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Physical aging and compressed exponential behaviors in a model soft colloidal system.
Qi Li1, Xiaoguang Peng, Gregory B McKenna
1Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409, USA. greg.mckenna@ttu.edu.
Soft Matter
|February 14, 2019
Summary
Diffusing wave spectroscopy (DWS) micro-rheology reveals length-scale dependent non-equilibrium dynamics in colloidal systems. Converting DWS data to mean square displacement (MSD) reconciles differences observed across geometries and scales.
Area of Science:
- Soft Matter Physics
- Colloidal Science
- Rheology
Background:
- Diffusing wave spectroscopy (DWS)-based micro-rheology probes system dynamics at various length scales using different optical geometries and sample thicknesses.
- Previous studies indicate DWS micro-rheology observes non-equilibrium behaviors differently from macro-rheology.
Purpose of the Study:
- To further explore non-equilibrium dynamics using DWS micro-rheology.
- To address the range of utility of DWS as a micro-rheological method.
- To investigate aging mechanisms in colloidal glasses.
Main Methods:
- Investigated a thermo-sensitive core-shell colloidal system during aging and in a metastable equilibrium state.
- Utilized temperature-jump induced volume fraction-jump experiments.
- Employed DWS in backscattering and transmission geometries to probe dynamics at different length scales.
Main Results:
- Observed significant differences in measured dynamics across geometries and length scales in the non-equilibrium state.
- Found compressed exponential relaxations for the autocorrelation function g2(t) at large length scales.
- Demonstrated that converting g2(t) to mean square displacement (MSD) diminished length-scale differences, showing diffusive behavior at long times.
Conclusions:
- Length-scale dependent observations in non-equilibrium dynamics question current interpretations in light scattering-based micro-rheology.
- Converting DWS data to MSD provides a more consistent view of colloidal system dynamics.
- Offers a broader perspective for interrogating aging mechanisms in colloidal glasses beyond traditional g2(t) measurements.
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