Magnetic Functionalization of Poly(N‐isopropylacrylamide) Hydrogels for Sensor Applications

To develop a hydrogel sensor system using the Hall effect to detect the degree of swelling, gels containing high concentrations of magnetic particles are necessary to induce a strong magnetic field. For this purpose, hydrogels based on poly( N ‐isopropylacrylamide) cross‐linked with Laponite XLS are modified with various magnetic nanoparticles. The focus of this work is to introduce high particle densities with a homogeneous distribution into the gel. Particles are coated with 3‐(trimethoxysilyl)propyl methacrylate to bind them into the network structure. The swelling behavior and temperature response of gels containing pure and modified particles are compared to the unmodified clay gel. Ferrogels are further synthesized in a magnetic field to permanently align magnetic nanoparticles in the network. This results in permanently embedded rod‐like structures spanning the entire length of the gel. The influence of this anisotropic distribution on the mechanical properties of the hydrogel is investigated through compression measurements.