Local and Global Dynamics of Transient Polymer Networks and Swollen Gels Anchored on Solid Surfaces

We employ fluorescence correlation spectroscopy to study length dependent dynamics in transient and grafted cross-linked poly( N -isopropylacrylamide) (PNIPAAm) networks at different concentrations and cross-link densities, respectively. For nondilute PNIPAAm solutions, the molecular diffusants appear to sense local dynamics on the length scale of the mesh size obtained from photon correlation spectroscopy, whereas a polymer probe, comparable to the PNIPAAm size, reveals global chain motions. The relation of the tracer Brownian diffusion to the mesh size can be utilized to characterize permanently cross-linked and grafted PNIPAAm networks.