Abstract
Hypothesis: The shape and quantity of hydrophilic silica nanoparticles (NPs) can be used to tune the microstructure, rheology, and stability of phase-separating polymer solutions. In thermoresponsive polymer systems, silica nanospheres are well-studied whereas anisotropic NPs have little literature precedent. Here, we hypothesize that NP shape and concentration lower the onset of rheological and turbidimetric transitions of aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions. Experiments: Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), turbidimetry, and oscillatory rheology are utilized to examine interactions between NPs, PNIPAM, and water and to track changes in phase separation and rheological properties due to NP concentration and shape. Findings: NP addition reduces phase separation enthalpy due to PNIPAM-NP hydrogen bonding interactions, the degree to which depends on polymer content. While NP addition minorly impacts thermodynamic and optical properties, rheological transitions and associated rheological properties are dramatically altered with increasing temperature, and depend on NP quantity, shape, and polymer molecular weight. Thus NP content and shape can be used to finely tune transition temperatures and mechanical properties for applications in stimuli-responsive materials.
| Original language | English |
|---|---|
| Pages (from-to) | 878-895 |
| Number of pages | 18 |
| Journal | Journal of Colloid and Interface Science |
| Volume | 629 |
| DOIs | |
| State | Published - Jan 2023 |
Funding
Research reported in this publication was 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. The authors thank the Anton Paar VIP program for the rheometer used in this work. Research reported in this publication was 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. 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 would like to thank Benjamin Yeh of the Bhan research group at the University of Minnesota-Twin Cities for running BET measurements and analysis. Solid state NMR data was provided by the Minnesota NMR Center. Funding for NMR instrumentation was provided by the Office of the Vice President for Research, the Medical School, the College of Biological Science, NIH, NSF, and the Minnesota Medical Foundation.
Keywords
- Differential scanning calorimetry
- Fourier-transform infrared spectroscopy
- Hydrogel
- Lower critical solution temperature
- Poly(N-isopropyl acrylamide)
- Rheology
- Silica nanospheres/nanorods
- Turbidimetry