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
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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.
Department
Description
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