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.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/macp.201900497. * η for the nanosuspensions.In the following article, [10] the authors demonstrated that a homologous liquid blend based on short and long PDMS chains behaves as if long chains moved within rigid tubes in which the entanglement sites were stabilized by the adsorption of the short chains on entanglement site (Entanglement Locking model). In contrast, the pure component based on long PDMS chains follows the expected tube dilation model. In the present work the entanglement locking model for polymer melt will be extended to the rubber network.The rubber elasticity theory was developed starting from the phantom-chain model of the pioneering works of James and Guth, [12,13] to the Flory random-coil model [14,15] in which the crosslinked active chains are considered isolated. In the Allegra and Ronca [16] and Flory [17] models, the phantom chains network presents the crosslink bound by a harmonic potential in order to take into account the entanglement constraints on the active chains. Therefore, Edwards [18] applied the ideas of the tube model to the rubber network: the crosslinked chains The viscoelasticity behavior of the polydimethylsiloxane (PDMS) rubber blends of high molecular weight polymers modified by low molecular weight agents is studied in compression mode by stress-strain curves, the creep and step-strain, and dynamic-mechanical experiments. The strain spectra highlight the dynamics of active chains at high frequencies and of dangling ends in the low frequencies field. At low deformation, the blending agent enhances the elastic properties by increasing the density of the active chains in the rubber network, in agreement with the classical theories of elasticity. At high deformation, in analogy with the rheological studies on similar liquid blends, the Entanglement Locking model is proposed: the short chains of the blending agent are adsorbed on entanglement sites of long dangling chains, giving effective crosslinks via high entropy dynamics. In this way, the longterm entanglement locking enhances the density of active chains and elastic behavior. At high deformation, the entanglement locking model enriches the rubber elasticity theories according to the tube network model and Mooney-Rivlin equation. The models herein and the possibility they offer for improving rubber viscoelasticity are valuable for the development of polymer physics and technology.

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The rheological behaviour of polydimethylsiloxane (PDMS) liquid blends has been investigated both in rotational and oscillating mode. Liquid silicone rubbers based on PDMS at low, medium, and high viscosity have been used for low/high or medium/high liquid blends. The flow, viscosity, creep, and stress‐relaxation curves, strain‐spectra of temperature‐ or frequency‐sweep have been determined and the behaviour at slow shear rate investigated in detail. The low/high homologous blend shows an unexpected behaviour: the zero‐shear viscosity η0 is higher, the compliance J 0 lower and viscoelastic moduli G 0, G(t), G′(ω) and G″(ω) higher, with respect to the components and medium/high blend. Moreover, the blend viscosity η(T), G′(T), and G″(T) exhibits an anomalous decreasing trend. The Entanglement Swelling Tube (EST) model is proposed. The nanosized chains swelled the entanglement of the long ones by means of dipolar interactions Si δ +–O δ − in the sites between the blobs of the tube chains, where the free‐volume is highest. The linked entanglements are stabilized and the lifetime lengthened; the entanglement density increases at long deformation times. As the temperature rises, the anomalous behaviour is reduced due to the Entanglement Deswelling‐Solvation mechanism of short chains up to the transition to ordinary behaviour for T = 65 °C.

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