Suppressing Convective Instabilities in Propagating Fronts by Tube Rotation

Density gradients caused by thermal and solutal gradients often cause double-diffusive and/or Taylor instabilities in propagating fronts. These instabilities manifest themselves as “fingering” that can affect the front shape and velocity and, in extreme cases, destroy the front. This is especially a problem with propagating fronts of polymerization when a monomer is used that does not produce a cross-linked polymer. We have found that it is possible to suppress the fingering by rotating the tube around the long axis of the tube. With the chlorate−sulfite system and methacrylic acid polymerization system, we found that the front velocities exhibited a fourth-order dependence on the rotational frequency, and the front shapes were parabolic. The amplitudes of the deviation of the fronts from a planar front exhibited a second-order dependence on the rotational frequency but not exactly as predicted from the hydrostatic analysis of a rotating fluid.