Tuning the Thermodynamic, Optical, and Rheological Properties of Thermoresponsive Polymer Solutions via Silica Nanoparticle Shape and Concentration

Authors

Christopher A P Neal
Valeria León
Michelle C Quan
Nondumiso O Chibambo
Michelle A Calabrese

Publication Date

1-1-2023

Journal

Journal of Colloid and Interface Science

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.

Keywords

Poly(N-isopropyl acrylamide), Lower critical solution temperature, Silica nanospheres/nanorods, Differential scanning calorimetry, Rheology, Hydrogel, Turbidimetry, Fourier-transform infrared spectroscopy

Comments

Supplementary Materials

PMID: 36202031