Tunable Piezoresistivity from Magnetically Aligned Ni(Core)@Ag(Shell) Particles in an Elastomer Matrix

Area of Science:

• Materials Science
• Nanotechnology
• Polymer Science

Background:

• Developing advanced composite materials with tailored electrical and mechanical properties is crucial for next-generation electronics.
• Poly(dimethylsiloxane) (PDMS) is a versatile polymer, but its electrical conductivity is typically low.
• Controlling the microstructure of conductive fillers within polymer matrices is key to enhancing composite performance.

Purpose of the Study:

• To investigate the effect of magnetic field-induced alignment of core-shell (Nickel-Silver) particles on the electrical properties of PDMS films.
• To explore the creation of pressure-sensitive resistance in these aligned composites.
• To demonstrate the tunability of pressure sensitivity through particle loading.

Main Methods:

• Utilizing a continuous roll-to-roll process with a magnetic field (52 mT) to align Ni@Ag core-shell particles within a PDMS matrix during curing.
• Comparing constrained and unconstrained film fabrication to assess surface topography and particle morphology.
• Employing X-ray tomography to analyze particle distribution and identify breaks in aligned chains.
• Measuring electrical resistance under varying applied pressures to characterize pressure sensitivity.

Main Results:

• Magnetic alignment reduced the electrical conductivity percolation threshold from 28 vol % to approximately 1 vol %.
• Unconstrained films exhibited rougher surfaces and more aggregated particle chains compared to constrained films.
• Below 3.6% Ni@Ag concentration in constrained films, breaks in particle alignment led to pressure-sensitive resistance.
• The threshold pressure for resistance change was controllable from approximately 15 to 290 kPa via Ni@Ag loading.

Conclusions:

• Magnetically aligned Ni@Ag/PDMS composites offer a facile route to highly conductive and mechanically responsive films.
• The ability to tune pressure sensitivity makes these materials suitable for disposable pressure sensors and structural health monitoring.
• While effective, the decrease in threshold pressure upon cyclic loading suggests limitations for applications requiring high cycle durability.