In this study, three hydrophobic polymers are investigated as potential adhesivesfor a shape memory polymer nerve cuff. At room temperature, the adhesivecandidate exhibited a maximum lap shear stress of 1.7251 MPa, compared to0.87641 MPa and 2.1815 MPa for two commercially available biocompatibleadhesives.

Commercial off-the-shelf (COTS) electronics are generally not specificallydesigned to perform in extremely transient high impact scenarios. This researchfocused on the development of a silver-decorated carbon black-based polymericnanocomposite with properties such as high conductivity, flexibility, and shockabsorbency. Polymeric rubber materials are generally very flexible and shockabsorbing, however, most polymeric materials are electrical insulators. Thedispersion of the silver-decorated carbon black into the polymeric matrix couldsignificantly improve the electrical conductivity. The processing andfabrication of Ag-CB (silver-carbon black)/Epoxy (thermosetting epoxy polymer)and Ag-CB/TPU (thermoplastic polyurethane) will be reported. Both Ag-CB/Epoxyand Ag-CB/TPU mixtures with solvents showed the shear-thinning behavior, whichwas an important characteristic for direct printing of traces and AdditiveManufacturing (AM). The mechanical properties of the nanocomposites weremeasured using Dynamic Mechanical Analysis (DMA) over a wide range oftemperatures. These nanocomposite materials were also successfully used to printflexible circuits using a 3D-printing machine. The electrical resistance changefor the Ag-CB/Epoxy on polydimethylsiloxane (PDMS) and Ag-CB/TPU on PDMS understrain was studied, and the results will be discussed.

In this work, we propose a model to quantify strain induced conductordiscontinuities based on measuring electrical resistance while applying tensilestrain to metal-polymer systems. Under strain, changing conductor geometry andinduced conductor discontinuity increase electrical resistance. On Kaptonsubstrates strained to ε = .07, evaporated gold films did notdeform and resistance increase was only caused by geometry change. Conversely,discontinuity caused 31% and 72% of the resistance increase in evaporated andprinted silver films at the same strain. On PDMS substrates, the same magnitudeof discontinuity, causing 31% of the resistance increase, occurred at onlyε = .024 in evaporated silver films. At the same strain,discontinuity caused 86% of the resistance increase in evaporated gold films.Printed silver films were inelastic. The results suggest that traditionalfabrication techniques may be more suitable to flexible hybrid electronicsapplications than additively manufactured conductors.

Organic solar (OPV) cells are cheap electronics that can replace the widely used high cost silicon-based electronics for electricity generation. They are cheap because of the easy techniques involved in their fabrication processes and they can be produced to cover a large surface area. However, the current low performance of organic electronics has been traced to failure due to interfacial adhesion problems, material processes, and service conditions. Therefore, transportation of charge carriers across the bulk heterojunction system of OPV cells becomes very difficult in the presence of these flaws. In this paper a combined experimental and computational technique is used to study the reliability and physics failure of stretchable OPV cells. Interfacial adhesion energies in the layered structures of OPV cells are measured and compared with theoretical estimated energies. The limit stresses/strains applied on layered OPV cells during service condition are estimated using critical values of the measured interfacial adhesion. The results obtained are, therefore, explained to improve the design of reliable OPV cells.

We are reporting the formation of free-standing graphene foam (GF) via a noveltwo-step process, in which a polyurethane (PU) foam is first dip-coated withgraphene oxide (GO) and subsequently the dried GO-coated-PU is heated innitrogen atmosphere at 1000°C. During the pyrolysis of theGO-coated-PU, GO is reduced to GF whereas PU is simultaneously decomposed andreleased completely as volatiles in a step wise mass-loss mechanism. Morphologyof the formed GF conforms to that of the pure PU foam as indicated by thescanning electronic micrographs. Polydimethylsiloxane (PDMS) was successfullyinfiltrated inside the GF to form flexible and stretch-able conductors. TheGF-PDMS composite was tested for it’s pressure and strain sensingcapabilities. It is shown that a 30% compressive strain changes resistance ofthe GF-PDMS composite to about 800% of it’s original value. Sincedensity of the formed GF is tunable, therefore, the pressure/strain sensivity ofthe GF-PDMS composite is also tunable.

Silicon wafers coated with a 5μm thick layer of polyimide were treated with different surface modification techniques such as chemical adhesion promoters, oxygen plasma and an Ar+ sputter etch. After surface modification, the wafers were molded with a 1mm thick layer of PDMS. The adhesion of the PDMS was tested by peel testing and by using a Nordson DAGE wedge shear tester. It was found that commercially available chemical adhesion promoters and oxygen plasma treatment resulted in a very poor PI/PDMS adhesion, whereas the Ar+ sputter etch resulted in an adhesion so strong that the PDMS could not be delaminated from the PI surface without the failure of the material.

Magneto active elastomers (MAE), particulate filled magneto-sensitive composites, were made with increasing volume contents of 325 mesh M-type barium hexaferrite (BAM) particles within a silicone elastomer matrix. The volume contents of BAM ranged from 10% to 35% v/v. Vibrating sample magnetometery measurements showed that the remanence and saturation, both per unit magnetic material, increased by 50% from 10%v/v to 20%v/v before slowing decreasing as v/v increased to 35%. The results clearly show in peak in the effectiveness of the embedded particles to produce bulk magnetization near 20% v/v. One possible means for the increase stems from alignment of the magnetization of the particles and hence of the magnetic domains within particles. To assess this possible alignment, Gaussian probability distribution of magnetization orientations was fit to the experimental data to ascertain the change in the distribution as a function of v/v. Results showed 20% v/v had the highest degree of alignment. The results highlight, at a bulk scale, the possible evolution of microstructure within the composite. Similar results have been seen in image analysis of physical particle distribution of other magneto-sensitive particulate composites. The results suggest that effective processing techniques can be used to greatly enhance the bulk magnetization of these and similar composites, paving the way for decreasing required magnetic content to achieve target response specification and possibly resulting miniaturization.

Controlling the bending properties of ionic polymer-metal composites may immediately affect their implementation in robotics and medicine. In the present work, we propose a direct patterning method for the ionic polymer Nafion using conventional electron-beam writing. In a proof-of-concept study, we show that patterns of arbitrary geometry and sizes between 1 µm and 50 µm can be engraved into the polymer surface without using resists. Pattern depth can be deliberately controlled by adjusting the exposure dose. The patterns were stable even after prolonged immersion in ionic solution. The presented technique therefore opens up the possibility to create unique electrode geometries and to investigate independently the effect of pattern size, density, depth as well as geometry on ionic polymer-metal composite bending.

This study investigates the use of shape memory polymers (SMPs) as a substrate for a self-coiling cochlear implant electrode array and investigates the self-coiling ability of a sham probe micromachined atop such a substrate. Through the use of a self-coiling cochlear implant, the capability to avoid contact with the tissue of the cochlear duct is investigated via the insertion of a dummy device into a model cochlea heated to an ambient 34 °C. Finally, a prototype straightening and insertion tool is developed for automated retraction and locking of the coiled shape into a bar geometry. Preliminary demonstration of the deployment of self-coiling cochlear implants is shown and paves the way for future studies focused on using histological analysis of the cochlear wall tissue to compare the degree of trauma resulting from linear cochlear implant arrays versus the self-coiling, non-contact probes demonstrated herein.

This research describes thiol-ene/epoxy hybrid networks for core-shell encapsulation of semiconductor devices. A thiol-ene network was formed using ultraviolet-induced radical polymerization, with unreacted thiols and epoxide monomers remaining in the network. Immersion in tributylamine catalyzed the thiol-epoxy coupling to produce a diffusion-limited hard outer shell. Tensile testing shows that the initial thiol-ene product (core) has elastomeric behavior, while the secondary curing creates a glassy material (shell) at room temperature due to thiol-epoxy coupling. Bulk samples of the material form a hard outer shell surrounding a soft core depending on the secondary cure conditions. There are positive relationships between wall thickness and secondary cure temperature and cure time, enabling control of shell thickness by varying reaction conditions. Shell thicknesses were measured up to 1.8 mm when immersed in tributylamine for up to 150 minutes and up to 140 °C. The ability to control core-shell thickness of dual-cured networks is applicable in device encapsulation processes. Core-shell encapsulants for microelectronics may provide further shock and impact protection for durable electronic devices. Further aging and operational studies will be needed to determine time-stability and optimal processing of the core-shell structure.

A novel pressure sensor is proposed exhibiting generative properties fromdisplacement-induced ionic charge separation in gel electrolytes. Amechano-ionic or ‘piezo-ionic’ effect, in analogy to thewell-known piezoelectric effect, is hypothesized to originate from a differencein mobilities between cationic and anionic species causing a localized ioniccharge gradient upon application of pressure. This gradient can be detected as avoltage or current by using copper electrodes placed at the sides or at regularintervals along a surface of the gel. The voltage generated may be a result ofthe local concentration gradient induced by the deformation of the gel orperhaps is the result of some ions moving faster through the porous gel thanothers. In this work, ionic polymer gels based on Poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) co-polymer were synthesized insitu to incorporate an organic electrolyte consisting ofbis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. With twoelectrodes placed under the gel, the samples were subjected to a sinusoidalmechanical force while open circuit voltage was measured to determine therelationship between electrical signal and mechanical input. The voltagesgenerated are 10’s of mV in magnitude at 1 kPa. Results suggest amaximum sensitivity of 25 µV/Pa at 10 mHz, comparable to the voltagesexpected in piezoelectric polymers such as PVDF (44 µV/Pa for similardimensions). The non-aqueous, solid-state ionic gels presented in this workprovide improved stability and is less prone to evaporation than its aqueous,hydrogel based counterpart. The new mechanism of sensing provides an alternativeto the more rigid and less stretchable piezoelectric sensors.

Over the last decade, the explosion in research and Development associated with nanoscalar materials has continued apace. In parallel with this has been the rapid rise of both sustainable materials and, as a consequence, Natural, Cellular and Responsive material systems. Many of these originate from inorganic, inorganic-organic hybrid composites and polymeric and bio-nano polymeric systems which exhibit intrinsic physico-chemical properties that can be classed as ‘soft’. That is flexible, malleable, lightweight, transparent or semi-transparent and stretchable in character and which can also offer both biocompatible and bioresorbable characteristics essential to useable and sustainable material systems.

This paper describes some of the ways in which we are beginning to understand, explain and exploit ‘soft’ technology. In particular the interactive role of creative design and innovative material science linked through new fabrication methodologies that have, as their common purpose, a focus on compelling Human centred needs. Examples are health, wellness, ambient assistance and urgent improvements in cleanliness, hygiene and nutrition.