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Development of a confocal rheometer for soft and biological materials
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View: Figures


Image of FIG. 1.
FIG. 1.

Photograph of the confocal rheometer. The base plate of an Anton Paar MCR301 rheometer is replaced with a metal cup. Optical access for a Leica SP5 confocal microscope is provided by a glass coverslip mounted in the cup, which serves as the rheometer bottom plate. The field of view of the microscope can be changed by moving the rheometer on a manual three-axis translation stage. The inset shows the device that clamps the cup to the microscope stand to reduce vibrations.

Image of FIG. 2.
FIG. 2.

Cut-away drawings of the (a) confocal rheometer assembly (including the microscope objective, metal cup that mounts to the rheometer, glass coverslip, and rheometer tool) and (b) the baseplate at the bottom of the cup. (c) Magnified cross section of the sample region.

Image of FIG. 3.
FIG. 3.

Radial position calibration. The measured linear shear velocity (symbols) of the rheometer tool displays the expected linear dependence (solid line) on the position of the rheometer stage.

Image of FIG. 4.
FIG. 4.

Polymerization of collagen. (a)–(c) The images show snapshots in the -plane of a sample during polymerization; the scale bar indicates 30 μm. (d) The storage (squares) and loss (circles) moduli both plateau as the gel is formed. The arrows indicate the times at which the images were acquired.

Image of FIG. 5.
FIG. 5.

Flow properties of two fluids. (a) Rheological flow curves for honey (circles) and a compressed emulsion (squares) show Newtonian and Herschel-Bulkley behavior, respectively. The -dependent flow profiles for (b) honey and (c) the emulsion have a very different dependence on the shear rate; here, the average shear velocity (normalized by the local tool speed ) is plotted for local shear rates of 10 (squares), 1 (triangles), and 10 (circles) 1/s. The images inset in (b) show an example of the analysis used to extract for the fastest rate.

Image of FIG. 6.
FIG. 6.

Focal shift measurements. The ratio Δ between changes in the position of the focal plane and the objective increases roughly linearly with the index of refraction of the sample being imaged. Measurements are shown for two objectives which use oil (solid circles) and water (open circles) as the immersion fluid.

Image of FIG. 7.
FIG. 7.

Sample loading. The (a) normal force and (b) coverslip deflection were monitored while a compressed emulsion was loaded under the different conditions described in the text. In the main plots, the gap decreases with time to a final value of 100 μm. The insets show the relaxation of the coverslip when the tool was rotated after loading, as a function of time .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Development of a confocal rheometer for soft and biological materials