Dynamic light scattering study on a bimodal end-linked polydimethylsiloxane network structure

The cooperative diffusion coefficient D_coop and the normalized variance μ₂ \ ̄qG^-2 for bimodal end-linked polydimethylsiloxane (PDMS) networks were determined by means of dynamic light scattering (DLS) measurements. D_coop was proportional to polymer weight concentration at the equilibrium state of swelling C_e to the power of 0.88, which was larger than the theoretical exponent, compared with the unimodal PDMS networks. Further, the value of μ₂ \ ̄qG^-2 at the lowest C_e was greater than that of the corresponding bimodal PDMS solutions in the semidilute regime, and the autocorrelation function of DLS could be reproduced by a double-exponential fitting. These facts suggested a spatially and compositionally heterogeneous structure of bimodal PDMS networks, especially in the case of the lowest C_e.