Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: An Optical Microscope for the Study of Biopolymer Solutions under Shear Field

Authors
item Kim, Sanghoon
item Willett, Julious

Submitted to: Review of Scientific Instruments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2001
Publication Date: N/A

Interpretive Summary: When the starch solutions are subjected to flow (shear) they display unusual behavior such as the formation of aggregates and separate phases, which become fully mixed at higher shear. These phenomena are not well understood and are important for the use of starch in various applications. For the study of these phenomena, an optical microscrope was constructed. This type of microscope is not commercially available because of several technical difficulties. The major difficulty is that we have to take images from fast-moving objects in the microscopic field. Our custom- built microscope solved this problem by adopting flash lamp and is capable of capturing images under shear field with a video camera. Temperatures can be controlled from ambient to 200 degrees C with +0.1 degree C accuracy. Several sample data are shown to demonstrate the performance and capability of the instrument. This instrument will be used as a tool for understanding the behavior of starch and other biopolymer solutions under shear field.

Technical Abstract: Recently, it has been found that some biopolymer solutions show aggregate formation or shear-induced mixing when they are exposed to shear field. An optical microscope was constructed for the study of these behaviors. A phase-contrast microscope is installed to obtain clear images from sample solutions where the refractive index difference of the domains is too small to be observed with common bright field microscopes. A modular type is adopted for the design of microscope for easy adjustment of optical components, alignment, and positioning it to the sample compartment. As a light source, a strobe type flash lamp is employed and its ignition is synchronized with CCD camera to avoid yielding smeared images. Shear fields are generated by a cone and plate geometry that is directly connected to a micro stepper motor with a controllable simple shear rate range of 0.025 to 2,500(1/s). In the case of oscillatory shear, accessible erange is 0 to 120 rad/s. A dual temperature controller allows temperature control of the sample compartment from ambient temperature to 200 degrees C with +/-0.1 degree C accuracy. Several starch solutions were used to demonstrate the performance and capability of the instrument.

Last Modified: 4/18/2014
Footer Content Back to Top of Page