Pyrolysis techniques are well-established methods for probing the chemical composition of polymers. Samples are simply heated so as to decompose them into small fragments which are then analysed by mass spectrometry (MS) or capillary Gas Chromatography-MS (GC-MS). With micro-thermal analysis it is easy to use the resistively heated probe as a means of locally ablating material from the surface. In order to carry out such experiments the probe is placed in contact with the region of interest and rapidly heated to the pyrolysis temperature. The evolved gases are trapped in a specially designed tube packed with a suitable sorbent such as Tenax or Carbopak. The tube comes to a fine point which is placed immediately adjacent to the heated thermal probe using a micro-manipulator (below). As the probe is heated, a syringe is used to draw gas through the tube which is then placed in a thermal desorbtion unit for analysis of the trapped volatiles by GC-MS. With this system it is possible to ablate a small (<10 x 10 µm) area of a sample (or a domain, feature or contaminant) and elucidate its composition under ambient conditions.

The image below shows a typical crater produced by rapidly heating the thermal probe to 600°C close to the surface of a sheet of perspex.

The gases from the pyrolysis experiment were trapped and then desorped into the GC-MS unit. The resulting chromatogram is shown below. The peak in the trace at 2.4 minutes corresponds to methyl methacrylate which is the monomer of poly(methyl methacrylate) or perspex from the area shown above.

This simple example illustrates the principle of combining micro-thermal analysis with chemical analysis of the evolved gases produced from spatially-resolved pyrolysis measurements. Further examples of this technique are illustrated for the identification of sub-surface layers and multi-layer film characterisation.