Phase behavior and rheology of attractive rod-like particles

Colloidal rods interacting with a temperature-dependant attraction are constructed by grafting the polymer poly(N-isopropylacrylamide) (PNIPAM) to the surface of the charged, semi-flexible filamentous fd virus. The phase diagram of fd-PNIPAM system becomes independent of ionic strength at high salt concentration and low temperature, i.e., the rods are sterically stabilized by the polymer. However, the network of rods undergoes a sol-gel transition as the temperature is raised. The viscoelastic moduli of fd and fd-PNIPAM suspensions are compared as a function of temperature, and the effect of ionic strength on the gelling behavior of fd-PNIPAM solution is measured. For all fluid-like and solid-like samples, the frequency-dependant linear viscoelastic moduli can be scaled onto universal master curves.