sensing array. The sensor was developed on a flexible Polyvinyl Chloride (PVC) sheet with column electrodes deposited on one side and row electrodes on the reverse side. It is intended for use as an assistive tactile communication interface for deafblind people who communicate using deafblind manual alphabets as well as the English block letters. An inductance-based pressure sensor was also designed, fabricated and characterised for use as an input interface for finger Braille as well as other tactile communication methods for deafblind people. It was realised with a soft ferromagnetic elastomer and a 17µm-thick coil fabricated on a flexible 50 µm-thick polyimide sheet. The ferromagnetic elastomer acts as the core of the coil, which when pressed, sees the metal particles moving closer to each other, leading to changes in the inductance. The coil, with 75µm conductor and 25µm pitch, was also realised using LIGA micromolding technique. Seven different sensors were fabricated using different ratios (1:1, 1:2, 1:3, 1:5, 2:1, 3:1, and 5:1) of Ecoflex to Iron particles. The performance of each sensor was investigated and generally, sensors with higher Iron particles gave better sensitivity, linear as well as dynamic range. In comparison with all other fabricated sensors, the sensor made with 1:5DD was recommended for application as a tactile interface

The Science and Technology of 3D Printing

Three-dimensional printing, or additive manufacturing, is an emerging manufacturing process. Research and development are being performed worldwide to provide a better understanding of the science and technology of 3D printing to make high-quality parts in a cost-effective and time-efficient manner. This book includes contemporary, unique, and impactful research on 3D printing from leading organizations worldwide