5:15 PM - 6:30 PM
[SCG39-P17] Spontaneous extension of viscoelastic fluids confined between rotating parallel plates
Keywords:viscoelastic fluid, pattern formation, brittle ductile transition
Slow earthquakes are observed at a marginal region between seismogenic and steady sliding zones[1]. Subducting plate at a boundary can be recognized as brittle elastic solids and viscous liquids in the seismogenic and steady sliding zones, respectively. Therefore, the viscoelastic behavior of subducting plate, especially macroscopic spatio-temporal patterns, should be explored to understand slow earthquakes. To observe these behaviors in accessible time and space, we make an analog experimental system using viscoelastic fluids with shorter viscoelastic relaxation time. Here, we continuously sheared a brittle viscoelastic fluid using rotating parallel plates.
The sample, an analog for a rock, was a physical gel. It was made of thermodynamically stable oil-in-water microemulsion bridged by telechelic polymers. The microemulsion was decane droplet dispersed in 0.2 mol/L NaCl aqueous phase with cetylpyridinium chloride and octanol. Telechelic polymer was polyethylene glycol distearate, and its concentration was varied as a parameter[2]. In short, increasing the conectivity of telechelic polymer r leads to longer viscoelastic relaxation time.
The sample was introduced at the central part of parallel circular plates whose gap was h, and the bottom plate was rotated with fixed angular velocity ω. The typical initial radius of a sample in the cell was R0. The sample showed viscous flow at low ω, as seen in the case of ordinary liquids. However, when ω exceeds critical values determined byω~ h/R0τ, the crack formation was observed in the sample. Furthermore, the sample starts to extend branches in the radial direction while their width continuously becomes smaller until the width reaches a steady value scaled with h. We anticipate this spontaneous extension of viscoelastic fluids is due to the first normal stress difference. To confirm this hypothesis, we measured the branch extension speed and took its statistics.
[1] K. Obara, A. Kato, Science 353, 253-257 (2016).
[2] M. Filali and J. Appell, J. Phys. Chem. B 103, 7293-7301 (1999).
The sample, an analog for a rock, was a physical gel. It was made of thermodynamically stable oil-in-water microemulsion bridged by telechelic polymers. The microemulsion was decane droplet dispersed in 0.2 mol/L NaCl aqueous phase with cetylpyridinium chloride and octanol. Telechelic polymer was polyethylene glycol distearate, and its concentration was varied as a parameter[2]. In short, increasing the conectivity of telechelic polymer r leads to longer viscoelastic relaxation time.
The sample was introduced at the central part of parallel circular plates whose gap was h, and the bottom plate was rotated with fixed angular velocity ω. The typical initial radius of a sample in the cell was R0. The sample showed viscous flow at low ω, as seen in the case of ordinary liquids. However, when ω exceeds critical values determined byω~ h/R0τ, the crack formation was observed in the sample. Furthermore, the sample starts to extend branches in the radial direction while their width continuously becomes smaller until the width reaches a steady value scaled with h. We anticipate this spontaneous extension of viscoelastic fluids is due to the first normal stress difference. To confirm this hypothesis, we measured the branch extension speed and took its statistics.
[1] K. Obara, A. Kato, Science 353, 253-257 (2016).
[2] M. Filali and J. Appell, J. Phys. Chem. B 103, 7293-7301 (1999).