Multiple particle tracking microrheology measured using bi-disperse probe diameters

Area of Science:

• Soft matter physics
• Materials science
• Physical chemistry

Background:

• Multiple particle tracking microrheology (MPT) is a key technique for rheological characterization.
• Traditional MPT using single particle sizes may not capture complex material behaviors.
• Material properties can be length scale dependent, necessitating probes of varying sizes.

Purpose of the Study:

• To develop and validate a bi-disperse MPT technique for enhanced material characterization.
• To simultaneously track and analyze two distinct particle populations within a single sample.
• To investigate the length scale dependent rheological properties of complex soft materials.

Main Methods:

• Simultaneous tracking of 0.5 and 2 μm probe particles within the same sample.
• Separation of particle populations using a brightness-based squared radius of gyration (Rg2).
• Validation using glycerol solutions and characterization of polymerizing gels and colloidal gels.

Main Results:

• Bi-disperse MPT measurements accurately predicted glycerol viscosity, aligning with literature values.
• Characterization of poly(ethylene glycol)-acrylate:poly(ethylene glycol)-dithiol gelation yielded consistent critical exponents and gelation times.
• Degradation of heterogeneous hydrogenated castor oil colloidal gel showed probe-size-dependent critical exponents, indicating probing of different structures.

Conclusions:

• Bi-disperse MPT offers a more comprehensive characterization of soft matter by probing multiple length scales simultaneously.
• The technique reveals length scale dependent structural and rheological heterogeneity in complex materials.
• This advanced MPT method enhances the understanding of diverse materials, from consumer products to biological systems.