Atomic force microscope (AFM) equipped with an liquid cell is used to observe surface of Taiheiyo coal exposed to water and methanol. Height data and mechanical properties obtained by force curve analyses were compared. In water, monotonous increase in height data and rapid decrease in hardness calculated from force curve data caused by swelling of coal surface were detected as expected. In methanol, monotonous increase in height data caused by swelling is also clearly observed. In this case, however, periodic changes in surface hardness was unexpectedly obtained indicating interaction between methanol and coal surface and transfer mechanism are entirely different from those of water.
