Colloidal Probes of PNIPAM-Grafted SiO₂ in Studying the Microrheology of Thermally Sensitive Microgel Suspensions

Abstract

The complex rheology and the phase behavior of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels have been investigated in both the swollen and collapsed states by using microrheology. To avoid the interactions between the tracer probes and the PNIPAM microgels, such as the adsorption or the depletion effect, the probes of silica (SiO2) particles have been grafted with PNIPAM chains (SiO2-PNIPAM) and characterized with Fourier transform infrared spectroscopy (FTIR). The successful preparation of SiO2-PNIPAM has also been proved by the investigation of the particle size and morphology with dynamic light scattering (DLS) and transmission electron microscope (TEM) below and beyond the phase transition temperature of PNIPAM. The microrheology of the PNIPAM microgel suspension has been investigated by using the prepared SiO2-PNIPAM particles as microrheological probes, and the results show that the diffusive coefficient of the probes in the swollen state is one-fifth of that in the collapsed state, and the viscosity of the PNIPAM microgel suspension in the swollen state is four times higher than that in the collapsed state, indicating SiO2-PNIPAM is a good probe in the microrheological study of PNIPAM microgel suspensions.

Thermoplastic Polyurethane-poly(N-isopropylacrylamide) Copolymer for Selective Uptake of Alcohol from Aqueous Solution

“…Two typical signals for amides were bands at 1647 cm −1 and 1535 cm −1 . The former was assigned to the stretching vibration of C=O, and the latter was assigned to the bending of N-H and the stretching of C-N [ 32 ]. The TPU spectrum exhibited vibrational peaks at 1730 and 1704 cm −1 , which were attributed to the free carbonyl and hydrogen-bonded carbonyl stretching vibrations, respectively.…”