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Abstract Although processing via external stimuli is a promising technique to tune the structure and properties of polymeric materials, the impact of magnetic fields on phase transitions in thermoresponsive polymer solutions is not well‐understood. As nanoparticle (NP) addition is also known to impact these thermodynamic and optical properties, synergistic effects from combining magnetic fields with NP incorporation provide a novel route for tuning material properties. Here, the thermodynamic, optical, and rheological properties of aqueous poly(N‐isopropyl acrylamide) (PNIPAM) solutions are examined in the presence of hydrophilic silica NPs and magnetic fields, individually and jointly, via Fourier‐transform infrared spectroscopy (FTIR), magneto‐turbidimetry, differential scanning calorimetry (DSC), and magneto‐rheology. While NPs and magnetic fields both reduce the phase separation energy barrier and lower optical transition temperatures by altering hydrogen bonding (H‐bonding), infrared spectra demonstrate that the mechanism by which these changes occur is distinct. Magnetic fields primarily alter solvent polarization while NPs provide PNIPAM–NP H‐bonding sites. Combining NP addition with field application uniquely alters the solution environment and results in field‐dependent rheological behavior that is unseen in polymer‐only solutions. These investigations provide fundamental understanding on the interplay of magnetic fields and NP addition on PNIPAM thermoresponsivity which can be harnessed for increasingly complex stimuli‐responsive materials.
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Resolving Optical and Catalytic Activities in Thermoresponsive Nanoparticles by Permanent Ligation with Temperature‐Sensitive Polymers
Abstract Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature‐sensitive polymer ligands. Strikingly, significant discrepancies in optical and catalytic properties of thermoresponsive noble‐metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM), in situ using a starlike block copolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises, plasmonic absorption of PNIPAM‐capped Au NPs red‐shifts with increased intensity in the absence of free linear PNIPAM, whereas a greater red‐shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably, the absence or addition of free linear PNIPAM also accounts for non‐monotonic or switchable on/off catalytic performance, respectively, of PNIPAM‐capped Au NPs.
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- PAR ID:
- 10115603
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 58
- Issue:
- 34
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 11910-11917
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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