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Creep and flow of glasses: strain response linked to the spatial distribution of dynamical heterogeneities.

Sentjabrskaja T, Chaudhuri P, Hermes M, Poon WC, Horbach J, Egelhaaf SU, Laurati M - Sci Rep (2015)

Bottom Line: We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow.These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions.Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

View Article: PubMed Central - PubMed

Affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, Universitätsstr. 1, 40225 Düsseldorf, Germany.

ABSTRACT
Mechanical properties are of central importance to materials sciences, in particular if they depend on external stimuli. Here we investigate the rheological response of amorphous solids, namely colloidal glasses, to external forces. Using confocal microscopy and computer simulations, we establish a quantitative link between the macroscopic creep response and the microscopic single-particle dynamics. We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow. These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions. Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

No MeSH data available.


Related in: MedlinePlus

Maps of average particle mobilities μlm(t) within boxes lm (Eq. (1)) for (top) stress σ ≈ σy and (bottom) σ ≈ 5σy and times  (a–f, indicated in Fig. 1c by dashed lines) as observed in experiments. The box size is (2.8 dL)2.
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f5: Maps of average particle mobilities μlm(t) within boxes lm (Eq. (1)) for (top) stress σ ≈ σy and (bottom) σ ≈ 5σy and times (a–f, indicated in Fig. 1c by dashed lines) as observed in experiments. The box size is (2.8 dL)2.

Mentions: To investigate the existence of heterogeneity in the dynamical activity, we consider the spatial distribution of active boxes. For σ ≈ σy , the distribution of local mobilities within the velocity-vorticity plane does not indicate any prominent features (Fig. 5, top). At any specific time, there are some active boxes with larger mobilities, but the locations of the boxes with the largest mobilities vary randomly with time. For σ ≈ 5σy, similar mobilities occur at short times, when the localisation plateau in the MSD is observed (Fig. 5a,b, bottom). In contrast, at , roughly coincident with the onset of super-diffusion in the MSDs determined for tw = 0 (Fig. 1c), a region with enhanced mobilities emerges (Fig. 5c,d, bottom), expands with time (Fig. 5e, bottom) and spans almost the whole field of view once the system flows (Fig. 5f, bottom). Hence, the onset of flow (Fig. 1a,b) coincides with the appearance of a region of higher local mobility (Fig. 5) and super-diffusive dynamics (Fig. 1c,d). Furthermore, it leads to the pronounced non-Gaussian tails in the van Hove correlation function at intermediate times (Fig. 3), which disappear once steady flow has developed and the dynamics again becomes more homogeneous (Fig. 3, inset).


Creep and flow of glasses: strain response linked to the spatial distribution of dynamical heterogeneities.

Sentjabrskaja T, Chaudhuri P, Hermes M, Poon WC, Horbach J, Egelhaaf SU, Laurati M - Sci Rep (2015)

Maps of average particle mobilities μlm(t) within boxes lm (Eq. (1)) for (top) stress σ ≈ σy and (bottom) σ ≈ 5σy and times  (a–f, indicated in Fig. 1c by dashed lines) as observed in experiments. The box size is (2.8 dL)2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495392&req=5

f5: Maps of average particle mobilities μlm(t) within boxes lm (Eq. (1)) for (top) stress σ ≈ σy and (bottom) σ ≈ 5σy and times (a–f, indicated in Fig. 1c by dashed lines) as observed in experiments. The box size is (2.8 dL)2.
Mentions: To investigate the existence of heterogeneity in the dynamical activity, we consider the spatial distribution of active boxes. For σ ≈ σy , the distribution of local mobilities within the velocity-vorticity plane does not indicate any prominent features (Fig. 5, top). At any specific time, there are some active boxes with larger mobilities, but the locations of the boxes with the largest mobilities vary randomly with time. For σ ≈ 5σy, similar mobilities occur at short times, when the localisation plateau in the MSD is observed (Fig. 5a,b, bottom). In contrast, at , roughly coincident with the onset of super-diffusion in the MSDs determined for tw = 0 (Fig. 1c), a region with enhanced mobilities emerges (Fig. 5c,d, bottom), expands with time (Fig. 5e, bottom) and spans almost the whole field of view once the system flows (Fig. 5f, bottom). Hence, the onset of flow (Fig. 1a,b) coincides with the appearance of a region of higher local mobility (Fig. 5) and super-diffusive dynamics (Fig. 1c,d). Furthermore, it leads to the pronounced non-Gaussian tails in the van Hove correlation function at intermediate times (Fig. 3), which disappear once steady flow has developed and the dynamics again becomes more homogeneous (Fig. 3, inset).

Bottom Line: We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow.These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions.Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

View Article: PubMed Central - PubMed

Affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, Universitätsstr. 1, 40225 Düsseldorf, Germany.

ABSTRACT
Mechanical properties are of central importance to materials sciences, in particular if they depend on external stimuli. Here we investigate the rheological response of amorphous solids, namely colloidal glasses, to external forces. Using confocal microscopy and computer simulations, we establish a quantitative link between the macroscopic creep response and the microscopic single-particle dynamics. We observe dynamical heterogeneities, namely regions of enhanced mobility, which remain localized in the creep regime, but grow for applied stresses leading to steady flow. These different behaviors are also reflected in the average particle dynamics, quantified by the mean squared displacement of the individual particles, and the fraction of active regions. Both microscopic quantities are found to be proportional to the macroscopic strain, despite the non-equilibrium and non-linear conditions during creep and the transient regime prior to steady flow.

No MeSH data available.


Related in: MedlinePlus