Anomalous roughening of viscous fluid fronts in spontaneous imbibition -: art. no. 104501

We report experiments on spontaneous imbibition of a viscous fluid by a model porous medium in the absence of gravity. The average position of the interface satisfies Washburn's law. Scaling of the interface fluctuations suggests a dynamic exponent z similar or equal to 3, indicative of global dynamics driven by capillary forces. The complete set of exponents clearly shows that interfaces are not self-affine, exhibiting distinct local and global scaling, both for time (beta=0.64 +/- 0.02, beta*=0.33 +/- 0.03) and space (alpha=1.94 +/- 0.20, alpha(loc)=0.94 +/- 0.10). These values are compatible with an intrinsic anomalous scaling scenario.