A Unique Oscillatory Phenomenon Revealed by A Microweighing Method

An earlier study of the interaction between solid urea and n-octane vapour in the presence of noncomplex-forming hydrocarbons by means of a vacuum microbalance technique revealed the oscillatory nature of urea-octane inclusion compound (complex) formation: process damping, occurrence in the reverse direction and repeated renewal without attainment of the complete saturation of the urea with octane. The phenomenon is interpreted on the basis of the recently discovered oscillatory adsorption, regarded as the surface competition between the spottily adsorbed A and B components, which results alternatively in spontaneous transitions from a state ‘A in B’ to a state ‘B in A’ and vice versa, with simultaneous dramatic change in the spot configurations under A and B, as well as changes in the chemical potentials of adsorbed A and B at the inversion points, certain minimal parts of the surface under A and B being permanently occupied by each of the components. This latter signifies that the non-complex-forming hydrocarbon hinders the complete transition of the urea to its inclusion compound phase. This revised version was published online in August 2006 with corrections to the Cover Date.