Unusual Rheological Properties of Lightly Crosslinked Polydimethylsiloxane

Abstract

The rheological behavior of elastomers of polydimethylsiloxane vinyl‐terminated has been investigated in both rotational and oscillating modes. Partially crosslinked liquid rubbers have been prepared, varying the curing agent‐to‐elastomer weight ratio p. Viscoelastic fluids with unusual rheological properties have been obtained. For small p, zero‐shear viscosity and storage dynamic modulus G′(ω) at low frequencies are obtained, lower than those of reference liquid elastomers. Outcomes are discussed according to the polymer tube model theory and an extension at nanoscale of the Einstein equation of viscosity proposed. The unentangled crosslinked nanodomain model has been proposed. At light networking, isolated crosslinked nanodomains would form and the longer chains will be preferentially bonded. This will determine a decrease in the entanglement density in the matrix. On the nanodomain surface the dangling chains will not be long enough to give stable entanglements, determining the formation of a free volume at the interface polymer matrix‐nanoparticles.

Multiple actions of poly(ethylene octene) grafted with glycidyl methacrylate on the performance of poly(lactic acid)

“…The lower the u at the mechanical loss peak, the relaxation time the longer was. 42 Aer the addition of POE-g-GMA, the tan d of PLA/POE-g-GMA blends were lower than that of pure PLA, indicating that the elastic response became fast, the viscous dissipation decreased gradually and thus the foamability was heightened. 43 This could be attributed to the fact that the number of entanglements between PLA molecular chains was enhanced by the formation of branching structures, which acted as physical network points to increase the melt elasticity of PLA/POE-g-GMA blends.…”

Entanglement Locking in the Unique Elasticity of Polydimethylsiloxane Rubbers

“…Liquid silicone rubbers at Low‐(L) and Medium‐viscosity (M), as defined in the previous papers, [ 9,11 ] have been considered; Low/Medium homologous rubber blends (L/M) at different L/M ratio have been prepared and cured by means of the medium component crosslinker at 30 °C for at least 3 d in a molding scaffold.…”

“…Sylgard liquid silicone rubbers (Dow Corning) were used. The low‐viscous liquid elastomer LE‐(L) showed a zero‐shear viscosity η 0 = 4.5 P; the medium LE‐(M) η 0 = 51 P. In the previous paper, [ 9 ] number average molecular weights were estimated of M n (LE‐(L)) = 15 300 unified atomic mass unit and M n (LE‐(M)) = 43 100. Then, for low LE‐(L) M n < M c ( M c = 21 000 − 33 000 is the critical molecular weight for the PDMS entangled chain), so LE‐(L) is an unentangled liquid prepolymer with n = 113 and the end‐to‐end distance D ee = 12.2 nm; conversely, LE‐(M) is in entangled state with n = 309 and D ee = 20.3 nm.…”

“…[ 8 ] Some of our recent articles related to this work are placed in this theoretical framework. [ 9,10 ] In our previous article, [ 9 ] it was demonstrated that the polymer melts of high molecular weight PDMS lightly crosslinked (to weight concentrations of crosslinker <10 −3 ) exhibit an anomalous reduction of zero‐shear rate viscosity η 0 and a drop of rheological properties. This was interpreted by means of the Nanointerface Slipping model, which proposes the formation of isolated crosslinked nanodomains with an entanglement free interface due to too short dangling chains; in this way, an unentangled interface volume V free with only viscous effects (slip‐condition) is realized.…”

“…This was interpreted by means of the Nanointerface Slipping model, which proposes the formation of isolated crosslinked nanodomains with an entanglement free interface due to too short dangling chains; in this way, an unentangled interface volume V free with only viscous effects (slip‐condition) is realized. We conjectured an Einstein–Batchelor modified equation [ 9,11 ] in order to take into account the decrease in zero‐shear rate viscosity for the nanosuspensions.…”