Stirring supercooled colloidal liquids at the particle scale.

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Rheology

Background:

• Understanding colloidal suspensions near the glass transition is crucial for materials science.
• Local disturbances provide insights into the dynamic response of dense colloidal systems.
• Superparamagnetic particle dimers offer a controllable method to induce local perturbations.

Purpose of the Study:

• To investigate the decay of tangential velocity profiles in hard-sphere colloidal suspensions.
• To characterize the system's response to a rotating magnetic dimer as the colloidal glass transition is approached.
• To analyze the effect of particle density on velocity profile decay and particle slip.

Main Methods:

• Utilizing confocal microscopy to track individual particle dynamics.
• Generating a local disturbance with a rotating superparamagnetic particle dimer.
• Fitting tangential velocity profiles to an exponential decay model.
• Quantifying particle slip against the rotating disturbance.

Main Results:

• Tangential velocity profiles exhibit an approximately exponential decay with distance from the disturbance.
• The characteristic length scale of velocity decay increases with particle density, approaching the glass transition.
• Colloidal particles demonstrate slip against the dimer, with slip decreasing as the system nears the glass transition.

Conclusions:

• The study reveals how local flow fields evolve in dense colloidal systems near the glass transition.
• Increased density significantly impacts the spatial extent of velocity decay and particle-ளின் mobility.
• These findings contribute to a deeper understanding of non-equilibrium dynamics in glassy soft matter.