General principles

Particle tracking microrheology may mean two different methods. One is single particle tracking technique, where the particle acts as a probe to investigate the rheology of the matrix. Another is general particle tracking microrheology where the ensemble of many particles itself is investigated. The particle tracking methods considered here involve the use of optical microscope. DWS which involve laser light scattering is not considered here. In DWS the MSD is not directly tracked but calculated from g₂(t)-1.

The detailed principles of optical and video microscopy were reviewed. Thierry Savin’s PhD dissertation (MIT, 2006) is a good source of information.

Microscope

An inverted microscope with fluorescent, live cell, time-lapse imaging, high-speed multi-fluorescence optical sectioning, polarization contrast and DIC, micromanipulation, etc. is favorable. Oil immersion objectives are required to correctly resolve Brownian colloidal particles.

• Leica DM IRB, now obsolete. Current suggestion: DMI4000 B — +86-20-87320225
• Olympus IX71 — 86-20-61227171
• Zeiss Axio Observer — 020-87755770*123 — RMB50万 13802758186

60X oil immersion type objective lens (Olympus, Japan) with numerical aperture of 1.40, while 500 nm probe particles were observed using 100X oil immersion type objective lens with numerical aperture of 1.42.

CCD/CMOS

Cooling reduces the array’s dark current, improving the sensitivity of the CCD to low light intensities, even for ultraviolet and visible wavelengths. Professional observatories often cool their detectors with liquid nitrogen to reduce the dark current, and therefore the thermal noise, to negligible levels. Magnification is characterized by nm per pixel. Generaly hundreds of nm per pixel can achieved, which yields spatial resolutions of tens of nm, well below the optical resolution of ~250 nm.

• Phantom v9, 20fps~500fps, 2e3 frames USD38000 — 13609003283谢先生
• ImageSource DMK 21AU04 — 上海英诚图像

Cells/Chambers

• Grace Bio-Labs CoverWell series

• Linkam CSS450 Optical Rheology Systems
• 安立佳2003年专利《便携式温控锥板剪切池》（CN200310115944.5）

Software

How to know which in the current frame is the particle in the last frame?

Calculation of: MSD, PDF

Routines here.

Aim: To aid the theoretical modeling of the rheological data.

Viscosity of PEO solutions

Used to calculate zeta-potentials.

Samples: PEG 35k aqueous solutions at c_p = 0, 0.063, 0.1, 0.25, 0.4, 0.63, 0.8, 1.0 wt%

Instrument: AR-G2

DLS and zeta-potential measurement

Procedure: yet to determine.

• Principles of zeta-potential measurement?

• http://goo.gl/aQVDU
• http://goo.gl/CQtD1
• http://goo.gl/HXNwJ
• How dilute must the samples be?
• Make sure everything is ready: filters, syringes, cuvettes, etc.

Samples: Neat Laponite suspension, Laponite/PEG suspension with PEG 35k of c_p = 0.063, 0.1, 0.25, 0.4, 0.63, 0.8, 1.0 wt%

Instrument: Malvern Zetasizer nano zs90

A full lest of rheometric investigation of Laponite/PEG suspension. Parts of the tasks have been submitted or published.

Observation during preshear

Comparison of different shear rates

Steady shear flow [math]\eta[/math] vs [math]\dot{\gamma}[/math]. Procedure: steady preshear at [math]\dot{\gamma}[/math] = 200 s^-1 for 200s, delay for 800s, steady state flow test.

Samples: L2S5, L2S5P35k0.1, 0.25, 0.63, 0.8, 1.0

Instrument: AR-G2

Comparison of different shear method: osc. vs cont.

Whether [math]\gamma_0\omega=\dot{\gamma}[/math], by checking the Cox-Merz rule

Sample: L2S5, L2S5P35k0.63

Instrument: AR-G2

Aging

Ageing under SAOS

Comparison of different preshear rates

Procedure: Steady preshear at [math]\dot{\gamma}[/math] = 1, 2.5, 6.3, 16, 40, 63, 160, 200 s^-1 for 200 s, oscillatory time sweep.

Samples: L2S5, L2S5P35k0.1, 0.25, 0.63, 0.8, 1.0

Instrument: AR-G2

Comparison of different preshear method: osc. vs cont.

Procedure: preshear at [math]\dot{\gamma}[/math] = 200 s^-1 or γ = 200 %, ω = 10 rad/s, for 200 s, oscillatory frequency sweep.

Samples: L2S5, L2S5P35k0.63

Instrument: AR-G2

Effect of PEG concentration

Submitted.

Time-resolved viscoelastic property

Procedure: steady preshear at [math]\dot{\gamma}[/math] = 200 s^-1 for 200 s, oscillatory time sweep at ω = 1, 1.6, 2.5, 4, 6.3, 10, 16, 25, 40, 63 rad/s for 400s.

Samples: L2S5P35k0.1, 0.25, 0.63, 0.8, 1.0

Instrument: AR-G2

Aging under LAOS

Procedure: steady preshear at [math]\dot{\gamma}[/math] = 200 s^-1 for 200 s, dynamic time sweep at ω = 6.283 rad/s and γ₀ = 1 ~ 25 %, focusing on the yielding strain amplitude region.

Samples: L2S5P35k0.063, 0.1, 0.25, 0.4, 0.63, 1.0

Instrument: ARES

Aged gel

Steady LAOS

Published.

Yielding under LAOS

References: PRL 2011, 106, 248303. Soft Matter 2010, 6, 3482.
Procedure: steady preshear at [math]\dot{\gamma}[/math] = 200 s^-1 for 200s, delay 800s, arbitrary waveshape test at ω = 6.283 rad/s and γ₀ = 10 ~ 100 % focusing on the yielding regime.

Samples: L2S5P35k0.1, 0.25, 0.4, 0.63, 0.8, 1.0

Instrument: ARES

Schedule