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Differential Scanning Calorimetry
The most often-used means of measuring a polymer's resistance to heat transfer is Differential Scanning Calorimetry, or DSC. The most common way this method is employed is for the sample and a control material to be placed in separate metal pans on a thermoelectric disk of a known thermal resistance. Then, a pure metallic substance is placed on the top of the sample, where it melts, thus controlling the temperature in the test chamber.
This method produces simple and rapid measurements but does not take into account the thermal contact resistance between the sample and the furnace. Also, the conductivity of the polymer sample can only be measured at the temperature at which the metallic substance melts.
Alternative DSC methods use an additional thermal reservoir equipped with temperature sensors. This allows researchers to measure thermal conductivity at a range of temperatures but requires additional temperature sensors.
Modulated Differential Scanning Calorimetry
Modulated DSC, or MDSC, is a patented technique that attempts to measure polymeric thermal conductivity without the need to modify commonly used DSC cells. It also lessens the need for scientists to pay attention to experimental detail. In this method the test specimen is exposed to a linear heating method, which oscillates sinusoidally -- hence, the temperature "modulates." The separation of the resulting heat flow during this cyclic treatment provides not only the total heat flow that would normally be provided by conventional DSC but also separates that total flow into its reversing and non-reversing components, thereby allowing the calculation of the polymer sample's thermal conductivity more directly.
Pulsed
To determine the conductivity of thin polymer films, special techniques must be employed. Several of these use a laser to heat one side of the sample in short "pulses." The change in temperature over time is then measured by an infrared sensor on the other side. This temperature change can also be sensed with a second laser beam in the modified "thermo-reflectance" method.
Pulsed methods measure thermal diffusivity, which requires scientists to know the density and specific heat of a sample before its thermal conductivity can be determined. These two values are often difficult to find exactly for a polymer.
Steady-State
"Steady-state" heat flow techniques include a number of methods for thin films in which a heat flow is forced through a sample by a heater on one side of it and a base with a fixed temperature on the other. The thermal resistance can then be calculated from the difference in temperature and used to calculate conductivity. In this method special care must be taken to ensure that no heat leaks to the outer environment instead of flowing through the sample to obtain reliable results. Also, once more, the contact resistance at the interfaces can influence the measurement of the film's thermal resistance and conductivity.