Extension of elastic liquids: Polyisobutylene

Abstract

An apparatus is described and a method discussed for determining the rheological characteristics of elastic liquids during extension at constant rates of deformation and extension. The material studied was polyisobutylene of molecular weight 7 × 104. At low constant deformation rates steady‐flow regimes were achieved, with corresponding equilibrium high elastic strains. A detailed study has been made of the process of attainment of steady‐flow regimes and it is shown that before steady flow is reached the curve of longitudinal viscosity versus strain passes through a maximum. As the rate of deformation rises, the strains at which steady–state flow regimes are achieved increase, and the time required to reach these regimes decreases. Qualitatively this occurs in the same way as upon shear. The dependence of equilibrium high‐elastic strains (under steady‐flow regimes) on the rate of deformation has been determined. At steady‐flow regimes the stress depends linearly on the rate of deformation at low values of the stress. Under such conditions Trouton's formula is valid. At constant rates of extension the stress versus time curve passes through a maximum which becomes higher with increasing extension rates.

One hundred years of extensional flow

“…Early work on polymer melts was carried out by Ballman at Monsanto [100], Meissner at BASF [101,36] and Cogswell at ICI [102,58]. The exception to this industrial base for extensional rheometry is the work of Vinogradov in the Soviet Union [103]; many Soviet results were collected in the book [104] and it is a mark of the rapid progress in extensional flow around 1977-78 that the English translation of this book [105] is significantly different from the Russian original. This period is reviewed in more detail in the author's book [5].…”

Towards a universal shear correction factor in filament stretching rheometry

“…To overcome the above-mentioned challenges, several improvements of the original filament stretching rheometers have been done. Different modifications of the pistons were implemented to reduce the deviations of uniaxial extension at the solid-liquid contact region, including fixing the sample with epoxy resin (Münstedt 1975), using grippers (Vinogradov et al 1970) and designing plates that dynamically change their diameter while the extensional test is ongoing (Berg et al 1994). By doing interrupted stretch experiments, it was also noticed that the error introduced by the non-homogeneous deformation at the end plates depends on the initial aspect ratio.…”

The Fluctuon States of Electrons in Disordered Systems

“…Experimental techniques include the constant strain rate (Ballman 1965, Meissner 1969, 1971, 1972, Vinogradov et al 1970) and the constant stress (Cogswell 1968, Meissner 1972) methods. However, in all these experiments the work has been concerned with polymer melts whose shear viscosities have rarely fallen below 104 N s m-2.…”