Nucleation and growth of thermoreversible polymer gels.

We study the spatiotemporal low-frequency microrheology of a gelatin gel during the sol-gel transition after a fast temperature quench by tracking the motion of embedded colloidal particles. From the particle dynamics two different mechanisms responsible for the gelation of the sol phase can be identified: a fast process associated to the local nucleation of triple helices and a slow fiber growth triggered by presence of an intact network. We associate the latter to a gelation front propagating into the sol phase whose speed depends linearly on the quench depth and which accelerates the local rate of the sol-gel transition.