Cone and plate rheometer
Falling ball and rising bubble viscosimeters
Bubble rise in complex fluids
Creep of ice
Size limitations in viscosity measurements
There was a question in class on the lower limit of samples where rheological properties may be measured. The Suhling lab at King's College recently announced in JACS that they can observe the viscosity in human ovarian carcinoma cell line SK-OV-3 using a fluorescent probe called a molecular rotor. Essentially, in a medium of high viscosity, the rotational Brownian motion of the the rotor as a whole is slowed down. This slowing increases linearly and can be used to accurately determine the viscosity of the cytoplasm of a cell. Their technique uses fluorescence lifetime imaging, and allows them to analyze fluorescent decays as a function of viscosity in spatially resolved manner; this can show valuable information on the inhomogeneity of the intracellular viscosity.
The case for measuring intracellular viscosity is made in their introduction, reproduced below:
"Viscosity is one of the major parameters determining the diffusion rate of species in condensed media. In biosystems, changes in viscosity have been linked to disease and malfunction at the cellular level.1 These perturbations are caused by changes in mobility of chemicals within the cell, inﬂuencing fundamental processes such as signaling and transport and the efﬁciency of bimolecular processes governed by diffusion of short-lived intermediates, such as the diffusion of reactive oxygen species during an oxidative stress attack. While methods to measure the bulk macroscopic viscosity are well developed, imaging local microscopic viscosity remains a challenge, and viscosity maps of microscopic objects, such as single cells, are actively sought after.2–6 We report a new approach to image local microviscosity using the ﬂuorescence lifetime of a molecular rotor.literature data for similar compounds."