Tracer diffusion

Semidilute solutions and networks a b s t r a c t The dynamics of fluorescently labeled linear macromolecules and spherical particles that are enclosed in semidilute polymer matrixes was studied by fluorescence recovery after photobleaching. The experi-ments were designed such that the transition from a semidilute solution to a permanent network could be covered. This was achieved by employing a matrix polymer, polyacrylamide, carrying pendant dimethylmaleimide groups. Stepwise irradiation of such samples in the presence of a triplet sensitizer causes successive dimerization of the maleimides leading to progressive crosslinking. Studies were performed with varying concentrations of matrix polymer (20–80 g L1) as well as different molar masses (200,000–1,300,000 gmol1) and particle radii (17 and 36 nm) of enclosed labeled probes. Results show notable differences between the behavior of linear and spherical tracers: while the mobility of flexible linear chains remains nearly unaffected by the transition from a semidilute polymer solution into a chemically crosslinked network, spherical tracers get completely immobilized when the degree of crosslinking exceeds a certain threshold. 2008 Elsevier Ltd. All rights reserved. 1