Biomedical Engineering Reference
In-Depth Information
and liquids, wide temperature range, excellent quantitative capability,
etc. Along with these advantages, DSC also has some limitations such as
improper analysis of complex transitions, lack of sui cient sensitivity and
resolution, etc. To overcome the disadvantages of conventional DSC, and
also to perform multiple experiments, some modii cations in DSC tech-
nique were made and a new technique called modulated dif erential scan-
ning calorimetry (MDSC) was developed.
Modulated dif erential scanning calorimetry (MDSC) is a new tech-
nique which provides not only the same information as conventional DSC
but also some unique information not provided by the conventional DSC
technique. h e result is an exciting new way to signii cantly increase the
basic understanding of material properties.
13.6.2.2 Modulated Dif erential Scanning Calorimetry
h e theory supporting modulated DSC can be easily understood by com-
paring it to conventional DSC. In conventional DSC, the dif erence in heat
l ow between sample and inert reference material is measured as a function
of time and temperature, as both the samples and reference material are
subjected to a controlled environment of time, temperature and pressure.
h e most common instrument designed for making those DSC measure-
ments is the heat l ux design. A metallic disk (made of constantan alloy) is
the primary means of heat transfer to and from the sample and reference.
h e sample contained in a metal pan and the reference (an empty pan) sit
on raised platforms formed in the constantan disc. As heat is transfered
through the disc, the dif erential heat l ow to the sample and reference is
measured by an area thermocouple formed by the junction of the constan-
tan disc and cromel wafers which cover the underside of the platforms.
h ese thermocouples are connected in series and measure the dif erential
heat l ow using the thermal equivalent of Ohm's law,
dQ
T
dt
R
(13.10)
D
where dQ/dt is the heat l ow, ΔT is the temperature dif erence between ref-
erence and sample, and R
D
is the thermal resistance of the constantan disc.
Chromel and alumel wires attached to the chromel wafer form thermo-
couple, which directly measures sample temperature.
Modulated DSC is a technique which also measures the dif erence in
heat l ow between a sample and inert reference sample as a function of
time and temperature. In this technique the same “heat l ux” cell design
