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The samples in the topographic images on the left are cross-sections of polyurethane coatings on steel substrates. The top sample was room-temperature cured while the bottom sample was heat cured. These samples were mounted together in the same potting compound and were sectioned and polished together. Although the topography near the interfaces obscures the microstructure, the size of the roughened area in the heat cured sample is significantly smaller than that of the room-temperature cured sample. A similar study was done for the epoxy samples shown in the topographic images on the right. The sample in the top image has a 1:1 epoxy-amine ratio, while the sample in the bottom image has a 1:1.2 epoxy-amine ratio. Here, the sample with an excess of amine actually appears to have a smaller interphase region, as denoted by the roughened region near the epoxy-steel interface.