Preservation of Isotropy at the Mesoscopic Stage of Phase Separation Processes

A practical conservation law related to isotropy is proposed for the deterministic Cahn·Hilliard equation, i.e., the order parameter conserving TDGL model. In order to examine it a dipole moment of the cirder parameter distribution in a two dimensional system is numerically calculated by using the cell· dynamics method and is shown to remain microscopic even at the mesoscopic, scaling stage of the phase separation process. This fact is related to the k4 law in small wavenumber region of the sc;aling form of the structure function. . The characteristic length scale is also calculated directly in two ways, and the t,,3 law for its growth at the mesoscopic stage is confirmed with good accuracy.