Unique and beneficial gallium based liquid alloys [1,2] have high potential to a compliant sensor,power source and wireless communication unit. There are several types of patterning techniques forliquid alloys have been reported such as injection , printing , selective wetting , stamping and direct writing . Our recently developed liquid alloy printing technique employing atomizationand tape transfer masking for batch type and large area fabrication is practically useful for micrometerscale conductor patterning to realize a compliant microsystem. The process provides a quick and easyfabrication scheme for soft and stretchable, liquid alloy applied microsystems.On the other hand, an elastomer as a packaging material has an important role in compliantmicrosystem performance. Polydimethylsiloxane (PDMS) based elastomer and silicone have beenwidely used due to their good processability with soft-lithography and versatile behaviors such asstretchability, inertness and transparency for microfluidics, soft robotics and stretchable electronics.Still, the PDMS based elastomer needs to be tuned in many properties, in order to meet requirementsof applications. Mechanical properties tuning of the PDMS based elastomers have been reported withdifferent approaches [10,11,12] to make more compliant and stretchable one. Here, we present ourrecently developed multi-functional elastomers, which are based on PDMS. One is a thermalelastomer composite (TEC) and the other is a soft, stretchable and sticky PDMS based elastomer(S3-PDMS). The former is useful for stretchable thermal systems such as a temperature sensor or athermoelectric generator to achieve higher sensitivity and higher efficiency. Nanometer scale liquidalloy droplet fillers to tune the elastomer to be softer or stiffer can be dispersed in the PDMS basedelastomer by high speed mixing. The thermal conductivity reaches twelve fold higher than the originalelastomer with keeping 100% stretchability. The latter is useful for skin applicable devices, whichdemands lower compliance than skin modulus, high stretchability and self-adhesive surface toreusable attach on human skin. Ethoxylated polyethylenimine (PEIE) enables the PDMS basedelastomer more compliant and stretchable with a simple one step mixing process. Less than a 0.1 wt%additive in PDMS prepolymer makes it sticky as well by heterogeneous crosslinking domainsincluding loosely crosslinked parts. The elastic modulus reaches 24 kPa and the elongation at break isover 300%. The adhesion force is more than 10 times of the original one. Both of tuning processes aretunable with the mixing conditions with additives in one step processing.Several compliant microsystems have been successfully fabricated with the developed patterningtechniques of the liquid alloy, and operated under dynamic conditions. A stretchable strain sensor,stretchable wireless power transfer coil, stretchable radio frequency identification (RFID, 13.56 MHz)tag and stretchable thermoelectric generator are made of liquid alloy patterns and multi-functionalelastomers, which is tuned with liquid alloy fillers and heterogeneous crosslink structures.
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