Polymer/clay nanocomposite hydrogels with anisotropic properties

Abstract

The use of magnetic fields has the potential to tailor the orientation and distribution of dispersed particles within polymer composites to create materials with anisotropic properties. However, limited literature exists on anisotropic nanocomposite hydrogels prepared under low magnetic fields, which are of interest for various soft and wet applications. This research reports polyacrylamide/montmorillonite-iron oxide (PAAm/MMT-IO), and poly(N-isopropylacrylamide)/MMT-IO (PNIPAM/MMT-IO) nanocomposite hydrogels prepared via low magnetic fields showing anisotropic mechanical properties. The magnetic field was studied as the parameter that produces anisotropy by controlling the orientation and distribution of the dispersed phase.

MMT-IO nanohybrids at a 2:1 clay to magnetite weight ratio showed suitable magnetic properties and surface characteristics to be used in the preparation of PAAm/MMT-IO and PNIPAM/MMT-IO nanocomposite hydrogels. These materials showed swelling ratios that depended on the nanohybrid content, porous morphology with nanohybrid particles distributed along the applied magnetic field and enhanced Young’s modulus, ultimate tensile strength, strain at break and toughness compared to pristine polymer hydrogel. The magnetic field was found to produce anisotropy, with superior mechanical properties along the direction of a 20 mT magnetic field produced by a couple of N35 Neodymium magnets and reduced properties on the transverse direction, compared to samples prepared in absence of a magnetic field. The Young’s modulus was estimated through the Halpin-Tsai and Mori-Tanaka micromechanical models, which had not been applied for this kind of materials.

The potential of PNIPAM/MMT-IO nanocomposite hydrogels was demonstrated through the design and fabrication of self-shaping multilayer structures that displayed complex deformations when subjected to a change in temperature due to their anisotropy and smart behaviour. The development of these anisotropic nanocomposite hydrogels could be useful in fields such as soft robotics and mechanobiology, where controlled deformations are desirable within a wet medium.

Thesis embargoed until 31.12.2026.

Date of Award	Dec 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	National Council of Science and Technology of Mexico
Supervisor	Biqiong Chen (Supervisor) & Brian Falzon (Supervisor)