Temperature-Controlled Transitions Between Glass, Liquid and Gel States in Dense p-NIPA Suspensions
Original entry by Sagar Bhandari, APPHY 225 Fall 2010
Temperature-Controlled Transitions Between Glass, Liquid and Gel States in Dense p-NIPA Suspensions, G. Romeo, A. Fernandez-Nieves, H. M. Wyss, D. Acierno and D.A. Weitz, Advanced Materials
microgels, p-NIPA, glass, liquid, temperature-controlled, transitions
In this paper, the authors demonstrate that concentrated p-NIPA suspensions in a low-temperature glassy state can liquefy and then solidify again as the temperature is raised across the LCST. They use temperature- and pH-responsive particles made of p-NIPA. To measure the LCST of the particles, they perform differential scanning calorimetry (DSC) and find an endothermic peak.
To determine the temperature dependence of the particle volume, V ( T ), dynamic light scattering (DLS) is used while to determine the temperature dependence of the particle volume fraction, they measure the viscosity using an Ubbelohde tube. They find that the intrinsic volume fraction k ( T ) and V ( T ) display the same temperature dependence, as shown in Figure 1.
The characterization of the relaxation dynamics in the glassy, liquid, and gel phases is done by analyzing the frequency dependence of the viscoelastic moduli. At low temperatures, the linear elastic moduli shows a frequency independent plateau and viscous modulus shows a minimum at a particular frequency as shown in Figure 2 for three different temperatures.
The variation of the elastic plateau modulus is analyzed as a function of temperature around the LCST, as shown in Figure 3 for two different polymer concentrations. Close to the liquidlike state, elastic modulus does not show a plateau.