Critical regimes of oscillatory deformation of polymeric systems above glass transition and melting temperatures

Abstract

SynopsisHigh molecular weight linear polymers and their concentrated solutions were investigated over a wide range of frequencies and amplitudes of oscillatory deformation. At definite critical deformation and stress amplitudes, the resistance to deformation drops abruptly as a result of the rupture of continuity of polymer specimens in the region of action of the highest shear stresses. The lowest critical values of deformation rate amplitudes are inversely proportional to the initial viscosity and correspond quantitatively to the critical shear rates at which the spurt occurs during the flow of polymeric systems in ducts. The spurt effect is due to the transition of the polymer systems to the forced high-elastic state, in which they behave like quasi-cured polymers whose deformability is always limited. Up to the critical values of the stress amplitudes, narrow-distribution high molecular weight linear flexible-chain polymers behave like Hookean bodies, whereas the broad-distribution polymers show a sharply defined nonlinear behavior which asymptotically passes to a spurt. The amplitude dependence of the dynamic characteristics of the high molecular weight linear polymers, as well as their non-Newtonian behavior, is due to polymolecularity. An increase in deformation amplitudes reduces the frequency at which the spurt, and hence the transition of the polymer systems to the high-elastic state, is observed. Therefore, under conditions of oscillatory deformation the physical state (fluid or high-elastic) is determined not only by the frequency but also by the value of deformation. In the high-elastic state region (estimated at low amplitude deformation), the critical deformation amplitude is frequency independent and has an unambiguous relationship with the molecular mass of the chain ( M e ) between the entanglements. For the bulk polymers studied, the spurt in the high-elastic state occurs at stress amplitudes of the order of lo5 N/m2 irrespective of frequency, molecular mass, or polymolecularity. In concentrated polymer solutions, in the highelastic state the critical stress amplitudes decrease with reducing polymer content, whereas the critical deformation amplitudes increase.

Rheology of silica-filled polystyrene: From microcomposites to nanocomposites

“…At a high frequency (1 s -1 ) values of G' and G'' continuously decreases with the strain amplitude and then suddenly drop. This drop is appar ently caused by the detachment of the sample from the solid surface of the measuring device leading to an ap parent slip, as earlier observed for various polymers in the strain amplitude sweep [32]. The strain amplitude dependence of the PS/Minusil mixture is mainly due the particle particle interaction, while in the PS/Aerosil 90 mixtures is due to a desorption of the adsorbed chains from the filler surface.…”

Correlations in rheological behavior between large amplitude oscillatory shear and steady shear flow of silica‐filled star‐shaped styrene‐butadiene rubber compounds: Experiment and simulation

“…Through these studies, it was discovered that there exists a strong strain amplitude dependence of the dynamic moduli at low strain amplitudes in CB‐filled rubber vulcanizates (the Payne effect). With respect to polymer solutions, the earliest tests were performed by Philippoff, 21 Tsiprin et al, 64 and MacDonald et al 65 The first LAOS tests on polymer melts were performed by Tsiprin et al, 64 Faitel'son and Tsiprin, 66 MacDonald et al, 65 Vinogradov et al, 67–70 and Tee and Dealy 71 . With regards to filled polymers, the first tests were carried out by Faitel'son and Tsiprin 66 and Briedis et al 72 on melts and by Onogi et al 73 and Matsumoto et al 74 on solutions.…”

Steady State and Dynamic Oscillatory Shear Properties of Carbon Black Filled Elastomers

“…Previous study on many different polymers has shown that fracture of the sample in measuring device is typically accompanied by a decrease of stress amplitude at some critical strain amplitude. 32 However, the present study indicated that stress amplitude did not decrease with the increase of strain amplitude even at its highest value 33 This is a clear indication that the sample fracture did not occur in present experiments. In addition, the occurrence of the sample fracture in measuring device at critical strain amplitude was directly observed using polarization optical technique during LAOS study of various rubbers.…”