Permanently Magnetizable Composite Polymer Ink for Textile-Based Wearables

We present the fabrication and characterization of magnetic nanoparticle polymer composites that can be patterned on textiles. The resulting structures can be permanently magnetized and used to develop wearable devices such as sensors and actuators for multiple applications that may include physical marker data collection for tracking; wearable microfluidics-based systems; haptic devices; and device-to-device alignment and interconnect. The development of permanently magnetizable polymer composite inks allows for simple and inexpensive system construction on the garment itself without the need for transfer or other separate microfabrication processes. In this paper, different compositions of an in-house developed NdFeB-based magnetic ink are investigated. Characterization is performed primarily on samples that are fabricated using an inexpensive and simple screen-printing process on cotton fabric using base inks that are designed specifically to adhere to textiles, but that we have embedded with magnetic particles at 5 different weight percentages (wt-%) ranging from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$29.8 \text{wt}-\%$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$69.9 \text{wt}-\%$</tex>. We screen-print patterns 3 mm by 10 mm in size, with penetration depths of the inks into the textile surface up to 0.438 mm and magnetize them under a 3T field. We perform quantitative adhesion tests and magnetic characterization. For the magnetic characterization, magnetized samples produce magnetic fields ranging from 0.066 mT to 0.496 mT at the center of the rectangular samples and 0.045 mT to 0.371 mT at the sides of the rectangles. We also characterize the material using a SQUID with an applied magnetic field ranging from -7.0 T to 7.0 T at room temperature (300 K), resulting in magnetization curves that generally show higher magnetic saturation at higher wt-% of particles. Overall, compositions with a lower concentration (wt-%) of magnetic particles perform better in adhesion and permeation tests, but compositions with higher concentrations of magnetic particles have superior magnetic performance.