Phase Behavior of Poly(N-isopropylacrylamide) Nanogel dispersions: Temperature Dependent Particle Size and Interactions

TL;DR

This study investigates how poly(N-isopropylacrylamide) nanogel particles change size and phase behavior with temperature, revealing a volume phase transition, crystallization, and fluid transitions using light scattering techniques.

Contribution

It provides detailed temperature-dependent particle size data and phase transition insights for poly(N-isopropylacrylamide) nanogels, including crystallization and fluid transitions.

Findings

Particle size decreases from 273 nm to 114 nm between 25°C and 40°C

Volume phase transition occurs at 32.4°C with particle collapse

Crystallization and fluid transitions observed at 26.2°C and 31°C

Abstract

The phase behavior of poly (N-isopropylacrylamide) nanoparticles dispersed in aqueous medium is investigated as a function of temperature using static and dynamic light scattering techniques. The diameter, d of the particles, as determined by dynamic light scattering measurements on dilute dispersion showed a decrease in size from 273 nm at 25C to 114 nm at 40C as function of temperature with a sudden collapse of particle volume (volume phase transition) at 32.4C. Further this nanoparticle dispersion is found to turn turbid beyond volume phase transition. Static light scattering measurements on samples with intermediate concentration and high concentration showed liquid-like order and crystalline order respectively. The intensity of the Bragg peak of the crystallized sample when monitored as a function of temperature showed crystal to liquid transition at 26.2C and a fluid to fluid transition at 31C. The occurrence of melting at a volume fraction of 0.85 and the absence of change in number density across the fluid-to-fluid transition suggest that interparticle interaction is repulsive soft-sphere below the volume phase transition. The reported results on the phase behavior of poly(N-isopropylacrylamide) nanogel suspensions are discussed in the light of the present results.