Critical viscoelastic behavior of polydimethylsiloxane networks around the sol-gel threshold

Abstract

Seven model polydimethylsiloxane (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with a SiH-containing cross-linker. Viscoelastic experiments, completed by size exclusion chromatography and static light scattering experiments, were performed in order to study the influence of molecular parameters on the dynamic properties around the sol-gel threshold. The dynamic critical parameter u was determined from experiments close to and above the sol-gel threshold. Our results show that the growth mechanism of PDMS clusters and the viscoelastic behavior are a function of the ratio NN_{e} , where N and N_{e} are, respectively, the numbers of Kuhn monomers between branch points and between entanglements. For NN_{e}<1 , the growth mechanism of clusters is the critical percolation and u=0.69 , and for NN_{e}>1 , the growth mechanim of clusters is the diffusion-limited cluster aggregation and u=0.76 .

Similarity in Linear Viscoelastic Behaviors of Network Formation and Degradation Processes

“…There have been many attempts to reveal and control the physical properties during gelation and degradation processes. In the fi eld of polymer rheology, the gelation process is one of the essential topics; not only the gelation point but also the critical behaviors observed near the gelation point are of great interest [5][6][7][8][9][10][11][12] . In the pioneering works by Winter et al, the gelation point was determined as a critical point where the viscosity diverges to infi nity using the dynamic viscoelastic measurement [13][14][15][16][17][18][19] .…”