We attribute similarities in the rheology of many soft materials (foams, emulsions, slurries, etc.) to the shared features of structural disorder and metastability. A generic model for the mesoscopic dynamics of “soft glassy matter” is introduced, with interactions represented by a mean-field noise temperature $x$. We find power-law fluid behavior either with $(x<\mathrm{}1\mathrm{})$ or without $(1<x<\mathrm{}2\mathrm{})$ a yield stress. For $1<x<\mathrm{}2\mathrm{}$, both storage and loss modulus vary with frequency as ${\omega }^{x-1\mathrm{}}$, becoming flat near a glass transition $(x=1\mathrm{})$. Values of $x\approx 1$ may result from marginal dynamics as seen in some spin glass models.

• Received 2 December 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.2020