An optical microscope for the study of biopolymer solutions under shear field

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 a charge coupled device camera to avoid yielding smeared images. Shear fields are generated by a cone and plate geometry that is directly attached to a microstepper motor with a controllable simple shear rate range of 0.025–2500 s−1. In the case of oscillatory shear, accessible range is 0–120 rad/s. A dual temperature controller allows temperature control of the sample compartment from ambient temperature to 200 °C with ±0.1 °C accuracy. Several starch solutions were used to demonstrate the performance and capability of the instrument.