Polymer liquids fracture like solids

Abstract

While fracture in brittle solids has been studied for centuries until today, there are few studies on fracture in polymer liquids. Recent developments in experimental techniques, especially the combination of controlled filament stretching rheometry and high speed imaging, have opened new windows into the detailed study of fracture processes for polymer liquids. High speed imaging shows that polymer liquids fracture like solids with initiation and propagation of an edge fracture. However, remarkable features such as highly reproducible critical stress, independent appearance of multiple fractures, and trumpet crack profiles, reveal mechanisms which are significantly different from solids.

On the origin of brittle fracture of entangled polymer solutions and melts

“…It assumes that catastrophic failure occurs when the frictional force of an entangled chain can no longer balance the tension in the molecular chain and predicts failure by disentanglement of the polymer chains considering the recoverable proportion of the total strain. It should be noted that the failure model of Joshi and Denn [2,24,25] predicts an increasing strain to failure with increasing Weissenberg number in the viscoelastic and the rubbery failure zone, and is therefore not in agreement with the experimental data of Huang et al [21] and Huang and Hassager [22] for well characterized monodisperse PS solutions featuring a constant critical strain within the experimental range of 4 Wi R 100.…”

“…Progress on the experimental side has recently been made by the seminal work of Huang et al [21] and Huang and Hassager [22] on well characterized monodisperse polystyrenes (PSs) dispersed in oligomeric styrene (OS) via VADER 1000, Rheo Filament ApS, a commercially available filament stretching rheometer [23]. By measuring the local diameter of the polymer sample during elongation, the true Hencky strain and strain rate can be determined, while from the global deformation of the sample, only nominal values of strain and strain rate can be obtained.…”

“…By measuring the local diameter of the polymer sample during elongation, the true Hencky strain and strain rate can be determined, while from the global deformation of the sample, only nominal values of strain and strain rate can be obtained. Huang and Hassager showed [22] that when true Hencky strain rates are utilized rather than nominal Hencky rates, the four zones in the Malkin plot are reduced to just two states: liquid and solid, and a clear distinction exists between liquid (steady-state elongation) behavior and solid (fracture) behavior. For two monodisperse PS solutions (with 33% and 17% polymer volume fractions), they found that the value of the critical stress for rupture is between the plateau (G e ) modulus and the glassy (G 0 ) modulus, and at least 2 orders of magnitude higher than G e .…”

“…Based on Vinogradov and coworker's dataset [8][9][10][11][12][13][14], several research groups attempted to analyze and rheologically model the failure phenomenon in melts [2,5,[16][17][18][19][20][24][25][26][27]. However, those modeling attempts were based on the conceptual and schematic failure master curve produced by Malkin and Petrie [15] and derived from elongational measurements based on nominal Hencky strain rates, which was recently challenged by the Filament Stretching Rheometer's ability to measure the true Hencky rate [21,22] as discussed earlier. The scaling theory of Joshi and Denn [2,24,25] demonstrated impressive qualitative agreement with the narrowdistribution polyisoprene failure data of Vinogradov's team within about 50% uncertainty in the reptation time [2].…”

Dynamics of viscoelastic filaments based on Onsager principle

“…These flow properties have found many industrial applications such as fiber spinning, film blowing, and jet printing [3]. One particular phenomenon that has been studied extensively is the necking and breakup of viscoelastic fluids under extensional flow [4][5][6][7]. A filament of Newtonian fluid is unstable due to Plateau-Rayleigh instability, and the fluid column rapidly separates into droplets [8].…”