Magnetic Field Influence on Phase Transition and Hydrogel Properties in Thermoresponsive PNIPAM: Mechanistic Insights
ORAL
Abstract
Recently, diamagnetic polymer solutions comprised of poly(ethylene oxide) and poly(propylene oxide) were shown to order under the influence of magnetic (B) fields, driven by changes in polymer-solvent hydrogen bonds. Nevertheless, the influence of B fields on polymer solutions that lack structural ordering remains poorly understood. This work elucidates the impact of B fields on the phase transition of aqueous poly(N-isopropyl acrylamide) (PNIPAM) and the properties of resulting disordered physical hydrogels commonly used for tissue engineering, controlled drug delivery, and self-healing materials. Specifically, in semi-dilute (5-15% wt.) PNIPAM solutions, B fields weaken the physical hydrogel network by impacting the interactions between PNIPAM-rich aggregates. This magnetic weakening is probed through magnetorheological temperature ramps, allowing for the simultaneous acquisition of rheological behavior while applying various strengths of B fields. Further, B effects on hydrogel strength are contingent upon both the duration of magnetization and the volume of the sample, as longer time and lower volume maximize magnetic effects. This study proposes changes in the mechanism underlying PNIPAM gelation under the influence of B fields, shedding light on the fundamental interactions between B fields and diamagnetic polymer solutions
*This research was also partially supported by the Office of the Vice President of Research, College of Science and Engineering, and the Department of Chemistry at the University of Minnesota. Research reported in this publication was supported by the Office of the Director, National Institutes of Health, [Award Number S10OD011952]; the content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was supported partially by the Partnership for Research and Education in Materials (PREM) Program of the National Science Foundation under Award Number DMR-2122178, and through the University of Minnesota MRSEC under Award Number DMR-2011401. The authors thank the Anton Paar VIP program for the rheometer and new tooling used in this work.
–
Publication:C. A. P. Neal et al., Rheo Acta, [Manuscript in preparation].
