A novel magnetochromic elastomer with a strong and rapid magnetochromic effect has been developed. In the system, citric acid surface-functionalized magnetic nanoparticles (MNPs) are dissolved in poly(ethylene glycol) (PEG-200) and ultrasonicated into an emulsion with polydimethylsiloxane (PDMS) by speedmixing. The MNPs are shown to change from random to field-aligned under an external magnetic field and thus enables an on/off function. The developed elastomer shows a great potential for a wide range of applications, such as sensors and anticounterfeiting labels.
Silicone elastomers are widely used due to the favourable properties, such as flexibility, durable dielectric insulation, barrier properties against environmental contaminants and stress-absorbing properties over a wide range of temperatures ≈ -100°C to 250°C. Additionally they are mechanically reliable over millions of deformation cycles, which makes them ideal candidates for dielectric elastomers and stretchable electronics. In research on dielectric elastomers and other emerging technologies, the most common silicone elastomer utilized is Sylgard 184. One of the main advantages of this formulation is the low viscosity which allows for easy processing resulting in almost defect-free samples. Furthermore, its curing is robust and not as sensitive to poisoning as other silicone elastomer formulations. Commonly, the shortcomings of the final properties of Sylgard 184 are overcome by mixing the base polymer and the curing agent in non‐stoichiometric ratios and also by blending it with softer types of commercially available elastomers. Researchers rarely formulate their own tailor‐made silicone elastomers, probably due to the scarcity of information in literature on how to do this. This report aims to equip the beginners in silicone research with knowledge on how to prepare silicone elastomers with specific properties without compromising the mechanical integrity of the elastomer and thereby avoiding mechanical failure. Here the main focus is put on designing and formulating soft, reliable, and reproducible elastomers.
Soft, stretchable and light-weight transducers are most sought after for research on advanced applications like stretchable electronics, soft robotics and energy harvesters. Stretchable electronics require elastomers that have high elongation at break, high dielectric permittivity and high breakdown strength. Commercial silicone elastomer formulations often do not encompass all the necessary properties required to function effectively as stretchable transducers but they are used out of familiarity. In this study, most commonly used commercial silicone formulations are formulated with different stoichiometry and also blends of these formulations are made in order to manipulate their resulting properties. The properties of these blends like ultimate stress and strain, Young’s modulus, dielectric permittivity and breakdown strength are investigated and mapped to identify those that have the best suited properties for fabricating soft stretchable devices. On a research level, Sylgard 184, Sylgard 186, Ecoflex 00-50, Ecoflex 00-30 and Ecoflex 00-10 are widely used for fabricating such soft devices and hence they will be worked upon in this study. The elastomers obtained using the methods of mixing illustrated here can act as a starting point for conceptualizing the feasibility of a product on research level.
The research on soft elastomers with high dielectric permittivity for the use as dielectric electroactive polymers (DEAP)
has grown substantially within the last decade. The approaches to enhance the dielectric permittivity can be categorized
into three main classes: 1) Mixing or blending in high permittivity fillers, 2) Grafting of high permittivity molecules onto
the polymer backbone in the elastomer, and 3) Encapsulation of high permittivity fillers. The approach investigated here
is a new type of encapsulation which does not interfere with the mechanical properties to the same content as for the
traditionally applied thermoplastic encapsulation. The properties of the elastomers are investigated as function of the
filler content and type. The dielectric permittivity, dielectric loss, conductivity, storage modulus as well as viscous loss
are compared to elastomers with the same amounts of high permittivity fillers blended into the elastomer, and it is found
that the encapsulation provides a technique to enhance some of these properties.
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