About Modulated DSC®About Modulated DSC®
MDSC is used to study the same material properties as conventional DSC including: transition temperatures, melting and crystallization, and heat capacity. However, MDSC provides unique capabilities that increase the amount of information that can be obtained from a single DSC experiment, thereby improving the quality of interpretation. These capabilities include:
Measurement of heat capacity and heat flow in a single experiment
Separation of complex transitions into more easily interpreted components
Increased sensitivity for detection of weak transitions
Increased resolution of transitions without loss of sensitivity
Increased accuracy in the measurement of polymer crystallinity
Direct determination of thermal conductivity.
The MDSC option includes special enhancements to the TA controller software and the DSC software.
For maximum experimental flexibility and highest quality results, MDSC experiments should be run using either a Refrigerated Cooling System (RCS) or a Liquid Nitrogen Cooling System (LNCS). The Finned air Cooling System (FACS) can be used to obtain MDSC results above ambient temperatures. However, experimental parameters (e.g., modulation amplitude) could be limited. The Quench Cooler is not compatible with MDSC.
In MDSC a more complex heating profile (temperature regime) is applied to the sample than is used in conventional DSC. Specifically, a sinusoidal modulation (oscillation) is overlaid on the conventional linear heating or cooling ramp to yield a profile in which the average sample temperature changes sinusoidally rather than linearly. The net effect of imposing this more complex heating profile on the sample is the same as if two experiments were run simultaneously on the material—one experiment at the traditional linear (average) heating rate and one at a sinusoidal (instantaneous) heating rate. The general equation that describes the resultant heat flow at any point in a DSC or MDSC experiment is:
dQ/dt = Cpb + f(T,t)
where:
dQ/dt = total heat flow
Cp = heat capacity
b = heating rate
f(T,t) = heat flow from kinetic (absolute temperature and time-dependent) processes
This equation clearly shows that the total heat flow (dQ/dt), which is the only heat flow measured by conventional DSC, is composed of two components. One component is a function of the sample's heat capacity and rate of temperature change, and the other is a function of absolute temperature and time. These components are generally referred to as the "reversing" and "nonreversing" heat flows respectively.
The actual complex temperature/time profile in MDSC depends on three variables—underlying heating/cooling rate, modulation period, and modulation temperature amplitude. There are three common types of operator-selectable MDSC experiments:
Conventional MDSC: In conventional MDSC experiments, all three variables are operator-selected and the experiment can be performed over some temperature range while either heating or cooling.
Heat-Only MDSC: Only modulation period and heating rate are operator-selectable in Heat Only MDSC experiments. The instrument automatically determines the modulation temperature amplitude required to ensure that the instantaneous heating rate goes to zero (isothermal) at one extreme of the temperature modulation cycle.
Quasi-Isothermal MDSC: In quasi-isothermal MDSC experiments the underlying heating rate is zero. However, by selecting a modulation temperature amplitude and period, the material is still exposed to an instantaneous heating rate, which permits the isothermal measurement of heat capacity.