Stimuli-responsive assembly of iron oxide nanoparticles into magnetic flexible filaments

TL;DR

This paper reports the creation of thermoresponsive magnetic nanoparticles that assemble into flexible microfilaments under external stimuli, offering potential for remotely controlled smart devices.

Contribution

It introduces a novel nanoplatform combining temperature, magnetic, pH, and ionic responsiveness, and demonstrates their assembly into functional microfilaments.

Findings

Nanoparticles exhibit LCST transition between 21°C and 28°C.

Nanoparticles aggregate and respond to magnetic fields above LCST.

Microfilaments can be formed and manipulated using external stimuli.

Abstract

The combination of multiple functionalities in a single material is an appealing strategy for the de-velopment of smart materials with unique features. In this work, we present the preparation of thermoresponsive magnetic nanoparticles and their one-dimensional assembly into transient micro-filaments. The material is based on 9.4 nm iron oxide nanoparticles grafted with poly(N-n-propylacrylamide) via multiphosphonic acid anchoring sites. The hybrid nanoparticles present a low critical solution temperature (LCST) transition between 21 {\deg}C and 28 {\deg}C, depending on the pH and the ionic strength. When heated above the LCST in defined conditions, the nanoparticles ag-gregate and respond to an external magnetic field. An intrinsic characteristic of the thermorespon-sive particles is an asymmetric transition between cooling and heating cycles, that was favorably exploited to build one-dimensional permanent microstructures, such as magnetic microfilaments and cilia. In summary, we present the development of a nanoplatform responsive to multiple stimu-li, including temperature, magnetic field, pH and ionic strength and its transformation into magneti-cally active microfilaments that could find potential applications in remotely controlled devices.