Optical-DSC for analysis of energy processes in transparent microscopic systems

Abstract

An optical-DSC system was designed, built, tested, calibrated, and verified to incorporate into a single device the capability for simultaneous optical cryomicroscopy and differential scanning calorimetery (DSC). This instrument can be used to obtain both optical and thermal data for a specimen subjected to a defined freezing and thawing protocol. There is very little compromise in quality or range of data available in comparison with dedicated single instruments. Temperature and caloric calibrations were performed based on phase transition states in water, nDodecane, and n-Decane. Experiments were conducted on biological cells to evaluate prior published studies on the osmotic response of cells to freezing stress evaluated independently via cryomicroscopy and DSC. The results were purported to define an energetic basis for measurement of the transport of water across cell membranes. The validity of this phenomenon was verified by the optical DSC by making direct measurements of both vii optically determined cell volume changes and energy flows for a single specimen subjected to a single experimental protocol. Further studies were conducted to obtain combined thermal and optical data on the freezing and thawing of ice cream. A unique protocol was designed to "simulate" the ice crystallization process in the manufacture and subsequent storage of ice cream. Quantitative data were obtained from optical image analysis for the first time to analyze growth rate of individual ice crystals. The simultaneous change in fraction of frozen water was obtained from the DSC thermogram. Comparison of the two data sets indicates the optical and thermal analyses provide complementary information about the crystallization process. Experiments were also conducted to study recrystallization in ice cream subjected to serial cooling and rewarming protocols. Optical images define a recrystallization rate and temperature range in agreement with DSC measurements. Correlation of an endothermic region on the DSC thermogram with optical data defines an explaination for the mechanism of ice recrystallization during the rewarming of rapidly cooled ice cream.